Inhomogeneity of Room‐Temperature Elastocaloric Effects in NiTi Alloys Fabricated by Laser Powder Bed Fusion

ABSTRACT NiTi shape memory alloys are among the most promising solid‐state refrigeration materials. In recent years, additive manufacturing methods for producing difficult‐to‐machine NiTi alloys have gained increasing attention from researchers. This work successfully produces NiTi alloys with good superelasticity at room temperature via laser powder bed fusion (LPBF). The results show that when the NiTi alloys undergo elastocaloric effects (eCE) during compression, the surface temperature distribution is inhomogeneous. The temperature difference between the highest and lowest points on the same test surface can reach 4.2 K, and there are many parallel strip‐shaped high and low temperature regions on the surface of the samples. Such inhomogeneity is shown to be attributed to the microstructure of the samples. The microstructure of the NiTi shape memory alloys manufactured via LPBF is found to be inhomogeneous, with obvious coarse and fine grain areas, and there are significant differences in dislocation density, precipitate phase size, and density in these two areas. The fine grain areas are mainly distributed near the boundary of the melt pool because the cooling rate at the boundary of the melt pool is the highest, and the grains do not have sufficient time to coarsen. This work provides a reference value for studying the relationship between microstructure uniformity and eCE uniformity in NiTi alloys.