Abstract: Ni-Mn based Heusler alloys undergo a first-order magneto-structural transition (FOMST) from high-temperature high magnetic austenite to low-temperature low magnetic martensite. The FOMST can be induced by external stimuli such as magnetic fields, uniaxial stress, or temperature. The sensitivity of FOMST to external stimuli results in large caloric effects and can be used for multicaloric solid-state cooling. A disadvantage of Ni-Mn-based Heusler alloys is their brittleness, limiting the shaping of those alloys required for further application. We used microstructure design by suction casting or additive manufacturing (AM) to process alloys with beneficiary microstructure to increase mechanical stability and cyclic performance. In addition, AM also enables the processing of complex geometries. We also investigate the correlation of microstructure and the thermal hysteresis of the FOMST and the transition width. By in-situ microscopy, we can identify the nucleation sides of the FOMST and the defect acting as pinning sides for the propagation of the phase transition. The FOMST and thermal hysteresis can be specifically designed for multicaloric cooling cycles by tailoring the processing method, parameters, and particle size. In addition, microstructural design by DED, PBF-LB, SPS, or hot compaction can significantly improve the mechanical and cyclic stability of brittle Heusler alloys. This work is supported by ERC (Adv. Grant "Cool Innov") and DFG 527201505 and CRC/TRR 270 "HoMMage". [1] F. Scheibel et al., Energy Techn. 6, 1397 (2018), DOI :10.1002/ente.201800264 [2] L. Pfeuffer et al., Acta Mater. 221, 117390 (2021), DOI:10.1016/j.actamat.2021.117390 [3] F. Scheibel et al., Materialia 29, 101783 (2023), DOI:10.1016/j.mtla.2023.101783 [4] F. Scheibel et al., Adv. Eng. Mater. 24, 2200069 (2022), DOI:10.1002/adem.202200069
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