【摘要】：在外場激勵作用下,固態(tài)相變材料微觀尺度的晶格微調會導致宏觀尺度的物理特性突變,其中巨熵變材料的突出應用是節(jié)能環(huán)保的固態(tài)制冷技術。利用機械外力對馬氏體相變合金加熱和冷卻的彈熱制冷已成為最有潛力的固態(tài)制冷技術,但相變滯后大、潛熱較低、驅動場高是彈熱材料的最大缺陷。因此本實驗采用XRD分析、DSC測試、TEM分析以及絕熱溫差測定及力學性能測試,分析研究了Ni-Mn-Ga-Co合金的組織結構、馬氏體相變行為、絕熱熵變及斷裂行為。實驗結果表明,Co摻雜樣品(Ni52-xMn25Ga23Cox)的室溫結構隨著Co含量的增加逐漸由完全的馬氏體結構向奧氏體結構過渡,當x=0.5時,室溫下為正方結構的5M馬氏體;當x=5時,室溫下為母相結構;當x介于0.5和5之間時,合金為母相與馬氏體兩相共存。樣品的馬氏體轉變溫度隨著Co含量增加整體呈下降趨勢,并在應力作用下會有所提高。Ni52-xMn25Ga23Cox居里溫度隨Co含量增加呈現(xiàn)逐漸升高的趨勢,但變化并不明顯。當Co含量一定時,磁場的變化并不會明顯改變合金的馬氏體相變溫度,但會使合金居里溫度略微下降。Co摻雜樣品的室溫屈服強度隨Co含量增加先增大后減小,當x=3時,合金的屈服強度達到最大值450MPa左右;同時,隨著Co含量的增加,合金的斷裂韌性總體呈現(xiàn)增加趨勢,斷裂方式由沿晶斷裂+解理斷裂過渡為解理斷裂,晶內抵抗裂紋產生和擴展的能力增強。Co取代Ni改變了母相與馬氏體之間的晶格差異,從而改變了材料的相變應變,材料的相變應變呈現(xiàn)先增加后減小再增加的趨勢,在x=2時達到最大并在此時獲得最大的彈熱溫差,為2.49K;同時合金的磁熵變隨著外加磁場的增大而增大,并且在同一磁場強度下,合金的磁熵變呈現(xiàn)先升高后降低的趨勢,并在相變溫度附近達到最大值。
[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.
【學位授予單位】：哈爾濱工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG139.6

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