The Effect of High-Temperature and High-Stress Martensite Aging on Martensitic Transformation and Microstructure of Ti-51.5 at% Ni Single Crystals

Timofeeva, E. E.; Panchenko, E. Yu; Eftifeeva, A. S.; Yanushonite, E., I; Zherdeva, M., V; et al. Proceedings Of The International Conference On Physical Mesomechanics. Materials With Multilevel Hierarchical Structure And Intelligent Manufacturing Technology.
In this work, the thermomechanical stability of heterophase [001]-oriented Ti–51.5 at % Ni single crystals was investigated. Experiments include a high-temperature and high-stress martensite ageing and also loading/unloading cycling at superelasticity (SE) during forward and reverse B2-B19′ martensitic transformations (MT). It was found that Ti–51.5 at % Ni single crystals containing large Ti3Ni4 particles (d ∼ 600 nm after ageing at 850 K for 1 h) is not resistant to stress-assisted martensite ageing and cycling. Stress-assisted martensite ageing at 423 K, 1.7–2 GPa, for 2–4 h leads to the deformation of large Ti3Ni4 particles, the appearance of dislocations at the particle-matrix boundaries, an increase in MT temperatures (by 10 K), and a strong diffusion of the MT (the intervals of forward and reverse MT 𝛥𝜎1Δ1σ and 𝛥𝜎2Δ2σ increase in 2 times). During loading/unloading cycling at 423 K and 1.0–2.0 GPa single crystals with large particles were destroyed after 20–25 cycles. It is possible to increase the thermomechanical stability due to the additional precipitation of nanosized Ti3Ni4 particles (d<30 nm by ageing at 673 K, 1 h), which appear in the B2 matrix between large particles. In such crystals with a bimodal structure no changes in the microstructure and functional properties were observed after stress-assisted martensite ageing and loading/unloading cycling.