Martensitic Transformation And Shape Memory Effect Of Rapidly Solidified Ti-Ni-Zr High Temperature Memory Alloy Ribbons

Ti-Ni-Zr alloy has the advantages of high Ms temperature,good thermal stability and two-way shape memory effect,and has a very wide application prospect,but its hot and cold processing performance is bad.In this paper,Ti-Ni-Zr memory alloy ribbons were prepared by rapid solidification and stripping method,and the mechanical properties and shape memory effect were improved by controlling the Zr content and annealing process.In this paper,the effects of process parameters on the composition and properties of Ti-Ni-Zr alloy ribbons were studied systematically.The optimum technological parameter of Ti50-x Ni50 Zrx alloy ribbons were as follows:injection temperature 1300?,furnace cavity pressure-0.035 MPa,copper roll speed 3000r/min(copper roller line speed 33m/s),jet pressure 0.03 MPa.The increase of the rotational speed of the copper roll and the increase of the pressure of the furnace cavity can improve the amorphous forming ability of the Ti50-xNi50 Zrx alloy ribbons.The Ti30Ni50Zr20 alloy ribbon has the strongest amorphous formation ability,and its crystallization activation energy is up to482.4kJ/mol.Through the study of the microstructure of Ti50-xNi50 Zrx alloy ribbon,it is found that the primary crystallization forms(Ti,Zr)Ni phase in Ti25Ni50Zr25 alloy,and the Ni content in Ti25Ni50Zr25 alloy is low actually,when heating is continued to 565.02?,the secondary crystallization forms ?1 phase.In the Ti20Ni50Zr30 alloy,the primary crystallization forms(Ti,Zr)Ni phase and the(Ti+Zr)/Ni is close to 1,so the Ni Zr phase was formed by secondary crystallization at 525.17 ?.After annealing at 700 ? for 1 h,the room temperature structure of Ti40Ni50Zr10 alloy ribbon is B2+?1,and the two-phase interface is coherent.The room temperature of Ti30Ni50Zr20 alloy ribbon is slag-like martensite+?1 phase,(011)type I twins.The room temperature structure of Ti20Ni50Zr30 alloy ribbon is B2+B19'+NiZr+?1 four-phase coexistence,in which the five-fold twins structure of B19' was found.Finally,the martensitic transformation behavior and shape memory effect of the Ti50-xNi50 Zrx alloy ribbons were studied.It was found that the martensitic transition temperature of the Ti50-xNi50 Zrx alloy ribbons with the increase of Zr content at different annealing temperatures.The phase transition temperature of the alloy ribbon is relatedto the content of NiZr phase,the more the content of Ni Zr phase in the alloy is,the lower the phase transition temperature of the alloy is.After the thermal cycling of the Ti30Ni50Zr20 alloy ribbon after annealing at 800 ? for 1h,the martensitic transition peak temperature Ap decreased by 11 K and the phase change hysteresis increased by 2.9K,which indicated that the Ti30Ni50Zr20 alloy ribbon showed good thermal cycling stability.After 800 ? annealing for 1 h,the fracture elongation of Ti50-x Ni50 Zrx alloy ribbons decrease with the increase of Zr content.The fracture strain of Ti30Ni50Zr20 alloy ribbon is 10.4% and the fracture stress is 626.8MPa.Ti30Ni50Zr20 alloy ribbon has the best shape memory effect,and the best heat treatment process is annealed at 800 ? for 1h.At this time,the maximum recoverable strain of Ti30Ni50Zr20 alloy ribbon is 3.6% at 4%pre-strain.