HIGH TEMPERATURE RESISTIVE AND DRY LUBRICATED FILM SURFACES
United States Patent 3857682
A high particulate energy level deposited composite film build up is presented with a layer atomically bonded to the substrate carrier material and graduated hardness material film layers including refractory material. The substrate carrier material has a relatively high thermal conductivity factor relative to refractory material used in a film layer. A dry lube reaction overcoating film or one of other dry lube films are also deposited over hard dense film surfaces for lubricity between moving parts in a heated environment.
US Patent References:
Metal-ceramic laminated skin surface
Aves et al. - April 1962 - 3031331
Method of providing a bearing surface
Haltner et al. - January 1963 - 3075279
High temperature coatings
Dillon - May 1963 - 3091548
Multi layer difusion coatings and method of applying the same
Chao - January 1964 - 3117846
WEAR RESISTANT COBALT BONDED TUNGSTEN CARBIDE COMPOSITE
Montgomery - July 1969 - 3454375
Metal-ceramic laminated skin surface
Aves et al. - April 1962 - 3031331
Method of providing a bearing surface
Haltner et al. - January 1963 - 3075279
High temperature coatings
Dillon - May 1963 - 3091548
Multi layer difusion coatings and method of applying the same
Chao - January 1964 - 3117846
WEAR RESISTANT COBALT BONDED TUNGSTEN CARBIDE COMPOSITE
Montgomery - July 1969 - 3454375
Application Number:
05/330294
Publication Date:
12/31/1974
Filing Date:
02/07/1973
View Patent Images:
Export Citation:
Primary Class:
Other Classes:
428/651, 428/627, 204/192.150, 428/629, 418/178, 428/926, 428/623, 428/652
International Classes:
C23C14/32; C23C24/00; C30B23/08; F01C19/04; F01D5/28; F16J10/00; F01C19/00; B32B15/04
Field of Search:
29/195A,195M,195R,195Y 148/31.5
US Patent References:
| 3640689 | COMPOSITE HARD METAL PRODUCT | February 1972 | Glaski et al. |
Primary Examiner:
Rutledge, Dewayne L.
Assistant Examiner:
Weise E. L.
Attorney, Agent or Firm:
Kintzinger, Warren H.
Claims:
I claim
1. A high temperature resistive film build-up deposited on substrate material, with a plurality of film materials with film material atoms mechanically driven into underlying material atomic lattice in phase zones of atoms of adjoining materials through use of a high particulate energy level film material deposition ion plating process, with at least two of the materials of the materials of said substrate and said plurality of film materials being metal based materials; and with at least one film material a hardened refractory material film deposited by a high particulate energy level ion plating process.
2. The high temperature resistive film build-up of claim 1, wherein said film build-up is a graduated hardness material film build-up from the substrate material progressively in higher hardness steps upward through refractory material filming. 3. The high temperature resistive film build-up of claim 2, wherein the maximum hardness ratio step is
3. The high temperature resistive film build-up of claim 1, wherein the plurality of film materials includes adjacent layers of chromium and
4. The high temperature resistive film build-up of claim 1, with the film build-up deposited on internal high temperature component surface areas of
1. A high temperature resistive film build-up deposited on substrate material, with a plurality of film materials with film material atoms mechanically driven into underlying material atomic lattice in phase zones of atoms of adjoining materials through use of a high particulate energy level film material deposition ion plating process, with at least two of the materials of the materials of said substrate and said plurality of film materials being metal based materials; and with at least one film material a hardened refractory material film deposited by a high particulate energy level ion plating process.
2. The high temperature resistive film build-up of claim 1, wherein said film build-up is a graduated hardness material film build-up from the substrate material progressively in higher hardness steps upward through refractory material filming. 3. The high temperature resistive film build-up of claim 2, wherein the maximum hardness ratio step is
3. The high temperature resistive film build-up of claim 1, wherein the plurality of film materials includes adjacent layers of chromium and
4. The high temperature resistive film build-up of claim 1, with the film build-up deposited on internal high temperature component surface areas of
Description:
This invention relates in general to high temperature surfaces in heat engines and other devices generating high temperatures and, in particular, to high particulate energy level deposited multi-layer films including refractory material having a relatively low thermal conductivity factor for limited heat loss through walls of a heat engine and other heat generating devices.
The automotive industry has utilized reciprocating piston internal combustion heat engines for years while aviation has come to wide usage of jet turbine heat engines. Action of burning petroleum hydrocarbon fuels with engine and turbine components built of cast or forged materials such as steel, aluminum, titanium and in some cases graphite exhibit physical properties combining to establish upper temperature performance limits. Efforts to achieve materially higher operational combustion temperatures and thereby improvement in efficiency contributes to component failures with corrosion, erosion and surface breakdown intensified in combination at higher temperatures along with decrease in mechanical properties such as tensile strength. There are some refractory materials that maintain chemical and physical stability to extremely high temperatures, present excellent functional surfaces for high temperature use and that have high lubricity factor surfaces particularly with dry lube films between moving parts. There has been an ever enlarging family of super-refractory materials discovered and developed at a faster pace generally than the ability of industry to keep pace in effectively utilizing them. Refractory materials distinguishable by their ability to resist heat are normally ceramics or cermets. A ceramic is composed of a metal and another element such as Al 2 O 3 (aluminum oxide), while a cermet is a material composed of a ceramic phase and a metal phase. One cermet is, for example, sintered tungsten carbide (WC) in the form of grains hot pressed into a binder of cobalt or chrome. While this is erronously identified in the trade as a binary carbide it is in fact a cermet as are most metal carbides presently in industrial usage. These cermets are highly susceptible to failure at the binder and the variation in their physical properties can be surprising such as, for example, thermal conductivity at high temperature. Silicon carbide conducts heat at 109BTU/Hr/ft 2 /° f/ in at 2,200°F, a heat transmission factor that is approximately 70% of the value for chrome and nickel steels and 11 times the conduction of fireclay. Zirconia materials, however, are excellent insulators with a thermal conductivity about one half that of fireclay brick although zirconia bulk density is twice that of fireclay.
In the thermodynamic expression Δh=mc p Δt, with Δh the change of enthalpy in the system, m is the mass undergoing transition in the process, c p is the specific heat of the mass and Δt is the temperature difference through which enthalpy (or energy) change takes place. This energy change is directly related to the work output of the system involved. Further, with the lower value of the temperature difference ideally approaching ambient, the most effective way to maximize the work output of a heat engine is to raise the higher operational temperature limit and thereby maximize the temperature difference range of operation. Additionally the more perfectly the system is insulated the more closely compression and expansion of gas mixtures in a gas heat engine may be to adiabatic actions. Engine design generally, however, has been concerned with materials with relatively rapid heat transfer characteristics to transfer heat from combustion chamber walls to engine coolant systems to prevent heat damage to the surfaces. Even were combustion chamber walls able to withstand materially higher temperatures by themselves where petroleum based hydrocarbons are used for lubrication upper operational temperatures are still quite limited. These features are simply inconsistent with the general energy equation suggesting high combustion chamber temperatures for greater energy output. Thus, with thermodynamic design calling for more temperature insulation rather than more cooling of combustion chamber walls higher temperature surface materials are required along with materials providing inherent lubricity at higher engine operating temperatures. Some of the materials required are super-refractory materials that are not only quite expensive but generally lack ductility and machineability to degrees such as to remove them from consideration as bulk material for engines. If they are to be used at all as hot surfaces they must be used as coatings on heat engine parts and other high temperature equipment. Previous efforts to provide such surface films with electroplating of refractory compounds have proven quite unsuccessful. Chemical vapor deposition while offering a wide choice of materials does not give faithful surface replication, lacks good adhesion, and requires entire parts to reach temperatures in excess of 700°C for such depositions to go to completion. Flame spraying deposition also has its full share of problems and is particularly difficult to do on internal diameter surfaces of openings. Further, even with a system for depositing films of very hard material such as, for example, titanium carbide on an aluminum surface the hardness differential at the interface would be 2,300 to 200 (using Knoop scale hardness values). This is severe enough that stresses at the interface, arising with either thermal or mechanical shock or a combination of both, as applied are likely at times to result in separation of the film from the substrate even though sputtering or ion plating were used to deposit the film. Dry lubricity between moving parts in contact is important particularly with seals that can present serious problems in a high temperature environment.
It is therefore, a principal object of this invention to provide heat engine high temperature operational surfaces permitting higher temperature more efficient engine operation.
Another object is to provide such high temperature operational surfaces through a high particulate energy level deposited composite film build-up.
A further object is to provide such a composite film build-up including refractory material limiting heat energy BTU through flow to low enough rates for the substrate material to handle without destructive overheating of substrate material such as an engine block.
Another object is to provide such a composite film build-up with graduated hardness film layers and eliminate any interface stress separation of the film build-up from the substrate material or between film layers.
A further object is to provide such composite film build-ups with film material phased into base material of the substrate and into intervening films from next successively higher film layers by high particulate energy level sputtering and ion plating used in the composite film deposition process.
Another object is to provide a composite film build-up with an exposed high temperature operational surface having good dry lubricity characteristics.
Still another object is to provide an outer dry lube film deposited over hard dense film surfaces for improved dry lubricity as well as thermal and corrosion resistance.
Features of the invention useful in accomplishing the above objects include, in high temperature resistive and dry lubricated film build-ups, a dense hard film of refractory material having a phase zone of atoms extended into an underlying intervening film of material also having a phase zone of atoms extended into material thereunder. High temperature heat engine surfaces are provided capable of operation as high as 2,000°C with, for example, a graded material film build-up having a ductile adhesion layer of pure metal atomically bonded to the substrate and with a plurality of sequential layers atomic particle phase zoned one into another. In one example an aluminum engine block is coated with sequential layers of nickle, chrome, chrome oxide and titanium carbide with Knoop hardness values running successively approximately 200 to 557 to 920 to 1,600 to 2,300. In areas where there is rubbing contact between components the high temperature film build-ups are provided with an overcoating of a dry lubricant material such as silver or gold or the upper surface itself is an oxide material with inherently good dry lubricity qualities. In various applications thickness of refractory material consistent with the heat flow characteristics of the material used is important in attaining desired heat engine operational temperatures while still limiting heat flow to engine block and other component materials to within non-destructive capability levels.
Specific embodiments representing what are presently regarded as the best modes of carrying out the invention are illustrated in the accompanying drawing:
In the drawing:
FIG. 1 represents an internal combustion engine of the rotary type with a forward portion removed having sliding seals moving over high temperature internal surfaces;
FIG. 2, an enlarged sectioned view showing of an engine rotor element tip seal vane insert with an outer dry lubricant film deposition;
FIG. 3, a partial sectional diagramatic showing of an internal combustion piston engine;
FIG. 4, a turbine blade of a jet engine;
FIG. 5, an enlarged partial section showing a two material composite film build-up for the high temperature surfaces of the engine of FIGS. 1 and 2 and the hot gas exposed surfaces of the turbine blade of FIG. 4;
FIGS. 6 and 7, enlarged partial sections showing a plurality of film layers deposited successively over base metal surfaces by high particulate energy level ion plating processes with a phase zone of atomic penetration into base metal and each film layer by the next higher layer; and,
FIG. 8, an enlarged partial section of a plurality of film layers deposited successively over combination seal and bearing surfaces of base material and with the highest layer a thin film of dry lubricant material.
Referring to the drawing:
With the Wankel rotary engine 10 of FIG. 1 the rotor 11 is shown to have three convex faces 12a, 12b and 12c each of which in combination with interior areas of epitrochoid housing 13 form a moving chamber. This moving chamber progresses from chamber A that draws in the fuel and air mixture to compression chamber B that proceeds to a minimum volume and ignition and then expansion to enlarged chamber C with exhaust. The rotor 11 transmits torque to drive shaft spur gear 14 from the larger diameter rotor internal gear tooth ring 15 that maintains tangential driving contact with spur gear 14 as the rotor advances in rotation. A seal vane insert 16 having a smooth rounded outer end 17 is received at the vane insert rear in each of three grooved 18 mount pins 19 mounted in the rotor at each of the three rotor tips with the seal vanes 16 extended through a rotor parallel walled passageway 20 between the mount pins 19 and the outer rotor tips. Additional sealing provided by curved seals 21 and 22 mounted in grooves in front and rear faces of rotor 11 and extended between seal vane insert mount pins 19 helps maintain engine chamber sealing.
Obviously, sealing of the different changing chambers and particularly the combustion chamber is an important consideration with such engines with sliding seal contact over hot high temperature surfaces. Further, it is important that long life high temperature operational surfaces permit higher heat engine temperature limits and thereby more efficient engine operation. In the attainment of suitable high temperature operational surfaces hard dense insulating material is deposited by a high particulate energy level ion deposition process in film build-up on high temperature heat engine surfaces and valve seal elements. Reference to the basic equation of heat transfer illustrates usefulness of insulating material films in maximizing combustion chamber operational temperatures. This heat transfer equation is: Q=UAΔt where Q is the total energy transition, U is the overall coefficient of heat transfer considering insulating material thickness, A is the area through which the heat is transferred, and Δt is the temperature difference between, for example, a combustion chamber inside wall and an engine block cooling system. Actually, the temperature difference from a combustion chamber wall to the bulk temperature of the engine block or housing should be theoretically as high as possible to optimize the operational temperature range for greater engine efficiency, yet the rate of heat transfer through combustion chamber wall films must not exceed the ability of substrate material to convey heat away and keep temperature behind the wall films low enough to prevent metallurgical damage. This applies for all cooling medias whether liquid or air and with heat sink cooling.
High temperature operational surfaces of the heat engine 10 are provided with dense hard heat insulating material films with a phase zone of atoms extended into underlying base metal or lower films. The phase zone is attained through atom penetration into the surface region of base metal, or of an adjacent underlying film, with high particulate energy level in an ion plating process sufficient to drive many atoms into substrate atomic lattice. With the rotor tip seal vane inserts 16 as shown in section in FIG. 2 the vane body 23 may be either solid graphite or aluminum with a high particulate energy level ion plating deposited chrome film 24 and a phase zone 25 of atom penetration into vane base material. An overlayer of dry lubricant film plating 26, gold in the example of FIG. 2, is deposited over the refractory chrome film 24 by high particulate energy level sputtering or ion plating process giving a phase zone 27 of atom penetration into the surface region of film 23. Other dry lubricant film materials could be used in place of gold such as silver, Molybdenum Disulphide (MoS 2 ), Titanium Nitride (TiN), and various metal oxides with a high particulate energy process giving phase zones of atom penetration into underlying material. These various dry lubricant materials impart lubricity to surfaces either by offering shearing action in lattice planes or by exhibiting a low coefficient of fricture. Heat engine surfaces provided herein include some allowing steady state operation with combustion chamber temperatures as high as 2,000°C and seal contacting sliding surface velocities up to over 15,000 linear feet per minute.
It is of considerable inportance for the engine designer to be able to change the value of U in the heat transfer equation over a wide range through selection of refractory material for film plating and plating thickness to attain a desired value of thermal conductivity for specific designs. The ability to vary film thickness in a controlled process over a range from angstroms to several mils and more with applicant's heat engine ion plating is very useful in arriving at desired film design thickness values. This combined with the thermal conductivity value for given refractory materials yields a desired wall temperature for a specific engine design. These design capabilities provide either greatly extended heat engine wear life and/or much higher engine operating temperature limits and improved efficiency. With design for higher engine operating temperature limits many of the internal combustion engines of necessity must be diesel engines with fuel injection for proper operation.
The following table of materials and thermal conductivities based on BTU/HR/Ft 2 /°F/Ft at approximately 400°F illustrate differences between some refractory materials and some common metals.
______________________________________ Copper 215 Silican Carbide 49 Aluminum 131 Titanium Carbide 24 Iron 36 Aluminum Oxide 14 Chromium Steel 14.9 Zirconium Oxide 2.45 Beryllium Oxide 92 ______________________________________
Refractories generally exhibit good resistance to combustion processes and the high temperatures involved. Some oxides are particularly resistant to combustion processes and high temperatures and are good insulators with relatively low thermal conductivity values. It should be noted that many refractory carbides, nitrides and silicides are unstable in oxygen at temperatures above 1,100°C. Their surfaces, however, and particularly those of the oxides generally exhibit low friction (i.e., dry lubricity) as is desired for hot surface engine parts in sliding contact.
The internal combustion piston engine 28 of FIG. 3 is shown as having a conventional crankshaft 29, connecting rod 30 and piston 31 moved in reciprocating motion up and down within cylinder 32 can also be improved with high temperature films just as with the heat engine 10 of FIG. 1. Upper cylinder walls, the piston top 33, valves 34 and 35 exhaust port 36 and piston rings 37 may all be surface treated just as their counterparts in the heat engine of FIG. 1. Should the piston engine 28 be converted to a high pressure pump generating high cylinder wall and piston temperatures with high speed operation high temperature resistive films and dry lubricant films are again quite advantageous in providing extended pump life and efficient reliable operation.
The turbine blade 38 of FIG. 4 is normally mounted to be in the hot gas stream of a jet engine during operation and in such high temperature useage temperature insulating film is useful just as with the heat engines of FIGS. 1 and 3. The heat flow through the heat resistive insulating film on the blade 38 is conveyed to the internal base material and therethrough down to the blade mounting base 39 from which it is transmitted to the blade 38 mounting structure and dissipated therefrom. While blade 38 is not in rubbing contact with other components a thin dry lubricant film of gold or silver deposited by a high particulate energy level sputtering or ion plating process creating a phase zone of atom penetration can still be helpful in preventing hot spot damage and erosion of the blade 38.
FIG. 5 shows in enlarged partial section a two layer film build-up of first a chromium film 40 on aluminum base metal 41 with a phase zone 42 of atom penetration into the surface region of base metal 41 and with the film 40 only about 1,000 angstroms thick. A top film 43 of chromium oxide also approximately 1,000 angstroms thick is deposited over the chromium film 40 with a phase zone 44 of atom penetration into the surface region of the film 40. While the chromium film 40 and the chromium oxide film 43 are relatively thin they still have good heat insulating qualities with low thermal conductivity such as to, in the form of an ion process deposited hard dense film build-up, minimize chemical and physical failure as well as thermal shock damage and have resulted in materially improved operational service life on heat engine combustion chamber surfaces.
With the surface treatment of FIG. 6 a plurality of film layers are deposited successively over base material 45 that is aluminum, iron or steel or other suitable material. The film layers deposited by a high particulate energy level ion plating process are successively, over aluminum 45, nickle 46, chromium 47, chromium oxide 48, and titanium carbide 49 as an internal high temperature surface in an engine 10 or 28 or on a turbine blade 38. The film of nickle 46 is deposited with a phase zone 50 of atom penetration into the surface region of base metal 45. The successively higher films have phase zones 51, 52 and 53, respectively, in the upper surface regions of the nickle 46, chromium 47, and chromium oxide 48 of penetration atoms. Another advantage provided with the attainment of the different surface region phase zones of penetration atoms is stress relieval of base metal through the phase zone and development of an advantageous surface material compressive state. This greatly lessens the chance of thermal and mechanical shock damage and film separation. Further, with the Knoop hardness values from the aluminum base metal 45 to the top titanium carbide film 49 ranging, in order 200 to 557 to 920 to 1,600 to 2,300, at most approximately a step of 21/2 to 1 instead of over a 10 to 1 hardness ratio, with a titanium carbide deposit directly on aluminum, any likelihood of thermal and/or mechanical film separation damage is virtually eliminated.
With the high temperature surface treatment of FIG. 7 first an adhesion layer of chromium 54 is deposited on substrate base metal aluminum 55 and then successively thereover a distributive layer of chromium oxide 56, an insulation layer of hafnium oxide 57, and finally an outer layer of about 3,000 angstroms of silver 58 by either ion plating or sputtering for dry lubricity along with thermal and corrosion resistance. The silver is cold worked during operation into any surface irregularities that may exist to further reduce overall surface friction. The other film layers below the outer layer of silver are deposited by high particulate energy level ion plating so that there is a phase zone 59 of atom penetration into the surface region of base metal 55 and successively higher film phase zones 60, 61 and 62, respectively, in the upper surface regions of the chromium 54, chromium oxide 56 and hafium oxide 57. A film build-up used had chromium oxide layers deposited to a thickness of approximately 10 mils with the transformation from pure chromium to chromium oxide accomplished by admitting oxygen in an oxygen-argon gas mixture into the vacuum system during deposition. The refractory material hafnium oxide was then deposited to approximately 10,000 angstroms thickness. While a 50% oxygen- 50% argon gas mixture was used in the film build-up of FIG. 7 a 50% methane-50% argon gas mixture may be used in producing carbides such as titanium carbide of FIG. 6. The hot plasma action cracks the CH 4 molecule into carbon that reacts with metal atoms coming from the evaporant source and hydrogen that is pumped away. The temperature of the process where film is being deposited is sufficiently high that hydrides do not form nor appear in ion plating laid down. It should be noted that the films deposited on the high temperature heat engine surfaces and even those deposited on elements such as seal vane insert 16 are generally uniform thickness epitaxial films even with film build-ups running up to more than several mils thickness.
The film build-up of FIG. 8 may be used in place of that shown in FIG. 2 for components such as seal vane insert 16, curved seals 21 and 22 of the FIG. 1 heat engine and the piston rings 37 of the FIG. 3 engine or pump. The FIG. 8 film build-up includes first an adhesion layer of chromium 63 deposited on base material 64, aluminum, graphite, iron or steel, etc. and then successively thereover a chromium oxide layer 65 as a refractory heat insulating material film and finally an outer layer of silver 66. The film layers below the outer silver layer are deposited by high particulate energy level ion plating and the silver layer is deposited either by ion plating or by sputtering. There is a phase zone 67 of atom penetration into the surface region of the base material 64 and there are successively higher film phase zones 68 and 69, respectively, in the upper surface regions of the chromium 63 and chromium oxide 65. Other three film build-ups that may be employed in some applications in place of that of FIG. 8 are, respectively, hafnium, hafnium oxide and molybdenum disulphide (H f ,H f O and MoS 2 ); titanium, titanium nitride, and gold (Ti, TiN and Au); and titanium, titanium carbide and titanium nitride or titanium oxide (Ti, TiC and TiN or TiO).
Where hot surfaces are not in rubbing sliding contact, such as rotor faces 12a, 12b and 12c on the rotor 11 of FIG. 1, a film build-up such as shown in FIG. 6 may be employed. This applies also for piston tops and turbine blades although there are still some advantages in having an uppermost layer of one of some of the dry lubricant materials.
Sputtering is a process whereby gas ions in a vacuum system are accelerated by a high voltage to bombard a cathode (target) and cause ejection of atoms of cathode material. These high energy atoms immediately deposit on a nearby substrate surface. Plasma is the classic term for the fourth fundamental state of matter, i.e., a uniform mixture of positive ions and electrons. A neutral plasma is used as a source for the positive ions that bombard a target during the sputtering process to liberate atoms of material for deposition. Thus, the essential elements for a sputtering system are: (1) a vacuum system containing a sputtering cathode of desired material and the desired substrates, (2) a source of electrical energy both to develop the initial glow discharge and to sustain the operation on a continuous basis, and (3) a controlled source of gas to maintain the right pressure despite a continual removal of gas from the system to assure purity. In actual operation of the sputtering process the voltage applied to the glow discharge is dropped across Crooke's dark space. Ions move by diffusion through the neutral plasma. A positive ion reaching the surface of the plasma is attracted into the dark space and accelerated across it to collide with the target. At constant temperature the thickness of Crooke's dark space is inversely proportional to pressure. For argon plasmas the product of pressure and thickness is equal to approximately 0.3 torr-cm.
It is the high energy developed by the impinging ion as it accelerates across the space to strike the cathode that brings about a basic advantage of sputtering over conventional plating processes. As ions strike the cathode, they cause atoms of target material to shoot back across the dark space where they bombard the substrate. The particulate energy level in sputtering can easily be 1,000 times or more greater than that exhibited by conventional plating processes and is sufficient to drive the atoms into the substrate atomic lattice. Also, since the atoms at typical sputtering pressures encounter about eight collisions in crossing the dark space, the process is capable of coating three-dimensional objects.
Since the foregoing sputtering description is generally valid for targets of conductive material but not for insulators an rf (radio frequency) sputtering process is used for deposition of sputtered insulator films. This rf sputtering utilizes alternate ion and electron bombardment of the cathode surface to achieve deposition. When an rf signal is applied to a target electrode made of insulating material, a negative DC self-bias develops on the surface of the target. This is essential for sputtering since it gives a steady direction to the flow of positive ions across the dark space. The charged particles present in the field are electrons and singly charged positive gas ions (usually argon). Particle mobility is a direct function of charge and varies inversely with mass and mobility of the electron is approximately 10 5 greater than that of the ion. Thus, during the negative half cycles of the rf signal, more electrons than ions collect on the cathode surface and, since this surface is non-conductive, the electrons cannot leave on the positive half cycles. This has the effect of presenting a constant negative charge to the positive ions accelerating from the glow. Radio frequency sputtering is advantageous in many instances of metal sputtering, and with rf sputtering of metals, requiring, as with insulator cathodes, a constant negative potential on the cathode. This requires only the insertion of a blocking capacitor in the power circuit.
Ion plating is an atomistic deposition process in which the substrate is subjected to a flux of high energy ions sufficient to cause appreciable sputtering before and during film deposition. The ion bombardment is usually done in a gas discharge system similar to that used in sputter deposition, except with ion plating the substrate is made a sputtering cathode. With ion bombardment for a thin film to form it is necessary that the deposition rate exceed the sputtering rate. Benefits with ion plating are an ability to sputter clean the substrate surface and keep it clean until the film begins to form, a high energy flux to the substrate surface giving a high surface temperature enhanced diffusion and chemical reactions without requiring bulk heating, altering the surface and interfacial structure, and physically mixing the film during film deposition. Ion plating offers fast deposition rates allowing thin film work in mils rather than solely angstroms and the throwing power imparted to atom ions in ion plating is far greater than with sputtering. This, advantageously facilitates coating larger irregularly shaped objects, internal diameters or convolutions with a uniformly deposited film in a range from extremely thin to thick films.
Whereas this invention is illustrated and described with respect to a plurality of embodiments thereof, it should be realized that various changes may be made without departing from the essential contributions to the art made by the teachings hereof.
The automotive industry has utilized reciprocating piston internal combustion heat engines for years while aviation has come to wide usage of jet turbine heat engines. Action of burning petroleum hydrocarbon fuels with engine and turbine components built of cast or forged materials such as steel, aluminum, titanium and in some cases graphite exhibit physical properties combining to establish upper temperature performance limits. Efforts to achieve materially higher operational combustion temperatures and thereby improvement in efficiency contributes to component failures with corrosion, erosion and surface breakdown intensified in combination at higher temperatures along with decrease in mechanical properties such as tensile strength. There are some refractory materials that maintain chemical and physical stability to extremely high temperatures, present excellent functional surfaces for high temperature use and that have high lubricity factor surfaces particularly with dry lube films between moving parts. There has been an ever enlarging family of super-refractory materials discovered and developed at a faster pace generally than the ability of industry to keep pace in effectively utilizing them. Refractory materials distinguishable by their ability to resist heat are normally ceramics or cermets. A ceramic is composed of a metal and another element such as Al 2 O 3 (aluminum oxide), while a cermet is a material composed of a ceramic phase and a metal phase. One cermet is, for example, sintered tungsten carbide (WC) in the form of grains hot pressed into a binder of cobalt or chrome. While this is erronously identified in the trade as a binary carbide it is in fact a cermet as are most metal carbides presently in industrial usage. These cermets are highly susceptible to failure at the binder and the variation in their physical properties can be surprising such as, for example, thermal conductivity at high temperature. Silicon carbide conducts heat at 109BTU/Hr/ft 2 /° f/ in at 2,200°F, a heat transmission factor that is approximately 70% of the value for chrome and nickel steels and 11 times the conduction of fireclay. Zirconia materials, however, are excellent insulators with a thermal conductivity about one half that of fireclay brick although zirconia bulk density is twice that of fireclay.
In the thermodynamic expression Δh=mc p Δt, with Δh the change of enthalpy in the system, m is the mass undergoing transition in the process, c p is the specific heat of the mass and Δt is the temperature difference through which enthalpy (or energy) change takes place. This energy change is directly related to the work output of the system involved. Further, with the lower value of the temperature difference ideally approaching ambient, the most effective way to maximize the work output of a heat engine is to raise the higher operational temperature limit and thereby maximize the temperature difference range of operation. Additionally the more perfectly the system is insulated the more closely compression and expansion of gas mixtures in a gas heat engine may be to adiabatic actions. Engine design generally, however, has been concerned with materials with relatively rapid heat transfer characteristics to transfer heat from combustion chamber walls to engine coolant systems to prevent heat damage to the surfaces. Even were combustion chamber walls able to withstand materially higher temperatures by themselves where petroleum based hydrocarbons are used for lubrication upper operational temperatures are still quite limited. These features are simply inconsistent with the general energy equation suggesting high combustion chamber temperatures for greater energy output. Thus, with thermodynamic design calling for more temperature insulation rather than more cooling of combustion chamber walls higher temperature surface materials are required along with materials providing inherent lubricity at higher engine operating temperatures. Some of the materials required are super-refractory materials that are not only quite expensive but generally lack ductility and machineability to degrees such as to remove them from consideration as bulk material for engines. If they are to be used at all as hot surfaces they must be used as coatings on heat engine parts and other high temperature equipment. Previous efforts to provide such surface films with electroplating of refractory compounds have proven quite unsuccessful. Chemical vapor deposition while offering a wide choice of materials does not give faithful surface replication, lacks good adhesion, and requires entire parts to reach temperatures in excess of 700°C for such depositions to go to completion. Flame spraying deposition also has its full share of problems and is particularly difficult to do on internal diameter surfaces of openings. Further, even with a system for depositing films of very hard material such as, for example, titanium carbide on an aluminum surface the hardness differential at the interface would be 2,300 to 200 (using Knoop scale hardness values). This is severe enough that stresses at the interface, arising with either thermal or mechanical shock or a combination of both, as applied are likely at times to result in separation of the film from the substrate even though sputtering or ion plating were used to deposit the film. Dry lubricity between moving parts in contact is important particularly with seals that can present serious problems in a high temperature environment.
It is therefore, a principal object of this invention to provide heat engine high temperature operational surfaces permitting higher temperature more efficient engine operation.
Another object is to provide such high temperature operational surfaces through a high particulate energy level deposited composite film build-up.
A further object is to provide such a composite film build-up including refractory material limiting heat energy BTU through flow to low enough rates for the substrate material to handle without destructive overheating of substrate material such as an engine block.
Another object is to provide such a composite film build-up with graduated hardness film layers and eliminate any interface stress separation of the film build-up from the substrate material or between film layers.
A further object is to provide such composite film build-ups with film material phased into base material of the substrate and into intervening films from next successively higher film layers by high particulate energy level sputtering and ion plating used in the composite film deposition process.
Another object is to provide a composite film build-up with an exposed high temperature operational surface having good dry lubricity characteristics.
Still another object is to provide an outer dry lube film deposited over hard dense film surfaces for improved dry lubricity as well as thermal and corrosion resistance.
Features of the invention useful in accomplishing the above objects include, in high temperature resistive and dry lubricated film build-ups, a dense hard film of refractory material having a phase zone of atoms extended into an underlying intervening film of material also having a phase zone of atoms extended into material thereunder. High temperature heat engine surfaces are provided capable of operation as high as 2,000°C with, for example, a graded material film build-up having a ductile adhesion layer of pure metal atomically bonded to the substrate and with a plurality of sequential layers atomic particle phase zoned one into another. In one example an aluminum engine block is coated with sequential layers of nickle, chrome, chrome oxide and titanium carbide with Knoop hardness values running successively approximately 200 to 557 to 920 to 1,600 to 2,300. In areas where there is rubbing contact between components the high temperature film build-ups are provided with an overcoating of a dry lubricant material such as silver or gold or the upper surface itself is an oxide material with inherently good dry lubricity qualities. In various applications thickness of refractory material consistent with the heat flow characteristics of the material used is important in attaining desired heat engine operational temperatures while still limiting heat flow to engine block and other component materials to within non-destructive capability levels.
Specific embodiments representing what are presently regarded as the best modes of carrying out the invention are illustrated in the accompanying drawing:
In the drawing:
FIG. 1 represents an internal combustion engine of the rotary type with a forward portion removed having sliding seals moving over high temperature internal surfaces;
FIG. 2, an enlarged sectioned view showing of an engine rotor element tip seal vane insert with an outer dry lubricant film deposition;
FIG. 3, a partial sectional diagramatic showing of an internal combustion piston engine;
FIG. 4, a turbine blade of a jet engine;
FIG. 5, an enlarged partial section showing a two material composite film build-up for the high temperature surfaces of the engine of FIGS. 1 and 2 and the hot gas exposed surfaces of the turbine blade of FIG. 4;
FIGS. 6 and 7, enlarged partial sections showing a plurality of film layers deposited successively over base metal surfaces by high particulate energy level ion plating processes with a phase zone of atomic penetration into base metal and each film layer by the next higher layer; and,
FIG. 8, an enlarged partial section of a plurality of film layers deposited successively over combination seal and bearing surfaces of base material and with the highest layer a thin film of dry lubricant material.
Referring to the drawing:
With the Wankel rotary engine 10 of FIG. 1 the rotor 11 is shown to have three convex faces 12a, 12b and 12c each of which in combination with interior areas of epitrochoid housing 13 form a moving chamber. This moving chamber progresses from chamber A that draws in the fuel and air mixture to compression chamber B that proceeds to a minimum volume and ignition and then expansion to enlarged chamber C with exhaust. The rotor 11 transmits torque to drive shaft spur gear 14 from the larger diameter rotor internal gear tooth ring 15 that maintains tangential driving contact with spur gear 14 as the rotor advances in rotation. A seal vane insert 16 having a smooth rounded outer end 17 is received at the vane insert rear in each of three grooved 18 mount pins 19 mounted in the rotor at each of the three rotor tips with the seal vanes 16 extended through a rotor parallel walled passageway 20 between the mount pins 19 and the outer rotor tips. Additional sealing provided by curved seals 21 and 22 mounted in grooves in front and rear faces of rotor 11 and extended between seal vane insert mount pins 19 helps maintain engine chamber sealing.
Obviously, sealing of the different changing chambers and particularly the combustion chamber is an important consideration with such engines with sliding seal contact over hot high temperature surfaces. Further, it is important that long life high temperature operational surfaces permit higher heat engine temperature limits and thereby more efficient engine operation. In the attainment of suitable high temperature operational surfaces hard dense insulating material is deposited by a high particulate energy level ion deposition process in film build-up on high temperature heat engine surfaces and valve seal elements. Reference to the basic equation of heat transfer illustrates usefulness of insulating material films in maximizing combustion chamber operational temperatures. This heat transfer equation is: Q=UAΔt where Q is the total energy transition, U is the overall coefficient of heat transfer considering insulating material thickness, A is the area through which the heat is transferred, and Δt is the temperature difference between, for example, a combustion chamber inside wall and an engine block cooling system. Actually, the temperature difference from a combustion chamber wall to the bulk temperature of the engine block or housing should be theoretically as high as possible to optimize the operational temperature range for greater engine efficiency, yet the rate of heat transfer through combustion chamber wall films must not exceed the ability of substrate material to convey heat away and keep temperature behind the wall films low enough to prevent metallurgical damage. This applies for all cooling medias whether liquid or air and with heat sink cooling.
High temperature operational surfaces of the heat engine 10 are provided with dense hard heat insulating material films with a phase zone of atoms extended into underlying base metal or lower films. The phase zone is attained through atom penetration into the surface region of base metal, or of an adjacent underlying film, with high particulate energy level in an ion plating process sufficient to drive many atoms into substrate atomic lattice. With the rotor tip seal vane inserts 16 as shown in section in FIG. 2 the vane body 23 may be either solid graphite or aluminum with a high particulate energy level ion plating deposited chrome film 24 and a phase zone 25 of atom penetration into vane base material. An overlayer of dry lubricant film plating 26, gold in the example of FIG. 2, is deposited over the refractory chrome film 24 by high particulate energy level sputtering or ion plating process giving a phase zone 27 of atom penetration into the surface region of film 23. Other dry lubricant film materials could be used in place of gold such as silver, Molybdenum Disulphide (MoS 2 ), Titanium Nitride (TiN), and various metal oxides with a high particulate energy process giving phase zones of atom penetration into underlying material. These various dry lubricant materials impart lubricity to surfaces either by offering shearing action in lattice planes or by exhibiting a low coefficient of fricture. Heat engine surfaces provided herein include some allowing steady state operation with combustion chamber temperatures as high as 2,000°C and seal contacting sliding surface velocities up to over 15,000 linear feet per minute.
It is of considerable inportance for the engine designer to be able to change the value of U in the heat transfer equation over a wide range through selection of refractory material for film plating and plating thickness to attain a desired value of thermal conductivity for specific designs. The ability to vary film thickness in a controlled process over a range from angstroms to several mils and more with applicant's heat engine ion plating is very useful in arriving at desired film design thickness values. This combined with the thermal conductivity value for given refractory materials yields a desired wall temperature for a specific engine design. These design capabilities provide either greatly extended heat engine wear life and/or much higher engine operating temperature limits and improved efficiency. With design for higher engine operating temperature limits many of the internal combustion engines of necessity must be diesel engines with fuel injection for proper operation.
The following table of materials and thermal conductivities based on BTU/HR/Ft 2 /°F/Ft at approximately 400°F illustrate differences between some refractory materials and some common metals.
______________________________________ Copper 215 Silican Carbide 49 Aluminum 131 Titanium Carbide 24 Iron 36 Aluminum Oxide 14 Chromium Steel 14.9 Zirconium Oxide 2.45 Beryllium Oxide 92 ______________________________________
Refractories generally exhibit good resistance to combustion processes and the high temperatures involved. Some oxides are particularly resistant to combustion processes and high temperatures and are good insulators with relatively low thermal conductivity values. It should be noted that many refractory carbides, nitrides and silicides are unstable in oxygen at temperatures above 1,100°C. Their surfaces, however, and particularly those of the oxides generally exhibit low friction (i.e., dry lubricity) as is desired for hot surface engine parts in sliding contact.
The internal combustion piston engine 28 of FIG. 3 is shown as having a conventional crankshaft 29, connecting rod 30 and piston 31 moved in reciprocating motion up and down within cylinder 32 can also be improved with high temperature films just as with the heat engine 10 of FIG. 1. Upper cylinder walls, the piston top 33, valves 34 and 35 exhaust port 36 and piston rings 37 may all be surface treated just as their counterparts in the heat engine of FIG. 1. Should the piston engine 28 be converted to a high pressure pump generating high cylinder wall and piston temperatures with high speed operation high temperature resistive films and dry lubricant films are again quite advantageous in providing extended pump life and efficient reliable operation.
The turbine blade 38 of FIG. 4 is normally mounted to be in the hot gas stream of a jet engine during operation and in such high temperature useage temperature insulating film is useful just as with the heat engines of FIGS. 1 and 3. The heat flow through the heat resistive insulating film on the blade 38 is conveyed to the internal base material and therethrough down to the blade mounting base 39 from which it is transmitted to the blade 38 mounting structure and dissipated therefrom. While blade 38 is not in rubbing contact with other components a thin dry lubricant film of gold or silver deposited by a high particulate energy level sputtering or ion plating process creating a phase zone of atom penetration can still be helpful in preventing hot spot damage and erosion of the blade 38.
FIG. 5 shows in enlarged partial section a two layer film build-up of first a chromium film 40 on aluminum base metal 41 with a phase zone 42 of atom penetration into the surface region of base metal 41 and with the film 40 only about 1,000 angstroms thick. A top film 43 of chromium oxide also approximately 1,000 angstroms thick is deposited over the chromium film 40 with a phase zone 44 of atom penetration into the surface region of the film 40. While the chromium film 40 and the chromium oxide film 43 are relatively thin they still have good heat insulating qualities with low thermal conductivity such as to, in the form of an ion process deposited hard dense film build-up, minimize chemical and physical failure as well as thermal shock damage and have resulted in materially improved operational service life on heat engine combustion chamber surfaces.
With the surface treatment of FIG. 6 a plurality of film layers are deposited successively over base material 45 that is aluminum, iron or steel or other suitable material. The film layers deposited by a high particulate energy level ion plating process are successively, over aluminum 45, nickle 46, chromium 47, chromium oxide 48, and titanium carbide 49 as an internal high temperature surface in an engine 10 or 28 or on a turbine blade 38. The film of nickle 46 is deposited with a phase zone 50 of atom penetration into the surface region of base metal 45. The successively higher films have phase zones 51, 52 and 53, respectively, in the upper surface regions of the nickle 46, chromium 47, and chromium oxide 48 of penetration atoms. Another advantage provided with the attainment of the different surface region phase zones of penetration atoms is stress relieval of base metal through the phase zone and development of an advantageous surface material compressive state. This greatly lessens the chance of thermal and mechanical shock damage and film separation. Further, with the Knoop hardness values from the aluminum base metal 45 to the top titanium carbide film 49 ranging, in order 200 to 557 to 920 to 1,600 to 2,300, at most approximately a step of 21/2 to 1 instead of over a 10 to 1 hardness ratio, with a titanium carbide deposit directly on aluminum, any likelihood of thermal and/or mechanical film separation damage is virtually eliminated.
With the high temperature surface treatment of FIG. 7 first an adhesion layer of chromium 54 is deposited on substrate base metal aluminum 55 and then successively thereover a distributive layer of chromium oxide 56, an insulation layer of hafnium oxide 57, and finally an outer layer of about 3,000 angstroms of silver 58 by either ion plating or sputtering for dry lubricity along with thermal and corrosion resistance. The silver is cold worked during operation into any surface irregularities that may exist to further reduce overall surface friction. The other film layers below the outer layer of silver are deposited by high particulate energy level ion plating so that there is a phase zone 59 of atom penetration into the surface region of base metal 55 and successively higher film phase zones 60, 61 and 62, respectively, in the upper surface regions of the chromium 54, chromium oxide 56 and hafium oxide 57. A film build-up used had chromium oxide layers deposited to a thickness of approximately 10 mils with the transformation from pure chromium to chromium oxide accomplished by admitting oxygen in an oxygen-argon gas mixture into the vacuum system during deposition. The refractory material hafnium oxide was then deposited to approximately 10,000 angstroms thickness. While a 50% oxygen- 50% argon gas mixture was used in the film build-up of FIG. 7 a 50% methane-50% argon gas mixture may be used in producing carbides such as titanium carbide of FIG. 6. The hot plasma action cracks the CH 4 molecule into carbon that reacts with metal atoms coming from the evaporant source and hydrogen that is pumped away. The temperature of the process where film is being deposited is sufficiently high that hydrides do not form nor appear in ion plating laid down. It should be noted that the films deposited on the high temperature heat engine surfaces and even those deposited on elements such as seal vane insert 16 are generally uniform thickness epitaxial films even with film build-ups running up to more than several mils thickness.
The film build-up of FIG. 8 may be used in place of that shown in FIG. 2 for components such as seal vane insert 16, curved seals 21 and 22 of the FIG. 1 heat engine and the piston rings 37 of the FIG. 3 engine or pump. The FIG. 8 film build-up includes first an adhesion layer of chromium 63 deposited on base material 64, aluminum, graphite, iron or steel, etc. and then successively thereover a chromium oxide layer 65 as a refractory heat insulating material film and finally an outer layer of silver 66. The film layers below the outer silver layer are deposited by high particulate energy level ion plating and the silver layer is deposited either by ion plating or by sputtering. There is a phase zone 67 of atom penetration into the surface region of the base material 64 and there are successively higher film phase zones 68 and 69, respectively, in the upper surface regions of the chromium 63 and chromium oxide 65. Other three film build-ups that may be employed in some applications in place of that of FIG. 8 are, respectively, hafnium, hafnium oxide and molybdenum disulphide (H f ,H f O and MoS 2 ); titanium, titanium nitride, and gold (Ti, TiN and Au); and titanium, titanium carbide and titanium nitride or titanium oxide (Ti, TiC and TiN or TiO).
Where hot surfaces are not in rubbing sliding contact, such as rotor faces 12a, 12b and 12c on the rotor 11 of FIG. 1, a film build-up such as shown in FIG. 6 may be employed. This applies also for piston tops and turbine blades although there are still some advantages in having an uppermost layer of one of some of the dry lubricant materials.
Sputtering is a process whereby gas ions in a vacuum system are accelerated by a high voltage to bombard a cathode (target) and cause ejection of atoms of cathode material. These high energy atoms immediately deposit on a nearby substrate surface. Plasma is the classic term for the fourth fundamental state of matter, i.e., a uniform mixture of positive ions and electrons. A neutral plasma is used as a source for the positive ions that bombard a target during the sputtering process to liberate atoms of material for deposition. Thus, the essential elements for a sputtering system are: (1) a vacuum system containing a sputtering cathode of desired material and the desired substrates, (2) a source of electrical energy both to develop the initial glow discharge and to sustain the operation on a continuous basis, and (3) a controlled source of gas to maintain the right pressure despite a continual removal of gas from the system to assure purity. In actual operation of the sputtering process the voltage applied to the glow discharge is dropped across Crooke's dark space. Ions move by diffusion through the neutral plasma. A positive ion reaching the surface of the plasma is attracted into the dark space and accelerated across it to collide with the target. At constant temperature the thickness of Crooke's dark space is inversely proportional to pressure. For argon plasmas the product of pressure and thickness is equal to approximately 0.3 torr-cm.
It is the high energy developed by the impinging ion as it accelerates across the space to strike the cathode that brings about a basic advantage of sputtering over conventional plating processes. As ions strike the cathode, they cause atoms of target material to shoot back across the dark space where they bombard the substrate. The particulate energy level in sputtering can easily be 1,000 times or more greater than that exhibited by conventional plating processes and is sufficient to drive the atoms into the substrate atomic lattice. Also, since the atoms at typical sputtering pressures encounter about eight collisions in crossing the dark space, the process is capable of coating three-dimensional objects.
Since the foregoing sputtering description is generally valid for targets of conductive material but not for insulators an rf (radio frequency) sputtering process is used for deposition of sputtered insulator films. This rf sputtering utilizes alternate ion and electron bombardment of the cathode surface to achieve deposition. When an rf signal is applied to a target electrode made of insulating material, a negative DC self-bias develops on the surface of the target. This is essential for sputtering since it gives a steady direction to the flow of positive ions across the dark space. The charged particles present in the field are electrons and singly charged positive gas ions (usually argon). Particle mobility is a direct function of charge and varies inversely with mass and mobility of the electron is approximately 10 5 greater than that of the ion. Thus, during the negative half cycles of the rf signal, more electrons than ions collect on the cathode surface and, since this surface is non-conductive, the electrons cannot leave on the positive half cycles. This has the effect of presenting a constant negative charge to the positive ions accelerating from the glow. Radio frequency sputtering is advantageous in many instances of metal sputtering, and with rf sputtering of metals, requiring, as with insulator cathodes, a constant negative potential on the cathode. This requires only the insertion of a blocking capacitor in the power circuit.
Ion plating is an atomistic deposition process in which the substrate is subjected to a flux of high energy ions sufficient to cause appreciable sputtering before and during film deposition. The ion bombardment is usually done in a gas discharge system similar to that used in sputter deposition, except with ion plating the substrate is made a sputtering cathode. With ion bombardment for a thin film to form it is necessary that the deposition rate exceed the sputtering rate. Benefits with ion plating are an ability to sputter clean the substrate surface and keep it clean until the film begins to form, a high energy flux to the substrate surface giving a high surface temperature enhanced diffusion and chemical reactions without requiring bulk heating, altering the surface and interfacial structure, and physically mixing the film during film deposition. Ion plating offers fast deposition rates allowing thin film work in mils rather than solely angstroms and the throwing power imparted to atom ions in ion plating is far greater than with sputtering. This, advantageously facilitates coating larger irregularly shaped objects, internal diameters or convolutions with a uniformly deposited film in a range from extremely thin to thick films.
Whereas this invention is illustrated and described with respect to a plurality of embodiments thereof, it should be realized that various changes may be made without departing from the essential contributions to the art made by the teachings hereof.