Formation of intermetallics in a porous powder titanium - Nickel diffusion couple

A method of fabricating porous powder Ti-Ni diffusion couples was developed, and the structure of the diffusion zone in these after isothermal annealing at 1073, 1173, and 1273 K studied. Microstructural analysis and microhardness measurements revealed that the width of the diffusion 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 growth in porous powder than in solid diffusion couples above 1173 K. This was related to the presence of rapid diffusion paths (surfaces, grain boundaries) which persisted at high temperatures in the porous powder diffusion couples, while those in solid couples (point and line defects) were eliminated when the temperature was raised.