Deposition and characterization of cold sprayed nanocrystalline NiTi

Binary 50Ni-50Ti mixture was prepared by mechanical alloying from elemental powders. After 48 h of milling, the nanocrystalline B2-NiTi powder was produced. Then, this as-milled powder was deposited by cold spraying in order to produce a target which can be used to create thin films by magnetron sputtering technique. The objective is to improve the electrical characterizations of the NiTi/SiO2/Si M.O.S structures. The morphology evolution of the powder particles, the phase identification and the alloying evolution process as function of milling time were studied using scanning electron microscopy, X-ray diffraction and transmission electron microscopy. In addition, the target was also characterized using X-ray diffraction, Scanning electron microscopy, and microhardness measurements. The milling of powders leads to the formation of disordered nanocrystalline B2-NiTi with a crystallite size of about 12 nm and a microstrain of level 2.10%, after 48 h of milling. The microstructure, the composition and grain size of the milled powders for 24 h and 48 h characterized by TEM are heterogeneous. The as-deposited intermetallic NiTi can be retained in the coating with a lattice parameter of 0.3 nm, crystallite size of 14 nm, microstrain and high microhardness of 2% and 694 Hv(0.25), respectively. (C) 2011 Elsevier B.V. All rights reserved.