Analytical TEM Investigations on Concentration Gradients Surrounding Ni_4Ti_3 Precipitates in Ni-Ti Shape Memory Material

摘要

Concentration gradients surrounding Ni_4Ti_3 precipitates grown by appropriate annealing in a Ni_(51)Ti_(49) B2 austenite matrix are investigated by a combination of analytical TEM techniques. A Ni depleted zone in the surrounding matrix up to 150 nm away from the matrix-precipitate interface was detected. The size and concentration change of the depletion zone perfectly compensate for the excess Ni in the precipitate. Moreover, since different precipitates are often found in nanoscale proximity, depletion zones from different precipitates can reinforce one another in certain regions.