Characteristics of the strain glass transition in as-quenched and 250 °C early-aged Ti _48.7 Ni _51.3 shape memory alloy

Characteristics of the strain glass transition exhibited in as-quenched and 250 °C 1–5 h aged Ti _48.7 Ni _51.3 SMA were studied by various tests/measurements. The results of frequency-dependent storage modulus vs. temperature measurement, the temperature-dependent resistivity, thermal conductivity, and specific heat tests demonstrated the signature and characteristics of the strain glass transition exhibited in as-quenched and 250 °C early-aged Ti _48.7 Ni _51.3 SMA. The plate-/disk-like morphology and spatially heterogeneous distribution of the real Ni-rich nanodomains in as-quenched and 250 °C 1–5 h aged specimens were quantitatively characterized using small-angle X-ray scattering (SAXS) technique. The formative origin of the real nanodomains and the relationship between the real nanodomains and the strain nanodomains are proposed accordingly. Experimental results indicated R-like phase and Ti ₃ Ni ₄ -like precipitates co-existing in the strain glass of 250 °C early-aged specimens, and they also demonstrated the growth behavior of the real nanodomains exhibited in specimens during thermal aging. It was also found that increasing the aging time can elevate the T _g from ∼−60 °C to ∼−20 °C, which indicates the tunable characteristic of T _g for as-quenched Ti _48.7 Ni _51.3 SMA.