高熵合金之於傳統合金擁有獨特的顯微結構以及優越的機械性質，在應用中引起極大的研究關注。過去十幾年，大部分的研究主要在多元等量的成分上。而本研究將探討非等量高熵合金之成分設計，欲設計出密度在5 g/cm3且具有高強度以及高延展性的高熵合金。 首先由低密度金屬元素Ti、Al開始進行成分設計並配合高熵合金相關參數，由四元合金Ti50系列(Ti50Al25V25-xCrx、Ti50Al25Nb25-xCrx、Ti50Al45-xNbxCr5)逐步至五元Ti60合金系列(Ti60Al40-x(NbVCr)X)，找出適當的合金成分進行微結構分析、機械性質分析、氧化分析以及電化學分析。根據XRD結果顯示，無論是Ti50或Ti60合金系統其微結構皆為單一BCC相；由密度分析結果顯示，五元合金較四元合金系統由更多原子種類結合，導致晶格扭曲效應更加明顯而造成體積膨脹現象；從硬度結果來看，在Ti50Al45-xNbxCr5系列合金中將Al含量由30%降至20%其硬度值從480Hv大幅下降至365Hv，顯示Ti、Al元素之間含量比對合金整體硬度有著非常大的影響力；以SEM觀察合金試片拉伸後之破斷面，可以在Ti60Al10(NbVCr)30中發現類似葉脈狀紋路的塑性行為，此合金成分在本研究中也具有最佳機械性質，其降伏強度1009MPa、抗拉強度1223MPa、塑性更高達27.1%；其磨耗性質也與商用合金Ti6Al4V相當。 在確定Ti60Al10(NbVCr)30合金具有優越的延展性之基本性質條件下，相信藉由冷軋變形使晶粒結構改變調整其機械性質，勢必能夠獲得具有更高強度且保有延展性之高熵合金。 ;High-entropy alloys (HEA) attract great attention in past few decades. Most HEA researches mainly concentrate on the heavier multi-principal elements with equiatomic or near-equiatomic alloys. In this study, we focus on the light-weight and non-equiatomic medium-entropy alloys (MEA) system with low density (below 5g/cm3). Series of non-equiatomic quaternary alloy system, Ti-Al-Cr-Nb、Ti-Al-Cr-V were firstly designed by using calculating parameter (∆S、∆H、δr), then further modified into quinary Ti-Al-Cr-Nb-V alloy system. All samples were prepared by vacuum arc melting and rapidly cooling process. The XRD results of Ti-Al-Cr-Nb 、Ti-Al-Cr-V and Ti-Al-Cr-Nb-V MEA reveal the single BCC structure. The hardness value of Ti60-Al-Cr-Nb reduced from 480Hv to 365Hv with decreasing the Al content which implies that the ratio of Ti/ Al elements plays an important role on the alloy hardness. The optimum mechanical performance occurs at Ti60-Al-Cr-Nb-V MEA with tensile yield strength of 1009 MPa, fracture strength of 1223 MPa, and plastic strain of 27.1%. In summary. the Ti60-Al-Cr-Nb-V MEA not only possesses higher mechanical properties than the commercial Ti6Al4V alloy, but also has similar density, wear resistance, and oxidation behavior to commercial Ti alloys. Therefore, it is believed that the Ti60-Al-Cr-Nb-V MEA can be a promising light-weight structure material for the applications of transportation vehicles and sport equipment.
