本研究旨在探討新型的中低密度高熵合金之成分設計，其目標為設計出密度低於5 g/cm3的高熵合金且其微結構經過熱處理後仍維持在單一相或是雙相。首先由低密度的元素Ti以及Al為基底著手進行成份設計，配合符合高熵相關參數之模擬計算從TiAlX三元合金逐步添加不同的元素至四元合金以及五元合金，並經由實驗結果找出最合適的成分設計。合金原料先經由真空電弧熔煉及墜落鑄造後形成合金鑄錠，然後再置於真空高溫爐中進行 800℃/24小時均質化熱處理。鑄造狀態及處理後的試片再經研磨拋光後進行XRD微結構分析、OM和SEM/EDS金相觀察及硬度試驗。由微結構分析發現TiAlVCrFe (=5.72 g/cm3), TiAlVCrMn (=5.55 g/cm3), TiAlVCrCu (=5.61g/cm3) 三種五元高熵合金的鑄錠均為單一相BCC結構，其硬度均在Hv 650左右。此外，TiAlVCrFe (=5.72 g/cm3), TiAlVCrMn (=5.55 g/cm3) 高熵合金經800℃/24小時熱處理後，由於析出強化作用，其硬度提升至Hv 800。相信此兩種五元系列合金經微調增高其Ti和Al元素成份比率，將可獲得密度低於5 g/cm3且具有單一相或是雙相結構的高熵合金。;In this study, we tried to design the medium-low density high entropy alloys (HEAs) (contains at least 5 elements and the density of the alloys are below 5 g/cm3) by empirical phase-formation rules. Meanwhile, these HEAs should remain a structure of single phase or two phases after heat treatment. Therefore, we start to study the HEAs from the TiAlX alloy (3 elements), then add the fourth and fifth elements step by step based on the parameter calculation which related to the requirement of HEA. The high entropy alloys ingots were firstly prepared by vacuum arc-melting and drop casting, and then homogenizing at 800℃for 24h in vacuum. The as-cast and heat treated samples were characterized by XRD analysis, OM and SEM/ESD examination, and Vickers’ hardness test. The XRD results reveal that the as-cast TiAlVCrFe (=5.72 g/cm3), TiAlVCrMn (=5.55 g/cm3), TiAlVCrCu (=5.61 g/cm3) HEAs showed the BCC single structure with hardness around 670 Hv. Moreover, the hardness of TiAlVCrMn and TiAlVCrFe HEAs can reach to 800 Hv after annealing at 800°C for 24 hr in vacuum due to the precipitation hardening. It is believed that the goal of medium-low density for the 5-components HEAs can be achieved by increasing the Ti and Al molar ratio in our further study.
