A selective laser melting (SLM)-fabricated NiTi with superior tensile property and shape memory recoverability was obtained by using a unique stripe rotation scanning strategy. The alloy characteristics, formation mechanisms and evolution in terms of twins, dislocations and precipitations of the alloy were systematically studied. Compared to the conventional smelting-followed-by-machining, the SLM fabrication process involves rapid solidification and repeated heating, which confer distinctive characteristics to the microstructures of SLM-fabricated NiTi alloys. Rapid solidification promotes the formation of a supersaturation solid solution matrix containing a high concentration vacancies, which in turn aggregate to generate a high density of dislocations. During subsequent repeated heating stages, these dislocations occur thermal motion along three directions of <001 > , <111> and <110 > , leading to the formation of thermal kinks, helical dislocations and wave morphology. Simultaneously, precipitated particles Ti₃Ni₄ repeatedly nucleate and heterogeneous grow with the movement of dislocation. Such precipitation behavior, termed repeated precipitation, has not been previously reported in the conventional NiTi alloys, suggesting that it could be a unique characteristic of such alloy. After martensitic transformation, only two twins, {1 $\overline{1}$ 1} type I twin and compound twin, are detected. The twinning lamellae of these two twins, where precipitation and dislocation pile-ups exist, often have uneven thickness and chaotic arrangement. Besides, the unique self-accommodated microstructures, such as secondary {1 $\overline{1}$ 1} type I twin and compound twin with “herring-bone’’ lamellae, which often appear in the deformed or nanocrystalline NiTi, can also be observed. These unique microstructures may confer the distinctive properties to the SLM-fabricated NiTi.

通过使用独特的条带旋转扫描策略，获得了具有卓越的拉伸性能和形状记忆可恢复性的选择性激光熔融（SLM）制造的NiTi。从合金的孪晶，位错和析出方面研究了合金的特性，形成机理和演变。与传统的熔炼跟加工相比，SLM的制造过程涉及快速凝固和反复加热，这赋予了SLM制备的NiTi合金微观组织独特的特性。快速凝固促进了包含高浓度空位的过饱和固溶体基质的形成，而空位又聚集而产生高密度的位错。在随后的重复加热阶段，这些位错沿<001>，<111>和<110>的三个方向发生热运动，导致形成热扭结，螺旋位错和波形。同时，析出的颗粒Ti₃ Ni ₄随着位错的运动而反复成核并异质生长。在常规的NiTi合金中以前没有报道过这种被称为重复沉淀的沉淀行为，这表明它可能是这种合金的独特特性。马氏体转变后，只有两个孪生子，{1$\overline{\mathrm{1个}}$1}检测到I型双胞胎和复合双胞胎。存在沉淀和位错堆积的这两个孪晶的孪晶薄片通常具有不均匀的厚度和混乱的排列。此外，独特的自适应微结构，例如次生{1$\overline{\mathrm{1个}}$1}还可以观察到经常出现在变形的或纳米晶态的NiTi中的带有“人字形”薄片的I型孪晶和复合孪晶。这些独特的微观结构可以赋予SLM制成的NiTi独特的性能。