FORMATION OF INTERMETALLICS IN A POROUS POWDER TITANIUM - NICKEL DIFFUSION COUPLE

A method of fabricating porous powder Ti-Ni diffusion couples was deve loped, and the structure of the diffusion zone in these after isotherm al annealing at 1073, 1173, and 1273 K studied. Microstructural analys is and microhardness measurements revealed that the width of the diffu sion zone and the thickness of the intermetallic layers increased with increasing temperature. Mutual diffusion coefficients were calculated and an explanation proposed for the more rapid intermetallic layer gr owth in porous powder than in solid diffusion couples above 1173 K. Th is was related to the presence of rapid diffusion paths (surfaces, gra in boundaries) which persisted at high temperatures in the porous powd er diffusion couples, while those in solid couples (point and line def ects) were eliminated when the temperature was raised.