Ni-Mn-Ga-Co铁磁记忆合金相变与弹热性能

发布时间：2018-11-17 20:24

【摘要】：在外场激励作用下,固态相变材料微观尺度的晶格微调会导致宏观尺度的物理特性突变,其中巨熵变材料的突出应用是节能环保的固态制冷技术。利用机械外力对马氏体相变合金加热和冷却的弹热制冷已成为最有潜力的固态制冷技术,但相变滞后大、潜热较低、驱动场高是弹热材料的最大缺陷。因此本实验采用XRD分析、DSC测试、TEM分析以及绝热温差测定及力学性能测试,分析研究了Ni-Mn-Ga-Co合金的组织结构、马氏体相变行为、绝热熵变及断裂行为。实验结果表明,Co掺杂样品(Ni52-xMn25Ga23Cox)的室温结构随着Co含量的增加逐渐由完全的马氏体结构向奥氏体结构过渡,当x=0.5时,室温下为正方结构的5M马氏体;当x=5时,室温下为母相结构;当x介于0.5和5之间时,合金为母相与马氏体两相共存。样品的马氏体转变温度随着Co含量增加整体呈下降趋势,并在应力作用下会有所提高。Ni52-xMn25Ga23Cox居里温度随Co含量增加呈现逐渐升高的趋势,但变化并不明显。当Co含量一定时,磁场的变化并不会明显改变合金的马氏体相变温度,但会使合金居里温度略微下降。Co掺杂样品的室温屈服强度随Co含量增加先增大后减小,当x=3时,合金的屈服强度达到最大值450MPa左右;同时,随着Co含量的增加,合金的断裂韧性总体呈现增加趋势,断裂方式由沿晶断裂+解理断裂过渡为解理断裂,晶内抵抗裂纹产生和扩展的能力增强。Co取代Ni改变了母相与马氏体之间的晶格差异,从而改变了材料的相变应变,材料的相变应变呈现先增加后减小再增加的趋势,在x=2时达到最大并在此时获得最大的弹热温差,为2.49K;同时合金的磁熵变随着外加磁场的增大而增大,并且在同一磁场强度下,合金的磁熵变呈现先升高后降低的趋势,并在相变温度附近达到最大值。
[Abstract]:Under the excitation of external field, the lattice fine tuning of solid phase change material on micro scale will lead to the physical characteristic abrupt change of macroscopic scale, and the outstanding application of giant entropy material is energy saving and environmental protection solid state refrigeration technology. The elasto-thermal refrigeration of martensitic transformation alloy heated and cooled by mechanical external force has become the most potential solid-state refrigeration technology, but the hysteresis of phase transformation is large, the latent heat is low, and the high driving field is the biggest defect of elastic-thermal material. Therefore, the microstructure, martensite transformation behavior, adiabatic entropy change and fracture behavior of Ni-Mn-Ga-Co alloy were studied by XRD analysis, DSC test, TEM analysis, adiabatic temperature difference measurement and mechanical properties test. The experimental results show that the room temperature structure of Co doped sample (Ni52-xMn25Ga23Cox) is transformed from complete martensite structure to austenitic structure with the increase of Co content. When x = 0.5, the structure of Ni52-xMn25Ga23Cox is 5M martensite with square structure at room temperature. When x = 5, the parent phase is formed at room temperature, and when x is between 0.5 and 5, the alloy coexists with martensite. The martensite transformation temperature of the sample decreases with the increase of Co content, and increases under stress. The Curie temperature of Ni52-xMn25Ga23Cox increases gradually with the increase of Co content, but the change is not obvious. When the content of Co is constant, the change of magnetic field will not change the martensite transformation temperature of the alloy obviously, but will make the Curie temperature of the alloy decrease slightly. The room temperature yield strength of the Co doped sample increases first and then decreases with the increase of Co content, and then decreases when x = 3. The yield strength of the alloy reaches the maximum value of 450MPa; At the same time, the fracture toughness of the alloy increases with the increase of Co content, and the fracture mode changes from intergranular cleavage fracture to cleavage fracture. Instead of Ni, Co changed the lattice difference between parent phase and martensite, thus changing the transformation strain of the material. The transformation strain of the material increased first and then decreased, and then increased. At x = 2, the maximum temperature difference is obtained, which is 2.49K; At the same time, the magnetic entropy change of the alloy increases with the increase of the applied magnetic field. At the same magnetic field intensity, the magnetic entropy change of the alloy increases first and then decreases, and reaches the maximum near the transition temperature.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139.6

【相似文献】