MECHANICAL-BEHAVIOR OF NI3AL - EFFECTS OF ENVIRONMENT, STRAIN-RATE, TEMPERATURE AND BORON DOPING

The mechanical behavior of polycrystalline Ni3Al was studied as functi ons of environment, strain rate, temperature and boron doping. We find that the ductility of boron-free Ni3Al increases with increasing stra in rate, increasing (or decreasing) temperature from room temperature, and decreasing amounts of water vapor in the test environment. The pr esent results are consistent with our earlier conclusion that moisture -induced environmental embrittlement is a major cause of the room-temp erature brittleness of Ni3Al. We also find in the present study that b oron suppresses environmental embrittlement in Ni3Al; however, its eff icacy depends on the amount added. Al a level of 100 wppm, it quite ef fectively suppresses environmental embrittlement, with ductility remai ning high and insensitive to strain rate in both air and water. At a l evel of 50 wppm, however, boron alleviates environmental embrittlement only in air-in water the ductility is strongly strain-rate sensitive. Boron also affects the fracture mode, tending in general to promote t ransgranular fracture if present in sufficient quantity.