• 作者： 方敦盈; 王文雄
• 作者服務機構： 國立臺灣大學材料科學與工程學研究所
• 中文摘要： 雙相、細而等軸的晶粒、高溫及低應變速率是超塑性的基本要求，因此，由高溫變形時晶粒成長所導致之成形後機械性質退化常無法避免；本實驗即針對此一缺點利用暫時充氫的方式以降低Ti-6A1-4V合金之成形溫度，進而改善其在低溫之超塑性成形特性。此外，對於暫時充氫所造成之顯微組識變化亦加以探討。實驗結果顯示，(1)低溫(600°C)充氫時顯微組織變化及α、β兩相體積分率的調整，隨著含氫量的增加，持續而緩慢地變化並漸趨向平衡；(2)高溫(700、800°C)充氫時存在一突然的顯微組織轉變，且α、β兩相體積分率的重新調整乃是透過一快速的再平衡機構在短時間內完成。對暫時充氫超塑性成形而言，經由適當地控制充氫量及充氫溫度可大幅提高成形高度，如800°C時含有0.25 wt% H的試片在相同成形溫度及壓力下成形高度增加了34%。
• 英文摘要： A fine, equiaxed duplex microstructure, high temperature and low strain rate are essential require-ments for superplastic forming (SPF). However, considerable property degeneration is unavoidable whengrain growth occurs during high temperature forming. In this study, temporary alloying of the hydrogentreatment was conducted to reduce the forming temperature and, thus, improve the superplastic propertyat lower temperatures; in addition, the influence of hydrogen on the microstructure was also investigated.The results indicate that two different procedures using hydrogen can be employed to modify microstructurechanges: (l) consecutive slow changes in the microstructure and gradual modification in the alpha-betavolume fraction at low temperatures, and (2) at higher hydrogenation temperatures, an abrupt change inthe microstructure and a new alpha-beta volume fraction achieved by using a fast re-equilibrium process.For superplastic forming, considerable improvement in the forming height is obtained through a smalladdition of hydrogen into the as-received material at the same forming temperature using a properhydrogenation temperature/hydrogen concentration combination.
• 中文關鍵字： superplastic forming; temporary alloying of hydrogen
• 英文關鍵字： --