Preparation Of Equalatomic TiNi Alloy By Hot Pressing Sintering At Lower Temperature

Coating equiatomic or near equiatomic Ti-Ni alloy layer on surface of titanium or its alloys can not only improve their abrasive wear resistance effectively, but also improve the fatigue feature for the coordinate deformation between coating layer and the substrate. In general, the coating was carried out by vacuum or protective atmosphere hot press sintering the mixed powders of Ti and Ni, and the higher the sintering temperature is, the sintering process of coating layer itself is enhanced. However, higher sintering temperature will cause a formation of a thick and brittle interlayer between coating layer and substrate, and this will decrease the bounding strength of coating layer and substrate. Sintering performance of equiatomic Ti-Ni alloy at relative lower temperature was carried in this research.Rough thermodynamic calculation shows that compounds like NiTi,Ni4Ti3,NiTi2 and Ni3Ti can form at the temperature of 800～1300K, and the phases of Ni4Ti3,NiTi2 and Ni3Ti have a tendency to change into TiNi phase under the hypothesis with thermodynamic aspect.Protective atmosphere hot-press sintering method was used to sinter mixed powders of the equiatomic Ti-Ni alloy at relative lower temperature. Phase analysis was made by X-ray diffraction. The effects of sintering temperature,holding time and pressure on transition characteristic were explored. The results are as follow:When the holding time and the pressure are 10min and 23.5MPa respectively, the amount of Ti-Ni compounds increase with increasing of measuring temperature in the range of 1023～1173K. The precursor Ti and Ni disappear completely at the measuring temperature of 1123K and 1173K respectively and phases are NiTi,Ni4Ti3 and Ni3Ti at measuring temperature of 1173K. Under the condition of measuring temperature of 1123K and pressure of 23.5MPa, phases are NiTi(β),Ni3Ti,NiTi2 and Ni at the holding time of 10min and 30min. Ni,Ni3Ti and NiTi2 phases disappears completely while NiTi(M)and Ni4Ti3 phases appear at the holding time of 60min and the amount of NiTi(β)phase seems to increase with prolonging holding time. Phases are NiTi,Ni4Ti3 and Ni3Ti at measuring temperature of 1173K and the phases keep unchanged with prolonging holding time, but the amount of NiTi(β)seems to increase and the amount of Ni3Ti seems to decrease.Phases are NiTi and Ni4Ti3 under the condition of measuring temperature of 1173K,holding time of 20min and pressure of 14.9MPa. Ni3Ti phase appears at the pressure of 19.2MPa. The phases remain unchanged and Ni4Ti3 seems increase at the pressure of 23.5MPa.