在此篇研究中，藉由改變MnNiSi鐵磁性形狀記憶合金之元素組成，可有效降低其麻田散體相變化溫度，並利用真空感應熔煉爐製備MnNiSi合金，藉由第四元素(Cr, Fe, Co, Ni, Cu)之添加，探討微結構、晶體結構、麻田散體相變化溫度及居禮溫度之影響，並利用場發射掃描式電子顯微鏡(SEM)、X光繞射儀(XRD)、示差掃描熱卡量計(DSC)及熱重量分析儀(TGA)分析。MnNiSi鐵磁性形狀記憶合金在950˚C發生麻田散體相變化，由正交(orthorhombic)結構之麻田散體轉變六方(hexagonal)結構之沃斯田體。Mn0.95NiSiM0.05，M=(Cr, Fe, Co, Ni, Cu)合金樣品中，以(Cr, Fe, Co, Ni, Cu)置換部分Mn，使元素有效固溶於MnNiSi合金之晶格位置，晶體結構仍維持正交結構；然而(Cr, Fe, Co, Ni, Cu)因原子半徑及與Ni及Si形成鍵結長度較Mn小，使正交結構之晶格產生扭曲，能量上升使結構傾向不穩定，進而降低麻田散體相變化溫度。其中Cu之添加，使正交結構之晶格扭曲程度最大，單位晶胞體積由0.146降至0.144 nm3，相變化溫度由950降至813˚C。居禮溫度由337 降至320.1˚C。因Cu造成之相變化溫度下降最大，故進一步提高Cu含量，以Mn1-xCuxNiSi, X= (0.05、0.1、0.2、0.3)合金樣品，隨Cu含量增加，Cu無法有效固溶在MnNiSi合金中，有偏析之狀況發生，形成Cu3Si相。由DSC分析得知，隨Cu含量提高，除了熔化之吸熱峰及相變化吸熱峰外，又額外增加不可逆相變化之吸熱峰，使合金系統複雜化，不利後續分析，故Mn0.95NiSiCu0.05合金為室溫下，為有潛力之磁致冷材料之一。

In this study, MnNiSi ferromagnetic shape memory alloy was prepared by vacuum induction melting furnace with adding the fourth element (Cr, Fe, Co, Ni, Cu), it was investigated the microstructure, crystal structure, martensitic transition and Curie temperature using SEM, XRD, DSC and TGA. The MnNiSi alloy undergoes a martensitic transition from the orthorhombic martensite to hexagonal austenite at 950˚C. In Mn0.95NiSiM0.05 alloys, the added elements were effectively dissolved in MnNiSi alloy still maintain the orthorhombic structure, the smaller radius of added the elements and the resulted shorter bond length were beneficial for the formation hexagonal structure. MnNiSi alloy was the most distortion the lattice of orthorhombic structure with adding Cu, and it was unit cell volume was decreased from 0.146 to 0.144 nm3, martensitic transition was decreased from 950 to 813˚C and Curie temperature was decreased from 337 to 320.1˚C. In the Mn1-xCuxNiSi, X = (0.05, 0.1, 0.2, 0.3) alloy sample, Cu could not be effectively dissolved in the MnNiSi alloy. while the Cu content increases, the more Cu segregation to forming Cu3Si phase. According to DSC analysis, with the increase of Cu content, in addition to the endothermic peak of melting and phase transition, the endothermic peak of irreversible phase transition was additionally added, which complicated the alloy system and was unfavorable for subsequent analysis. Therefore, Mn0.95NiSiCu0.05 alloy was one of the potential magnetic refrigeration materials at room temperature.

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