Note: Descriptions are shown in the official language in which they were submitted.
_ D-9435
~036390
This invention relates to a novel powder for
use in producing articles and coatings having unique wear
and frictional characteristics. More particularly this
invention relates to powders which are to be applied as
a coating on a substrate using metal spraying techniques
and to the articles and coatings made thereby.
Chromium metal has been used as an electro-
plated coating (i.e., "hard chromium plating") for many
years to restore worn or damaged parts to their original
dimensions, to increase wear resistance, reduce friction,
and provide corrosion resistance. Chromium's excellent
wear and frictional characteristics have been attributed
to its low ratio of energy of adhesion to hardness when
mated against a number of materials that are commonly used
in engineering applications. Hard chromium electroplate,
however, has a number of limitations. The electroplating
of chromium is economically feasible when the configuration
of the part is relatively simple and the number of the
parts and/or their size is relatively small. When the
configuration of the part becomes complex, obtaining a
uniform coating thickness by electro-deposition is dif-
ficult and requires precise placement of electrodes and
thieves. Without a uniform coating thickness, grinding
to a finished surface configuration becomes necessary,
and it is both difficult and expensive with electroplated
- - .
- - , -
_ D-9435
1 ~ 39~D
chromium because of its inherent brittleness and hardness.
The rate of deposition by electroplating is relatively low,
and thus for a large number of parts andtor large areas
and/or thick coatings a very substantial capital investment
in plating tanks and power supplies i8 required. In chro-
mium electroplating it is often necessary to use expensive
surface cleaning and etching procedures to prepare sub-
strates. Further, with many substrate materials it is
not possible to directly apply chromium electroplating
and one or more undercoats of other metals must be used.
Spent plating baths present a disposal problem because
they are a serious pollution source, and hence handling
them adds significantly to the cost of the process.
An alternative method of depositing chromium
metal is by metal spraying such as with 8 pla~ms or
detonation gun. These methods offer a number of process-
ing advantages. Surface prepartion is relatively simple
and inexpensive. The coatings can be applied to almost
any metallic substrate without using undercoats. The rate
of deposition is very high so that a large volume of parts
can be coated with a minimal capital investment. The
coating thickness can be controlled very closely so that
any subsequent finishing can be kept to a minimum. The
overspray can be easily contained and recovered making
pollution control a simple matter.
-- 3 --
. _ ,
.
- : D-9435
1 ~ 3 ~
Unfortunately, plasma-deposited chromium is not
as wear-resistant at ambient temperature as hard electro-
plated chromium. This is because the wear-resistance of
chromium plate is not an inherent property of elemental
chromium but is believed to arise largely from impurities
and ~tresqes incorporated in the coating turing plating.
Plasma deposited chromium being a purer form of chromium
thus lacks the wear resistances of hard chromium plate
while retaining the corrosion-resistance characteristics ?
of chromium.
It has now been discovered that coatings made
by the plasma or detonation-gun process can be made that
are remarkably superior to hard chromium electroplate in
compatibility, frictional characteristics and wear resist-
ance by incorporating 9 dispersion of chromium carbide
particles in a chromium matrix.
Coatings of this type have been made from mechan-
ical mixtures of powders as described in my co-pending
Canadian application Serial No. 206,051, filed July 31, 1974.
While such mechanical mixtures are advantageous, there are
certain limitations to the quality of coatings made from them. ;-~
Both plasma and detonation-gun deposition result in a coating --
with a multilayer structure of overlapping, thin, lenticular -
particles or "splats." Each coating particle or splat is
derived from a single particle of the powder used to
- 4 -
~-. ' , . . :
D-9435
~ 036390
produce the coating. There is little, if any, combining or
alloying of two or more powder particles during the coating
deposition process. This results in some of the splats being
completely chromium and some being completely chromium
carbide, with the "fineness" or interparticle spacing being
controlled by the ~izes of the initial chromium and chromium
carbide powder particles, Thus, the "fineness" of the
chromium csrbide dispersi~ in the coating is limited by
the fineness of the powder that can be handled by the coat-
ing process. Since many desirable properties of the coatingare improved by reducing the interparticle spacing or
increasing the "fineness" of the dispersion and since it
is desirable from a coating application standpoint to use
powders with particles much larger than desired from the
coating "fineness" standpoint, it woult be ~d~an~ageous to
produce a coating in which each splat is a mixture of
chromium and chromium carbide. This in turn requires that
each powder particle contain a mixture of chromium metal
and chromium carbide.
Accordingly, it is an object of this invention to
provide a powder which, when sprayed by a plasma or
detonatlon-gun, will produce an article or coating wherein
each "splat" is a mixture of chromium metal and chromium
carbides.
-- 5 --
.' :
~ D-9435
~Q36390
;
Another object is to provide such a powder which
contains chromium and chromium carbide in each particle.
A further object is to provide a method for making
such powder.
Yet another object is to provide a chromium/
chromium carbide coating having superior property to hard
chromium electroplate.
Still another ob~ect is to provide a coated tro-
choid surface for a rotary combustion engine.
These and other objects will either be pointed
out or become apparent from the following description and
drawings wherein:
Figure 1 i9 a pictorial representation of the
structure obtained by depositing mechanical mixture of
chromium and chromium carbides;
Figure 2 is a pictorial representation o~ the
type structure obtained by depositing the powder of this
invention;
Figures 3, 4 and 5 show possible distribution of
the carbide phases in the powder particles;
Figure 6 shows the variation of wear scar volumes
with carbon content of the powder used to produce the coat- -
ing tested, compared to coatings of hard chrome plate; and,
Figure 7 shows the hardness of coatings obtained
with powders of various carbon content compared to hardness
of hard chrome plate. 6
.. . .~ . .
. ~ - - , .
D-9435
lV36390
The methods of this invention, which will be
described shortly, produce a compositepowder containing
the desired amount of chromium carbide and chromium in
which substantially each particle contains at least some
chromium and chromium carbide. Examples of the possible
distribution~ of the carbide phases in the powder particles
are shown in Figures 3, 4 and 5. For use in producing
plasma or detonation-gun coatings, the exact composition
of the carbide phases in the powder or the distribution of
the carbide phases as shown in Figures 3, 4 and 5 are not
important, only the total carbon content, since during
deposition the particles become essentially completely
molten. As the individual splats Rolidify during deposi-
tion, the carbides reprecipitate from the melt forming
Cr23C6, Cr7C3, or Cr3C2, or a combination of these, depend-
ing on the totsl 8mount of C present and the rate of solidi-
fication. The preferred composition results in a predomin-
antly Cr23C6 dispersion.
Basically, the material is prepared by chemical
reaction of an intimate mixture of a source of Cr and a
source of C; temperatures of 1000-1400C are suitable for
hov~s ~ ~p
solid state reactions. Times of from about 1-50~are suit- a~ /73
able. Temperatures in excess of 1500C are required for
production of the powder by melting referred to hereinafter.
- . .~ . .
D-9435
1036390
The principal reaction involved is
xCr + yC ~ CrxCy (1)
The principal product is Cr23C6, with minor amount of Cr7C3
and Cr3C2
When oxygen is present in the Cr (as Cr203) or
Cr203is used as the Cr source, reaction (1) is preceded or
accompanied by
Cr23 + 3C ~ 2Cr ~ 3C0 (2)
The Cr formed in reaction (2) may react with C present in
excess of the amount required to bring reaction (2) to
completion to form Cr carbide by reaction (1).
The source of Cr may be commercial Cr powder
(e.g., Union Càrbide Mining and Metals Division electro-
lytic chromium powder), Cr203 as in reaction (2), or any
compound that decomposes on hesting or by reaction with C
or H2 on heating to form essentially Cr and volatile
products.
The source of carbon may be any commercial carbon
consisting of essentially elemental C and volatile impuri- -
ties. Decolorizing carbon, lampblack, and powdered graphite .
have been used with equal success. In addition, a higher
carbide of Cr may be used as the C source, since it may
react with Cr to form another carbide, the resulting prod-
uct having the characteristic intimacy of the invention.
As an example,
-- 8 --
... .. ... . . . . .. .. ..
: .~ , - , .
~- ~
' ' ~ ~" '
D-9435
~36390
14Cr ~ 3Cr3C2 > Cr23C6 ( )
would produce a carbide on the surface of the Cr particles
(present in excess of the amount consumed in reaction (3)).
A gaseous hydrocarbon or hydrocarbon/hydrogen gas
mixture is also a suitable carbon source, provided its
composition is such that the carbon activity is high enough
to permit carbide formation. This reaction has not been
u8ed directly, but powdered mixtures of Cr and C heated in
a H2 atmosphere are found to consist, after reaction, of
two-phase particles in which the c~rbide phase essentially
encapsulates the original Cr particles as shown in Figure
3. This structure differs from that found in similar
mixtures heated in the absence of H2, which show mainly
isolated areas of carbide formation on the Cr particles,
a8 shown in Figure 4, corresponding to points o 801id-
801id contact of the original Cr and C partlcle8. The
difference instructure is clear evidence that carbon has
been transported through the vapor phase in the H2 atmos-
phere, by the reaction
xC + ~ H2 > CXHy (4)
occurring at the carbon particles and the reaction
CXHy+ zCr ~ CrzCx+ 2Y H2 (5)
occurring at the Cr particles. This vapor transport re- -
action may be the principal source of Cr carbide formation
or it may supplement reaction (1). Some oxygen removal
', - ;.
D~9435
~ ~ 6 39HD
reaction, either reaction (2) or reaction (6)
y CrxCy ~ Cr23 > (2 ~ 3yx) Cr + 3C0 (6)
also occurs.
The intimately mixed Cr/Cr carbide structure may
also be prepared by melting Cr and C (present either as
the element or as a Cr carbide) mixtures of appropriate
totfll analy8is, allowing thé homogeneous liquid to freeze
and the Cr carbide to precipitate out, and then crushing
the solidified melt to powder. Temperatures greater than
1500C are required for this method. Limitations of higher
melting temperatures and difficulty in crushing the ~olidi-
fied melt practically limit this method of prepar8tion to
carbon content of 3% by weight or more
The reaction of Cr and C is preferably carried out
in vacuum because this promotes the removal of the gaseous
C0 formed in reaction ~2) or (6). The vacuum does not h8ve
to be extraordinarily good, ultimate system pressures be-
tween 0.01 and 100 microns having been found to yield
products of essentially the same oxygen content. The re-
action can also be carried out in any atmosphere with
oxygen potential sufficiently low to prevent oxidation of
Cr. A hydrogen atmosphere i8 quite suitable and is par-
ticularly useful for the preparation of a composite of low
C content with a uniform carbide distribution, since the H2
takes part in the reaction and promotes uniform distribu-
tion. - 10 -
, '~ -: ' ;
D-9435
1C~36 39~D
The product of the Cr ~ C or Cr203 + C reaction
is a sintered cake, however the reaction i8 carried out.
Sintering is least, and reduction to powder by ball-milling,
hammer-milling, and other conventional techniques is easier,
when the Cr203 ~ C reaction i9 used or when the Cr ~ C
reaction is carried out in H~. Lower reaction temperatures
favor ease of reduction when the Cr + C reaction is carried
out in vacw m.
The carbide distribution within the powder par-
ticle is a function of the method of production. When a
mixture of solid carbon and chromium is heated in vacuum,
the predominant form is that shown in Figure 4 because the
carbon tends to react with the chromium surface closest to
it. The finer and more uniform the distribution of carbon
in the starting mixture, the more uniform the distribution
of carbides around the surface of the chromium will be.
The ultimate extension of this trend is achieved when a
gaseous source of carbon is used either by directly supply- p
ing a hydrocarbon gas or (-Vh~} by heating the solid car- ~/ l/73
bon plus chromium in a hydrogen atmosphere (which results
in a hydrocarbon gas). The carbide distribution which
results is like that in Figure 3. A distribution of carbon
particles throughout the powder particle, Figure 5, ~sy
result when a solid ingot of the proper total composition
is reduced to powder.
- 11 -
D-9435
~Q36390
~ o3~
Oxygen content (in the range ~ rb) does not ~ 3
affect the wear properties of coatings made from powders
of this invention. The carbon content of the powder of
this invention ma~ be between 0.2% and 5.4% by weight. At
thelower limit, plasma deposits made from the powder are
superior in tests to similar deposits made from commercial
electrolytic chromium powder. The high end of the range
is defined by the complete conversion to the compound
Cr23C6, which contains 5.6% by weight; at this point, the
material no longer contains free Cr. The wear resistance
of coatings made from the powder varies with carbon content
as shown in the band curve on Figure 6. The range of values
observed for commercial hard chrome plate i8 also shown in
the Figure 6 by the cross-hatched area ad~acent to the
vertical ~Xi8.
The optimum composition is believed to lie in the
range 0.8-1.7% C by weight, and may vary somewhat with the
method of preparation. Coatings, made from powders in this
composition range,are equivalent to or superior to com-
mercial electrolytic Cr plate in laboratory lubricatedrubbing wear tests at high load (see Figure 6). Further-
more, the hardness, see Figure 7, is at a minimum, making
it possible to readily fini~h the coating with conventional
grinding or honing tools. Low-surface-speed, high-deposition-
rate plasma plating produces well-bonded, uncraeked coatings.
- 12 -
. . .
~ .~
D-9435
~a36390
Specifically, it has been found that powders
containing about 1 wt % carbon produce plasma deposited
coatings on interior trochoid surfaces of rotary com-
bustion engines which have remarkedly and unexpectedly
superior propertles, as shown hereinafter in Example 9
The coating of this invention i8 characterized
by the presence in substantially every splat of both Cr
and Cr carbide. As pictorially illustrated in Figure 2,
the relative amounts of Cr and Cr Carbides will vary
between splats as a necessary result of the use of powder
with a range of partial sizes and adventitious difference
in the degree to which esch Cr particle is carburized and
in the conditions to which the various particles are sub-
~ected in passing through the coating device Neverthe-
less, the coating of this invention is distinguished from
tha~ produced from a powder which is a simple mixture of
~hlcl. ~ f~
Cr and Cr carbide,~E~ is pictorially represented in U
Figure 1, in that the splats in the latter type of coating
are each individually either all Cr or all Cr carbide.
Figure 2 i8 to be understood as being merely
illustrative of one feature of the distribution of the
carbides in the coating. Upon extraction by chemical
methods of carbides from the invention and examination of
these carbides by optical and electron micro~copy, it has
been found that at least some, and probably most, of the
- 13 -
,
- . ,
.
~ 9-9435
1(~36390
carbides are much finer than suggested by Figure 2. The
majority of the carbide particles were found to be of sub-
micronsize and most were predominantly in the shape of a
lace-like network, suggesting that the coatings contained
~ine-grained interlocking, continuous networks of both
carbide and Cr, the separation between the interstices
of these networks being so small that they are not resolv-
able in optical microscopy.
The coatings produced with the powder of this
invention have a number of advantages in addition to the
general processing advantages previously described as being
associated with metal spray deposition.
1) Coatings are superior to those formed by
the plflsma deposition of commercial electrolytic chromium
powder in that increased wear resistance and resistance to
spalling are found, though there is minimal increase in
hardness as measured by diamond pyramid indentations.
2) Coatings are superior to coatings in which
nitrogen rather than carbon is the strengthening additive,
in that carbide-strengthened material is much less brittle
and much less prone to spalling.
3) In the laboratory lubricated rubbing wear
test described in Example I, the coatings of this invention
with a carbon content in the preferred range of 0.8 - 1.7
wt % C,performed as well as or better than commeri~al
electrolytic chrome plate. - 14 -
. .
~, ' '
D-9435
1C~39N~
4~ Coatings of this invention performed far
superior to electrolytic chrome plate coating on internal
trochoid surfaces in rotary combustion engines as described
in detail in Example 9.
The following examples illustrate the invention
but are not intended to limit the variations in processing
that would be apparent to those skilled in the art. More-
over, the use of the powder of this invention is not in-
tended to be limited to plasma or detonation-gun deposition.
EXAMPLE 1.
8879 grams of Union Carbide Mining and Metals
Division electrolytic chromium, screened through a 230-mesh
sieve, was mixed with 200 grams of Fisher Scientific Com-
;pany Norit A~decolorizing carbon, similarly screened, and
blended for two hour8 in a cone blender. A portion o~ this
mixture wa8 used to fill eight pans, each about 0.6 cm deep,
so that each pan contained between 210 and 230 grams of the
mixture. The pans were vertically stacked in a vacuum
furnace so that there was about 0.4 clearance between pans.
The furnace was evacuated slowly to about 500-micron
pressure and then more rapidly to about 0.5 micron, using
an oil-diffusion pump. Power was then applied to tantalum
strip heaters s~rrounding the stack of pans and the pans
heated over a period of about 80 minutes to a temperature
of 1080C as indicated by a thermocouple in contact with
- 15 -
~tra~e~a~
D-9435
1~6390
the powder in the uppermost pan; system pressure was main-
tained below 50 microns during this period by adjusting
the rate of heating. The powder was maintained at 1080C
for four hours, during which time the pressure gradually
dropped to about 0.3 micron. The furnace was then allowed
to cool to room temperature with pumping continued. When
the pan8 were re~oved from the ~urnace, the material was
in the form of sintered cakes of a significantly more
metallic appearance than the original powder mix. These
cakes were crushed in a mechanical pulverizer until about
95% of the material was reduced to powder that would pass
a 325-mesh screen. The balance of the original mixture
of chromium and carbon powders was processed identi¢ally
in four additional furnacings.
The -325 mesh powders from the five furnace
run8 were individually analyzed for combined carbon, ~ree
carbon, and oxygen. All showed less than 0.1% free carbon,
between 300 and 420 ppm oxygen, and 1.05-1. 08% combined
carbon. The distribution of carbides on the chromium was
similar to that in Figure 4.
The products of the five runs were blended to-
gether and used to produce coatings by deposition through
a plasma torch. Coatings so produced, when separated from
the substrates on which they were plated, analyzed 1.03-
1.06% C. The wear resistance of these plasma-deposited
- 16 -
... . ~ ...... . ...... .. ~ ........... .
,
'' '- ~
_ D-9435
1C~36 3 ~
coatings were measured using a Dow-Corning LFW-l Friction
and Wear Test Machine according to ASTM Standard Method
D2714-68. Coatings deposited 12 mils thick on the wear
surface of mild steel wear blocks were ground to a final
thickne~s of 5 mils and tested against carburized AISI 4620
steel rings (surface hardness 58-63 Rockwell "C") at 450 lb
specific load for 5400 ring revolutions at about 180 rpm;
MIL-5606A hydraullc fluid was used as lubricant. Wear scar
volumes, calculated from the projected scar aress and the
known ring diameter, ranged between 24 and 49 x 10 6cm3.
These test results are included in Figure 6.
EXAMPLE 2.
Numerous mixtures differing only ln the amounts
of electrolytic chromium and decolorizing carbon used were
processed a8 described in Example 1. The re8ulting powders,
which r~nged in c~rbon content from 0.6 to 5.4%, were used
to form plasma-deposited coatings and tested for wear re-
sistance using the techniques and procedures described in
Example 1. Results of these tests are included in Figure 6.
EXAMPLE 3.
5400 grams of the same electrolytic chromium
powder used in preceding examples was mixed with 87 grams
of lampblack for one hour in a ceramic ball mill and then
further mixed for 30 minutes in a cone blender. The mixed
powders were loaded into pans and heated in the vacuum
- 17 -
D-9435
1036390
.
furnace exactly as described in Example 1. The product,
after reduction to -325 me~h powder, analyzed 0.81/~ carbon
and 335 ppm oxygen. Plasma-deposited coatings were made
and tested as described in Example 1. Scar volumes of 21
to 34 x 10 6cm3 were observed; these results are included
in Figure 6.
EXAMPLE 4.
1476 grams of the same electrolytic chromium
powder used in p~evious examples and 24 grams of the same
screened decolorizing carbon used in previous examples
were blended for two hours in a cone blender. Two boats,
each 0.6 cm deep and about 25 cm long, were filled with
this powder and placed in a 10 cm diameter ceramic tube
furnace which was then ~ealed and evacuated with a mechan-
ical pump for several hours. The furnace was then filled
with hydrogen, heated to 1150C, and maintained 8t thi8
temperature for 22 hours, a flow of 15 scfh of hydrogen
being maintained during the entire cycle. The product was
a sintered cake much more readily reduced to -325 mesh
powder than the products of the vacuum processing previously
described. This powder analyzed 1.06% carbon, 630 ppm ;~
oxygen. Plasma-deposited coatings made and tested as de-
scribed earlier had scar volumes of 21 to 42 x 10 6cm3. A
portion of the powder was mounted and polished to metal-
lographic examination; at 500X magnification, it appeared
- 18 -
.
- ~ .
D-9435
1036390
that most, and possibly all~ of the powder particles con-
sisted of a shell of chromium carbide surrounding a core
of chromium metal similar to that in Figure 3. In this
respect, the structure differed from that of powders pre-
pared by vacuumprocessing; in the latter carbide and metal
were observed in the same particles, but complete encap-
sulation was not observed.
EXAMPLE 5.
1773 grams of the same electrolytic chromdum
powder used in previous examples and 27 grams of the same
screened decolorizing carbon used in earlier examples were
blended by shaking and rolling in a 32-oz ~lass jar. Using
this powder, eight separate heats, each with between 80
and 105 grams of mix, were made in a 4 cm diameter tube
furnace. Each heat was for five hours at 1140C in a flow
of about 110 9cfh hydrogen without preliminary evacuation.
The eight cakes were easily powdered by light hammering
and when blended together and screened yielded a -325 mesh
powder containing 1.13% C and 1730 ppm oxygen. The micro-
structure of this powder was very similar to that of the
powder described in Example 4, consisting of chromium
carbide surrounding chromium; in addition, a small amount
of very fine precipitates was noted decorating the!carbide-
chromium interface.
- 19 -
- . -
D-9435
~036390
EXAMPLE 6.
.
A powder analyzing 1.13% C prepared by the method
described in Example 1 was plated onto test blocks using a
detonation gun. Microstructural differences between these
coatings and those formed by plasma deposition were observed
consistent wlth the difference in method of coating forma-
tion, For wear-test conditions identical with those employed
for the plasma-deposited materials, scar volumes of 15-19 x
10 6cm3 were measured on the detonation-gun coatings.
EXANPLE 7.
Four hundred lb of Cr203 was blended with 94.8 lb
of lampblack in a twin-shell blended and then more thor-
oughly blended in a vibratory ball mill. This product was
then mixed with 9.5 lb cornstarch binder and enough water
to mske a mix ~uitable for forming briquettes in a standard
briquetting pres8. It w~ then pres~ed into briquette8 of
about 2-inchmaximum dimension and dried to remove excess
water. The briquetted mix, charged to a large vacuum fur-
nace in an l9-inch-deep bed covered with graphite plates,
was heated to 1000C without letting the pressure exceed
5000 microns, held one hour at 1000C after the pressure
had dropped below 2000 microns, then heated to 1400C and
held at that temperature for 50 hours, at the end of which
time the pressure had dropped to less than 150 microns.
- 20 -
'
_ D-9435
1036390
A portion of this product was pulverized to -325 mesh size
and found to contain 1.14% C and 460 ppm oxygen. The car-
bide dispersion in the powder was similar to Figure 4. Wear
samples formed from this material by plasma deposition and
te~ted as described previously exhibited wear scars of
21-24- x 10 6cm3 volume.
EXAMPLE 8.
A mixture of 9900 grams of commercial grade elec-
trolytic chromium sized to pass through a 65-me~h screen
and 100 grams of lampblack was blended dry, then mixed with
water and cornstarch binder and formed into briquettes as
described in Example 7. The briquetted mixture was then
furnaced in vacw m under graphite covers for one hour at
1000C snd for eight hours at 1385C. The pressure in the
~urnace was maintained below 500 microns and was 50 microns
at the end of the heating period. This mat~ria~ was then
crushed, yielding about 30% -325 mesh material that analyzed
1.3% C and 721 ppm oxygen, with a carbide dispersion similar
to Figure 4. Wear samples made from this powder by plasma
deposition and tested in the standard manner exhibited wear
scars of 18-23 x 10 6cm3.
EXAMPLE 9.
Plasma deposited coatings produced in a manner
similar to Example 1 were applied to the interior trochoid
surfaces of rotary combustion engines fitted with graphite-
- 21 -
- : ,
D-9435
1036390
aluminum composite rotor apex seals. The engines were run
in laboratory test stands and in test vehicles. The tro-
choids were made of several different types of materials
and of two different sizes, examples of which are shown
in Table I. Over 3113 hr of test stand operation have
accumulated on the small en8ine size and 331 hr of test
stand and 7000 hr of vehicle operation on the large engine
size. In comparison with hard electropleted chromium the
coatings of this invention showed the following advantages:
a) Essentially no wear of the coated surface
has been observed and no roughening or "wash boardlng,"
as occurs with electroplated chromium, has developed.
b) The wear of the mating seal surface is
approximately one-half that caused by hard electroplated
chromium, which is greater than .005~' per 100 hr.
c) Performance of the coating is less sensi-
tive to surface finish than hard electroplated chromium.
There was no appreciable difference in wear of either the
coated surface or the seal surface between as-ground coat-
ing surfaces of 16 to 32 microinches rms and honed sur-
faces of approximately 6 rms. In comparison, a hardelectroplated chromium surface must be finished to better
than 6 microinches rms to perform satisfactorily.
d) Finishing of the plasma-deposited ooating
is far simpler and may be cheaper since it can be used
- 22 -
: ..
.- ~ .
_ D-9435
i036390
as-ground while a hard electroplated chromium coating must
be ground, then etched to enhance the micro cracked texture
of the surface, and then honed to improve the ~urface fin-
ish. Because thickness control is better with plasma
deposition than with electroplating, the amount of material
that must be removed in finishing is also less.
e) The performance of englnes with the coatings
of this invention i9 far less sensitive to fluctuation ln
coolant temperatures than those coated with hard electro-
plated chromium.f) The performance of engines with the coatings
of this invention is far less sensitive to fluctuation in
oil lubrication than that of engine~ coated with hard
electroplated chromium. The latter require continuou8
addition of oil to the combustion chamber, but an engine
provided with the coating of this invention continued to
perform satisfactorily when the oil addition was stopped.
g) The cost of engines and the vehicles can be
reduced using the coatings of this invention because they
can be applied directly to aluminum trochoid housings while
the use of hard electroplated chromium requires a steel
liner. This reduces not only the cost of the housing, but
also the weight of the engine and therefore the cost of
vehicle frame, suspension, etc. In addition, engine cooling
is more efficient. With lower total vehicle weight, fuel
- 23 -
- .
. ..
D-9435
.,
~Q3~
efficioncy is increased.
TABLE I
Coating Total Average Seal
Trochoid Trochoid Thickness Time of Wear Rate
T~e Size*(in.) (in.) Test(hr.) (in./100 hr,)
Aluminum with 9.5 x 7.1 .015 to800 .0026
Steel Liner x 2.75 .017
Aluminum with 9.5 x 7.1 .019 to444 .0026
No Liner x 2.75 .020
Aluminum with 11.5 x 8.6 .018 to220 .0026
Steel Liner x 2.75 .015
Aluminum with 11.5 x 8.6 .016 to76 .0026
No Liner x 2.75 .018
Cast Iron 9.5 x 7.1 .010 to200 .006
x 2.75 .0115
* M~or Axis x Minor Axis x Width
Having described the invention with reference to
certain preferred embodiments, it shou~d be understood that
minor modifications can be made thereto without departing
from the spirit ard ~cope thereof.
- 24 -
