Functional architected Al–NiTi interpenetrating phase composites with primitive aluminum cores fabricated using spark plasma sintering

Interpenetrating phase composites (IPCs) are composite materials characterized by co-continuous and interlocked matrix and reinforcing phases. This distinctive combination often leads to superior performance compared to conventional composite assemblies. The present work investigates nitinol-aluminum metal-metal (MM) IPCs fabricated for the first time using a combination of additive manufacturing and spark plasma sintering (SPS) techniques. Using this approach, aluminum lattice constructs are first obtained by means of laser powder bed fusion. The constructs are then filled with pre-alloyed nitinol powder, which is subsequently sintered using SPS. Our investigation considers five different combinations of sintering temperatures and pressure. The samples are examined at both proximal and distal positions relative to the aluminum phase in order to evaluate the influence of temperature, stress, and possible alloying on the microstructure of the IPC and the phase transformation behavior of the nitinol phase. The interface between the nitinol and aluminum phases, as well as the elemental distribution within the IPCs, are characterized using scanning electron microscopy that reveal clear penetration and alloying of nickel and titanium within the aluminum phase. Differential scanning calorimetry further reveals variations in phase transformation temperatures within each sample. The nitinol phase in the IPC samples is shown to retain its shape memory properties. This study opens a new pathway for designing nitinol composites combining low melting point additively manufactured aluminum preforms with a high melting point nitinol matrix. This approach deviates from conventional metal-metal IPC fabrication methods, while still preserving the functional response of the nitinol phase.