Abstract
Phase changes in Ni75−xCuxSn25 and Ni75−xMnxSn25 alloys were studied by X-ray diffraction, differential thermal analysis and optical microscopy. Four kinds of structures, i.e. DO19-type hexagonal (βm phase), β-Cu3Ti(2H)-type orthorhombic (γ1′ phase), DO3-type cubic (β1 phase) and Heusler (L21)-type cubic (β3 phase), were observed. Martensitic and massive transformations and ferromagnetism were observed. The results are summarized as follows:(1) In Ni-Cu-Sn alloy, βm, γ1′ and β1 phases appear successively with increase in Cu content at room temperature. In Ni-Mn-Sn alloy, βm, β1, β3 and β1 phases appear successively with increase in Mn content at room temperature.(2) The high temperature β1 phase undergoes a martensitic transformation to the 2H structure during quenching and a massive transformation to the DO19 structure during slow cooling in a region of Cu(or Mn) content below about 6.5 at% in both alloys. In Ni-Cu-Sn alloy, martensitic transformation is observed in the region of less than 19 at%Cu.(3) The β1 phase undergoes a martensitic transformation in the range of electron concentration (e⁄a*) from about 10.7 to 11.2 in these alloys (e⁄a* represents the average number of d+s+p electrons in the outer shell of an atom).
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