Martensitic transformation and good ductility in all-d-metal NiMn-based Heusler magnetic shape memory alloys from first-principles prediction

The possible martensitic transformation (MT) and ductile properties of all- d -metal Ni 2 Mn Z ( Z =Sc, Ti, V, Cr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Re, Os, Ir, and Pt) Heusler alloys have been systematically investigated using first-principles calculations. In the cubic austenite, the alloys with Z =Sc, Ti, Y, Zr, Nb, Pd, and Pt possess the ferromagnetic (FM) Cu 2 MnAl structure, whereas the remaining alloys have the antiferromagnetic (AFM) Hg 2 CuTi structure. All the thirteen FM alloys, excluding Z =Sc, Y, and Zr, can undergo MT. Compared to Ni 2 MnTi, most of these alloys display larger transformation strains and higher MT temperatures ( T M ). They also demonstrate improved ductility, as indicated by higher Pugh ratios, Poisson’s ratios, and Pettifor’s Cauchy pressures in the austenite. Ni 2 MnNb alloy may exhibit enhanced elastocaloric, barocaloric, and magnetocaloric effects, accompanied by significant volume and magnetic discontinuities during the MT. It is also revealed that the paramagnetic (PM) ordering promotes MT, enabling it to occur in the PM alloys with Z =Sc, Y, and Zr. Under hydrostatic pressure, the FM Z =Zr alloy can also undergo MT. Mn- Z disorder reduces the driving force for MT, causing it to disappear in Ni 2 (Mn 1 − y Ti y )(Ti 1 − y Mn y ) when y ≥ 0 . 3 . The face-centered cubic (FCC) phase tends to precipitate when both the volume and magnetic moment of the structure are smaller than those of the martensite. This precipitation can be accelerated by phonon vibrations, which, nevertheless, further improve the good ductility of the martensite. The insights provide valuable guidance for the experimental design and application of these magnetic shape memory alloys with excellent mechanical properties. • All the Ni 2 Mn Z alloys, excluding Z =Sc, Y, and Zr, can undergo martensitic transition. • Compared to Ni 2 MnTi, most of the alloys exhibit larger transformation temperatures. • Both magnetic disorder and hydrostatic pressure can promote the transformation. • The BCT-FCC transition occur in the alloys with Z =Ti, V, Cr, Mo, Nb, Rh, Pd, and Pt. • Most of the alloys exhibit better ductility than Ni 2 MnTi.