A martensitic TiNi shape memory alloy was processed by high-pressure torsion (HPT) for 1.5, 10 and 20 turns followed by post-deformation annealing (PDA) at 673 and 773 K for various times in order to study the microstructural evolution during annealing and the shape memory effect (SME). Processing by HPT followed by the optimum PDA leads to an appropriate microstructure for the occurrence of a superior SME which is attributed to the strengthening of the martensitic matrix and grain refinement. A fully martensitic structure (B19' phase) with a very small grain size is ideal for the optimum SME. The results indicate that the nanocrystalline microstructures after PDA contain a martensitic B19' phase together with an R-phase and this latter phase diminishes the SME. Applying a higher annealing temperature or longer annealing time may remove the R-phase but also reduce the SME due to grain growth and the consequent decrease in the strength of the material. The results show the optimum procedure is a short-term anneal for 10 min at 673 K or only 1.5 min at 773 K after 1.5 turns of HPT processing to produce a maximum recovered strain of ~8.4% which shows more than 50% improvement compared with the solution-annealed condition.

对马氏体TiNi形状记忆合金进行高压扭转（HPT）处理1.5、10和20圈，然后在673和773 K下进行变形后退火（PDA）进行不同的时间，以研究退火和退火过程中的微观组织演变。形状记忆效应（SME）。通过HPT加工，再加上最佳的PDA，可以形成合适的微观结构，以产生优良的SME，这归因于马氏体基体的强化和晶粒细化。具有非常小的晶粒尺寸的全马氏体结构（B19'相）是最佳SME的理想选择。结果表明，PDA后的纳米晶体微观结构包含马氏体B19'相和R相，而后者则减少了SME。施加较高的退火温度或较长的退火时间可能会去除R相，但由于晶粒长大并因此导致材料强度降低，也会降低SME。结果表明，最佳方法是在1.5倍HPT处理后，在673 K处进行10分钟的短期退火，或在773 K处进行仅1.5分钟的退火，以产生约8.4％的最大恢复应变，与50％相比，提高了50％解决方案退火的条件。