【作者】 丰焱；

【导师】 蔡伟；

【作者基本信息】 哈尔滨工业大学 ， 材料物理与化学， 2009， 博士

【摘要】 本文采用扫描电镜观察、透射电子显微分析、X射线衍射分析、示差扫描量热分析、室温压缩试验、交流磁化率测试、物性测量及相变应变测试等方法系统研究了Ni-Mn-In基磁性记忆合金的相变行为及组织结构和性能;阐明了In含量及Co和Fe掺杂对相组成、马氏体相变、力学性能和磁性能的影响规律和机制。研究发现,Ni50Mn50-xInx(x=16, 15, 14, 13, 12)合金为单一固溶体;Co和Fe的掺杂改变了Ni-Mn-In合金的相组成:当Co含量达3at.%或Fe含量达5at.%时,合金基体中形成短棒状富Co或富Fe的面心立方γ相;且γ相的尺寸和体积分数随Co或Fe含量的增加而增大。试验结果表明,Ni50Mn50-xInx合金在冷却/加热过程中发生热弹性马氏体相变及逆相变,In含量降低相变温度升高。当In含量为15at.%时,马氏体为单斜5M调制结构;当In含量为13at.%时,马氏体为单斜7M结构;当In含量为12at.%时,马氏体为单斜7M调制与少量非调制结构;当In含量为14at.%时,合金降温过程中发生立方L21→正交4O→单斜7M调制结构的两步马氏体转变。Ni50Mn50-xInx合金马氏体变体间主要为(102)M I型孪晶关系。Ni50Mn34In16-yCoy(y=0, 2, 3, 4, 5, 8)与Ni50Mn34In16-yFey(y=0, 2, 3, 4, 5, 8)合金降温过程中主要发生立方L21→单斜7M调制结构的一步热弹性马氏体相变;Co或Fe的掺杂改变了合金的基体成分,随Co含量增加,马氏体相变温度先升高后降低,Fe含量增加,马氏体相变温度升高;掺杂后马氏体变体间除呈(102)M I型孪晶关系外还观察到(111)M I型孪晶关系。室温压缩实验表明,Ni50Mn50-xInx合金的断裂强度和断裂应变随着In含量的降低稍有增加,而Co和Fe掺杂均使合金断裂强度和断裂应变显著提高。Co的掺杂量为8at.%时,断裂强度和断裂应变分别达1420MPa和20.5%。Co或Fe掺杂提高塑性的主要原因在于:合金基体中的面心立方γ相阻碍了裂纹扩展;同时,合金的断裂方式从沿晶脆断逐渐转变为穿晶断裂,并出现韧性的撕裂棱。磁性测量表明,In含量改变,Ni50Mn50-xInx合金的居里温度无明显变化,当In含量大于等于15at.%时,居里温度高于马氏体相变温度,在外磁场作用下发生顺磁马氏体→铁磁母相的转变;当In含量低于15at.%时,居里温度低于马氏体相变温度,未观察到磁场诱发马氏体逆相变。掺Co或Fe部分替代In后,居里温度增加,使得Ni50Mn34In8Co8与Ni50Mn34In14Fe2合金居里温度高于马氏体相变温度,施加磁场后发生了马氏体逆相变。另外,在居里温度附近施加磁场,Ni50Mn36In14Fe2合金呈现大的磁热效应,当磁场强度为8T时,其磁熵变达53J/kgK。更多还原

【Abstract】 The martensitic transformation behavior, microstructures and properties of Ni-Mn-In based alloys have been investigated systematically by means of SEM, TEM, XRD, DSC, compressive tests, AC susceptibility, PPMS and transformation strain measurements. The influence and mechanics of In content, Co and Fe doping on phase constitute, phase transformation, mechanical properties and magnetic properties are illuminated.The research found that the Ni50Mn50-xInx(x=16, 15, 14, 13, 12) alloys are single solid solution. The phase constitute of Ni-Mn-In alloy is changed by doping Co and Fe element: As the Co content is 3at.% or Fe content is 5at.%, there are short stick-like Co-rich or Fe-rich fccγphase in matrix, and the demention and volume fraction ofγphase increase with the increase of Co or Fe content.The experimental results indicate that the Ni50Mn50-xInx alloys undergo thermal-elastic martensitic transformation and inverse phase transformation as cooling or heating. As In content is 15at.%, the martensite is monoclinic 5M modulated structure. As In content is 13at.%, the martensite becomes monoclinic 7M modulated. As In content is 12at.%, the martensite is monoclinic 7M modulated with few unmodulated structure. As In content is 14at.%, the alloy undergoes two-step transformation from cubic L21→orthogonal 4O→monoclinic 7M modulated structure. The relationship between variants is mainly (102)M I-type twin. Ni50Mn34In16-yCoy(y=0, 2, 3, 4, 5, 8) and Ni50Mn34In16-yFey(y=0, 2, 3, 4, 5, 8) alloys undergo one-step transformation from cubic L21→monoclinic 7M modulated structure as cooling. The martensitic transformation temperatures firstly increase then decrease with the increase of Co content, and increase with the increase of Fe content. This is because the doping changes the matrix composition. At this time, there is not only (102)M I-type twin but also (111)M I-type twin relationship between variants in these 7M martensite.The compressive experiment indicated that the fracture stress and fracture strain of Ni50Mn50-xInxalloys increase slightly with the decrease of In content, but increase significantly after doping Co and Fe element. When the Co content is 8at.%, the fracture stress and fracture strain are as high as 1420MPa and 20.5%. The main reason of the plastic increase by doping Co and Fe is that the fccγphase particles delay the crack of grain boundaries, and the fraction type changes from intergranular crack to transgranular crack as the Co or Fe content increase. This also indicates that the ductility of the alloys is improved significantly.The magnetic measurement illustrates that the Curie temperature has no obvious changes with the change of In content. As the In content is no less than 15at.%, the Curie temperature of the alloy is higher than martensitic transformation temperature, and transform from paramagnetic martensite to ferromagnetic parent phase. As the In content is less than 15at.%, the Curie temperature is lower than martensitic transformation temperature, and then magnetic field induced phase transformation can not be observed at this time. The Curie transformation temperatures increase after the addition of Co and Fe replacing In partially, the Curie temperatures of Ni50Mn34In8Co8 and Ni50Mn34In14Fe2 alloys are higher than the martensitic transformation temperatures, and could observe the magnetic field induced phase transformation behaviour. In addition, Ni50Mn34In14Fe2 alloy has large magnetocaloric effect, and the magnetic entropy change is as large as 53J/kgK with a magnetic field of 8T.更多还原