【作者】 陈晓琴；

【导师】 陆兴；

【作者基本信息】 大连铁道学院 ， 材料学， 2003， 硕士

【摘要】 本文采用电阻测试、金相分析、透射电子显微分析和X射线衍射等手段，研究了Ni-Mn-Ga系列合金的马氏体相变特征和微观组织结构。 Ni-Mn-Ga系列合金中的马氏体变体有交叠的现象。在降温过程中，大部分马氏体沿试样结晶方向生长，只有非常少量的马氏体垂直于晶界方向生长。 在Ni_54.85Mn_20.09Ga_25.05、Ni_54.48Mn_21.69Ga_23.83、Ni_45.03Mn_32.8Ga_22.17、Ni_54.9Mn_19.6Ga₂₅C_0.5和Ni_55.4Mn_20.3Ga_22.9C_1.4合金中，发现了两次马氏体相变。NiMn（GaSi）、NiMn（GaGe）和NiMn（GaCo）合金在测量温度范围内只发生一次马氏体相变，合金元素Si和Ge的加入，降低了第一次马氏体相变温度，抑制了第二次马氏体相变；对于含Co系列合金，当Co替代Mn时，随着Co含量的降低，合金马氏体相变的温度变化不大，当Co替代Ga时，随着Co含量的增加，马氏体相变温度升高，热滞后增大。 Ni-Mn-Ga合金X射线衍射的结果表明，母相L2₁结构的衍射谱符合面心立方结构的衍射谱。合金马氏体相变产物共有三种结构：Ni_56.3Mn_19.4Ga_22.7C_1.6，Ni_48.19Mn_27.1Ga_21.52Co_3.19，Ni_47.99Mn_27.43Ga_20.32Co_4.26合金的马氏体为非调制结构；Ni_54.48Mn_21.69Ga_23.83合金的马氏体为五层调制结构；Ni₍54.85_Mn_20.09Ga_25.05合金的第一次马氏体相变产物为七层调制结构，第二次马氏体相变产物为五层调制结构。 透射电子显微分析的结果表明，Ni_54.48Mn_21.69Ga_23.83合金的马氏体为五层调制结构，Ni_56.3Mn_19.4Ga_22.7C_1.6合金的马氏体为非调制结构，与X射线衍射的结果一致。在分析电子衍射花样时，对母相L2₁结构做面心立方处理，对五层调制马氏体的结构做底心单斜处理，初步探索了Ni_54.48Mn_21.69Ga_23.83合金马氏体相变的取向关系。 结合已发表文献，详细分析了合金元素对Ni-Mn-Ga合金马氏体相变温度的影响，通过多元线性回归拟合，得到如下关系式：M_S=1858-17.23X_Mn-49.02X_Ga-61.92X_Si-65.43X_Ge+1.24X_Co-51.6X_C-58.92X_In大连铁道学院工学硕士论文，其中X、。、X。“、Xs‘、X。。、Xco、X。和X。分别表示Mn、Ga、51、G。、C。、C和In的原子百分比。确认电子浓度和点阵常数均影响马氏体相变温度。根据金属电子论，进一步提出电子密度（单位体积的价电子数）可能是合金成分影响马氏体相变温度更确切的途径。随着电子密度的增加，马氏体相变温度升高。 结合合金的具体情况，将马氏体相变的表象理论运用于Ni一Mn一Ga“金，得出了一系歹」理论上的市目变晶体学数“:在{“O}（“O）切变系中，只“采用(“O!“。]切变方式，才育旨使得表象理论的计算自洽;合金的成分不同，计算出的惯习面等晶体学参数也不同，说明马氏体相变晶体学与合金成分有关。更多还原

【Abstract】 The characteristics of martensite transformation and microstructure of Ni-Mn-Ga alloys were investigated by means of resistivity measurement, optical microscopy, transmission electron microscopy and X-ray diffraction analysis.An intersecting or overlapping type of martensite morphology was observed. Most martensite grow along the solidification direction and only a few martensite are perpendicular to the boundaries of the austenite during cooling.Two kinds of martensitic transformations were examined inNi43.85Mn20.09Ga25.05,Ni54.48Mn2l.69Ga23.83, Ni45.03Mn32.gGa22.17,nI54.9mN19.6-Ga25C0.5 and Ni55.4Mn2o.3Ga22.gC 1.4 alloys. Only the first martensite transformation occurred in NiMn(GaSi), NiMn(GaGe) and NiMn(GaCo) alloys. The Si and Ge additions obviously decrease the first martensitic transformation temperature of the alloys and depress the second martensitic transformation completely. The substitution of Co for Mn has hardly any influence on martensite transformation temperature; the substitution of Co for Ga increases the first phase transformation temperature and the thermal hysteresis of martensitic transformation.The X-ray diffraction spectrum of L21 structure accords with that of face-centered cubic structure. There are three kinds of martensite structure in the alloys: non-modulated martensite in Ni56.3Mni9.4Ga22.?Ci.6, Ni48.19Mn27.1Ga21.52Co3.19 and Ni47.99Mn27.43Ga20.32Co4.26 alloys, five-layered martensite in Ni54.4sMn21.69Ga23.83 alloy and seven-layered martensite of the first phase transformation and five-layered martensite of the second phase transformation in Ni54.85Mn20.09Ga25.05 alloy.The results of transmission electron microscopy (TEM) show that the martensite in Ni54.48Mn21.69Ga23.83 alloy is five-layered martensite, and thatof Ni563Mn19.4Ga22.7C1.6 alloy is non-modulated one, which are consistentwith the results of X-ray diffraction. The treatments of face-centered cubic structure for the L21 structure and base-centered monoclinic structure for five-layered modulated martensite were applied when analyzing the results of TEM. The orientation relationship between austenite and martensite of Ni54.48Mn21.69Ga23.83 alloy martensite transformation was studied.The effect on Ni-Mn-Ga martensite transformation temperature of composition was analyzed in detail. The martensite transformation temperature of Ni-Mn-Ga alloys can be evaluated as Ms = 1858-17.23X Mn -49.02XCa -61.92XSi -65.43XGe+1.24Co -51.6XC -58.92XIn by means of multiple linear regression, where XMn, XCa, XSi, XGe, XCo, Xc and XIn are mole percent numbers for elements Mn, Ga, Si, Ge, Co, C and In. Both electron concentration and austenite lattice parameter influence martensite transformation temperature, however, electron density (valence electrons per volume) may be a more appropriate or accurate factor regarding the martensitic transformation temperature, based on the electron theory of metal and our results. With increasing electron density, the phase transformation temperature increases.The crystallography data was acquired by applying phenomenological theory of martensite crystallography to Ni-Mn-Ga alloys. Only when assuming that the plane and direction of the lattice-invariant shear are - and respectively is the calculation ofphenomenological theory of martensite crystallography self-congruent. The martensite transformation crystallography such as theoretical habit plane was dependent on the alloy composition.更多还原