Ductile CuAlMn shape memory alloys with higher strength by Fe alloying and grain boundary engineering

A higher yield strength of parent phase in shape memory alloys is necessary for achieving a higher recovery stress. Fe alloying combined with grain boundary engineering (GBE) were investigated to improve the yield strength of ductile Cu17Al11Mn alloy. Results showed that the precipitation of low strength ductile α phase through the GBE remarkably enhanced the ductility while not obviously reducing the yield strength in the step-quenched Cu17Al11Mn4.5Fe alloy due to the precipitation of nanoscale κ phase inside them. Compared to the Cu17Al11Mn alloy, a 200 MPa higher yield strength and better ductility could be realized in the Cu17Al11Mn4.5Fe alloy step-quenched into two-phase region between 993 K and 1003 K. The recovery strains of ∼6.5% could be guaranteed in the step-quenched Cu17Al11Mn4.5Fe alloy. The Fe alloying combined with the GBE through the step-quenching will be a direction for developing ductile CuAlMn based alloys with both high strength and recovery strain.