Ti35-xZr15HfxNi35-yCoyCu15 (x= 5, 10, 15; y= 5, 10)擬二元高熵形狀記憶合金之麻田散體相變態行為與機械性質之研究

Research on Martensitic Transformation Behaviors and Mechanical Properties of Pseudobinary Ti35-xZr15HfxNi35-yCoyCu15 (x= 5, 10, 15; y= 5, 10) High Entropy Shape Memory Alloys

張至善(Chih-Shan Chang)

指導教授 ： 陳志軒

國立臺灣大學/工學院/機械工程學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103250

摘要

本研究針對Ti35-xZr15HfxNi35-yCoyCu15 (x= 5, 10, 15; y= 5, 10)擬二元高熵形狀記憶合金之相變態溫度、顯微結構、晶體結構、形狀記憶效應、超彈性以及彈熱效應進行研究，並分別對爐冷試片與固溶試片進行探討。Ti35Zr15Ni35Cu15固溶試片添加Hf會使麻田散體相相變態溫度上升，Mp上升幅度為16.57°C /(at.% Hf)；再添加Co會使麻田散體相相變態溫度下降，Mp下降幅度為-18.53°C/(at.% Hf)。這些結果顯示可透過調整合金元素比例以設計不同變態溫度與應用之高熵形狀記憶合金。所有試片經過固溶處理後皆為固溶體與(Ti,Zr,Hf)2(Ni,Cu)或(Ti,Zr,Hf)2(Ni,Co,Cu)析出物之組成，並且固溶處理後所有試片之相變態溫度皆往上升，這是由於部分(Ti,Zr,Hf)2(Ni,Cu)或(Ti,Zr,Hf)2(Ni,Co,Cu)溶解回基底，導致基底之Ti類含量往上升，也使得相變態溫度往上升。在XRD中觀察到，不管是爐冷試片或是固溶試片都有麻田散體或沃斯田體相變態殘留的行為，推斷是由於添加的元素較多造成晶格嚴重扭曲，使得部分麻田散體相或母相無法透過溫度來誘發相變態。形狀記憶效應測試顯示，固溶處理後由於部分脆性的(Ti,Zr,Hf)2(Ni,Cu)或(Ti,Zr,Hf)2(Ni,Co,Cu)溶解回基底，也使得試片可以承受的應力皆更高，並且在更高的應力下都沒有斷裂，也有更大的相變應變，試片之承受應力皆提升至500MPa以上，可回復應變提升至4.75%以上。超彈性測試下也可以看到經過固溶處理後，所有試片在不同應變下試片之可回復應變明顯上升，不可回復應變下降。在彈熱效應中觀察到，Hf5固溶試片之彈熱效應最大，在5%應變量時有最大的彈熱效應△T=-15.3°C，與其他固溶試片相比，接下來依序為Hf10、Co5與Co10，這個順序與超彈性之可回復應變量相符。研究結果顯示，固溶處理可提高高熵形狀記憶合金之性能。

關鍵字

高熵合金 ； 形狀記憶合金 ； 形狀記憶效應 ； 麻田散體相變態 ； 超彈性

並列摘要

This research focuses on the phase transformation temperature, microstructure, crystal structure, shape memory effect, and mechanical properties of Ti35-xZr15HfxNi35-yCoyCu15 (x=5, 10, 15; y= 5, 10) high entropy shape memory alloy (HESMA). Properties of furnace-cooled and the solution-treated samples were studied and compared. Addition of Hf to substitute for Ti in Ti35Zr15Ni35Cu15 increased the phase transformation temperatures with a rate of 16.57 °C/at.% Hf. On the other hand, addition of Co to replace Ni in Ti20Zr15Hf15Ni35Cu15 decreased its transformation temperature with a rate of -18.53 °C/at.% Co. These features enable desiging HESMAs with different transformation temperatures by adjusting its chemical composition. After solution treatment, all samples were composed of B2 solid solution and (Ti, Zr, Hf)2(Ni, Cu) or (Ti, Zr, Hf)2(Ni, Co, Cu) precipitates. After the solution treatment, the phase transformation temperatures of all the samples increased due to the partial dissolution of (Ti, Zr, Hf)2(Ni, Cu) or (Ti, Zr, Hf)2(Ni, Co, Cu) into the matrix. The (Ti, Zr, Hf) contents in the matrix increased and caused the higher transformation temperatures. The dissolution of the (Ti, Zr, Hf)2(Ni, Cu) or (Ti, Zr, Hf)2(Ni, Co, Cu) phase also improved the functional performance of these HESMAs by reducing its brittleness and increasing its phase transformation strain. For shape memory effect, these samples sustained flextural stress higher than 500MPa and exhibited 4.75% recoverable strain. Superelasticity tests showed that, after solution treatment, the recoverable strains of all the samples increased significantly, while the non-recoverable strain decreased. The solution-treated Hf5 sample exhibited the largest elastocaloric effect of △T=-15.3°C under 5% applied strain, followed by the Hf10, Co5 and Co10, samples. This order is consistent with the recoverable strain of superelasticity. The experimental results presented in this study demonstrate that solution treatment can effectively improve the performance of the HESMAs.

並列關鍵字

high entropy alloy ； shape memory alloy ； shape memory effect ； martensitic transformation ； pseudoelasticity

參考文獻

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