Laser beam powder bed fusion of NiTiFe shape memory alloys by in-situ alloying: microstructural evolution and generation of strain glass

In this study, ternary NiTiFe shape memory alloys with different volume energy densities were fabricated by laser beam powder bed fusion technique via mixed pre-alloy NiTi powder and 3 at. % pure Fe powder. The exceptionally low porosity of <0.1% was attained at a volume energy density of 229 J/mm3. The underlying mechanism between the processing parameter and forming quality associated with the Marangoni effect was analysed by the Archimedes method. The grain size with different volume energy densities can be well verified by the growth restriction factor and its corresponding grain size prediction model. Additionally, this work devised a novel approach to synergistically induce strain glass in NiTiFe alloy through the integration of dislocations and precipitates resulting in stable quasi-linear superelasticity with narrow hysteresis. In summary, our work demonstrates the feasibility of synthesising ternary NiTi-based shape memory alloys via additive manufacturing and offers a new-fangled insight for developing novel alloys with strain glass characteristics.