Thermal expansion anisotropy formed by extrusion for Ni2.26Mn0.80Ga0.89Si0.05 alloy

• Published in: Journal of magnetism and magnetic materials Vol. 514; p. 167160
• Main Authors: Musabirov, I.I., Galeyev, R.M., Safarov, I.M.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.11.2020; Elsevier BV
• Subjects: Alloys; Anisotropy; Crystallographic texture; Crystallography; Deformation; Extrusion; Ferromagnetism; Forging; Grains; Heusler alloys; Martensitic transformations; Mechanical properties; Metallographic texture; Multiple isothermal forging; Shape effects; Shape memory alloys; Texture; Thermal expansion; Thermomechanical properties; Thermomechanical treatment; Heusler alloys; Extrusion; Multiple isothermal forging; Crystallographic texture; Anisotropy; Metallographic texture
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2020.167160

[Display omitted] •Ni2.26Mn0.80Ga0.89Si0.05 alloy was treated by forging and extrusion at 700 °C.•Large grains of 100–200 μm are surrounded by fine-grained structure after forging.•The metallographic texture is observed after extrusion.•Anisotropy of thermal expansion 0.13% and 0.09% values is observed after extrusion. Heusler alloys demonstrate various effects, such as the ferromagnetic shape memory effect, the magnetocaloric effect, etc. But these alloys are also liable to destruction during multiple cycles of martensitic transformation. In order to increase stability of functional properties of the alloys, thermo-mechanical treatment by various methods is carried out. In this work, a Heusler Ni2.26Mn0.80Ga0.89Si0.05 alloy was subjected to combined deformation processing: multiple isothermal forging and subsequent direct extrusion. The multiple isothermal forging was carried out at 700 °C in 5 upset transitions and a total true degree of deformation of e ≈ 2.42. The extrusion was also carried out at 700 °C with an extrusion ratio of 2:1 (e = 1.39). Analysis of the microstructure shows that, resulting from combined treatment, metallographic and crystallographic textures are formed. The metallographic texture is characterized by coarse grains of approximately 1 mm in length and hundreds of microns in diameter. The coarse grains are in turn surrounded by a layer of fine-grained structure. The crystallographic texture is axial of the 〈110〉 type. This kind of structure enhances mechanical properties of the alloy. According to the study of thermal expansion anisotropy in the region of martensitic transformation, contribution of the martensitic transformation to the relative change in the length of the extruded sample is 0.13% in the direction, normal to the extrusion axis, and 0.09% - along it. These values are comparable to those observed on Heusler alloys in the as-cast state. Thus, it is found that thermo-mechanical treatment by the combined method allows obtaining a significant amount of thermal expansion anisotropy while remarkably increasing mechanical properties of the material.