Significant enhancement of room-temperature shape recovery properties of Ta-modified Fe-Mn-Si shape memory alloys fabricated by laser powder bed fusion

In this study, fully dense and crack-free Fe-30Mn-6Si-xTa (x = 0, 0.5, 1.0, 2.0 wt%) shape memory alloys (SMAs) were manufactured by laser powder bed fusion (LPBF). The effects of tantalum (Ta) addition and post-heat treatment (600 °C for 30 min) on microstructure and shape memory properties were systematically investigated. It was found that Ta effectively leads to the grain refinement in the Fe-based SMAs, which is mainly attributed to solute redistribution and the formation of Ta precipitate during rapid solidification. Post-heat treatment further improved room-temperature (RT) shape recovery properties of the Fe-30Mn-6Si-0.5Ta (wt%) alloy, achieving a recovery strain of ∼2.84 % and a shape recovery ratio of ∼71 %, which is 70 % higher than previously reported LPBF-fabricated Fe-based SMAs (i.e., ∼1.64 % recovery strain and ∼41 % shape recovery ratio). This enhancement is attributed to the increased stacking fault (SF) density facilitated by Ta precipitates and the positive influence of heat treatment, both of which promote the phase transformation from γ-austenite to ε-martensite. The research demonstrates that the Fe-based SMAs with enhanced shape memory properties can be fabricated by the LPBF technique, which provides new insights and practical guidance for designing high-performance SMAs via additive manufacturing techniques.