| Abstract: | 在過去十幾年，大部分的高熵合金研究主要著重在多元等量的合金組成上，且已知合金系列密度偏高(> 8 g/cm3)。為達到輕量化目的，本研究將探討以五元Ti60AlX(NbVCr) 40-x系列合金為基礎，藉由調整鋁元素含量觀察機械性質及微結構趨勢，同步探討不同熱處理條件後機械性質的變化。
本研究選取Ti60Alx(NbVCr) 40-x (X = 6-18 at.%)詳細合金成分如下：Ti60Al6(NbVCr)34、Ti60Al8(NbVCr)32、Ti60Al10(NbVCr)30、Ti60Al12(NbVCr)28、Ti60Al18(NbVCr)22，以電弧融煉製備鑄錠後再以墜落式鑄造製備樣品，根據XRD結果顯示，上述五種五元高熵合金其微結構皆為單一BCC相；隨著Al含量增加密度會逐漸下降;硬度值由Ti60Al6(NbVCr)34的311 Hv上升至Ti60Al18(NbVCr)22的399 Hv；壓縮試驗的降伏強度由Ti60Al6(NbVCr)34的973 Mpa上升至Ti60Al18(NbVCr)22的1269 MPa；拉伸試驗中Ti60Al18(NbVCr)22並無延展性，為脆斷材料，但降伏強度還是由Ti60Al6(NbVCr)34的895 Mpa上升至Ti60Al12(NbVCr)28的960 MPa，顯示Al元素的多寡對合金整體機械性質有顯著的影響。在本研究中嘗試以800ºC - 1000ºC、時間分別6小時、12小時、24小時進行熱處理，隨著熱處理時間越長，降伏強度越高、延展性越低，其中Ti60Al12(NbVCr) 28均質化熱處理溫度900ºC、24小時，其降伏強度雖可達1048 MPa但延展性為3%。
透過不同Al含量五元高熵合金熱處理條件工作窗的建立，Ti60AlX(NbVCr) 40-x系列合金可以根據不同的應用需求來調整其機械性質，亦可應用到其他合金系列的調控上藉以達到更好的應用。
;Over the past decade, high-entropy alloys caught attention due to their unique alloy design and properties. Most of high-entropy alloys (HEAs) are composed of equal-ratio transition elements, and it led to high density (> 8 g/cm3). In this study, the effect of Al on the evolution of microstructure and mechanical properties of light-weight Ti60AlX(NbVCr) 40-x alloy in the as-cast condition and after heat treatment will be investigated. The resulting alloys are Ti60Al6(NbVCr)34, Ti60Al8(NbVCr)32, Ti60Al10(NbVCr)30, Ti60Al12(NbVCr)28, and Ti60Al18(NbVCr)22. These alloys are denoted as Al6, Al8, Al10, Al12, and Al18, respectively.
All samples were produced by vacuum arc melting (VAM) and drop casting. The XRD results reveal that the as-cast samples are BCC structured. The Hv hardness of the as-cast sample exhibited an increasing trend with increasing Al content, from 311 Hv of Al6 to 399 Hv of Al18. The compressive yield strength increased from 973 MPa of Al6 to 1269 MPa of Al18, and even, the tensile yield strength increase from 895 MPa of Al6 to 960 MPa of Al12. Unfortunately, the as-cast Al18 alloys did not present ductile property.
After heat treatment at 900ºC for 6, 12 and 24 h, all annealed samples exhibit slightly higher strength, but siginificantly decrease in ductility. At noted that all became more brittle at 900ºC for 24 h.
These light-weight Ti60AlX(NbVCr) 40-x alloys demonstrated excellent tensile ductility in the as-cast condition. With high specific strength and ductility, these alloys are promising in the application of energy and transportation industries. |
