Torsional behavior and microstructure characterization of additively manufactured NiTi shape memory alloy tubes

Abstract The large reversible strain upon heating (shape memory effect) or unloading (superelasticity), high power-to-weight ratio, good functional stability, compact size, and lightweight make the rotary NiTi shape alloys actuators an interesting candidate for various engineering applications. Additive manufacturing (AM) provides a single step freeform process that not only fabricates complex geometries but also tailors properties of printed parts profoundly. In selective laser melting (SLM) technique, parameters (PPs) scanning strategy show remarkable effect on microstructure, properties, size accuracy as-built parts. Impurity pick-up during AM is unintended incident altering microstructure thermomechanical fabricated significantly. this paper, slightly Ni-rich powder utilized to fabricate tubes with three different thicknesses via SLM method. It shown bidirectional results in deviation thin-wall tubes. Transformation temperatures (TTs) as-fabricated samples are assessed compared those starting powder. A shift TTs found between x-ray diffraction pattern shows martensite phase at room temperature powder, while austenite coexisting secondary Ti-rich oxide. Scanning electron microscopy (SEM) confirms Ti4Ni2Ox precipitates form along grain boundaries. characterization under pure torsional loading localized shear tube surface. behavior investigated exhibit superelastic response stable transformation 2.3% after 10 cycles.