The adhesion, friction, and wear properties of sputtered refractory coatings on substrates of materials that form stable nitrides is improved by placing each substrate directly below a titanium carbide target of a commercial radiofrequency diode apparatus in a vacuum chamber. Nitrogen is bled into the system through a nozzle resulting in a small partial pressure of about 0.5% to 2.5% during the first two minutes of deposition. The flow of nitrogen is then stopped, and the sputtering ambient is reduced to pure argon through a nozzle without interrupting the sputtering process. When nitrogen is deliberately introduced during the crucial interface formation, some of the titanium at the interface reacts to form titanium nitride while the metal of the substrate also forms the nitride. These two nitrides atomically mixed together in the interfacial region act to more strongly bond the growing titanium carbide coating as it forms on the substrate

Brainard, W. A.

Wheeler, D. R.

English

NASA Technical Reports Server

United States Patent [191 
Brainard et al. 
[111 4,336,117 
1451 Jun. 22, 1982 
[54] REFRACTORY COATINGS AND METHOD 
[75] Inventors: William A. Brainard, Arlington, Va.; 
OF PRODUCING THE SAME 
Donald R. Wheeler, Bay Village, 
Ohio 
[73] Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 102,003 
[22] Filed: Dec. 7,1979 
[51] Int. (3.3 .............................................. C23C 15/00 
[52] U.S. Cl. ................................................. 204/192 C 
[58] Field of Search ...................... 204/192 C, 192 SP 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,503,787 3/1970 Penose ............................... 117/93.1 
3,793,175 2/1974 Joly ................................. 204/192 C 
3,798,145 3/1974 Fournier ......................... 204/192 C 
3,912,461 10/1975 Wakefield ........................... 204/192 
4,098,956 7/1978 Blickensderfer .................... 428/627 
FOREIGN PATENT DOCUMENTS 
1117009 6/1968 United Kingdom .......... 204/192 SP 
OTHER PUBLICATIONS 
Stephen Pepper et al., Shear Strength of Metal-Si02 
Contacts, NASA TM-78838, 3/78. 
J. E. Greene and M. Pestes, Adhesion of Sput- 
ter-Deposited Carbide Films to Steel Substrates, Thin 
Solid Films, 37 (1976), pp. 373-385. 
William A. Brainard et al., “An XPS Study of the Ad- 
herence of Refractory . . .  Coatings”, J. Vac. Sci. 
Technol. 15(6), Nov./Dec. 1978, pp. 1800-1805. 
Primary Examiner-Delbert E. Gantz 
Assistant Examiner-William Leader 
Attorney, Agent, or Firm-Norman T. Musial; John R. 
Manning; Gene E. Shook 
1571 ABSTRACT 
This invention is concerned with improving adhesion, 
friction and wear properties of sputtered refractory 
coatings on substrates of materials that form stable ni- 
trides. 
Each substrate (10) is placed directly below a titanium 
carbide target (16) of a commercial radiofrequency 
diode apparatus (14) in a vacuum chamber (26). Nitro- 
gen is bled into the system through a nozzle (30) result- 
ing in a small partial pressure of about 0.5% to 2.5% 
during the first two minutes of deposition. The flow of 
nitrogen is then stopped, and the sputtering ambient is 
reduced to pure argon through a nozzle (28) without 
interrupting the sputtering process. 
When nitrogen is deliberately introduced during the 
crucial interface formation, some of the titanium at the 
interface reacts to form titanium nitride while the metal 
of the substrate also forms the nitride. These two ni- 
trides atomically mixed together in the interfacial re- 
gion (38) act to more strongly bond the growing tita- 
nium carbide coating (12) as it forms on the substrate 
(10). 
5 Claims, 2 Drawing Figures 
https://ntrs.nasa.gov/search.jsp?R=19820021539 2020-03-21T17:15:21+00:00Z
U.S. Patent Jun. 22, 1982 4,336,117 
F I G .  I 
FIG. 2 
4.336,117 
1 
REFRACTORY COATINGS AND METHOD OF 
PRODUCING THE SAME 
DESCRIPTION 
ORIGIN O F  THE INVENTION 
The invention described herein as made by employ- 
ees of the United States Government and may be manu- 
factured and used by or for the Government for govern- 
mental purposes without the payment of any royalties 
thereon or therefor. 
TECHNICAL FIELD 
This invention is concerned with improving the prop- 
erties of sputtered refractory coatings on a substrate of 
a material that forms stable nitrides. Adhesion, friction, 
and wear properties of refractory coatings produced in 
accordance with the invention are superior to similar 
properties of conventional coatings. 
Various hard coatings that are applied by rf sputter- 
ing have been proposed for improving wear resistance 
and providing low friction characteristics. It is the ad- 
herence of these coatings to the substrate rather than 
other coating properties that is the limiting factor in 
their use. Failures are generally observed to occur at the 
coating-substrate interface. 
Titanium carbide coatings are used in anti-wear appli- 
cations. Such coatings are used to prevent fretting fa- 
tigue and wear in titanium alloy aircraft parts. Titanium 
carbide has been proposed for cutting tool coatings as 
well as for bearing and seal applications. 
BACKGROUNDART 
US* Pat. No. 4,098,956 to Blickensdorfer et a1 dis- 
closes a process for making spectrally selective solar 
absorbers by depositing layers of metal or carbides, 
including titanium, wherein oxides, suboxides, or ni- 
trides can be produced using the appropriate atmo- 
sphere of oxygen or nitrogen with argon during sputter- 
ing. In one embodiment a subnitride of the metal is 
produced. Pendse US. Pat. No. 3,503,787 is concerned 
with making refractory aluminum nitride coatings by 
plasma spraying. Titanium nitride is formed by the use 
of nitrogen in the plasma. Wakefield US .  Pat. No. 
3,912,461 is directed to the sputtering of titanium car- 
bonate onto a substrate to produce a hard, wear-resist- 
ant surface. None of these patents is concerned with 
providing metal nitrides in the interfacial region be- 
tween a substrate and refractory coating. 
DISCLOSURE OF INVENTION 
In accordance with the present invention a thin sput- 
tered film is provided that exhibits improved adherence 
to a substrate and has improved friction and wear char- 
acteristics. These improvements are achieved by coat- 
ing the substrate by rf sputtering with a film of titanium 
carbide using an argon sputtering plasma. A small nitro- 
gen partial pressure from about 0.5% to 2.5% is added 
in the initial stages of the deposition during which the 
interface is formed. The improvements in adhesion of 
the titanium carbide coating to the substrate results 
from the presence of both titanium nitride and a nitride 
of the substrate in the interfacial region. 
5 
10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
BRIEF DESCRIPTION O F  DRAWINGS 
The details of the invention will be described in con- 
nection with the accompanying drawings wherein 
2 
FIG. 1 is a perspective view of an apparatus utilized 
in sputtering B refractory coating onto a substrate; and 
FIG. 2 is an enlarged sectional view of a substrate 
coated in accordance with the present invention. 
DETAILED DESCRIPTION O F  THE 
INVENTION 
Referring now to the drawings there is shown in 
FIG. 2 a substrate 10 coated with a refractory film 12. 
The substrate 10 is of a material that forms stable ni- 
trides and is preferably a metal. 
Test specimen substrates 10 in the form of 440-C 
bearing-steel discs were coated in accordance with the 
invention. All of the disc specimens were mechanically 
polished in the same manner. The discs were abraded on 
silicon carbide paper down to 600 grit. Then they were 
polished with three pm diamond paste and lapped with 
one pm alumina. After lapping the discs were rinsed 
with alcohol and dried. The metal disc substrates were 
then individually mounted in a commercial radiofre- 
quency diode apparatus 14 in a manner described below 
for coating in accordance with the invention. This appa- 
ratus operated at 13.56 MHz. 
Each polished disc substrate 10 to be coated is placed 
directly below a titanium carbide target 16 on an electri- 
cally insulated block 18. A substrate table 20 that is 
grounded by a conductor 22 supports the block 18. 
Each disc substrate 10 is positioned in this manner 
approximately 2.5 centimeters directly below the target 
16. The grounded table 20 and the target 16 constitute 
the rf diode. The rf voltage and target cooling are sup- 
plied through a support 23. An additional voltage from 
zero to - 1500 v dc may be applied directly to the disc 
10 through a conductor 25 either for cleaning by direct- 
current sputter etching or for biasing during film depo- 
sition and growth. 
Provision is made for the entire substrate table 20 to 
be rotated selectively about a support post 24. By rotat- 
ing the table 20 the target 16 can be cleaned without 
contaminating the disc specimen 10. Cleaning the disc 
specimen 10 is accomplished by sputter etching at 
-1200 v for 15 minutes after the target cleaning i s  
completed. The cleaning and coating operations are 
performed in a vacuum chamber 26 which houses the 
target 16 as well as the grounded table 20. 
A regulated flow of high purity argon is selectively 
introduced into the vacuum chamber 26 through a noz- 
zle 28. A second nozzle 30 admits a controlled flow of 
nitrogen from a supply cylinder 32. The flow of nitro- 
gen is controlled by variable leak valves. 
After cleaning, the flow of argon through the nozzle 
28 is interrupted and the chamber is pumped by a vac- 
uum line 34 connected to a vacuum pump 36. The sys- 
tem is pumped down to a base pressure of about 10-6 
torr. 
According to the invention, nitrogen is then bled into 
the system through the nozzle 30 from the cylinder 32 at 
a pressure in the range of about 1.3 X 10-2 to 6.6x 
Newtons per square meter. Once the desired pressure is 
reached, argon is again admitted through the nozzle 28, 
and the total pressure is raised to the sputtering pressure 
of approximately 20 pm. 
The voltage on the disc specimen is reduced to - 500 
v for biasing in a manner well known in the art. The disc 
specimen 10 is rotated by the table 20 back under the 
target 16, and deposition is begun. 
According to the present invention the critical inter- 
facial region 38 is formed during the first two minutes of 
4,336,117 
3 4 
deposition. After this first two minutes, the flow of 
nitrogen through the nozzle 30 is stopped, and the sput- 
tering ambient is again reduced to pure argon without 
interrupting the sputtering process. The balance of the Of 
5 manufacture wherein a titanium carbide coating is de- deposition is then completed. posited on a steel substrate from a radiofrequency sput- The power density is about 1.64 Wcm-2. Coatings tering plasma, the improvement comprising 
are approximately 2000 angstroms in thickness for fric- introducing nitrogen into the sputtering environment 
tion and wear testing. These thicknesses were measured during the formation of the interfacial reg,on of the 
by surface profilometry of a deposition step. coating at the substrate thereby forming a mixture of 
When nitrogen is deliberately introduced during the titanium nitrides and iron nitrides in said interfacial 
crucial interface formation, some of the titanium of the region which improves the bond between the coating 
interface reacts to form titanium nitride while iron in and the substrate. 
the substrate 10 forms a nitride. These two nitrides, 2. The method of claim 1 wherein nitrogen is intro- 
atomically mixed together in the interfacial region 38 15 duced at a partial pressure sufficient to comprise about 
shown in FIG. 2, act to more strongly bond the grow- 
3. The method of claim 2 wherein the nitrogen is ing titanium carbide coating. 
4. A method of producing a hard coated article of A number of test specimens were coated in accor- 
dance with the invention with various nitrogen partial 2o manufacture having improved adhesion between a tits- 
pressures in the range Of 6.6x lo-' to 6hx New- nium carbide refractory coating and a steel substrate 
tons per square meter. The coatings were evaluated in a comprising the steps of 
Pin-on-disc apparatus of the type used for solid film placing the substrate in a vacuum chamber containing 
lubrication evaluation. This test apparatus has a stainless radiofrequency diode apparatus, 
steel pin selectively loaded against each test specimen as 25 reducing the pressure in said chamber to a base pressure 
the disc is rotated. A strain gauge is used to measure the of about 10W6 torr, 
friction force. supplying nitrogen to said vacuum chamber at a pres- 
Each disc specimen was tested for 30 minutes in a dry Sure in the range of about 1.3 x to about 
nitrogen atmosphere at a constant speed. The results are 6.6x Newtons per 'quare meter, 
30 admitting argon into said vacuum chamber to raise the shown in the table. 
total pressure to about 20 pm, 
sputtering to deposit from a plasma an interfacial region 
Nitrogen which contains a mixture of titanium nitride and iron 
partial Percent Friction and nitride, 
pressure of wear behavior 35 interrupting the supply of nitrogen to said vacuum 
6 6  X 0.25 Film failure sputtering to deposit the remainder of the titanium car- 
1.3 x lo-* 0 50 Smooth low bide refractory coating in an environment substan- 
tially free of nitrogen so that said remainder of the 
6.6 x 2.5 Smooth low 40 titanium carbide refractory coating is substantially 
free of titanium nitride and iron nitride. 
1.3 x 10-1 5 Film failure 5. A method of producing a hard coated article of 6.6 x 10-1 25 Film failure 
manufacture as claimed in claim 4 wherein the supply of 
nitrogen to the vacuum chamber is interrupted about 
Although the invention has been described relative to 45 two minutes after the radiofrequency sputtering i s  
started. 
in these embodiments without departing from the scope 
and spirit of the invention. 
We '. In a method Of producing a hard coated 
10 
0.5% to 2.5% Of the plasma. 
introduced for about two minutes. 
chamber, and (N m2) Plasma at 10 N load 
fnction, p = 0.35 
friction, p = 0.35 
exemplary embodiments thereof, it will be understood 
that other variations and modifications can be effected * * * * *  
50 
55 
60 
65 


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