Deformable and transformable nitinol alloys enable enhanced strain hardening in aluminum

Abstract

Secondary rigid fillers reinforce the metals, yet usually at the cost of strain localization and reduced plasticity/toughness. Nitinol (NiTi) alloy, as a representative of shape memory materials, exhibits reversible phase transformation ability and considerable deformability upon loading. Here, we introduced age-treated NiTi particles into aluminum (Al) via powder metallurgy, where the sufficient matrix constraint maintains metastable R phase in the NiTi particles. The resultant composite with 30 weight ratio NiTi particles achieves the optimal ultimate tensile strength (UTS) and uniform elongation, 8% and 48% surpassing those of pure Al without NiTi filler. Such salient property gains are attributed to the stress-induced R-phase reorientation and particle deformation, thus effectively accommodating strain localization, alleviating stress concentration near the NiTi/Al interface, and activating micro-crack toughening effect. Our strategy can be readily extended to other matrices with deformable or phase-transformable fillers, offering broad potential for applications in energy dissipation, damping, and intelligent material systems.