Martensite aging – Avenue to new high temperature shape memory alloys

Abstract

High-temperature shape memory alloys are attractive for efficient solid state actuation. A key criterion for shape memory alloys is the martensite start temperature. The current study introduces a concept for increasing this temperature of alloys initially not suited for high-temperature actuation. Aging of stress-induced martensite, referred to as SIM-aging in the current work, is able to increase the martensite start temperature by about 130°C as demonstrated in the present study for a Co–Ni–Ga shape memory alloy. The increase of transformation temperatures can be explained based on the concept of symmetry-conforming short-range order. Following SIM-aging the Co–Ni–Ga alloy shows cyclic actuation stability at elevated temperatures. While martensite aging has always been viewed as detrimental in the past, it can actually be exploited to design new classes of high-temperature shape memory alloys with excellent properties.