|
The results of investigation of the microstructure of two polycrystalline Ni-Mn-Ga
alloys subjected to thermo-mechanical treatment by multiple isothermal forging and extrusion
are presented. Alloy forging at a temperature of 680œC and 700œC leads to the formation of a
bimodal structure which has large grains of several hundred micrometers surrounded by a
layer of the fine-grained structure. As the result of the further treatment by extrusion at 710œC
the volume fraction of the fine-grained structure is increased. At the same time, anisotropy of
thermal expansion during the martensitic transformation is observed in the alloys in both
states due to residual tensile stresses introduced in the last stages of treatment. The performed
investigation shows high potential of the thermo-mechanical treatment for obtaining
structurally modified Heusler alloys having a sufficient level of functional and service
properties for practical applications.
Keywords: Heusler alloys, martensitic transformation, thermo-mechanical treatment, multiple isothermal forging, extrusion, EBSD, texture, anisotropy |
full paper (pdf, 1616 Kb)