Titanium matrix composites (TMCs), as a new generation of lightweight and high-performance metals are considered to be one of the most promising structural materials in fields of aerospace, automotive and other high-tech industries. Compared with conventional micron-reinforced TMCs, nano-reinforced TMCs (NRTMCs) exhibit more significant advantages such as the desirable strength and ductility synergies and thermal deformation capacity. However, the performance potential of NRTMCs has not been sufficiently developed due to the problems of dispersion and thermal stability of the nano-reinforcements. How to introduce nano-reinforcements and maintain their stability during thermal mechanical processing has been a serious challenge for NRTMCs. This paper reviews the progress of the process features, fabrication methods, microstructure characteristics and mechanical properties, analyzes and identifies a series of fundamental issues that constrain its development, and points out the research direction for future research.

Because of the unique shape memory effect and superelasticity, equiatomic Ni-Ti alloys have become the most typical shape memory materials in academic research and engineering applications. Numerous investigations have revealed that the martensitic transformation in Ni-Ti alloys could be retarded by incorporating the third element or increasing Ni/Ti ratio, and the characteristics of transformation and shape memory effect could be tailored. The theoretical and experimental studies in recent years indicated that when doping sufficient amounts of defects including excess solute atoms, foreign alloying dopants, vacancies, dislocations and nanosized precipitates into equiatomic Ni-Ti alloys, the resistance from such defects could suppress the first-order martensitic transformation and achieve strain glass transition with the formation of randomly short-range ordered nanodomains. The strain glass transition is characterized by some typical features such as invariant macroscopic structure, appearance of dynamic elastic modulus dip and frequency dispersion in the elastic modulus, broken ergodicity, shape memory effect and unique superelasticity with slim hysteresis over a wide temperature range. In the present paper, the proposition, novel properties and the research progress in the strain glass transition in Ni-Ti based alloys were reviewed. In addition, the principle for designing Ni-Ti based alloys with superelasticity in broad temperature range and their applications in engineering are briefly introduced.