Refinement of built-in superelasticity in LPBF-NiTi
Additive manufacturing, after its hype in the early 2010s, is still an intensely discussed manufacturing route in the field of research & development as well as in industrial applications [1]. However, complex post-processing slowed down the rise and caused delays in the comparatively rapid production process, along with poor component performance. With the increasing wealth of experience and technical progress in the industry, additive manufacturing now manages the transition from prototype construction to series production [2]. Laser Powder Bed Fusion (LPBF) offers good potential since chemical contamination can be lowered to a minimum due to the reduction of the melting zone and the absence of binding agents.
NiTi, with its exceptional superelastic properties, exhibits high potential in various fields of application. Basis of these properties are reversible phase transformations under loading conditions which can be tailored by processing and heat treatments [4]. Combining both, NiTi and LPBF-processing, leads to new challenges in obtaining superelasticity.
Within this work, an LPBF parameter set is investigated which was tailored to exhibit good superelasticity in the as-built condition. Heat treatments were performed to optimize materials properties and exploit AM-based superelasticity. Mechanical testing revealed superior properties with plateau stresses of up to 650MPa under compression as well as tensile loading. Residual elongations were below 0.1% after compression loading up to 14% and 0.2% for tensile loading of 4%.
Microstructural characterization is carried out including X-Ray diffractions as well as TEM-analysis to explore underlying mechanisms of superelasticity in AM-based microstructures.