ENVIRONMENTAL-EFFECT ON MECHANICAL-PROPERTIES OF RECRYSTALLIZED LL2-TYPE NI3(SI,TI) INTERMETALLICS

The environmental effect on the mechanical properties of boron-doped and undoped Ni3 (Si, Ti) polycrystals was investigated by tensile testing in air from room temperature to 1073 K, and the results were compared with those obtained previously by tensile testing in vacuum. The environmental effect for the Ni3 (Si, Ti) alloys was significant at ambient temperatures whereas that for the boron-doped Ni3 (Si, Ti) alloys was considerable at elevated temperatures. When these samples at associated temperatures were tensile tested in air and also at low strain rate, intergranular fracture was dominant. It was suggested that the environmental embrittlements at low and high temperatures were due to hydrogen and oxygen absorbed from the air, respectively, and were caused by the weakening of the grain-boundary cohesion. It was proposed that boron competing with hydrogen, for site occupation or for its effectiveness at grain boundaries, has the effect of suppressing hydrogen embrittlement, whereas it was suggested that the low-melting phases, consisting of boron and oxygen (and/or constituent atoms), may be responsible for the ductility loss in the boron-doped Ni3 (Si, Ti) alloys.