先前實驗室設計出密度接近5 g/cm3、降伏強度能達到1200 MPa以及塑性能維持15 %以上之Ti65(AlCrNbV)28Zr7中熵合金，本研究目的為利用不同滾軋製程與升溫速率將機械性質再一次提升。首先將選定之元素，用高溫電弧融煉技術鑄成具有簡單固溶相之六元Ti65(AlCrNbV)28Zr7中熵合金，並透過滾軋製程使其厚度降低累積應變能，再將其以短時間不同升溫速率之退火熱處理使材料晶粒細化，藉由分析微結構與機械性質探討其強化機制，找出最合適的加工製程與熱處理參數。 研究結果顯示，鑄造態的Ti65(AlCrNbV)28Zr7為單一BCC相，並能達到1000 MPa以上的降伏強度與20.0 %以上的拉伸塑性。將此系列合金以熱機處理強化，發現給予冷滾軋試片較大的加工量，在熱處理後能得到較佳的機械性質組合，另外若使用較快加溫速率的熱機處理，可以更進一步得到優秀的機械性質組合。此外在冷滾軋前合金材料可藉由熱滾軋製程提高整體之延展性。本實驗中，將材料以90%冷軋，以25°C/s退火熱處理能達到期望之機械性質，能達到預期的1220MPa與17.0%延性。 ;The developed light weight medium entropy alloy, Ti65(AlCrNbV)28Zr7 (Ti-65MEA), owns the ideal characteristic such as density is close to 5 g/cm3, yield strength of 1200 MPa and plastic strain maintained above 15%. The purpose of this study is to improve mechanical properties by various hot/cold rolling process couple with annealing heating rate. The as-cast samples are successfully cast into alloy ingots by vacuum metallurgy and rapidly solidification technology. The as-cast samples show the single BCC phases and the mechanical properties are 1015 MPa and 23% for yield strength and tensile ductility, respectively. The ingots then strengthened through the rolling process which can accumulate the strain energy by reducing the thickness of ingot. Secondly, through 15 and 25 ℃/sec annealing heating rate in a several certain time period to verify the change of the grain size. According to the tensile test results, as-cast Ti65(AlCrNbV)28Zr7 remain single BCC phases. Also, it can achieve yield strength above 1000 MPa and tensile ductility above 20.0%. In addition, the alloys were applied a larger amount of processing to the cold-rolled test pieces can possess mechanical properties after heat treatment, moreover, faster heating rate can also have better mechanical properties. Reducing the thickness of material by 90% by cold rolling and annealing in 25°C/s can achieve the goal. Due to the reducing of the recrystallization temperature, the closest processing parameters obtained in this experiment did not reach the goal by reducing the thickness by 50 % first by hot rolling, and then reduce the thickness by 80 % by cold rolling. So the best parameters of this material is reducing by 90% by cold rolling. After processing annealing, Ti65(AlCrNbV)28Zr7 can achieve the desired mechanical properties, which is tensile yield strength of 1220 MPa and plastic strain of 17.3 %.
