A Comparative Study of Residual Stresses in Single and Multilayer Composite Diamond Coatings
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391 Mat. Res. Soc. Symp. Proc. Vol. 505 ©1998 Materials Research Society
EXPERIMENTAL PROCEDURE Four types of diamond films were used in the present analysis which include discontinuous diamond film of 4 pim thickness, continuous diamond film of thickness 12 jim, multilayer diamond films of thickness 14 pjm, continuous diamond films of thickness 18 jpm that was partly peeled. The diamond films with the substrates were analyzed for different phases present in the diamond coatings using X-ray powder diffraction method. A rotating anode X-ray source operated at 35 KV and 300 mA was used in these studies with a three-axis goniometer. Identification of different peaks in the single layer diamond film showed that molybdenum carbide layer is formed on the surface of molybdenum substrate before diamond is nucleated [3]. We have chosen the high angle 331 reflection of diamond, 320 and 321 reflections of molybdenum carbide and 320 reflection of molybdenum for accurate measurements of 20 values of these reflections as a function of +/- values of the angle y at equally spaced values of ý=O 0,45 o and 900 in the plane of the diamond film. Texture associated with diamond and molybdenum carbide films was evaluated and the films were found to be randomly oriented. Raman spectroscopy was carried out to identify the presence of graphitic or diamondlike films in diamond in all the samples. The shift in the Raman peak associated with diamond was measured to determine the magnitude of stresses in the diamond films. The results of residual stresses in these three different types of substrates are compared. RESULTS X-ray stress analysis: Three-dimensional stress analysis was performed from the results of 20 vs. sin2 y graphs. This analysis used the following formulations. A 1=(d++d-)/2do- 1=[(I +v)/E] {Icycos2 4+oC2sin 24+o22 sin2 -(7 33 }sin2 +[(I +v)/E]o3 3-v/E[coj + G322- Cy 33]
A2=(d t+d-)/2do=[(l+v)/E] {o1 3cos 4i+ o 23sin di } sin 2y
(1)
In the above equation, the super script of+ and - refers to d values at positive and negative values of y. Thus all the stress components are obtained from the slope and intercept of A1 vs. sin 2 and A 2 vs. sin 2y graphs. The very weak diamond (331) reflection observed close to 20 =141.30 was covered under molybdenum carbide (321) peak near 20 =142.250. Peak fitting was used to separate these peaks. The unstressed diamond (331) peak is known to appear close to 140.57' which is separated from the observed peak by 0.73'. Larger 20 values may be expected from diamond films under compression, i.e smaller d spacings. However, using & tan(0)=-d 0, the expected value of 2(dO) is 0.48' for s=-0.0015, estimated from Raman spectroscopy. This value differs significantly from 0.73'. This large increase in 20 value associated with the diamond (331) peak is indicative of improper peak identification arising either because of low intensity of the diamond 331 reflection or due to the presence of other nonstoichiometric carbides. The results of different components of stress determined from X-ray analysis are s
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