Ti30Zr15Hf5Ni35Cu15與Ti30Zr5Hf15Ni35Cu15高熵形狀記憶合金中Zr與Hf元素換置對於顯微結構與相變態之影響

Abstract

本研究針對Ti30Zr15Hf5Ni35Cu15(下稱Zr15Hf5合金)與Ti30Zr5Hf15Ni35Cu15(下稱Zr5Hf15合金)兩種比例的高熵形狀記憶合金透過置換Zr與Hf的比例來觀察固溶處理與時效處理對於相變態行為、顯微結構、晶體結構與析出物產生何種影響。經過400℃時效處理後，兩者合金相變態溫度皆隨著時間大幅下降；經過500℃時效處理，Zr5Hf15合金相變態溫度也呈現下降趨勢，而Zr15Hf5合金則是先下降後上升；在經過600℃與700℃時效處理後，兩合金皆呈現明顯的上升趨勢。500℃時效處理中，除了原始黑色析出物(Ti,Zr,Hf)2(Ni,Cu)，兩種合金都觀察到高密度的白色條狀析出物H相與黑色顆粒狀析出物Ti2Cu的析出現象。而600℃與700℃時效處理中，兩者合金則觀察到白色析出物(Zr,Hf)7Cu10與新生的黑色析出物(Ti,Zr,Hf)2(Ni,Cu)。從析出物分布情形，可以發現Zr15Hf5合金的析出物較多且分佈密集，在600℃與700℃時效處理中更可以看出析出物大範圍的共析狀態，而Zr5Hf15合金則析出物較少，分佈較不密集，共析狀態幾乎只見於晶界區域內。在XRD實驗中，兩者合金的600℃時效處理觀察到Zr7Cu10相與Ti2Cu相等析出相，而700℃時效處理在兩者合金中則觀察到析出物Zr7Cu10相與Ti2Ni相，此部分與SEM觀察結果相同。Zr5Hf15合金的爐冷、固溶、400℃與500℃試片都較Zr15Hf5合金硬，該現象可能是由於Zr5Hf15合金的平均原子半徑差δ值較Zr15Hf5合金大，因此Zr5Hf15合金內部晶格扭曲程度較大，進而導致硬度較高。本研究結果顯示了不同時效溫度下會有不同的顯微結構，並且可以透過置換Zr與Hf比例來調整合金內部的析出物分布情形，為合金設計策略的再建構提供了一個新方向。

This study investigated Ti30Zr15Hf5Ni35Cu15 and Ti30Zr5Hf15Ni35Cu15 two high entropy shape memory alloys with the effects of solution treatment and aging treatment on phase transformation behavior, microstructure, crystal structure and precipitates that observed by substituting the ratio of Zr and Hf. After 400°C aging treatment, the phase transformation temperature of both alloys decreased significantly with time; after 500°C aging treatment, the phase transformation temperature of Zr5Hf15 alloy also showed a decreasing trend, while Zr15Hf5 alloy decreased first and then increased; after 600°C and 700°C aging treatment, both alloys showed an obviously increasing trend. During the aging treatment at 500°C, in addition to the original black precipitates (Ti,Zr,Hf)2(Ni,Cu), a high density of white strip-shaped precipitates H phase and black granular precipitates Ti2Cu were also observed in both alloys. After the aging treatment at 600℃ and 700℃, white precipitates (Zr,Hf)7Cu10 and new black precipitates (Ti,Zr,Hf)2(Ni,Cu) were observed in the two alloys. From the distribution of the precipitates, it can be found that the precipitates of Zr15Hf5 alloy are high-densely distributed, for the aging treatment at 600℃ and 700℃, the eutectoid condition of the precipitates can be seen in a large range. However Zr5Hf15 alloy has fewer precipitates with less-densely distribution, and the eutectoid condition is almost only seen in the grain boundary region. In the XRD experiment, the Zr7Cu10 phase and Ti2Cu phase precipitates were observed in the two alloys after 600°C aging treatment, and the Zr7Cu10 phase and Ti2Ni phase were observed in the two alloys after 700°C aging treatment, which is in the same condition as the SEM observation. Zr5Hf15 alloy has higher hardness than Zr15Hf5 alloy in furnace cooling, solid solution, 400°C and 500°C samples. This phenomenon may due to the larger average atomic radius difference δ value of Zr5Hf15 alloy than that of Zr15Hf5 alloy, so that Zr5Hf15 alloy has larger degree of internal lattice distortion, resulting in higher hardness. The results of this study show that there will be different microstructures at different aging temperatures, and the distribution of precipitates in the alloy can be adjusted by substituting the ratio of Zr and Hf, which provides a new direction for the reconstruction of alloy design strategies.