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Temperature dependence of residual stress in TiC coated Mo
Journal
of Nuclear
Materials
TEMPERATURE I. YOSHIZAWA
128 & 129 (1984) 919-924
DEPENDENCE
919
OF RESIDUAL
STRESS IN TiC COATED
MO
*, M. FUKUTOMI ** and K. KAMADA
Insiituie of Plasma Physics, Nagoya University, Nagoya 464, Japan
Key words:
residual
stress, TIC coated
MO, fabrication
temperature
The effects of fabrication temperature and heat treatment on the residual stress in Tic coated MO have been studied by using X-ray diffractometry. Tic coatings on MO single crystal substrates with (100) and (111) surfaces were carried out with the Activated Reactive Evaporation (ARE) method. It was found that all MO substrates measured show tensile residuaI stresses, and their values decrease as the fabrication temperature increases from 300 to 700 o C. On the other hand, Tic films measured showed compressive residual stresses, for both TiC/Mo(lOO) and TiC/Mo(lll) specimens. These compressive stresses also decreased with increasing the fabrication temperature. The residual stresses measured were higher in TiC/Mo(lOO) than in TiC/Mo(lll). It was found that the compressive stresses in as-grown Tic films change to the tensile stresses after annaling at 1700 o C for 30 min. The preferred orientations of Tic films were observed to depend on the fabrication temperature. However, no epitaxial growth of Tic films was found as far as the present experiment was concerned.
1. Introduction A surface coating of low-Z materials on the inner wall of a tokamak type nuclear fusion reactor has been considered as one of the effective methods to prevent the plasma losses originating from wall-released impurities [l-3]. We have reported that residual stress of the coated thin films is an excellent measure of the resistance against the damage due to plasma discharge [4-61. In plasma devices, in-situ coating is an attractive method to repair the damaged surface. The ARE method is one of the candidate methods for the in-situ coating, because this technique has the advantage of deposition at lower temperatures in comparison with that of chemical vapor deposition (CVD) [7]. However, the relationship between the residual stress and the fabrication temperature, and the effect of thermal annealing have not yet been fully understood [6]. The present work was mainly conducted to investigate the effects of fabrication temperature and heat treatment on the residual stresses in Tic film and MO substrate prepared by the ARE method. Also the preferred orientation of the Tic layer deposited at various temperatures, and epitaxial growth on MO substrates with different orientations are examined,
2. Experimental MO single crystals with (100) and (111) surfaces, and MO polycrystals for a reference were used as substrate materials for Tic coating. Single crystals are used to avoid the overlap between diffraction peaks from the (511) plane of the Tic polycrystal and from the (321) * Ibaraki University, Mito-shi, Ibaraki-ken 310, Japan. ** National Research Institute for Metals, Tsukuba Laboratories, Ibaraki-ken 305, Japan. 0022-3115/84/$03.00 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
plane of the MO polycrystal, which are used as reflection indices for the stress measurement. The size of the MO substrate was approximately 10 mm in diameter and 0.5 mm in thickness. MO single crystals were cut from a rod of 10 mm in diameter and 30 mm in length by using a multi-wire saw of Japan Machine Trading Co. The single crystal rods were obtained commercially from Johnson-Matthey & Co. Ltd., London. An X-ray back-reflection photograph from the as-cutting surface of the MO single crystal showed very weak Debye rings from the (321) plane of the polycrystalline MO. This means that the deformation z,one is formed in near surface during the cutting. We used MO as substrates after light polishing with an emery paper, therefore, substrates may have a polycrystalline layer on the surface region. The coatings on MO substrates were carried out by the same ARE method as in a previous paper [6]. The thickness of the coating layer is from about 8 to 11 pm as shown in table 1. The coatings were done at substrate temperatures of 300, 450, 580 and 7OO’C. The residual stresses were determined by the 28-sin’+ method as reported in a previous paper [4]. The intensity of the X-ray reflection peaks from the (511) plane of the TIC films deposited at fabrication temperatures below 580°C was very weak. Therefore, the stresses in these specimens were determined by the lattice constant measurement [8,9]. The residual stresses in MO substrates of the same specimens were also determined by the 2 t9-sin2# method using the (321) reflection peak from the MO polycrystalline layer formed in the surface region of the single crystal. For both TiC/Mo(lOO) and TiC/Mo(lll) specimens deposited at 700’ C, the residual stresses in both the Tic film and the MO substrate were determined. TiC/Mo(lOO) and TiC/Mo(lll) specimens prepared at 300 and 700°C were annealed at 17OO’C for 30 min in a vacuum of 4 x low4 Pa using the tungsten 15. COATINGS
I. Yoshirawa et ul. / Residual stress in Tic coated MO
920 Table 1
Residual stresses determined in the present experiment and experimental conditions. Stress values of q and o2 were determined from 2 B-sin*+ method and from lattice constant measurement, respectively. Stress values of oj show the residual stresses in TIC film after heat treatment at 17OO’Cfor 30 min determined from the 26-sin2# method. The positive and negative values correspond to tensile and compressive residual stresses, respectively. No.
Coated film Substrate
Fabrication temperature (“Cl
Film thickness (rm)
1 2 3 4
TiC/Mo(lOO) TiC/Mo(lOO) TiC/Mo(lOO) TiC/Mo(lOO)
300 450 580 700
10 10 8 10
1.93 x 1.33 x 6.02 x 3.51 x { - 4.89 x
5 6 7 8
TiC/Mo(lll) TiC,‘Mo(lll) TiC/M~lll) TiC/Mo(lll)
300 450 580 700
10 10 9 11
8.72 x lo9 (MO) 7.68 x lo9 (MO) 3.21 x lo9 (MO) 1.92~10~ (MO) t -1.?5x109(TiC)
Stress (a,) (dWcm2 1
10” (MO) 10” (MO) lo9 (MO) lo9 (MO) lo9 (Tic)
electric furnace. The residual stresses after annealing were measured using a reflection peak of the (511) plane of the TiC film. For all specimens used, X-ray back-reflection photographs and X-ray diffraction profiles in the range of 23’ and 140 * in 26 were taken by using an X-ray apparatus of Rigaku-Denki Ltd. (1 kW, Cu target, 45 kV, 15 mA) and an X-ray Rataflex diffractometer of the same company (RAD-yA, 12 kW, Cu target, 40 kV, 140 mA), respectively. The former was conducted to examine the crystalline state of the TIC layer and the MO substrate. The latter was carried out using parallel beams for stress measurement in order to investigate the preferred orientation of the Tic layer. The surface morphology of the Tic film to compare the difference before and after heat treatment was observed using a scanning electron microscope (SEM).
Lattice constant ofTiC (A)
Stress in TiC ((12) (dyn/cm* 1
Stress in Tic after annealing ( 03) (4Wcm2 )
4.3693 4.3528 4.3418
-1.23~10” - 7.33 x 10’0 - 4.01 x 10’0
1.51 x 10’0 -
4.3317
-9.65X109
5.33x109
4.3670 4.3547 4.3407
-1.16X10” -7.90x 10’0 - 3.68 x 10’0
1.95x10’” --
4.3299
-4.22~10~
4.26x109
mens prepared at 300 and 700 o C after heat treatment at 1700’ C for 30 min. For these specimens, the reflection peaks of the (511) plane of TiC films were observed more clearly after the heat treatment than before the annealing. Therefore, the use of these diffraction peaks
3. Results and dimsion
Fig. 1 shows the relationship between 28 and sin*+ for the Mo(321) plane in TiC/Mo(lll) specimens prepared at various fabrication temperatures. The same relationship for TiC/Mo(lOO) specimens was also obtained, but is not shown in the present paper. The result at the top in fig. 1 shows the 2&-sin’+ relation for TiC(511) prepared
plane in the Tic film on Mo(ll1) substrate at 700°C. It should be noted that slopes of
the TiC and MO substrate have an opposite gradient, meaning opposite residual stress. Fig. 2 shows the relationship between 20 and sin*+ in Tic films of TiC/Mo(lOO) and TiC/Mo(lll) speci-
132.6
300°C 012
>. 0.4
j 0.6
SIN*!?+ Fig. 1. Relationship between 26 and sin*+ for TiC/Mo(lll) specimens prepared at various fabrication temperatures as denoted in the figure. Two curves of the specimen prepared at 700 o C were obtained from the (511) plane of the Tic film and the (321) plane of the MO substrate in the same sample.
I. Yoshirawa et al. / Residual stress in Tic coated MO
0 : TiC/Mo(lOO) A: TiC/Mo(lll)
136.4
fabrication
STRESS IN MO SUBSTRATE 0 . TiC/Mo( 100) o~TiC/Mo(lll)
temp.300”C
i-i:
* 0
0.2
0.4
0.6
SINZF-+ Fig. 2. 28 vs. sin’+ relation obtained with the TIC film after annealing at 1700°C for 30 min. TiC/Mo(lOO) and Tic/ Mo(ll1) specimens prepared at 300 and 700 -aC were used.
-12
I 0
I 200
FABRICATION was possible. It is worth noting that the slope becomes opposite on this annealing in comparison with that of the as-deposited specimen shown in the top of fig. 1. This means that the residual stress in the Tic film changes from compression to tension on annealing at 1700 ‘C for 30 min. Residual stresses before annealing (a,) and after annealing (as) are tabulated in table 1. These stresses were calculated from the slopes of 2B-sin2# curves as shown in figs. 1 and 2 by using the same equation as reported in the previous paper [4], u 1.3
For [lo] (E) (v)
=
------+0te
E
2(1 i- v)
Zip
W@)
O I80 a(sin’#)
the calculation of the stress, we adopted 3.63 x lOi and 4.96 X lOI dyn/cm2 [ll] as Young’s moduli for MO and TIC, respectively. As Poisson’s ratios of MO and TIC, 0.277 [lo] and 0.19 [12] were used. In table 1, the lattice constants (a) of Tic films measured and residual stresses (u2) in Tic films before annealing, which were calculated from lattice constants using the equation, uz = E. (a, - a). (2~0,)~’ [8,9], are also shown. For the calculation we postulated a, = 4.3280 A as a strain-free lattice constant of Tic [6]. The residual stresses determined from the lattice constant measurement show values of a factor of 2.0 higher than those for the same specimen obtained with the 2t9-sin24 method as seen in the table. Thus the tendency agrees with that reported in the previous paper [6]. Fig. 3 demonstrates the effect of the fabrication temperature on the residual stresses for the Tic film
I
I 400
measurement
I
I
1
600
TEMPERATURE
;0
(“C)
Fig. 3. Fabrication temperature dependence of the residual stress in the Tic film and the MO substrate. In the figure the curve of the Tic film (0) deposited on the polycrystalline MO substrate was taken from a previous paper [6]. and the MO substrate. In this figure the relationship between residual stress and fabrication temperature for the TiC film deposited on the MO polycrystal is also shown. This was taken from the previous paper [6]. The residual stresses obtained with all MO substrates showed a tensile type. On the other hand, all TiC films showed compressive residual stresses. As seen in table 1, the residual stresses determined in the Tic film and the MO substrate of the same specimen were -4.9 X lo9 and 3.5 X lo9 dyn/cm2, respectively, for the TiC/Mo(lOO) specimen prepared at 700 ‘C. For the TiC/Mo(lll) specimen prepared at the same temperature, these values were - 1.8 X lo9 in TIC and 1.9 X lo9 dyn/cm2 in the MO substrate, respectively. It is worth noting that the absolute values obtained in both TIC and MO of the same specimens are about the same. In the present work, it was also found that the residual stress in the MO substrate of the TiC/Mo(lOO) specimen decreases from 1.9 X 10” to 3.5 X lo9 dyn/cm2, as the fabrication temperature increases from 300 ’ to 700 o C. The same tendency was also observed in the TiC/Mo(lll) specimen, as seen in fig. 3. The compressive residual stress in the TiC layer of TiC/Mo(lOO) and TiC/Mo(lll) specimens, which was determined from the lattice constant measurement, also decreases with an increase of the fabrication tempera15. COATINGS
922
I. Yoshizawa et al. / Residual stress in Tic coated MO
ture. This tendency agrees with that of the TIC film deposited on the MO polycrystals, which was taken from the previous paper [6], as seen in fig. 3. It should be noted that the absolute values of the residual stresses in the Tic film and in the MO substrate deposited at low temperatures are higher in comparison with those of the specimen prepared at high temperature. This is attributed to a more perfect material produced at the higher deposition temperature as mentioned in the previous paper [6]. From the bimetallic effect due to the difference of the thermal expansion coefficients between the Tic film (7.6 X 10-60C-’ [2]) and the MO substrate (5.8 x 10-60C-’ [2]), we can expect the tensile stress for the Tic film and the compressive stress for the MO substrate. The result obtained, however, shows opposite values as shown in table 1. This fact suggests, as mentioned already in previous papers [4-61, that the residual stress originates from some intrinsic defects developed in the film during the coating. As seen in table 1, the residual stress after annealing changes from compressive stress to tensile stress. The reason for this change is not clear from the present experiments. However, we can expect as one of the origins that the annealing at 17OO’C releases intrinsic defects introduced during the coating of the TiC layer, and after the heat treatment the tensile residual stress due to the difference in thermal expansion coefficients is generated in the film. 3.2. X-ray diffraction ring
profile and back-reflected
Debye
Fig. 4 shows diffraction profiles of TiC/Mo(lll) specimens deposited at 300, 450, 580 and 700°C. In this figure, the diffraction profile taken from the Tic powder specimen is also shown in the bottom for a reference. For specimens prepared at deposition temperatures below 58O“C, diffraction peaks from the MO polycrystal with indices such as 220, 310 and 321 were also faintly observed. As seen in the figure, the reflection peak of the (222) plane in the MO substrate shows a strong intensity, because the substrate is the (111) MO single crystal. Reflection peaks from the (511) plane of the Tic layer are not seen below 580 o C as shown in the figure. For TiC/Mo(lOO) and TiC/Mo(lll) specimens prepared at 700°C reflection peaks from the (321) plane of MO and from the (511) plane of TIC were observed. Relative intensities of X-ray diffraction peaks from the TIC layer are different depending on the fabrication temperatures. For the specimen at 700°C the (200) peak is most prominent. For other specimens peaks from the (220) planes are relatively strong. A similar tendency between the relative intensity and the fabrication temperature was also observed for TiC/Mo(lOO) specimens and TiC/Mo(polycrystal) specimens. This
TiC/Mo(lll) fabrication
40
’
G
o-’ 40-
’
temperature
3Oo’C
h
’ 450°C
A
*O[ I 10 0
TiC powder 200 220
I
23
50
311 222
80
420 400 331
110
422
L
511
A.
140
28 (degree)+ Fig. 4. The X-ray diffraction pattern of the TIC layer deposited on the (111) plane of the MO substrate at 300, 450, 580 and 700°C. The diffraction pattern of the TiC powder sample is also shown. means that the growth of Tic films strongly depends on substrate temperatures rather than crystal orientations of substrate materials. Fig. 5 shows X-ray back-reflected Debye rings and Laue spots taken from TiC/Mo(lll) specimens before (fig. 5(A) and (C)) and after ((B) and (D)) annealing at 1700 OC for 30 min. In fig. 5(A) of an as-deposited specimen at 300° C, Debye rings from the (321) plane of the MO polycrystal formed on the near surface region of the single crystal and Laue spots from the (111) MO single crystal are observed. On the other hand, an as-deposited specimen prepared at 700“ C (fig. 5(C)) shows Debye rings from the (511) plane of the TiC film and the (321) plane of the MO polycrystal, and Laue spots from the MO single crystal. For both specimens, Debye rings from the (511) plane of the TIC film become very clear after annealing, as seen in fig. 5(B) and (D). Especially the rings of the latter specimen become strong and spotty as seen in fig. 5(D). This originates from grain growth of the Tic film during the heat treatment. It should be noted that Debye rings from the (511) plane of the Tic film for the former specimen appear after annealing (see fig. 5(A) and (B)). This is believed to be related with the perfection of the TiC crystal and/or grain growth. The experimental results described above were also found in the TiC/Mo(lOO) specimens. 3.3. Surface morphology of the Tic coating layer SEM Mo(ll1)
observations of TiC/Mo(lOO) and TIC/ specimens prepared at 300 and 700 o C were
I. Yoshizawa et al. / Residual stress in Tic coated MO
carried out before and after annealing at 1700 ’ C for 30 min. Micrographs obtained with these observations are not shown here. For both specimens prepared at 700 ’ C, crystal grains could not be observed in as-deposited specimens. However, they become about 2-7 pm in diameter after annealing. This result agrees with the features of Debye rings as shown in fig. 5. Namely, Debye rings from the (511) plane of the TiC film
923
become strong and spotty after annealing, originating from grain growth. Grains of specimens at 300°C were smaller than 1 pm in diameter after annealing. Therefore, it was very difficult to distinguish them on micrographs. The difference in surface morphology due to the fabrication temperatures appeared prominently before and after annealing.
TiC/Mo(lll) fabrication
temp. 300°C
after annealing at 1700°C for 30 min.
before annealing
fabrication
before annealing
temp. 700°C
after annealing at 17OO’C for 30 min
Fig. 5. X-ray back-reflection photographs of TiC/Mo(lll) specimens before (A, C) and after annealing (B, D). Examples of two specimens prepared at fabrication temperatures of 300 o C (A, B) and 700 ‘C (C, D) are shown. Debye rings from the (321) plane of the MO polycrystal and from the (511) plane of the Tic film are shown in the photographs by arrows.
15. COATINGS
924
I. Yoshizawa ef al. / Residual stress in Tic coated MO
4. conelwions The results obtained in the present work are summarized as follows. (1) The residual stresses in the Tic film and the MO substrate prepared by the ARE method were measured as a function of fabrication temperatures. It was found that all MO substrates measured show tensile residual stresses in the as-deposited state, and their values decrease from 1.9 x 10” to 3.5 x lo9 dyn/cm*, for the TiC/Mo(lOO) specimen, as the fabrication temperature increases from 300 to 700°C. The same tendency was also found in the TiC/Mo(lll) specimen. On the other hand, Tic films measured showed compressive residual stresses, for both TiC/Mo(lOO) and TiC/Mo(lll) specimens. These compressive stresses decrease with an increase in the fabrication temperature. (2) It was found that the residual stress of the compressive type in Tic films changed to tensile stress after
annealing at 1700°C for 30 min. (3) The epitaxial growth of the Tic layer on MO single crystals was not observe in the temperature range from 300 to 700 o C. However, the preferred orientations were observed to depend on the fabrication temperature.
References [l] D.M. Mattox, Thin Solid Films 63 (1979) 213. [2] D.M. Mattox and M.J. Davis, J. Nucl. Mater. 111/112 (1982) 819. [3] Y. Murakami, T. Abe and II. Nakamura, J. Nucl. Mater. 111/112 (1982) 861. [4] I. Yoshizawa and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1309. [5] I. Yoshizawa, Z. Kabeya and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1315. [6] I. Yoshizawa, M. Fukutomi and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1320. [7] M. Fukutomi and M. Okada, Seimitsu-kikai 45 (1979) 1509, in Japanese. [8] A. Kinbara, Japan. J. Appl. phys. 4 (1965) 243. (91 I. Yoshizawa, R. Urao, Y. Hot-i, A. Akaishi and K. Kamada, J. Nucl. Mater. 103/104 (1982) 267. [lo] H.M. ‘Dent, D.E. Stoneand L.A. Beau&en, in: American Institute of Physics Handbook, 2nd ad. (M&raw-Hill, New York, 1%3) Section 2, p. 52. [ll] J.J. Oilman and B.W. Roberts, J. Appl. phys. 32 (1961) 1405. [12] P.T.B. Shaffer, In: Handbook of H&h Temperature Materials, Material Index (Hemutt press, New York, Washiqton, 1964) p. 273.
of Nuclear
Materials
TEMPERATURE I. YOSHIZAWA
128 & 129 (1984) 919-924
DEPENDENCE
919
OF RESIDUAL
STRESS IN TiC COATED
MO
*, M. FUKUTOMI ** and K. KAMADA
Insiituie of Plasma Physics, Nagoya University, Nagoya 464, Japan
Key words:
residual
stress, TIC coated
MO, fabrication
temperature
The effects of fabrication temperature and heat treatment on the residual stress in Tic coated MO have been studied by using X-ray diffractometry. Tic coatings on MO single crystal substrates with (100) and (111) surfaces were carried out with the Activated Reactive Evaporation (ARE) method. It was found that all MO substrates measured show tensile residuaI stresses, and their values decrease as the fabrication temperature increases from 300 to 700 o C. On the other hand, Tic films measured showed compressive residual stresses, for both TiC/Mo(lOO) and TiC/Mo(lll) specimens. These compressive stresses also decreased with increasing the fabrication temperature. The residual stresses measured were higher in TiC/Mo(lOO) than in TiC/Mo(lll). It was found that the compressive stresses in as-grown Tic films change to the tensile stresses after annaling at 1700 o C for 30 min. The preferred orientations of Tic films were observed to depend on the fabrication temperature. However, no epitaxial growth of Tic films was found as far as the present experiment was concerned.
1. Introduction A surface coating of low-Z materials on the inner wall of a tokamak type nuclear fusion reactor has been considered as one of the effective methods to prevent the plasma losses originating from wall-released impurities [l-3]. We have reported that residual stress of the coated thin films is an excellent measure of the resistance against the damage due to plasma discharge [4-61. In plasma devices, in-situ coating is an attractive method to repair the damaged surface. The ARE method is one of the candidate methods for the in-situ coating, because this technique has the advantage of deposition at lower temperatures in comparison with that of chemical vapor deposition (CVD) [7]. However, the relationship between the residual stress and the fabrication temperature, and the effect of thermal annealing have not yet been fully understood [6]. The present work was mainly conducted to investigate the effects of fabrication temperature and heat treatment on the residual stresses in Tic film and MO substrate prepared by the ARE method. Also the preferred orientation of the Tic layer deposited at various temperatures, and epitaxial growth on MO substrates with different orientations are examined,
2. Experimental MO single crystals with (100) and (111) surfaces, and MO polycrystals for a reference were used as substrate materials for Tic coating. Single crystals are used to avoid the overlap between diffraction peaks from the (511) plane of the Tic polycrystal and from the (321) * Ibaraki University, Mito-shi, Ibaraki-ken 310, Japan. ** National Research Institute for Metals, Tsukuba Laboratories, Ibaraki-ken 305, Japan. 0022-3115/84/$03.00 0 Elsevier Science Publishers (North-Holland Physics Publishing Division)
B.V.
plane of the MO polycrystal, which are used as reflection indices for the stress measurement. The size of the MO substrate was approximately 10 mm in diameter and 0.5 mm in thickness. MO single crystals were cut from a rod of 10 mm in diameter and 30 mm in length by using a multi-wire saw of Japan Machine Trading Co. The single crystal rods were obtained commercially from Johnson-Matthey & Co. Ltd., London. An X-ray back-reflection photograph from the as-cutting surface of the MO single crystal showed very weak Debye rings from the (321) plane of the polycrystalline MO. This means that the deformation z,one is formed in near surface during the cutting. We used MO as substrates after light polishing with an emery paper, therefore, substrates may have a polycrystalline layer on the surface region. The coatings on MO substrates were carried out by the same ARE method as in a previous paper [6]. The thickness of the coating layer is from about 8 to 11 pm as shown in table 1. The coatings were done at substrate temperatures of 300, 450, 580 and 7OO’C. The residual stresses were determined by the 28-sin’+ method as reported in a previous paper [4]. The intensity of the X-ray reflection peaks from the (511) plane of the TIC films deposited at fabrication temperatures below 580°C was very weak. Therefore, the stresses in these specimens were determined by the lattice constant measurement [8,9]. The residual stresses in MO substrates of the same specimens were also determined by the 2 t9-sin2# method using the (321) reflection peak from the MO polycrystalline layer formed in the surface region of the single crystal. For both TiC/Mo(lOO) and TiC/Mo(lll) specimens deposited at 700’ C, the residual stresses in both the Tic film and the MO substrate were determined. TiC/Mo(lOO) and TiC/Mo(lll) specimens prepared at 300 and 700°C were annealed at 17OO’C for 30 min in a vacuum of 4 x low4 Pa using the tungsten 15. COATINGS
I. Yoshirawa et ul. / Residual stress in Tic coated MO
920 Table 1
Residual stresses determined in the present experiment and experimental conditions. Stress values of q and o2 were determined from 2 B-sin*+ method and from lattice constant measurement, respectively. Stress values of oj show the residual stresses in TIC film after heat treatment at 17OO’Cfor 30 min determined from the 26-sin2# method. The positive and negative values correspond to tensile and compressive residual stresses, respectively. No.
Coated film Substrate
Fabrication temperature (“Cl
Film thickness (rm)
1 2 3 4
TiC/Mo(lOO) TiC/Mo(lOO) TiC/Mo(lOO) TiC/Mo(lOO)
300 450 580 700
10 10 8 10
1.93 x 1.33 x 6.02 x 3.51 x { - 4.89 x
5 6 7 8
TiC/Mo(lll) TiC,‘Mo(lll) TiC/M~lll) TiC/Mo(lll)
300 450 580 700
10 10 9 11
8.72 x lo9 (MO) 7.68 x lo9 (MO) 3.21 x lo9 (MO) 1.92~10~ (MO) t -1.?5x109(TiC)
Stress (a,) (dWcm2 1
10” (MO) 10” (MO) lo9 (MO) lo9 (MO) lo9 (Tic)
electric furnace. The residual stresses after annealing were measured using a reflection peak of the (511) plane of the TiC film. For all specimens used, X-ray back-reflection photographs and X-ray diffraction profiles in the range of 23’ and 140 * in 26 were taken by using an X-ray apparatus of Rigaku-Denki Ltd. (1 kW, Cu target, 45 kV, 15 mA) and an X-ray Rataflex diffractometer of the same company (RAD-yA, 12 kW, Cu target, 40 kV, 140 mA), respectively. The former was conducted to examine the crystalline state of the TIC layer and the MO substrate. The latter was carried out using parallel beams for stress measurement in order to investigate the preferred orientation of the Tic layer. The surface morphology of the Tic film to compare the difference before and after heat treatment was observed using a scanning electron microscope (SEM).
Lattice constant ofTiC (A)
Stress in TiC ((12) (dyn/cm* 1
Stress in Tic after annealing ( 03) (4Wcm2 )
4.3693 4.3528 4.3418
-1.23~10” - 7.33 x 10’0 - 4.01 x 10’0
1.51 x 10’0 -
4.3317
-9.65X109
5.33x109
4.3670 4.3547 4.3407
-1.16X10” -7.90x 10’0 - 3.68 x 10’0
1.95x10’” --
4.3299
-4.22~10~
4.26x109
mens prepared at 300 and 700 o C after heat treatment at 1700’ C for 30 min. For these specimens, the reflection peaks of the (511) plane of TiC films were observed more clearly after the heat treatment than before the annealing. Therefore, the use of these diffraction peaks
3. Results and dimsion
Fig. 1 shows the relationship between 28 and sin*+ for the Mo(321) plane in TiC/Mo(lll) specimens prepared at various fabrication temperatures. The same relationship for TiC/Mo(lOO) specimens was also obtained, but is not shown in the present paper. The result at the top in fig. 1 shows the 2&-sin’+ relation for TiC(511) prepared
plane in the Tic film on Mo(ll1) substrate at 700°C. It should be noted that slopes of
the TiC and MO substrate have an opposite gradient, meaning opposite residual stress. Fig. 2 shows the relationship between 20 and sin*+ in Tic films of TiC/Mo(lOO) and TiC/Mo(lll) speci-
132.6
300°C 012
>. 0.4
j 0.6
SIN*!?+ Fig. 1. Relationship between 26 and sin*+ for TiC/Mo(lll) specimens prepared at various fabrication temperatures as denoted in the figure. Two curves of the specimen prepared at 700 o C were obtained from the (511) plane of the Tic film and the (321) plane of the MO substrate in the same sample.
I. Yoshirawa et al. / Residual stress in Tic coated MO
0 : TiC/Mo(lOO) A: TiC/Mo(lll)
136.4
fabrication
STRESS IN MO SUBSTRATE 0 . TiC/Mo( 100) o~TiC/Mo(lll)
temp.300”C
i-i:
* 0
0.2
0.4
0.6
SINZF-+ Fig. 2. 28 vs. sin’+ relation obtained with the TIC film after annealing at 1700°C for 30 min. TiC/Mo(lOO) and Tic/ Mo(ll1) specimens prepared at 300 and 700 -aC were used.
-12
I 0
I 200
FABRICATION was possible. It is worth noting that the slope becomes opposite on this annealing in comparison with that of the as-deposited specimen shown in the top of fig. 1. This means that the residual stress in the Tic film changes from compression to tension on annealing at 1700 ‘C for 30 min. Residual stresses before annealing (a,) and after annealing (as) are tabulated in table 1. These stresses were calculated from the slopes of 2B-sin2# curves as shown in figs. 1 and 2 by using the same equation as reported in the previous paper [4], u 1.3
For [lo] (E) (v)
=
------+0te
E
2(1 i- v)
Zip
W@)
O I80 a(sin’#)
the calculation of the stress, we adopted 3.63 x lOi and 4.96 X lOI dyn/cm2 [ll] as Young’s moduli for MO and TIC, respectively. As Poisson’s ratios of MO and TIC, 0.277 [lo] and 0.19 [12] were used. In table 1, the lattice constants (a) of Tic films measured and residual stresses (u2) in Tic films before annealing, which were calculated from lattice constants using the equation, uz = E. (a, - a). (2~0,)~’ [8,9], are also shown. For the calculation we postulated a, = 4.3280 A as a strain-free lattice constant of Tic [6]. The residual stresses determined from the lattice constant measurement show values of a factor of 2.0 higher than those for the same specimen obtained with the 2t9-sin24 method as seen in the table. Thus the tendency agrees with that reported in the previous paper [6]. Fig. 3 demonstrates the effect of the fabrication temperature on the residual stresses for the Tic film
I
I 400
measurement
I
I
1
600
TEMPERATURE
;0
(“C)
Fig. 3. Fabrication temperature dependence of the residual stress in the Tic film and the MO substrate. In the figure the curve of the Tic film (0) deposited on the polycrystalline MO substrate was taken from a previous paper [6]. and the MO substrate. In this figure the relationship between residual stress and fabrication temperature for the TiC film deposited on the MO polycrystal is also shown. This was taken from the previous paper [6]. The residual stresses obtained with all MO substrates showed a tensile type. On the other hand, all TiC films showed compressive residual stresses. As seen in table 1, the residual stresses determined in the Tic film and the MO substrate of the same specimen were -4.9 X lo9 and 3.5 X lo9 dyn/cm2, respectively, for the TiC/Mo(lOO) specimen prepared at 700 ‘C. For the TiC/Mo(lll) specimen prepared at the same temperature, these values were - 1.8 X lo9 in TIC and 1.9 X lo9 dyn/cm2 in the MO substrate, respectively. It is worth noting that the absolute values obtained in both TIC and MO of the same specimens are about the same. In the present work, it was also found that the residual stress in the MO substrate of the TiC/Mo(lOO) specimen decreases from 1.9 X 10” to 3.5 X lo9 dyn/cm2, as the fabrication temperature increases from 300 ’ to 700 o C. The same tendency was also observed in the TiC/Mo(lll) specimen, as seen in fig. 3. The compressive residual stress in the TiC layer of TiC/Mo(lOO) and TiC/Mo(lll) specimens, which was determined from the lattice constant measurement, also decreases with an increase of the fabrication tempera15. COATINGS
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I. Yoshizawa et al. / Residual stress in Tic coated MO
ture. This tendency agrees with that of the TIC film deposited on the MO polycrystals, which was taken from the previous paper [6], as seen in fig. 3. It should be noted that the absolute values of the residual stresses in the Tic film and in the MO substrate deposited at low temperatures are higher in comparison with those of the specimen prepared at high temperature. This is attributed to a more perfect material produced at the higher deposition temperature as mentioned in the previous paper [6]. From the bimetallic effect due to the difference of the thermal expansion coefficients between the Tic film (7.6 X 10-60C-’ [2]) and the MO substrate (5.8 x 10-60C-’ [2]), we can expect the tensile stress for the Tic film and the compressive stress for the MO substrate. The result obtained, however, shows opposite values as shown in table 1. This fact suggests, as mentioned already in previous papers [4-61, that the residual stress originates from some intrinsic defects developed in the film during the coating. As seen in table 1, the residual stress after annealing changes from compressive stress to tensile stress. The reason for this change is not clear from the present experiments. However, we can expect as one of the origins that the annealing at 17OO’C releases intrinsic defects introduced during the coating of the TiC layer, and after the heat treatment the tensile residual stress due to the difference in thermal expansion coefficients is generated in the film. 3.2. X-ray diffraction ring
profile and back-reflected
Debye
Fig. 4 shows diffraction profiles of TiC/Mo(lll) specimens deposited at 300, 450, 580 and 700°C. In this figure, the diffraction profile taken from the Tic powder specimen is also shown in the bottom for a reference. For specimens prepared at deposition temperatures below 58O“C, diffraction peaks from the MO polycrystal with indices such as 220, 310 and 321 were also faintly observed. As seen in the figure, the reflection peak of the (222) plane in the MO substrate shows a strong intensity, because the substrate is the (111) MO single crystal. Reflection peaks from the (511) plane of the Tic layer are not seen below 580 o C as shown in the figure. For TiC/Mo(lOO) and TiC/Mo(lll) specimens prepared at 700°C reflection peaks from the (321) plane of MO and from the (511) plane of TIC were observed. Relative intensities of X-ray diffraction peaks from the TIC layer are different depending on the fabrication temperatures. For the specimen at 700°C the (200) peak is most prominent. For other specimens peaks from the (220) planes are relatively strong. A similar tendency between the relative intensity and the fabrication temperature was also observed for TiC/Mo(lOO) specimens and TiC/Mo(polycrystal) specimens. This
TiC/Mo(lll) fabrication
40
’
G
o-’ 40-
’
temperature
3Oo’C
h
’ 450°C
A
*O[ I 10 0
TiC powder 200 220
I
23
50
311 222
80
420 400 331
110
422
L
511
A.
140
28 (degree)+ Fig. 4. The X-ray diffraction pattern of the TIC layer deposited on the (111) plane of the MO substrate at 300, 450, 580 and 700°C. The diffraction pattern of the TiC powder sample is also shown. means that the growth of Tic films strongly depends on substrate temperatures rather than crystal orientations of substrate materials. Fig. 5 shows X-ray back-reflected Debye rings and Laue spots taken from TiC/Mo(lll) specimens before (fig. 5(A) and (C)) and after ((B) and (D)) annealing at 1700 OC for 30 min. In fig. 5(A) of an as-deposited specimen at 300° C, Debye rings from the (321) plane of the MO polycrystal formed on the near surface region of the single crystal and Laue spots from the (111) MO single crystal are observed. On the other hand, an as-deposited specimen prepared at 700“ C (fig. 5(C)) shows Debye rings from the (511) plane of the TiC film and the (321) plane of the MO polycrystal, and Laue spots from the MO single crystal. For both specimens, Debye rings from the (511) plane of the TIC film become very clear after annealing, as seen in fig. 5(B) and (D). Especially the rings of the latter specimen become strong and spotty as seen in fig. 5(D). This originates from grain growth of the Tic film during the heat treatment. It should be noted that Debye rings from the (511) plane of the Tic film for the former specimen appear after annealing (see fig. 5(A) and (B)). This is believed to be related with the perfection of the TiC crystal and/or grain growth. The experimental results described above were also found in the TiC/Mo(lOO) specimens. 3.3. Surface morphology of the Tic coating layer SEM Mo(ll1)
observations of TiC/Mo(lOO) and TIC/ specimens prepared at 300 and 700 o C were
I. Yoshizawa et al. / Residual stress in Tic coated MO
carried out before and after annealing at 1700 ’ C for 30 min. Micrographs obtained with these observations are not shown here. For both specimens prepared at 700 ’ C, crystal grains could not be observed in as-deposited specimens. However, they become about 2-7 pm in diameter after annealing. This result agrees with the features of Debye rings as shown in fig. 5. Namely, Debye rings from the (511) plane of the TiC film
923
become strong and spotty after annealing, originating from grain growth. Grains of specimens at 300°C were smaller than 1 pm in diameter after annealing. Therefore, it was very difficult to distinguish them on micrographs. The difference in surface morphology due to the fabrication temperatures appeared prominently before and after annealing.
TiC/Mo(lll) fabrication
temp. 300°C
after annealing at 1700°C for 30 min.
before annealing
fabrication
before annealing
temp. 700°C
after annealing at 17OO’C for 30 min
Fig. 5. X-ray back-reflection photographs of TiC/Mo(lll) specimens before (A, C) and after annealing (B, D). Examples of two specimens prepared at fabrication temperatures of 300 o C (A, B) and 700 ‘C (C, D) are shown. Debye rings from the (321) plane of the MO polycrystal and from the (511) plane of the Tic film are shown in the photographs by arrows.
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4. conelwions The results obtained in the present work are summarized as follows. (1) The residual stresses in the Tic film and the MO substrate prepared by the ARE method were measured as a function of fabrication temperatures. It was found that all MO substrates measured show tensile residual stresses in the as-deposited state, and their values decrease from 1.9 x 10” to 3.5 x lo9 dyn/cm*, for the TiC/Mo(lOO) specimen, as the fabrication temperature increases from 300 to 700°C. The same tendency was also found in the TiC/Mo(lll) specimen. On the other hand, Tic films measured showed compressive residual stresses, for both TiC/Mo(lOO) and TiC/Mo(lll) specimens. These compressive stresses decrease with an increase in the fabrication temperature. (2) It was found that the residual stress of the compressive type in Tic films changed to tensile stress after
annealing at 1700°C for 30 min. (3) The epitaxial growth of the Tic layer on MO single crystals was not observe in the temperature range from 300 to 700 o C. However, the preferred orientations were observed to depend on the fabrication temperature.
References [l] D.M. Mattox, Thin Solid Films 63 (1979) 213. [2] D.M. Mattox and M.J. Davis, J. Nucl. Mater. 111/112 (1982) 819. [3] Y. Murakami, T. Abe and II. Nakamura, J. Nucl. Mater. 111/112 (1982) 861. [4] I. Yoshizawa and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1309. [5] I. Yoshizawa, Z. Kabeya and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1315. [6] I. Yoshizawa, M. Fukutomi and K. Kamada, J. Nucl. Mater. 122/123 (1984) 1320. [7] M. Fukutomi and M. Okada, Seimitsu-kikai 45 (1979) 1509, in Japanese. [8] A. Kinbara, Japan. J. Appl. phys. 4 (1965) 243. (91 I. Yoshizawa, R. Urao, Y. Hot-i, A. Akaishi and K. Kamada, J. Nucl. Mater. 103/104 (1982) 267. [lo] H.M. ‘Dent, D.E. Stoneand L.A. Beau&en, in: American Institute of Physics Handbook, 2nd ad. (M&raw-Hill, New York, 1%3) Section 2, p. 52. [ll] J.J. Oilman and B.W. Roberts, J. Appl. phys. 32 (1961) 1405. [12] P.T.B. Shaffer, In: Handbook of H&h Temperature Materials, Material Index (Hemutt press, New York, Washiqton, 1964) p. 273.