Effect of annealing time on solid solution microstructure and memory properties of additive Fe-Mn-Si-Cr-Ni alloy

Abstract

Annealing plays a pivotal role in optimizing the morphology and quantity of cooling martensite within the solid solution matrix of additively manufactured Fe-based memory alloys. In this study, we utilized laser filament deposition to create Fe-17Mn-6Si-9Cr-5Ni alloy, and subsequently compared the microstructure and memory properties of the alloy following two treatments: a 900[Formula: see text]C×60 min solution treatment and a solid solution + annealing treatment at various durations at 600[Formula: see text]C. Our aim was to investigate how annealing time impacts the memory properties of additively manufactured Fe-Mn-Si-Cr-Ni alloys in their solid solution state, focusing on microstructural changes during the metamorphic and revertive states. The findings reveal that after the solution treatment, the alloy contains a higher number of cooling martensite units, but their arrangement is disordered, indicating a lower degree of order. However, after a 10 min annealing treatment, the quantity of cooling martensite slightly diminishes, while their arrangement becomes more orderly. With prolonged annealing, both the quantity of cooling martensite and the grain size of the alloy decrease significantly. Consequently, after a 10-min annealing treatment, the alloy exhibits a 31% increase in shape recovery rate under a 6% pre-deformation compared to the alloy subjected solely to the solution treatment, and the recoverable strain reaches 4.59%. This demonstrates that an appropriately timed annealing process can transform the disordered cooling martensite within the solid solution structure of additive manufacturing Fe-based memory alloys into a more regular arrangement, thereby enhancing their memory performance.