Polycrystalline Shape-Memory Alloy and Strain Glass

Abstract

AbstractPrecipitation and coarsening kinetics of H-phase in Ni50Ti30Hf20 high-temperature shape-memory alloy and their effect on age hardening and transformation temperature behavior are discussed in the first part of this chapter. The critical size of H-phase precipitates responsible for breaking down the precipitate/matrix interface coherency, determined from experimental data, increases with increasing aging temperature. It is shown that transformation temperatures as well as transformation hysteresis can be controlled through the temperature and duration of aging. In the second part, the strain glass is discussed. Strain glass is a glassy phenomenon in shape-memory alloy systems, characterized by the frozen of martensitic nano-domains. It can be generated by doping sufficient defects into normal martensitic alloys and displays typical glassy features: invariability in average structure, dynamic freezing, broken ergodicity, and nano-domains. The strain glass can exhibits multiple functionalities such as new shape-memory effect and superelasticty due to the response of martensitic nano-domains to temperature and physical field. The third part is devoted to the elastocaloric effect in shape-memory alloys. Several criteria have been proposed that make it possible to predict a large elastocaloric effect during stress-induced martensitic transformation. Moreover, recent progress of advanced elastocaloric effect in additively manufactured, high-entropy, and other shape-memory alloys is also presented and discussed.KeywordsPrecipitation hardeningStrain glassElastocaloric effectShape-memory alloys