Local precipitation phase inhomogeneity enables superior elastocaloric effects in additively manufactured NiTi alloys via <i>in situ</i> and post-heat treatment

NiTi shape memory alloys have been widely recognised for their functional properties, especially the elastocaloric effect. However, the elastocaloric performance is often limited by intrinsic phase transformation hysteresis. Herein, we propose a novel manufacturing strategy, integrating in situ and post-processing to achieve microstructure-engineered reinforcement. By precisely controlling Ni content and thermal history, we induce inhomogeneous Ni4Ti3 precipitation phase within the NiTi matrix, forming tailored phase distribution. After aging, the R-phase nanodomain structure was developed, which minimises energy dissipation by suppressing transformation hysteresis. The Ni4Ti3 phase and heterogeneous microstructure synergistically enhance the matrix’s phase transformation enthalpy and boost the adiabatic temperature change (ΔTad). This manufacturing strategy yields a 231.6% improvement in the material coefficient of performance (COPmat)for the L-PBFed NiTi alloy. This work demonstrates how precipitate-matrix interactions and multiscale microstructure engineering can optimise functional material, offering a new paradigm for high-efficiency elastocaloric cooling components.