ENVIRONMENTAL EMBRITTLEMENT OF BORON-DOPED NI3(AL, TI) SINGLE-CRYSTALS AT ROOM-TEMPERATURE

Environmental embrittlement of L1(2)-type Ni3(Al, Ti) single crystals doped with 0.05 mass % boron was investigated at room temperature as functions of environmental media and strain rate. Environmental embrittlement occurs in air, water, and hydrogen gas, and is also very sensitive to strain rate with a decrease of elongation with decreasing strain rate. Environmental embrittlement is little influenced by boron doping, indicating no strong interaction with hydrogen in lattice. In embrittled condition, tensile elongation and fracture stress are reduced, and fracture mode is primarily {001} cracking with a river pattern. Based on these results, it is proposed that hydrogen affects lattice bonding and thereby reduces the cohesion strength on {001} atomic plane. Also, it is suggested that the major cause of environmental embrittlement of boron-doped Ni3(Al, Ti) single crystals is due to the reaction of water (i.e., H2O) in environment with the reactive element of Al (and/or Ti) and of H-2 in environment with the surface reactive element of Ni.