Evaluation of palladium diffusion in Ti-Rich TiNi alloys

Abstract

In order to study the diffusion kinetics of Pd into Ti-rich TiNi alloys, diffusion annealing treatments of palladium-coated Ti53Ni47 and Ti50.2Ni49.8 alloys were carried out at temperatures ranging from 700 to 1000 °C. Linear Arrhenius temperature dependencies with the pre-exponential factors of 2 ± 1.1 × 10−10 and 1.05 ± 1.5 × 10−8 m2 s−1 and the activation energies of −128 ± 4 and −153 ± 10 kJ mol−1 were obtained for Pd diffusivity into Ti53Ni47 and Ti50.2Ni49.8 alloys, respectively. The suggested mechanism for Pd diffusion in Ti53Ni47 was anti-site bridge mechanism. While the rapid diffusion of Pd in Ti50.2Ni49.8 was attributed to the high volume fraction of vacancies in Ni sub-lattice of TiNi lattice and Next Nearest jumps of Pd atoms into abundant Ni vacancies. The lower diffusivity of Pd in Ti53Ni47 was related to the dominant diffusion mechanisms in two systems and low solubility of Pd in Ti2Ni precipitates which located in grain boundaries, as well.The other part of the study was denoted to inter-diffusion studies in Ti53Ni47/Pd and Ti50.2Ni49.8/Pd diffusion couples, which confirmed the higher diffusivity of Pd in Ti50.2Ni49.8.