| 摘要: | 本研究以先前開發的Ti65(AlCrNbV)35輕量化富鈦中熵合金為基礎，將原有合金中的Nb以原子半徑更大且密度更低的Zr取代，設計出TiX(AlCrZrV)100-X系列合金，並藉由調控Ti含量來提升合金的延性，同時分析不同Ti含量對合金微觀結構與機械性質的變化影響，並配合熱機處理進一步優化合金性能 。
本研究所用合金材料皆經由真空電弧熔煉製成，首先將各個原料成分在真空環境下熔煉，形成圓錠，再利用墜落式鑄造技術將圓錠鑄造成板材。經XRD分析發現，所有合金皆呈現單一BCC結構，未觀察到析出物，這一結果也獲得OM與SEM觀察的證實。就鑄造態而言，隨著Ti含量提升，合金的強度由1247 MPa減少至981 MPa，但延性則由1.9%大幅上升，最高上升至18.2%。進一步計算顯示，均質化後合金的強度幾乎完全來自固溶強化，最高可達1048 MPa。整體來看，Ti67合金在鑄造態時強度與延性之間達到最佳平衡，降伏強度為1116 MPa，延性為16.4%，均值化熱處理後，降伏強度還能維持1116 MPa，延性為17%。
TiX(AlCrZrV)100-X系列合金經過滾軋製程後進行700°C、800°C及900°C熱機處理，發現機械性質均有明顯提升。隨著再結晶溫度從700°C升至900°C時，合金強度呈現下降趨勢，而再結晶速度從Ti65到Ti70合金時，隨Ti含量增加而減緩，但Ti75合金卻出現提高的現象，因為Ti75已離開中熵合金範圍。在800°C熱處理條件下，所有成份合金於變形帶周圍可見再結晶晶粒，值得注意的是，Ti70合金在800°C下展現出最佳的強度與延性組合，其降伏強度達1316 MPa，延性亦有16.2%。
;In this study, TiX(AlCrZrV)100-X alloys was developed, which was based on the previously designed Ti65(AlCrNbV)35 lightweight Ti-rich medium-entropy alloy. In order to reduce the density and strengthened the alloy. The Nb had been replaced by Zr.
All alloys were fabricated using vacuum arc melting. The raw materials were first melted in an argon atmosphere to form ingots, followed by drop casting to produce plate samples. XRD analysis revealed that all alloys exhibited a single BCC phase without any other detectable phase. This result was further verified by OM and SEM observations.
In the as-cast condition, increasing Ti content led to a decrease in strength from 1247 MPa to 981 MPa. On the other hand, the elongation gradually improved with the increase of Ti concentration, reaching up to 18.2% from an initial 1.9%. Further calculations indicated that the strength of the homogenized alloys was almost entirely attributed to solid solution strengthening. With a maximum contribution of 1048 MPa. Overall, the Ti67 alloy in the as-cast condition achieved the best balance between strength and ductility, with a strength of 1,116 MPa and an elongation of 16.4%. After homogenization treatment, the strength remained at 1,112 MPa while the elongation increased to 17%
After thermomechanical treatments at 700°C, 800°C, and 900°C, the mechanical properties of the TiX(AlCrZrV)100-X alloys were significantly enhanced. As the recrystallization temperature increased from 700°C to 900°C, the alloy strength showed a linearly decreasing trend. While the recrystallization rate decreased as Ti content increased from Ti65 to Ti70. However, the recrystallization rate would elevate again in Ti75 due to the decrease of entropy.
Under the 800°C treatment condition, recrystallized grains were observed around the deformation bands in all compositions. It is worth noting that the Ti70 alloy exhibited the optimal combination of strength and ductility at 800°C, with a yield strength of 1316 MPa and an elongation of 16.2%. |
