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Structure and mechanical properties of gold-dispersed titanium carbide films
Lll
Thin Solid Films, 43 (1977) Lll-L13 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
Letter Structure and mechanical properties of gold-dispersed titanium carbide films Y. ENOMOTO Mechanical
Engineering
Laboratory,
12-1 Igusa-4 chome,
Suginami-ku,
Tokyo
(Japan)
(Received February 21, 1977; accepted February 25,1977)
In order to improve the mechanical properties of titanium carbide films, Nimmagadda and Bunshah’ recently made a feasibility study of the synthesis of fine grain Tic-Ni cermets, where Ti-10% Ni alloy was evaporated by electron beam heating in an experimental arrangement of the activated reactive evaporation (ARE) process described by Bunshah and Raghuram2. A similar study is described in this paper; gold-dispersed titanium carbide films were deposited onto stainless steel (SUS 304) for tungsten substrates by ARE2. The gold content @ in the evaporant was varied from 0 to 13.3% in order to clarify how the structure and mechanical properties of the film change on increasing the gold content. To prepare evaporants having different gold contents, titanium blocks were drilled by means of electrospark machining to make a few or several holes of diameter 1 mm in which gold wires were inserted. The structure of the Tic-Au cermet films was characterized by scanning electron microscopy, X-ray diffraction and electron probe microanalysis (EPMA). The hardness and specific wear rate were measured as a function of gold content using an Akashi Vickers micro-
TABLE 1 Sample
CzH2 pressure (X lo-* Torr)
Electron power (kw)
TC 1 TC 2 TC3 TA 1 TA2 TA3 TA4 TA5 TA6
3.5 6.5 6.5 3.5 6.5 6.5 6.5 6.5 3.5
3.8 3.9 3.8 2.5 3.8 3.8 4.0 3.8 2.5
beam
Substrate ;;;;erature
Thickness (pm)
Deposition Gold rate content (ymmin -1 ) fv (%)
710 700 700 715 710 715 700 700 700
14 16.3 16.5 9.0 9.0 11.0 10.9 11.9
1.8 1.7 1.1 0.8 1.6 1.4
0 0 0
5.0 3.5 4.7 7.0 12.6 13.3
LETTERS
LI2
(A)
,a
(B)
(a)
.
.
.
.
.
(b) Fig. 1. The cross-sectional (A) and surface (B) views of (a) TiC (TC 3), (b) TiC-Au (TA 6) on a tungsten substrate: (A) magnification 2700X ; (B) magnification 6700x. hardness tester and an Ohkoshi wear machine, respectively. T h e conditions o f deposition are given in Table I. Figure l( a) shows surface and fracture cross-sectional views of a TiC film (TC 3~ and Fig. l ( b ) shows the corresponding views o f a T i C - A u cerm et film with W = 13.3% (TA 6). T he TiC film shows a coarse grain col um nar m o r p h o l o g y , whereas the T i C - A u film shows a fine grain m o r p h o l o g y . EPMA o f the T i C - A u films (TA 1 - 6 ) showed t hat the gold is dispersed u n i f o r m l y th r o u gh the thickness o f the film. F u r t h e r m o r e , X-ray diffraction analysis o f the films TA 5 and T A 6 did n o t show any Au phase but did indicate a Ti3Au phase in addition t o the TiC phase; this results from a reac-
LETTERS
L13
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.;
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SUBSTRATE
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(a) 0 5 Fig. 2. (a) Hardness
,
, ..,
0
5
I0
I'5
I0 15 (b) W=WAu/(WTi+WAu)xlO0 (%) vs. gold content. (b) Specific wear rate us. gold content.
tion o f Ti in the vapor phase with Au to form Ti~Au, as mentioned b y Nimmagadda and Bunshah 1 for TiC-Ti2Ni cermets. The Vickers hardness was measured under a load of 25 g in two ways, i.e. vertically to the surface o f the film (H~) and vertically to the cross section o f the film (/T~). Figure 2(a) shows the value of H~ and ~ as a function o f the gold c o n t e n t W in the evaporant. It is seen that H~ is in general larger than/-/~; this is probably due to the coarse columnar structure o f the film which leads to anisotropy in the mechanical properties. The value o f H~ at W = 12.6%, however, is almost equal to the value of/-/~. It is noted that the structure o f this film shows a fine columnar morphology as in Fig. l(b). A gold c o n t e n t o f a few per cent does n o t change the hardness from that o f a TiC film; with greater gold content, the hardness decreases with increasing W. The wear test was made using an Ohkoshi wear machine at room temperature in dry air, at a sliding velocity of 1.6 m s - l , with a sliding distance o f 66.6 m and a final load o f 2.2 and 19.8 kg. The details o f this machine have been reported in ref. 3. Figure 2(b) shows the specific wear rate Ws of T i C - A u cermet films a b o u t 10 p m as a function o f gold content. The wear rate was almost unchanged with gold contents up to several per cent and increased for higher gold contents. By dispersing a metal phase in a TiC film, one can expect to obtain a cermet film with high strength and toughness 1. Further investigation of the frictional behaviour o f these films at high temperature is needed, and such work is n o w in progress.
1 R. Nimmagadda and R. F. Bunshah, J. Vac. Sci. Technol., 12 (1975) 585. 2 R. F. Bunshah and A. C. Raghuram, J. Vac. Sci. Technol., (1972) 1385. 3 R Takagi and Y. Tsuya, Wear, 5 (1962) 435.
Thin Solid Films, 43 (1977) Lll-L13 0 Elsevier Sequoia S.A., Lausanne - Printed in the Netherlands
Letter Structure and mechanical properties of gold-dispersed titanium carbide films Y. ENOMOTO Mechanical
Engineering
Laboratory,
12-1 Igusa-4 chome,
Suginami-ku,
Tokyo
(Japan)
(Received February 21, 1977; accepted February 25,1977)
In order to improve the mechanical properties of titanium carbide films, Nimmagadda and Bunshah’ recently made a feasibility study of the synthesis of fine grain Tic-Ni cermets, where Ti-10% Ni alloy was evaporated by electron beam heating in an experimental arrangement of the activated reactive evaporation (ARE) process described by Bunshah and Raghuram2. A similar study is described in this paper; gold-dispersed titanium carbide films were deposited onto stainless steel (SUS 304) for tungsten substrates by ARE2. The gold content @ in the evaporant was varied from 0 to 13.3% in order to clarify how the structure and mechanical properties of the film change on increasing the gold content. To prepare evaporants having different gold contents, titanium blocks were drilled by means of electrospark machining to make a few or several holes of diameter 1 mm in which gold wires were inserted. The structure of the Tic-Au cermet films was characterized by scanning electron microscopy, X-ray diffraction and electron probe microanalysis (EPMA). The hardness and specific wear rate were measured as a function of gold content using an Akashi Vickers micro-
TABLE 1 Sample
CzH2 pressure (X lo-* Torr)
Electron power (kw)
TC 1 TC 2 TC3 TA 1 TA2 TA3 TA4 TA5 TA6
3.5 6.5 6.5 3.5 6.5 6.5 6.5 6.5 3.5
3.8 3.9 3.8 2.5 3.8 3.8 4.0 3.8 2.5
beam
Substrate ;;;;erature
Thickness (pm)
Deposition Gold rate content (ymmin -1 ) fv (%)
710 700 700 715 710 715 700 700 700
14 16.3 16.5 9.0 9.0 11.0 10.9 11.9
1.8 1.7 1.1 0.8 1.6 1.4
0 0 0
5.0 3.5 4.7 7.0 12.6 13.3
LETTERS
LI2
(A)
,a
(B)
(a)
.
.
.
.
.
(b) Fig. 1. The cross-sectional (A) and surface (B) views of (a) TiC (TC 3), (b) TiC-Au (TA 6) on a tungsten substrate: (A) magnification 2700X ; (B) magnification 6700x. hardness tester and an Ohkoshi wear machine, respectively. T h e conditions o f deposition are given in Table I. Figure l( a) shows surface and fracture cross-sectional views of a TiC film (TC 3~ and Fig. l ( b ) shows the corresponding views o f a T i C - A u cerm et film with W = 13.3% (TA 6). T he TiC film shows a coarse grain col um nar m o r p h o l o g y , whereas the T i C - A u film shows a fine grain m o r p h o l o g y . EPMA o f the T i C - A u films (TA 1 - 6 ) showed t hat the gold is dispersed u n i f o r m l y th r o u gh the thickness o f the film. F u r t h e r m o r e , X-ray diffraction analysis o f the films TA 5 and T A 6 did n o t show any Au phase but did indicate a Ti3Au phase in addition t o the TiC phase; this results from a reac-
LETTERS
L13
_
#
.!~
|
Hi
.;
v
SUBSTRATE
~oot;
# ,Or
. ioooi.
"',
,
g:22kg
I~ ,
(a) 0 5 Fig. 2. (a) Hardness
,
, ..,
0
5
I0
I'5
I0 15 (b) W=WAu/(WTi+WAu)xlO0 (%) vs. gold content. (b) Specific wear rate us. gold content.
tion o f Ti in the vapor phase with Au to form Ti~Au, as mentioned b y Nimmagadda and Bunshah 1 for TiC-Ti2Ni cermets. The Vickers hardness was measured under a load of 25 g in two ways, i.e. vertically to the surface o f the film (H~) and vertically to the cross section o f the film (/T~). Figure 2(a) shows the value of H~ and ~ as a function o f the gold c o n t e n t W in the evaporant. It is seen that H~ is in general larger than/-/~; this is probably due to the coarse columnar structure o f the film which leads to anisotropy in the mechanical properties. The value o f H~ at W = 12.6%, however, is almost equal to the value of/-/~. It is noted that the structure o f this film shows a fine columnar morphology as in Fig. l(b). A gold c o n t e n t o f a few per cent does n o t change the hardness from that o f a TiC film; with greater gold content, the hardness decreases with increasing W. The wear test was made using an Ohkoshi wear machine at room temperature in dry air, at a sliding velocity of 1.6 m s - l , with a sliding distance o f 66.6 m and a final load o f 2.2 and 19.8 kg. The details o f this machine have been reported in ref. 3. Figure 2(b) shows the specific wear rate Ws of T i C - A u cermet films a b o u t 10 p m as a function o f gold content. The wear rate was almost unchanged with gold contents up to several per cent and increased for higher gold contents. By dispersing a metal phase in a TiC film, one can expect to obtain a cermet film with high strength and toughness 1. Further investigation of the frictional behaviour o f these films at high temperature is needed, and such work is n o w in progress.
1 R. Nimmagadda and R. F. Bunshah, J. Vac. Sci. Technol., 12 (1975) 585. 2 R. F. Bunshah and A. C. Raghuram, J. Vac. Sci. Technol., (1972) 1385. 3 R Takagi and Y. Tsuya, Wear, 5 (1962) 435.