Examination of mechanical as well as corrosion properties in Flouride solution of NiTiMo shape memory alloy was the aim of present study. The NiTiMo was prepared with vacuum arc melting in cupreous crucible. To insure homogeneity of alloy, the alloy was remelted for six times. The as-cast alloy was annealed at 950°C for 1 hour followed by quenching in liquid nitrogen. The microstructure was studied by X-ray diffraction analysis, optical and electron microscopes. Tensile and three point bending tests were employed to examinate tensile and shape memory properties. The corrosion resistance of NiTiMo alloy was investigated by Electrochemical Impedance Spectroscopy as well as Tafel polarization test. The recoverable strain of NiTiMo alloy after anealling and quenching was 7.79 percent achieved. The NiTiMo alloy was immersed in flouride solution for 8, 16 and 72 hour followed by tensile testing. The results showed that with the increase of immersing-time, beginning stress of detwinning increased and the fracture stress decreased. The decrease of tensile strength is due to absorption of Hydrogen and embrittlement effect of hydrogen. Fracture surface of the non-immersed specimens was incorporated cleavage facets. Fracture of large intermetallic precipitates, within the microstructure, was found to be the source of the cleave cracks. For immersed specimens both of internal and surface opened cracks was observed. Surface opened cracks was initiated from interaction of the surface of alloy and Flouride solution and extended to internal regions. With the increase of immersing time the number of surface cracks as well as as the length of surface cracks per unit length of the specimens was increased. It was observed that the region behind the contact surface of the alloy and fluoride solution, up to a distinct depth, showed completely brittle fracture behavior. It could be due to the high concentration of hydrogen atoms. The results showed that presence of Mo in NiTi alloy caused form the passive film on NiTiMo alloy and increase of corrosion resistance. Keywords: shape memory alloys, Ni-Ti-Mo, corrosion, Hydrogen embrittlement.
