Microstructure and Superelasticity of NiS/TiNi Composite Electrode

摘要

Surface Ni sulfides layers were formed on the surface of a Ti-50.0Ni alloy by reacting sulfur and Ni film deposited on the alloy, and then microstructures, transformation behavior, shape memory characteristics, superelasticity and electrochemical properties of a Ti-50.0Ni(at%) alloy with the sulfides were investigated. When Ni film deposited on a Ti-50.0Ni alloy was annealed under the sulfur pressure of 100 kPa at 623 K, sulfides layers consisted of NiS and NiS_(1.97) were formed. When annealing was made at 648 K annealing with annealing time less than 0.9 ks, sulfides layers consisted of NiS and NiS_(1.97) were formed also, while only NiS_(1.97) was formed when it was made for 1.8 ks. When annealing was made at 673 K annealing with annealing time longer than 0.9 ks, only NiS_(1.97) was formed. A Ti-50.0Ni(at%) alloy with surface NiS_(1.97) layer showed the two-stage B2-R-B19' transformation behavior, the perfect shape memory effect and a partial superelasticity with a superelastic recovery ratio of 78 %. NiS_(1.97) cathode showed a clear discharge behavior with multi voltage plateaus. Discharge capacity of NiS_(1.97) cathode decreased abruptly with increasing number of cycles up to 3, above which it decreased gradually.