Thermal degradation of sintered diamond compacts

Characterisation of thermally degraded polycrystalline diamond

“…Several works [5,10,11] have considered the influence of the metallic sintering aid on the thermal stability of PCD, and two different hypotheses have emerged as a means of explaining the influence of the metallic binder on the thermal stability of the material. The metallic sintering aid (usually cobalt) has a greater coefficient of thermal expansion (α) than diamond.…”

“…Although PCD is an excellent abrasive material, it suffers from thermal instability when exposed to high temperatures in excess of 700°C [4][5][6]. This instability leads to a reduction in wear performance and premature failure of PCD tools.…”

“…The metallic sintering aid (usually cobalt) has a greater coefficient of thermal expansion (α) than diamond. At elevated temperatures cobalt (α = 14 × 10 − 6 /°C) will expand more than the rigid diamond skeleton (α = 1 × 10 − 6 /°C) causing stresses that are thought to contribute to cracking and microchipping during machining operations [5,6]. The second mechanism involves cobalt metal dissolving the diamond grains and converting it into graphite, its thermodynamically stable phase at atmospheric pressure.…”

“…The first instance occurs during tool manufacturing where high temperature brazing is used to fix the material to the tool. The second instance occurs during drilling or machining operations where frictional forces at the contact surface are converted into heat energy during operation [7][8][9].Several works [5,10,11] have considered the influence of the metallic sintering aid on the thermal stability of PCD, and two different hypotheses have emerged as a means of explaining the influence of the metallic binder on the thermal stability of the material. The metallic sintering aid (usually cobalt) has a greater coefficient of thermal expansion (α) than diamond.…”

“…The material is usually manufactured by placing diamond powder onto a WC/Co substrate. During sintering, the cobalt in the WC/Co substrate melts and infiltrates the diamond layer, causing the diamond grains to bond together.Although PCD is an excellent abrasive material, it suffers from thermal instability when exposed to high temperatures in excess of 700°C [4][5][6]. This instability leads to a reduction in wear performance and premature failure of PCD tools.…”