Crossover strain glass alloy exhibiting large recoverable strain over a wide temperature range

Superelastic alloys, being successfully used in cutting-edge space technologies, are desired to possess large recoverable strain and wide working temperature range simultaneously. However, achieving such a combination has proven challenging. Here we report a finding of crossover strain glass transition in the crossover region between martensite and strain glass regimes of temperature vs. annealing-time phase diagram of cold-rolled Ti₅₀Ni₅₀ alloys. The crossover strain glass alloy exhibits a large recoverable strain of ∼ 4%-6% and ultrawide working temperature range from 453 to 93 K, outperforming previously reported superelastic alloys. Moreover, such exceptional properties were revealed to stem from the crossover strain glass transition occurring at a high transition temperature T_g ∼276 K, which possesses a unique transition behavior of strain glass transition accompanied by a sluggish and partial martensitic transformation from strain glass to martensite with cooling. This transition was further characterized by in-situ microscopic observations: upon cooling both several nanometer-sized and dozens of nanometer-sized B19’ martensitic domains gradually appear and increase in the matrix of B2 parent phase over a wide temperature range, which contribute to large recoverable strain and ultrawide working temperature range. Our work indicates that the crossover strain glass may provide a new mechanism to achieve large recoverable strain over a wide temperature range, and large field-induced strain over a wide temperature range may be obtained in other crossover ferroic glasses.