Metallic film diffusion for boundary lubrication in aerospace engineerin

Buckley, D. H.

Johnson, R. L.

English

Metallic film diffusion into metal or ceramic surfaces for boundary lubrication in aerospace environment

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON. D.C. 20546 
October 16, 1970 
TO : USI/Scientific SI Technical Information Division 
Attention: Miss Winnie M. Morgan 
FROM s GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT:: Announcement of NASA-Owned 
U . S ,  Patents in STAR 
In accordance with the procedures contained in the code GP 
to Code U S 1  memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U , S .  patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U,S. Patent No, 3,317,341 
Corporate Source E Lewis Research Center 
Supplementary 
Corporate Source 
NASA Patent Case NO. : XLE-01765 
Giy2.e Parker 
Enclosure: 
Copy of Patent 
- PB (THRlU d2 
(COPE) 
(CATEGORY) 
-G / 9 (NASA CR OR TMX OR AD NUMBER) 
y. 
NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710001298 2020-03-17T02:34:57+00:00Z
United States Patent ffice Patented 
3,317,341 
METALLIC FILM DIFFUSION FO 
 CATION 
Donald H. Buckley, North Olmsted, and Robert L. John- 
son, Fairview Park, Ohio, assignors to the United 
States of America as represented by the Administra- 
tor of the National Aeronautics and Space Adminis- 
tration 
No Drawing. Filed Qct. 15, 1963, Ser. No. 316,477 
1 Claim. (Cl. 11745.2) 
The invention described herein may be manufactured 
and used by or for the Government of the United States 
of America for governmental purposes without the pay- 
ments of any royalties thereon or therefor. 
The invention relates generally to metallic film lubri- 
cants and, more particularly, to diffusing a metallic film 
into a metal or other material for use as a lubricant. 
In aerospace applications where high reliability is de- 
sirable, it becomes necessary for moving parts to operate 
over substantial temperature ranges in the vacuum of 
outer space. Difficulty is experienced with available 03 
and grease lubricants because of their high evaporation 
rates. Some inorganic solid and soft materials having 
very low evaporation rates in vacuum appear to have 
promise as solid film lubricants for space. Where such 
lubricants are used as a liquid or in dispersed powder 
form, prcblems of zero gravity prohibit adequate lubrica- 
tion as the lubricant will not maintain itself within the 
enviTonment of the surfaces to be lubricated. Consequent- 
ly, a lubrication system is used whereby a solid film lubri- 
cant is formed on a surface to be lubricated which would 
act as a boundarv lubricant. However, where metallic 
alumina or other s imi lar  grinding compounds with a soft 
cloth. This polishing continues until the surface is per- - 
fectly clean. 
After polishing the surface and thereby improving to a 
5 degree the surface finish, the surface is thoroughly rinsed 
with tap water followed by distilled water. The rinsing 
urocess can also be accomulished with alcohol or another 
similar type of fluid. 
After cleaning the surface to which the lubricating film 
is to be applied, the metal which is to comprise the lubri- 
lo cant film is applied to the surface at a temperature above 
which it is in a liquid state. The liquified metal is applied 
to the surface by means of an applicator which, depending 
upon the surface and/or the temperature of the metal, 
15 can be a polishing cloth. The metal is rubbed over and 
diffused into the surface by applying a sufficient amount 
of pressure to the applicator. Where the temperature of 
the metal is beyond that which can be handled by a human 
hand, the applicator can be of a soft heat resistant ma- 
2o terial not reactive with the liquified metal nor abrasive 
to the surface upon which the liquid metal film is to be 
applied. 
After the liquid metal is uniformly distributed over the 
surface, the sample is heated to a temperature of approxi- 
25 mately 100" F. above its initial liquid phase temperature 
to allow the liquified metal to completely coat the surface 
and diffuse into the material surface. The sample is then 
allow to cool to its lower liquid phase temperature and 
wiped dry with a nonabrasive cloth to remove any excess 
3o metal. I t  has been found that this method will form a 
solid metallic film boundary lubricant on a surface ap- 
proximately 0.001 inch thick. 
It has been further found that for most films, a post- - . _.. 
film lubricants ark required, difficulty is experienced in heat treatment is preferable. The post-heat treatmentkon- 
applying them to material surfaces used in aerospace en- sists of placing the surface with the metallic film thereon 
vironments. The main difficulty is that these metallic 35 into an enclosed chamber for heating to a temperature of 
films will not maintain themselves on the Surface to be approximately 400" F. above its initial liquid phase tem- 
lubricated after application. Further, the conditions of perature for a period of approximately one hour. In a 
outer space dictate high operating temperatures due to method for accomplishing the aforesaid, a vacuum furnace 
solar radiation and heat generation experienced from 4o can be used to eliminate oxidation problems. The sur- 
rocket engine combustion. Therefore, it is a h  necessary face with the lubricant film thereon is then removed from 
to have lubricant films which will be resistant to tempera- the furnace and is allowed to cool to room temperature. 
tures to 1,000" F. The post-heat treatment temperature and the length of 
Accordingly, an object of the invention is to Provide time in the furnace can be varied; accordingly, this vari- 
for a method to apply to metal, ceramic and cermet Sur- ance would affect the friction and wear properties of the 
faces metallic films which can be used as boundary lubri- 45 surfaces associated with the film. 
cants in an aerospace environment. By use of the aforesaid method of the present invention, 
Another object of this invention is the production of it is possitble to impremate materials with a metal which 
articles with surfaces Of a metallic film diffused therein heretofore could not be done wherein the impregnated 
as distinguished from a mere coating Of a metallic film. metals would form a film on the surfaces and act as a 
tallic film lubricants having low friction properties which For space applications, it is preferable that materials 
can withstand temperatures to 1,000" F. and have a low selected for a boundary lubricant for use with the method 
evaporation rate. of the present invention have a low shear rate to give 
Briefly, these and other objects of the invention are low friction coefficients, have as low a melting or liquid 
attained by preparing the surface to be lubricated, rubbing 55 phase temperature as possible, and have a low evapora- 
thereon liquified metals Such as gallium and galliUm in tion rate. Further, the film should have as low an oxida- 
combination with tin, indium and lead, heating the Surface tion rate as possible. A metal which can be used with 
with the metal thereon, allowing the surface to COO1 and the method of the present invention is gallium. Tin, lead 
wiping the excess metal therefrom. Subsequently, a Post- and indium can be added to the gallium in various 
heat treatment is given wherein the surface with the me- 60 amounts to provide for metallic film lubricants having re- 
tallic film thereon is reheated and allowed to cool to room duced corrosion properties and, in Some instances, a lower 
temperature thereby improving the friction and wear prop- liquid phase temperature. 
erties of the surface with the metallic film. The following examples describe in greater detail the 
Other objects and advantages of the Present invention metallic film lubricants and the procedure for applying to 
will be described and will be apparent from the following 65 a surface the aforesaid metals for use as a metallic film 
description and the several embodiments thereof. for boundary lubrication: 
The method of the present invention consists of clean- As a first example, gallium is used as the metallic film 
ing the surface upon which the lubricant film is to be lubricant. Gallium is in liquid form over a temperature 
applied. The surface is prepared by rinsing it with ace- range of more than 3.500" F. At atmospheric pressures, 
tone or another solvent to remove grease and oil. Sub- 70 the liquid range is from approximately 86" F. to 3600" F. 
sequently, the surface is polished with moist levigated Gallium also has a low evaporation rate, that being 
Still another object of the invention is to provide me- 50 boundary lubricant. 
the post-heat treatment was substantially less than one 
hour and at temperatures substantially lower than 500" 
F., the friction and wear for the disc-film combination 4o 
was higher. Whereas, when the post-heat treatment 
temperature was 1,000" F., the friction and wear proper- 
ties were the same as for 500" F. Consequently, in the 
Pressure 
Gallium Indium 
(Percent Weight) (Percent Weight) I;I 
4400 Stainless Steel on 
4400 Stsinless Steel 
CoetacIent Wear, in.a/ft. Coefficient Wear in "ft. I of Friction I ofsliding I ofFriction 1 of sfid& 
I I I I 
In use of any type of metallic film applied to a surface steel. Tin, indium and lead added to the gallium in vari- 
as herein described, it is preferable that for the purposes ous amounts reduces the corrosivity of the gallium with 
of the method of the present invention that the metal various materials. 
used for the film have as low an initial liquid phase tem- As a fourth example, lead is added to the gallium in 
perature as possible. For gallium at normal atmospheric 70 various amounts from 5 percent to 50 percent. The 
conditions, the following can be achieved by the addition addition of lead to gallium will not reduce its liquid 
of tin or indium to the gallium. phase temperature. The corrosivity of the alloy can, 
As a second example of the present invention, approxi- however, be reduced. Friction and wear tests for the 
mately 8 percent tin is added to gallium which lowers gallium-lead alloy with amounts of lead by percent 
the initial liquid phase temperature of the pure gallium 75 weight contained therein, up to 50 percent, indicated that 
3,317,341 
the friction and wear properties of this alloy did not 
vary significantly from that of pure gallium alone. 
In an embodiment using the method of the present in- 
vention, a metallic lubricant film can be formed on the 
contacting surfaces of rotating machinery such as gears, 
elements of rolling-contact bearings and rotating face 
seals. A further embodiment using the method of the 
present invention can be the formation of an intermediate 
metallic film between two heat transfer surfaces in con- 
tact whereby the contact of the surfaces is not on the 
asperities of the surfaces but rather, the contact is over 
the entire area as defined by the metallic film. 
The present invention and specific embodiments there- 
to provide not only for metallic film boundary lubricants 
to and beyond 1,000' F., but also lubricants having low 
friction coefficients and low evaporation rates in aero- 
space applications. 
It is apparent from the above description that various 
modifications in the specific materials and procedures 
described may be made within the scope of the invention. 
Therefore, the invention is not intended to be limited to 
the particular materials and procedures described in de- 
tail herein except as may be required by the appended 
claim. 
We claim: 
A method of forming a metallic film of gallium and 
alloys thereof having low friction and wear properties 
on alumina and stainless steel surface which comprises 
removing foreign material from the surface upon which 
said metallic film is to be applied, polishing said surface 
5 to improve said surface finish, applying a gallium coating 
to said surface, rubbing said surface whereby said metal- 
lic film is formed and impregnates said surface, heating 
said surface with said metallic film to a temperature of 
200" F., cooling said surface with said metallic film to 
10 room temperature, removing excess metallic film on said 
surface, reheating said surface with said metallic film to 
a temperature from 450" F. to 550" F. for approximately 
one hour, and cooling to room temperature. 
15 References Cited by the Examines 
UNITED STATES PATENTS 
2,567,762 9/1951 Burkholder _ _ _ _ _ _  117-131 X 
2,700,623 1/1955 Hall _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _  117-71 
20 3,141,238 7/1964 Harman _ _ _ _ _ _ _ _ _ _ _ _  2 9 4 9 8  
3,184,330 5/1965 Carter _ _ _ _ _ _ _ _ _ _  117-131 X 
ALFRED L. LEAVITT, Primary Exuminer. 
J. R. BATTEN, JR., Assistartt Exominer. 
25 


Metallic film diffusion for boundary lubrication  Patent

REPLY TO 
ATTN OF: ep 
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON. D.C. 20546 
3 0 ,  19 
TO z USI/Scientific & Technical Information Division 
Attention: Miss Winnie M e  Morgan 
GP/Office of Assistant General 
Counsel for Patent Matters 
SUBJECT: Announcement of NASA-Owned 
UoS. Patents in STAR 
In accordance with the procedures contained in the Code GP 
to Code U S 1  memorandum on this subject, dated June 8, 1970, 
the attached NASA-owned U . S ,  patent is being forwarded for 
abstracting and announcement in NASA STAR. 
The following information is provided: 
U , S ,  Patent No. 
Corporate Source 
Supplementary 
Corporate Source 
SA Patent Case No,: 
"U 
Gayle Parker 
Enclosure: 
Y- 
(NASA CR OR TMX OR AD NUMBER) NASA-HQ 
https://ntrs.nasa.gov/search.jsp?R=19710014570 2020-03-17T03:04:19+00:00Z
ABS 
Gallium diffused into a surface forms a &eta& fib 
lubricant. Tin, lead, and indium are added to the gallium 
to reduce corrosjon properties and lower liquid phase 
lernperakres. 
The invention described herein was made by employees 
of the United States Government and may be manufac- 
tured and used by or for the Government for govern- 
mental purposes without the payment of any royalttes 
thereon or therefor. 
The invention relates generally to metallic film lubri- 
cants. More particularly, the invention i s  concerned with 
a metallic film which is diffused into a metal or other 
material for use as a lubricant. 
T h i s  application is a division of copendng application 
Ser. No. 316,477 which was filed Oct. 15, 1963 and issued 
as U.S. Patent No. 3,317,341. 
Bn aerospace applications where high reliability is de- 
sirable, i t  becomes necessary for moving parts to operate 
over substantial temperature ranges in the vacuum of outer 
space. Difficulty is experienced with available oil and 
gtease lubricants because of their high evaporation rates. 
Some inorganic solid and soft materials having very low 
evaporation rates in vacuum appear to b 4 e  pomise as 
solid film lubricants for space. Where svoh tubricants are 
used as a liquid or in dispersed powder form, problems of 
zero giavity prohibit adequate lubrjcatim as the lubricant 
will not maintain itself within the environment of the sur- 
face to be lubricated. Consequegtly, a lubrication system is 
used whereby a solid film lubricant is formed on  a surfacc 
to he lubricated which would act as a boupdary lubricant. 
However, where metalli; film lubricants are required, 
difficulty is experienced in applying them to material sur- 
face9 used i n  aerospace environments. The mgin difficulty 
is that these metallic films will not maintain themselves 
on the surface to be lubricated after application. Further, 
the conditions of outer space dictate high operating tem- 
peratures due to solar radiation and heat generation ex- 
perienced from rocket engine combustion. Therefore, it 
is also necessary to have lubricant films which will be 
resistant to temperatures to 1000" F. 
provide 
metallic films to be applied to metal, ceramic and cermet 
surfaces which can be uscd as boundav lubricants in qp 
aerospace environment. 
Another object of thig invention is to provide articles 
with surfaces of  a metallic film diffused therein as dis- 
tinguished from a mere coating of a metallic film. 
Still another object of the invention is to provide 
metallic film lubricants having low friction properties 
which can withstand temperatures to 10wO F. and have 8 
low evaporation rate. 
Briefly, these and other objects of the invention are 
attained by preparing the surface to be lubricaid, rubbing 
thereon liquified metals such as gallium and gallium in 
combination with tin, indium and lead, heeting mr- 
Accordingly, an object of the invention i s  
face with the metal thereon, allowing the surface to cool 
and wiping the: excess metal therefrom. Subsequendy, a 
post-heat treatment is given wherein the surface with the 
metallic film thereon is reheated and allowed to cool t~ 
room temperature thereby improving the friction and 
weae prnperties of the surface with the metallic film. 
Other objects and advantages of the present invention 
will be described and will be apparent from the following 
description and the several embodiments thereof. 
The surface upon which the lubricant film of the present 
invention is to be applied is cleaned. This is accomplished 
by rinsing the surface with acetone or another soIvent to 
replove grease and oil. Subsequently, the surface is 
polished with moist levigated aluminum or other ShilaS 
15 grinding compounds with a soft cloth. T h i s  polishing con- 
tinues until the surface is perfectly clean. 
After polishing,the surface and thereby improving .to 8 
degree the surface finish, the surface is thoroughly &IS& 
with tap water followed by distilled water. The rinsing 
similar type of fluid. 
After cleaning the surface to which the lubricating film 
is to be applied, the metal which is to comprise the Iubri- 
cant film is applied to the surface at a temperature above 
25 which it is in a liquid state. The liquified metal is applied 
to the surface by means of an applicator which, depeade 
ing upon the surface and/or the temperature of the metal, 
can be a polishing cloth. The metal is rubbed over and 
diffused into the surface by applying a sufficient amount 
30 of pressure to the applicator. Where the temprature of 
the metal is beyond that which can be handled by B 
human hand, the applicator can he of a soft heat resismt 
material not reactive with the liquified metal nor abrasive 
to the surface upon which the liquid metal film is to b 
After the liquid metal is uniformly distributed over &he 
surface, the sample is heated to a temperature of approxi- 
mately 100" F. above its initial liquid phase temperabre 
to allow the liquified metal to completely coat the surface 
413 and diffuse into the material surface. The sample is then 
allowed to cool to its lower liquid phase temperature and 
wiped dry with a nonabrasive cloth to remove any excess 
metal. It has been found that this method will form. 8 
solid metallic film boundary lubricant on a surface a p  
It has been further found that for most films, a post- 
heat treatment is preferable. The post-heat treatment COPI- 
sists of placing the surface with the metallic film thereon 
into an enclosed chamber for heating to a temperature of 
50 approximately 400' F. above its initial liquid phase tem- 
perature for a period of approximately one hour. In a, 
method for accomplishing the aforesaid, a vacuum furnace 
can be used to eliminate oxidation problems. The surface 
with the lubricant film thereon is then removed from the 
55 furnace and is allowed to cool to room temperature. The 
post-heat treatment temperature and the length of time In 
%he furnace can be varied; accordingly, this variance 
would affect the friction and wear properties of the sur- 
faces associated with the film. 
By use of the aforesaid method of &he present invention, 
it is possible to impregnate materials with a metal which 
heretofore could not be done wherein the impregnated 
metals would form a film on the surfaces and act as a 
boundary lubricant. 
For space applications, i& is preferable that materiais 
selected for a boundary lubricant have a low shear rate to 
givc low friction coeacients, have as low a melting or 
liquid phase temperature as possible, and have a low evap- 
oration rate. Further. the film should have as low an 
oxidation rate as possible. A metal which can be used with 
thc method of the present invention is gallium. Tin, lead 
and indium can be added to the gallium in various amounts 
20 process can aiso be 'accomplished with alcohol or 
35 applied. 
I 
45 proximately 0.001 inch thick. 
60 
65 
e' P * .  
. j  
- 8  
fob'prbviile for metallic fil lubricants having redaced possible. a1 atmospheric conditions, 
corrosion properties and, in some instant&, a IoWM liquid the foIlo*ing can' Be Iichiev-i by the addition bf tin'or 
phase temperature. indium to the gallium. 
TABLE 1 . -  
44OC Btainless Steel oq AlzOa on 44OC &ainless 
% * , I peiJicient Wear c o e m c i ~ t  Wear In.J/ 
44OC Btalnleas Bteel Steel , 
P- 
of Friction kt. of hlldlng of Friction Ft.of hiding 
' ..$.. 
The following examples describe in greater detail the 15 As a second example of the present invention, approxi- 
metallic film lubricants and the procedure for apptying mately 8 percent tin is added to gallium which lowers the 
to a surface the aforesaid metals for use as a metallic film initial liquid phase temperature of the pure gallium frbm 
for boundary lubrication: approximately $6' F? to 68' F. This Eacilitates the ap,di- 
As a first example, gallium is used as the metallic filnt cation of the metallic film lubricant. Using 92 percent by 
lubricant. Gallium is in liquid form over a temperature 20 weight gallium and 8 percent by weight tin, the eutectic 
range of more than 3500" F. At atmospheric pressures, alloy is applied as heretofore described for gallium in Ex- 
the liquid range is from approximately 86" F. lo 3600" F. ample 1 ;  however, the application temperature is at room 
Gallium also has a low evaporation rate, that being temperature that being approximately 72" F. 
1 x grams/cm.a/sec. While the gallium in actual ap- The following additional eutectic alloys of tin-gallium 
plication is applied to  the surface of face seals which are 25 are found to provide adequate boundary lubrication to 
made out of metals and ceramics, such as tool steels and temperatures beyond 1000" F. and have an initial liquid 
alumina, or to bearing cages made out of graphite, lead phase temperature below that of pure gallium. 
and titanium, for the purposes of this example the gallium 
Percent Weight 
surface made out of 44OC stainless steel which can be 30 Gallium Tin 
measurements. 85 16 '. 
as well as the other metaIs were applied to a flat disc 
used in conjunction with a rider for friction an8 wear 
by rinsing with acetone to remove greases, oils and other 
- 
96 4 
78 n 
60 40 
As previously described, the disc specimen is prepared 70 a0 
contamivadts contained thereon. Subsequently, the disc is 35 
pollshed with levigated alumina on a soft cloth and The tin-gallium eutectic alloys give approximately the 
t$oroughly rinsed with tap water followed by distilled same friction and wear properties as the pure gallium film 
water, Subsequently, liquid gallium is applied under pres- in Table 1. 
sure to the surface by means of a soft polishing c b t h  As a third example, approximately 24.5 percent by 
appficator in order to uniformly distribute the gallium 40 weight indium is added to the gallium which produces an 
over and into the surface of the disc. The aforesaid was initial liquid phase temperature of approximately 60" F. 
accomplished at  the lower liquid phase temperature of giving the additional advantage of applying this eutectic 
the gallium which is approximately 86" F. The disc with alloy at a lower temperature than that of pure gallium. 
the gallium contained thereon and diffused therein is 
. 
The indium-gallium eutectic alloy is applied as in Ex- 
heated to a temperature of approximately 200" F. lo allow 45 ample 2 for the tin-gallium eutectic alloy. 
the gallium to more completely coat and diffuse into the The following additional eutectic alloys of indium- 
surface of the disc. The sample is subsequently wimd with gallium are found to provide adequate boundary lubrica- 
a dry cloth to remove excess gallium immediately after lion to temperatures beyond 1000" F. and have an iniitial 
heating. Subsequently, the sample is allowed to cool liquid phase temperature below that of pure gallium. 
. 
- -  
Percent Weinht 
forming a film o f  approximately 0.801 inch thick on the 50 
surface of the disc. 
The disc with the gallium film is given an additionat &allium Indlum 
87.8 12. 8 treatment consisting of placing the disc specimen with the 
M) w) 
PO 500" F. for a period of approximately one hour. The 55 29 . 71 
disc is then removed from the furnace and allowed to cool 
to raom temperature. The indium-gallium metallic surface films produce fric- 
fo  has been found tbst for gallium where the h e  of don and wear results which do not vary significantly from 
the post-heal treatment was substantially less than One khat presented for the gallium metallic film lubricant sum- 
hour and at  temperatures substantially lower than 500' F., 00 marized in Table I .  
&e friction and wear for the disc-film combination was In many instances, pure gallium will be corrosive to 
higher. Whereas, when the post-heat treatment tempera- certain materials. Over a period of time, such corrosion 
ture was 1000" IF., the friction and wear properties were will occur in apparently inert materials such as stain- 
the same as for 5Q5" E Consequently, in the Present em- less steel. Tin, indium and lead added to the gallium in 
bodiment ob the invention, optimal friction and wear re- 65 various amounts reduces the corrosivity of the galrium 
sulis were obtained with a post-heat temperature between with various materials. 
F. and 550" F. for an approximate period of one As a fourth example, lead is added to the gallium in 
various amounts from 5 percent to 50 percent. The ad- 
The following table is an example Of friction and wear dition of Iedd to gallium will not reduce its liquid phase 
PRJPefiies of the gallium as a metallic Surface film a w ~ r d -  70 temperature. The corrmivity of the alloy can, however, 
b g  to the present invention Using two material combina- be reduced, Friction and wear tesk for the gallium-bad 
tiofis under atmospheric conditions and in a vacuum. alloy with amounts o f  lead by percent weight contained 
%I? U s e  of any type of metallic film applied to a Surface! therein, up to 50 percent, indicated that the friction and 
as herein described, it is preferable that the metal used for wear properties of this alloy did not vary significantTy 
metallic film into a vacuum furnace and heating the disc 
a w  as low an initial Iiquid @a* temperature as 75 from thatof pure gellium alone. . -  
~ , 3 ~ ~ ~ Q 8 ~  
In an embodiment of the resent invention, a metallic claim 1 consisting of a ctic alloy of gallium and 
lubricant film can be formed on the contacting surfaces lead. 
of rotating machinery such as gears, elements of rolling- 3. A metallic film boundary lubricant as claimed in 
contact bearings and rotating face seals. A further em- claim 2 comprising a binary alloy of gallium and be- 
bodiment of the present invention can be the formation 6 tween about 5 percent and about 50 percent by weight 
of an intermediate metallic film between two heat trans- lead. 
fer surfaces in contact whereby the contact of the sur- 4. A metallic film boundary lubricant as claimed in 
faces is not on the asperities of the surfaces but rather, claim 1 consisting of a eutectic alloy of gallium and 
the contaot is over the entire area as defined by the indium. 
metallic film. 5. A metallic film boundary lubricant as claimed in 
The preseht invention and specific embodiments there- lo claim 4 comprising a binary alloy of gallium and in- 
to provide not only for metallic film boundary lubri- dium between about 12.5 percent and about 71 percent 
cants to and beyond 1000" F., but also lubricants having by weight indium. 
low friction coefficients and low evaporation rates in 6. .A metallic film boundary lubricant as claimed in 
aerospace applications. 16 claim 1 consisting of a eutecti,c alloy of gallium and tin. 
It is apparent from the above description that various 7. A metallic film boundary lubricant as claimed in 
modifications in the specific materials and procedures de- claim 6 comprising a binary alloy of gallium and between 
scribed may be made within the scope of the invention. about 4 percent and about 40 percent by weight tin. 
Therefore, the invention is not intended to be limited 
to the particular materials and procedures described in 20 
detail herein except as may be required by the appended 
claims. UNITED STATES PATENTS 
What is claimed is: 2,700,623 1/1955 Hall __________-____ 117-71 . A metallic film boundary lubricant having an ini- 2,980,475 4/1961 wolfe _ _ _ _ _ _ _ _ _ _ _ _ _ _  252-25 
7/1964 Harman _ _ _ _ _ _ _ _ _ _ _ _  2 9 4 9 8  tial liquid phase temperature below 100" P. comprising 26 a eutectic alloy of gallium and a corrosion reducing 
metal having a melting point under 1000" F. selected 
the group consisting of lead, indium, and tin. 
A metallic film boundary lubricant as claimed in 
3,141,238 
DANIEL E. WYMAN, primary 
I. VAUGHN, Assistant Examiner, 


Metallic film diffusion for boundary lubrication Patent

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