W. Jin, Institute of Metal Research, Chinese Academy of Sciences, Shenyang, China
Effect of oxygen content and heat treatment on the transformation temperature were investigated in Ni47Ti44Nb9 shape memory alloy. The results indicated that if the oxygen content exceeds the limit of solid solution, the over saturated oxygen mainly exists in the form of oxide, i.e., (Ti,Nb)4Ni2O phase. The formation of (Ti,Nb)4Ni2O leads to a decrease in transformation temperature. If the alloy is slow rate cooling or low-temperature aging after solution treatment, the β-Nb phase precipitate, which decreases transformation temperature, increases the critical stress of stress-induced matensitic transformation. The transformation temperature of Ni47Ti44Nb9 alloy mainly depends on the Ni/Ti ratio in NiTi matrix phase. The Ni/Ti ratio increases, the transformation temperature decreases. The variety of oxygen content and heat treatment results in the change of Ni/Ti ratio in NiTi matrix phase and then results in the change of transformation temperature in Ni47Ti44 Nb9 Alloys.
Summary: Effect of oxygen content and heat treatment on the transformation temperature were investigated in Ni47Ti44Nb9 shape memory alloy. The results indicated that if the oxygen content exceeds the limit of solid solution, the over saturated oxygen mainly exists in the form of oxide, i.e., (Ti,Nb)4Ni2O phase. The formation of (Ti,Nb)4Ni2O leads to a decrease in transformation temperature. If the alloy is slow rate cooling or low-temperature aging after solution treatment, the â-Nb phase precipitate, which decreases transformation temperature, increases the critical stress of stress-induced matensitic transformation.
