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 f unctions of environmental media and strain rate. Environmental embritt lement occurs in air, water, and hydrogen gas, and is also very sensit ive to strain rate with a decrease of elongation with decreasing strai n rate. Environmental embrittlement is little influenced by boron dopi ng, indicating no strong interaction with hydrogen in lattice. In embr ittled condition, tensile elongation and fracture stress are reduced, and fracture mode is primarily {001} cracking with a river pattern. Ba sed on these results, it is proposed that hydrogen affects lattice bon ding and thereby reduces the cohesion strength on {001} atomic plane. Also, it is suggested that the major cause of environmental embrittlem ent 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 (a nd/or Ti) and of H-2 in environment with the surface reactive element of Ni.