A method of coating a substrate with an amorphous metal is described. A solid piece of the metal is bombarded with ions of an inert gas in the presence of a magnetic field to provide a vapor of the metal which is deposited on the substrate at a sufficiently low gas pressure so that there is formed on the substrate a thin, uniformly thick, essentially pinhole-free film of the metal

Khanna, S. K.

Thakoor, A. P.

Williams, R. M.

English

NASA Technical Reports Server

United States Patent I191 
Khanna et al. 
[I  I] Patent Number: 4,522,844 
[45] Date of Patent: Jun. 11, 1985 
[54] CORROSION RESISTANT COATING 
[75] Inventors: Satish K. Khanna; Anilkumar P. 
Thakoor, both of Pasadena; Roger M. 
Williams, Azusa, all of Calif. 
[73] Assignee: The United States of America as 
represented by the Administrator, 
National Aeronautics and Space 
Administration, Washington, D.C. 
[21] Appl. No.: 537,616 
[22] Filed: Sep. 30, 1983 
[5 11 Int. Cl.3 .............................................. C23C 15/00 
[52] US. C1. ........................................ 427/38; 427/47; 
204/192 N 
[58] Field of Search ............................. 427/38, 39, 47; 
204/192 R, 192 C, 164, 192 N 
1561 References Cited 
U.S. PATENT DOCUMENTS 
4,094,764 6/1978 Boucher et al. ................ 204/192 N 
4,108,751 8/1978 King ............................... 204/192 N 
Primaiy Examiner-John H. Newsome 
Attorney, Agent, or Firm-Paul F. McCaul; John R 
Manning; Thomas H. Jones 
[571 ABSTRACT 
Disclosed is a method of coating a substrate with an 
amorphous metal comprising the step of bombarding a 
solid piece of the metal with ions of an inert gas in the 
presence of a magnetic field to provide a vapor of the 
metal which is deposited on the substrate at a suffi- 
ciently low gas pressure so that there is formed on the 
substrate a thin, uniformly thick, essentially pinhole-free 
film of the metal. 
13 Claims, 6 Drawing Figures 
'r IO 
16 1 
https://ntrs.nasa.gov/search.jsp?R=19850020693 2020-03-22T19:40:52+00:00Z
U.S. Patent Jun. 11,1985 Sheet 1 of 3 4,522,844 
FIG. I 
I 8, 
I 05 
104 
103 
I02 
L I I 
16 
FIG. 2 
0.5 1.0 1.5 2.0 
DEPTH(Am) 
e S e  Patent Sheet 2 of 3 4,522,844 
FIG. 3A 
FIG. 3 
U.S. Patent Jun. 11,1985 Sheet 3 of 3 4,522,844 
FIG. 3C 
FIG. 30 
4,522,844 
1 2 
gether in the solid state. In accordance with our 
method, these solid materials will be vaporized by ion CORROSION RESISTANT COATING 
bonbardment and form a metal film on the substrate. 
Third, the film so formed will always be of a single BACKGROUND OF T H E  INVENTION - 
1. Origin of the Invention 
The invention described herein was made in the per- 
formance of work under a NASA Contract and is sub- 
ject to the provisions of Section 305 of the National 
Aeronautics and Space Act of 1958, Public Law 85-568 
(72 STAT 435; 43 USC 2457). 
2. Field of the Invention 
phase. This improves corrosion resistance because there 
will not be an electrochemical potential between differ- 
ent segments of the film which might be a source of 
corrosion. Fourth, the film so formed, if it is subjected 
to corrosion, will corrode uniformly without pitting or 
lo  crevice corrosion. This is in contrast to, for example, 
stainless steel, which when corrosion begins, forms a pit 
corrosive action. 
This invention relates to a method of applying a thin or puncture which Serves as the site for the expanding 
film of amorphous metal to a substrate, and in particular 
a method for applying the film at a sufficiently low 
pressure so that the film is essentially devoid of micro- l 5  BRIEF DESCRIPTION O F  THE DRAWINGS 
structure such as columns, voids, pinholes, etc. and is 
homogeneous, uniform, dense and exhibits a smooth 
mirror-like surface finish. 
3. Background Discussion 
To minimize corrosion, many metal parts are coated 
with, for example, chrome which is a corrosion-resist- 
ant metal. Nevertheless, these chrome plated parts are 
still subject to corrosion and it costs several billions of 
dollars annually to combat or replace corroded equip- 
ment. 
20 
25 
FIG. 1 is a schematic illustration of the method of our 
invention; 
FIG. 2 is a graph illustrating the composition of the 
film as a function of film thickness. 
FIG. 3A is a micrograph of a substrate coated with an 
amorphous metal film at low pressure according to our 
invention. 
FIG. 3B is a micrograph of a substrate coated with an 
amorphous metal film at high pressure. 
FIG. 3C is a micrograph of a-substrate coated with an 
FIG. 3D is a micrograph o f a  substrate coated with an 
amorphous metal film in the presence of oxygen. SUMMARY OF THE INVENTION 
We have invented a method for coating substrates 
with an amorphous metal (as ~ e d  herein metal means amorphous metal film in the presence of nitrogen. 
metal and metal alloys) so that there is applied to the 30 
substrate a thin, uniform, essentially pinhole-free film. DETAILED DESCRIPTION OF THE DRAWING 
The pinhole-free film is dense and mirror-smooth. Es- illustrated in FIG. 1, a substrate 10 is coated with 
Our method’ and are the netron sputtering process. A target 12 of the amorphous most common substrates. According to this method, a 35 metal disposed in a vacuum chamber (not shown) is solid piece of the amorphous metal, which serves as the 
target, is bombarded with ions derived from an inert gas bombarded with positive ions. The ions are formed by 
presence of a magnetic field near the target. The born- target 12. A cathode 16 holds the substrate 10, which in 
bardment of the piece of metal produces vapor of the 40 effect is also the cathode because it is in electrical. 
metal which is deposited on the substrate. Deposition of contact with it. When the potential is applied across the 
the vapor is conducted at a very low pressure sufficient anode 14 and cathode 16, the gas in the chamber ionizes. 
to form the desired uniform, dense, pinhole-free film. The preferred gas is argon. Upon ionization electrons 
Typically the gas pressure is no greater than about 10 are liberated and the positively charged argon ion 
micrometers. We have found that at higher pressures, or 45 strikes the surface of the target 12. There is an exchange 
if the gas constituents react with the metal, the desired of momentum, the argon ion mowing at a high velocity 
pinhole-free film is not formed. If, on the other hand, knocks out atoms of the metal from the surface of the 
there are no reactive gases Present and the gas Pressure target. The knocked out atoms of the metal essentially 
is low, a thin, uniform, homogeneous, essentially pin- constitute a vapor beam, which is. carried to the surface 
hole-free film is formed on the substrate. The combina- 50 of the substrate and deposited on the surface, The pres- 
tion of the substrate coated with such film also is a novel ence of a magnet 18 adjacent to the target 12 provides a 
magnetic field which serves to trap the secondary elec- article of manufacture. 
The amorphous is an Of One Or trons near the cathode 16. The absence of the magnet 18 
more transition metals and metalloids. The transition would result in the electrons to the substrate metals are selected from the group scandium, yttrium, 5 5  and excessively heating it. This would be undesirable, lanthanum, titanium, zirconium, hafnium, vanadium, especially if a plastic substrate was being coated. In niobium, tantalum, chromium, molybdenum, tungsten, 
manganese, technetium, rhenium, iron, ruthenium, os- accordance with this invention, the method is carried 
sentially any substrate Of any shape may be coated using a thin film of amorphous metal by employing the mag- 
plasma. The bombarding of the target takes place in the imposing a high across an anode l4 adjacent the 
mium, cobalt, rhodium, iridium, nickel, palladium and 
platinum. The metalloids are selected from the group 60 which is essentially pinhole-free. Typically the pressure 
Out at a very low pressure sufficient to form a 
consisting of silicon, boron, carbon, germanium and 
phosphorus. Specific alloys employed included (Moo,. 
6R~0.4)82B 18; (Moh2B 18; and (Wo.6Reo.4)76B24. 
This invention has several advantages. First, there is 
provided a highly corrosion resistant, thin film which 65 Kern (Academic, New York, 19781, P. 60. 
prptects the substrate. Second, a wide variety of amor- 
phous metals may be employed and they need not be 
first melted, but may simply be mixed thoroughly to- 
will be no greater than 10 micrometers of mercury and 
Preferably is about 2 micrometers of mercury Or less. 
The magnetron sputtering process is disclosed in detail 
in Thin Film Processes, edited by J. L.  Vossen and W. 
The following is a specific example of the method of 
our invention and an article of manufacture produced 
by this method. 
4,522,844 
3 
EXAMPLE 
( M O O . ~ R U O . ~ ) ~ ~ B ~ ~  films were deposited onto clean 
glass slides by d c  magnetron sputtering in dry argon 
from a water-cooled composite target using an S-gun 
sputtering system (Sputter Films, Inc.). A hydrocarbon- 
free, turbomolecular-pumped vacuum system was ini- 
tially pumped down to a base pressure of -5X lo-’ 
Torr, and flushed with dry argon gas several times 
before dynamically maintaining the chamber at the 
desired sputtering pressure. A large capacity liquid- 
nitrogen-cooled trap, resulting in pumping speed of 900 
liters/sec, was provided in the sputtering chamber. 
The  target was fabricated by hot-pressing a mixture 
of high-purity Mo, Ru, and B powders in the desired 
proportion. The target was preconditioned by sputter- 
ing at constant rate and constant, usually 5 micrometer 
(pm), A r  pressure. Chemical composition of the films 
was determined by using energy dispersive spectros- 
copy (EDS) and ion microprobe (Cameca, Inc.). The  
composition of several initial deposition runs was moni- 
tored to verify that the preconditioning of the target 
was complete. After about 100-pm erosion of the target 
surface, the target had completely equilibrated itself 
with the sputtering conditions so as to yield the same 
chemical composition throughout the thickness of the 
film and in films deposited in subsequent runs. In addi- 
tion, in each deposition run the target was presputtered 
for several minutes onto the shutter prior to deposition 
onto the substrates. 
T w o  to four pm-thick films were deposited in vary- 
ing pressures of pure Ar, A r  and 0 2  mixture, or A r  and 
N2 mixture. The  substrates were clamped onto a water- 
cooled copper block with a thin layer of vacuum grease 
to assure good thermal contact. The temperature of the 
substrates was monitored by a copper constanta ther- 
mocouple, and was found to rise only a few degrees 
above room temperature during deposition under 
steady-2tate conditions. A typical rate of deposition was 
-350 A/min onto substrates held - 15 cm away from 
the target, for -500-W dc power applied to the target. 
The  films were checked for crystallizing and short 
range structure by X-ray diffraction. Their surface mor- 
phology and tensile fracture cross-sections were ob- 
served at different tilt angles by using scanning electron 
microscopy (SEM). Corrosion behavior of the films 
was studied by potentiostatic and potentiodynamic 
techniques in I N  H2S04 and other corrosive solutions. 
The potentia-dynamic polarization curves were re- 
corded by using Ag/AgCl reference electrodes and 10 
mV/sec scan rate, and potential static corrosion rates 
were determined by measuring current flow after hold- 
ing the potential constant for 20 minutes to three hours. 
A. Composition 
FIG.  2 shows a depth profile of the chemical compo- 
sition measured using ion microprobe for a film depos- 
ited under 5 pm pressure of Ar, whose scanning elec- 
tron micrograph is shown in FIG. 3(A). The uniformity 
of the composition throughout the film thickness is 
remarkable. Since composition is an important parame- 
ter affecting chemical corrosion, it was verified when- 
ever a new film was deposited under altered sputtering 
conditions. 
B. Structure 
The film deposited at 5-pm-Ar pressure has an ex- 
tremely smooth surface and almost featureless tensile 
fraction cross-section, as shown in the SEM picture in 
FIG.  3(A). The surface roughness increased rapidly 
4 
with increasing A r  pressure, and the film cross-section 
showed a dense but distinct vertical columnar structure 
as shown in FIG.  3(B). This film was deposited at -35- 
pm-Ar pressure. It must be mentioned here that the 
5 films deposited at as high as 75-pm-Ar pressure were 
nevertheless observed to be amorphous according to 
X-ray diffraction. The rate of deposition, however, 
decreased drastically with increasing Ar  pressure. 
Amorphous films deposited under the mixture of - 5 
10 p m  of A r  and -2 p m  of 0 2  exhibited highly developed 
zone structure with poorly bonded vertical columns, 
large voids, and dispersed surface mounts. The lumpy 
top surface and multiply cracked fracture cross-section 
of such a film are shown in FIG. 3(C). Increased pres- 
l5 sure in the chamber, due to the introduction of oxygen, 
contributed to the oblique flux component. The ion 
microprobe analysis of these films did not show any 
appreciable amount of oxygen in them. 
On the other hand, the X-ray diffraction pattern of 
the film deposited under -5-pm-Ar and -2-pm-N? 
mixture showed several diffraction peaks superimposed 
onto the broad halos characteristic of the amorphous 
structure. Although it appears that the films might have 
some segregated regions as crystalline inclusions, the 
25 diffraction pattern lacks the required clarity for any 
unambiguous and meaningful identification. The  films 
deposited in argon-nitrogen mixture exhibited a void- 
free and dense vertical columnar structure in their frac- 
The  above description presents the best mode con- 
templated of carrying out the present invention. This 
invention is, however, susceptible to modifications and 
alternate constructions from the embodiments shown in 
35 the drawing and described above. Consequently, it is 
not the intention to limit this invention to the particular 
embodiments disclosed. On the contrary, the intention 
is to cover all modifications and alternate constructions 
falling within the spirit and scope of the invention as 
3o ture cross-section as shown in FIG. 3(D). 
40 expressed in the appended claims. 
What is claimed is: 
1. A method of providing a substrate with a thin, 
(a) selecting one or more transition metals; 
(b) selecting one or more metalloids; 
(c) thoroughly mixing said metals and metalloids to 
form a solid material in the shape of a target suit- 
able for deposition sputtering; 
(d) bombarding the target with ions of an inert gas in 
the presence of a magnetic field to provide a vapor 
of the target material and deposit the vaporous 
target material onto the substrate; and 
(e) maintaining the pressure of the gas sufficiently 
low to cause the target material to deposit onto the 
substrate in a thin, uniformly thick, essentially pin- 
hole-free amorphous metallic alloy film. 
2. The method of claim 1 wherein the metal is se- 
lected from the group scandium, yttrium, lanthanum, 
titanium, zirconium, hafnium, vanadium, niobium, tan- 
60 talum, chromium, molybdenum, tungsten, manganese, 
technetium, rhenium, iron, ruthenium, osmium, cobalt, 
rhodium, iridium, nickel, palladium and platinum and 
the metalloids are selected from the group consisting of 
silicon, boron, carbon, germanium and phosphorus. 
3. The method of claim 1 wherein the gas pressure is 
no greater than about 10 micrometers of mercury. 
4. The method of claim 1 wherein the target material 
corrosion-resistant coating comprising the steps of: 
45 
50 
55 
65 
is (Moo.6Ruo.4)82Biz; (Mo)z2Biz; or  (W0.6Re0.4)76B?4. 
4,522,844 
5 6 
5. The method of claim 1 wherein the substrate is boron, carbon, germanium and phosphorus; (c) mixing 
glass, plastic ceramic, or metal. the selected transition metals and metalloids together; 
6.  The method of claim 1 wherein the bombarding is (d) pressing the mixture of selected metals and metal- 
conducted in an electric field which ionizes the inert loids into a solid shape in the form of a target; (e) sur- 
gas. 5 rounding the target and substrate with an inert gas hav- 
7. The method of claim 6 wherein the electric field is ing a pressure no greater than about 10 micrometers of 
established between an anode and a cathode, with the mercury; and (f) bombarding the target with ions of the 
target being positioned adjacent the anode. inert gas in the presence of a magnetic field to provide 
8. The method of claim 1 wherein the substrate is a vapor of the target material and deposit the vaporous 
cleaned prior to applying the thin film. 10 target material onto the substrate in a thin, uniformly 
9. The method of claim 1 wherein the metal piece is thick, essentially pinholefree amorphous metallic alloy 
cleaned by bombarding the substrate with ions of the film. 
inert gas. 11. The method of claim 10 wherein the target mate- 
10. A method of coating a substrate with a corrosion- rial is one of ( M o o . ~ R u o . ~ ) ~ ~ B ~ ~ ;  (MO)g2B13 and 
resistant coating comprising the steps of: (a) selection 15 (W0.6Re0.4)76B24. 
one or more transition metals from the group consisting 12. The method of claim 10 wherein the target is 
of scandium, yttrium, lanthanum, titanium, zirconium, bombarded with ions until the coating is about 2 to 4 
hafnium, vanadium niobium, tantalum, chromium, mo- micrometers thick. 
lybdenum, tungsten manganese, technetium, rhenium, 13. The method of claim 10 wherein the inert gas is 
iron, ruthenium, osmium, cobalt, rhodium, iridium, 20 argon and the pressure of said gas is maintained at about 
nickel, palladium and platinum; (b) selection one or 5 to 10 micrometers of mercury. 
more metalloids from the groups consisting of silicon, * * * * *  
25 
30 
35 
40 
45 
50 
55 
60 
65 


Corrosion resistant coating

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