The concept of high-entropy alloy provides a new metallurgical approach for designing shape memory alloys with complex compositions. Our group is developing high-entropy shape memory alloys based on the pseudobinary TiNi system. These alloys exhibit higher mechanical strength while retaining their excellent functional properties. The concept of high-entropy alloy enables development and investigation of various novel high-entropy shape memory alloys with unique and fantastic properties.

Shape memory alloys are regarded as highly potential materials for serving as solid-state cooling devices. The TiNi-based and Cu-based shape memory alloys are investigated to reveal their elastocaloric effect and operating temperature window. The operating temperature of TiNi-based shape memory alloys can be extended to a lower temperature by introducing an intermediate R-phase or high-entropy design. For Cu-based shape memory alloys, a wide temperature window of about 200 °C can be obtained. These studies promote the understanding and applications of the elastocaloric behavior of shape memory alloys.

Functional stability is a critical issue when shape memory alloys are going to be utilized for applications. The functional fatigue of Ti-rich TiNi shape memory alloy is effectively improved by introducing the melt-spinning technique, precipitation hardening, and high-entropy design. The rapidly solidified Ti-rich TiNi shape memory ribbon exhibits great functional stability and retains considerable transformation strain. This study provides a new way to effectively improve the functional stability of Ti-rich TiNi shape memory alloys. Various alloy design strategies are applied to improve the functional stability of shape memory alloys.

To investigate the functional properties of TiNi-based shape memory ribbons for their applications as miniatured actuators or microelectromechanical systems (MEMS), researchers fabricated these ribbons using the melt-spinning technique. The thickness of these ribbons was about 20-30 μm. The ribbons exhibited a unique precipitation process, which resulted in excellent strength, functional stability, shape memory effect, and pseudoelasticity. These studies provide a deep understanding of the outstanding properties of rapidly solidified TiNi-based shape memory ribbons.

Non-contact measurements enable recording strain and temperature fields during deformation and phase transformation of shape memory alloys. These methods allow for clear observation of the distributions of 2D and 3D strain fields, as well as the temperature field. They provide a deep understanding of the position and homogeneity of martensitic transformation. Local strains can be detected to evaluate the transformation fraction of shape memory alloys. 

A novel method combining the electron backscattering diffraction (EBSD) technique and orientation contrast imaging is developed for identifying the self-accommodation morphologies of R-phase martensite variants. The variants can be observed clearly, and this method can easily identify the twinning plane. This method provides the advantages of easily identifying twinning relationships, higher magnification, and simple observations for polycrstalline samples than the conventional method with an optical microscope.