微量摻雜硼對輕量六元TiAlCrNbVNi中熵合金微結構改良與機械性質提升之研究;Microstructure modification and mechanical properties improvement of senary-element TiAlCrNbVNi medium-entropy alloy by microdoping with boron

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Title:	微量摻雜硼對輕量六元TiAlCrNbVNi中熵合金微結構改良與機械性質提升之研究;Microstructure modification and mechanical properties improvement of senary-element TiAlCrNbVNi medium-entropy alloy by microdoping with boron
Authors:	黃義程;Huang, Yi-Cheng
Contributors:	機械工程學系
Keywords:	輕量化中熵合金;非等原子比;微量元素摻雜;熱機處理;lightweight medium-entropy alloys;non-equiatomic ratio;microalloying;thermomechanical treatment
Date:	2024-07-10
Issue Date:	2024-10-09 17:19:23 (UTC+8)
Publisher:	國立中央大學
Abstract:	有別於傳統合金，輕量化高熵合金因合金設計造成的低密度與優良機械性質等特質，於航空太空其他工業領域吸引大量的研究與投入。本研究主要探討多元非等量中熵合金的成分設計，基於先前所開發之Ti65(AlCrNbV)34Ni1輕量化富鈦中熵合金，藉由微量摻雜硼元素的方式製備成(Ti65(AlCrNbV)34Ni1)100-xBx(X=0.05, 0.1, 0.2, 0.3)系列合金，將合金密度控制在5 g/cm3¬並分析硼元素摻雜對合金機械性質與微結構之影響，將合金的強度與延性進一步提升。本研究利用電弧融煉法製備輕量化富鈦中熵合金，由於硼元素之原子半徑明顯小於合金內其他元素，分析X-ray繞射圖可以觀察到，隨著硼元素摻雜量提高，繞射峰有靠右偏移的趨勢。透過光學顯微鏡可以發現各組合金有析出物於晶界上產生，並使合金之硬度由(Ti65(AlCrNbV)34Ni1)99.95B0.05的341 Hv提升至(Ti65(AlCrNbV)34Ni1)99.7B0.3的365 Hv，當合金經均質化處理後，其機械性質由(Ti65(AlCrNbV)34Ni1)99.95B0.05的1022 MPa降伏強度，提升至(Ti65(AlCrNbV)34Ni1)99.7B0.3的1122MPa 降伏強度但延性則從26.8%降低至11.9%。接著將(Ti65(AlCrNbV)34Ni1)99.95B0.05進行熱機處理進一步改善性能，其硬度與強度隨著退火溫度的提高而降低，原因是合金經滾軋後累積之應變能隨著退火溫度的提高，而釋放的越多，在未進行再結晶退火熱處理的合金降伏強度1559MPa，延性僅有8.6%，在再結晶退火溫度889°C時，在金相圖中可以觀察到有部分再結晶於晶界上產生，其降伏強度降至1147MPa，延性則提升至24.3%，綜合比較再結晶熱處理退火參數，可以得到再結晶退火熱處理溫度為817°C時，(Ti65(AlCrNbV)34Ni1)99.95B0.05具有最佳的綜合性能，其降伏強度為1289 MPa，延性為15.4%。 ;Unlike traditional alloys, lightweight high-entropy alloys have attracted significant research and investment in the aerospace and other industrial fields due to their low density and excellent mechanical properties resulting from alloy design. This study primarily investigates the composition design of multicomponent non-equiatomic medium-entropy alloys. Based on the previously developed Ti65(AlCrNbV)34Ni1 lightweight titanium-rich medium-entropy alloy, we prepared a series of alloys by microalloying with boron in the forms of (Ti65(AlCrNbV)34Ni1)100-xBx (X=0.05, 0.1, 0.2, 0.3). Keeping the alloy density at around 5 g/cm³, we analyze the effects of boron doping on the mechanical properties and microstructure of the alloy and aim to further enhance the alloy strength and ductility. In this study, lightweight titanium-rich medium-entropy alloys were prepared using arc melting. X-ray diffraction analysis showed that as the amount of boron doping increases, the diffraction peaks tend to shift to the right due to the significantly smaller atomic radius of boron compared with other elements in the alloy. Optical microscopy revealed that precipitates form at the grain boundaries in each alloy composition, resulting in an increase in hardness from 341 Hv for (Ti65(AlCrNbV)34Ni1)99.95B0.05 to 365 Hv for (Ti65(AlCrNbV)34Ni1)99.7B0.3.The mechanical properties improved after homogenization treatment, with the yield strength increasing from 1022 MPa for (Ti65(AlCrNbV)34Ni1)99.95B0.05 to a yield strength of 1122 MPa for (Ti65(AlCrNbV)34Ni1)99.7B0.3, But the ductility decreasing from 26.8% to 11.9%. (Ti65(AlCrNbV)34Ni1)99.95B0.05 was then chosen for further improving mechanical properties via thermomechanical treatment. The hardness and strength decrease with increasing annealing temperature because the stored strain energy from rolling is progressively released as the annealing temperature increase. The alloy has a yield strength of 1559 MPa and ductility of 8.6% before recrystallization annealing. After undergoing recrystallization annealing at 889°C, partial recrystallization at the grain boundaries can be observed in the SEM image. Meanwhile, the yield strength reduces to 1147MPa and ductility increases to 24.3%. After comparing the annealing parameters for recrystallization heat treatment, it was found that (Ti65(AlCrNbV)34Ni1)99.95B0.05 exhibited the best synergy of mechanical property after 817°C recrystallization annealing, with a yield strength of 1289 MPa and a ductility of 15.4%.
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