HPHT welding of CVD polycrystalline diamond films

Abstract

Chemical vapour deposition (CVD) rates are limited, making the preparation of thick diamonds challenging. We propose an efficient high pressure high temperature (HPHT) welding method for polycrystalline CVD diamond films. Multiple layers of CVD polycrystalline diamond films are welded into a monolithic structure under 15 GPa and 2100 °C. HPHT treated samples have an extremely high bond strength and the hardness of the weld layer exceeds 120 GPa. Microstructural analyses suggest the mechanism of HPHT welding: laser treatment transforms the carbon atoms on the CVD diamond film surface from SP3 to SP2 hybridization, forming a non-diamond-carbon/diamond coherent interface. Under HPHT conditions, the carbon atoms are again transformed from SP2 to SP3 hybridization, forming a strong interlayer bond through diffusion at the coherent interface. This method provides a new approach for rapidly preparing diamond bulk materials.