Study on the Microstructure and Mechanical Properties of 60NiTi Alloy Quenched by Hot Oil

Abstract

60NiTi alloys have a tremendous potential to be used in aerospace, marine and automotive industries. There is still a need to further improve the deformability due to the high brittleness of the previously prepared 60NiTi. In this work, 200 °C hot silicone oil was selected as the quenching medium for 60NiTi for the first time to overcome its high brittleness. It is found that the unique microstructure of 60NiTi quenched by hot oil has a lamellar structure composed of a channel-like NiTi matrix and lenticular Ni4Ti3 phase containing a nano-lath NiTi phase. The 60NiTi exhibits a high compression fracture strain of 10% and large reversible strain of 7.5%; which originates from the superelastic behavior of the NiTi SMA constituent. Upon loading, the R phase reorientation releases the stress concentration at the initial stage; while the stress-induced martensitic transformation accommodates the large elastic deformation of the Ni4Ti3 phase at the later stage. This synergistic effect of the two promotes the compressive deformability.