Slow crack growth of CVD diamond
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Slow crack growth of CVD diamond M. D. Drory and C. F. Gardinier Crystallume, 125 Constitution Drive, Menlo Park, California 94025 (Received 3 September 1991; accepted 10 December 1991)
Slow crack growth in CVD diamond has been observed from indentation experiments. Diamond films of 400 /xm thickness were prepared by plasma-enhanced CVD on a silicon substrate, subsequently removed from the substrate, and polished for indentation testing. A microhardness tester was used to produce Vickers indentations under low load. Crack length measurements over time revealed susceptibility to slow crack growth in ambient testing conditions. The stress-corrosion susceptibility coefficient, N, was measured as 9.3.
The extreme Young's modulus, hardness, and high thermal conductivity of CVD diamond make it an attractive material for a number of applications, including detector windows, tooling, and heat sinks. Despite the broad interest in CVD diamond, only a few of the mechanical properties have been reported. The elastic and plastic properties have been examined with a nanoindenter to determine Young's modulus and hardness at room temperature.1 Strength has been measured for thin windows by burst testing,2 while the fracture toughness was measured with the Vickers indentation method.3 The extreme properties of diamond make mechanical properties measurements difficult. For example, fracture toughness is determined at reduced load to avoid indenter failure, thereby producing radial crack length which can be difficult to resolve.3 Despite this difficulty, the indentation test provides a useful tool for first order property measurements, and is used here to examine the long-term reliability of CVD diamond. Slow crack growth is observed in many ceramic materials.4"6 In particular, slow crack growth, or static fatigue of glass, has been the most characterized of these materials in which the effects of environment on crack growth velocity, dc/dt, have been found to be represented by a power law function of the mode I stress intensity factor4: dc
(1) N is the stress corrosion susceptibility coefficient that is an environmentally dependent material parameter, and f3 is a constant. Slow crack growth in glass has been shown to be strongly influenced by temperature, humidity, and the presence of reactive species. The focus here is to examine the susceptibility of CVD diamond to J. Mater. Res., Vol. 7, No. 4, Apr 1992
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slow crack growth at room temperature under ambient humidity. Diamond films were grown using plasma-enhanced chemical vapor deposition at 2.45 GHz. Diamond deposition was achieved in the range of 1.5-2.0 KW and a total gas pressure of 50-100 Torr. Reactant gases, H 2 , and carbon precursors were metered with flow controllers at flow rates of 200-300 seem. The substrates were two-inch diameter, [100] silicon wafers with a surface roughness of
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