Temperature dependence of Young’s modulus and degradation of chemical vapor deposited diamond

Abstract

Temperature dependent measurements of Young’s modulus were performed for the first time on black and transparent bulk material of chemical vapor deposited (CVD) diamond by a dynamic three point bending method in a temperature range from −150 to 850 °C. The CVD specimens correspond to a room-temperature Young’s modulus of single crystal diamond (1143 GPa). A lower Young’s modulus of polycrystalline diamond is caused by crystal imperfections and impurities. At temperatures between −150 and 600 °C (black type) or −150 and 700 °C (transparent type) the Young’s modulus is only slightly temperature dependent and decreases monotonically with an average temperature coefficient of −1.027×10−4 K−1, which is much higher than theoretically expected. At higher temperatures the bending stiffness and apparent Young’s modulus of the diamond beams are drastically reduced to one third of the initial value before fracture occurs due to oxygen etching effects in air. The onset temperature of this degradation phenomenon and the rate of decline are dependent on grain size, texture and the crystal lattice imperfections of the CVD diamond material.