Microstructure of NiTi superelastic alloy manufactured by selective laser melting

Nitinol is used in dental tools for its superelasticity, shape memory and biocompatibility. Selective laser melting (SLM) on a powder bed is a potential process for manufacturing such as dental tools. Microstructural studies are conducted on NiTi-SLM using a parallel strip strategy and 90 degrees laser beam rotation. The multi-scale (nano-, micro- and mesoscopic) microstructure is revealed. Similar cast type microstructure features are found. The SLM melt is casted in a micro-mold. Fine micro-grains with random crystallographic orientation are formed near the mold walls and served as seats for the rapid growth of columnar dendritic grains along the < 001 > direction with epitaxial crystallographic relationships. The growth of the columnar grains curves towards the center of the micro-mold, coinciding with the center of the laser beam. It is proposed that SLM processing resembles Metallic Self Micro-Mold Casting (MS mu MC) and/or Self Micro-Molding (S2M).

Automated summary

This study investigates the microstructure of NiTi-SLM, revealing the formation of fine random grains and columnar dendritic grains in a micro-mold. It suggests that SLM processing resembles Metallic Self Micro-Mold Casting and/or Self Micro-Molding.