Orientation Dependent Compression Behavior of Co\u3csub\u3e35\u3c/sub\u3eNi\u3csub\u3e35\u3c/sub\u3eAl\u3csub\u3e30\u3c/sub\u3e Single Crystals

The shape memory effect (SME) and superelasticity (SE) behavior of homogenized Co35Ni35Al30 single crystals were systematically characterized along the [100], [110] and [111] orientations under compression. The shape memory behavior of CoNiAl was found to be highly orientation and stress/temperature dependent. Maximum compressive recoverable strains were 3.98 % in [110], 3 % in [100] and 0.30 % in [111] orientations, respectively. The Co35Ni35Al30 demonstrated a very high superelastic temperature window of more than 350 °C along the [100] and [110] orientations. Moreover, two-way shape memory effect with very low thermal hysteresis of about 6 °C was observed along the [110] orientation. The large decrease of recoverable strain and hysteresis with stress (or temperature) was mainly attributed to the difference of elastic moduli of transforming phases

On the Impact of Additive Manufacturing Processes on the Microstructure and Magnetic Properties of Co–Ni–Ga Shape Memory Heusler Alloys

Microstructure design allows to prevent intergranular cracking and premature failure in Co–Ni–Ga shape memory alloys. Favorable grain boundary configurations are established using additive manufacturing techniques, namely, direct energy deposition (DED) and laser powder bed fusion (L‐PBF). L‐PBF allows to establish a columnar grain structure. In the Co–Ni–Ga alloy processed by DED, a microstructure with strong ⟨001⟩ texture is obtained. In line with optimized microstructures, the general transformation behavior is essential for performance. Transition parameters such as transition temperature and thermal hysteresis depend on chemical composition, homogeneity, and presence of precipitates. However, these parameters are highly dependent on the processing method used. Herein, the first‐order magnetostructural transformation and magnetization properties of Co–Ni–Ga processed by DED and L‐PBF are compared with single‐crystalline and as‐cast material. In the alloy processed by L‐PBF, Ga evaporation and extensive formation of the ferromagnetic Co‐rich γ'‐phase are observed, promoting a very wide transformation range and large thermal hysteresis. In comparison, following DED, the material is characterized by minor chemical inhomogeneity and transition and magnetization behavior being similar to that of a single crystal. This clearly renders DED‐processed Co–Ni–Ga to become a promising candidate material for future shape memory applications