Control of microstructure and shape memory properties of a Fe-Mn-Si-based shape memory alloy during laser powder bed fusion

Abstract

• Microstructure modification by varying the laser scan velocity is demonstrated for a Fe-Mn-Si based shape memory alloy fabricated by laser powder bed fusion. • Pronounced Mn evaporation affects the primary solidification phase and, thus, the phase fraction in the samples. • Phase-transformation bcc-δ → fcc-γ induced by the intrinsic heat treatment refines the microstructure and reduces the crystallographic texture. • Microstructural changes result in variation of the alloy's shape memory and mechanical properties. Fe-Mn-Si shape memory alloys are materials, whose functional properties strongly depend on microstructural factors such as grain size and orientation, phase fraction and chemical composition. The present study demonstrates the possibility of microstructure modification via process parameter variation on a Fe-Mn-Si based shape memory alloy fabricated by laser powder bed fusion. By varying the scan speed, samples characterized by coarse elongated grains with strong <001> orientation along the build direction or by finer equiaxed grains without preferential orientation can be fabricated. Changes in the volume phase fraction of bcc-δ ferrite and fcc-γ austenite are also introduced by selective Mn evaporation. A direct correlation between the generated microstructure and achieved mechanical and shape memory properties is found.