鈦合金多道次熱加工之製程圖模擬

Abstract

鈦合金為高經濟價值的材料，在許多應用上的特性完全由熱加工成形期間的製程參數而定，而大多數的熱機製程中往往需要經多道次方能成形，因此加工溫度、應變率等參數必須極為嚴格控制與管理。本研究主要利用Gleeble熱加工試驗機對Ti-6Al-4V(ELI)做單道次和二道次壓縮模擬；實驗條件包括各5個溫度與應變率，而除荷時間為10秒。最後再以製程圖的方法來分析與比較兩者的差異。 實驗結果顯示出二道次壓縮除荷後，在高應變率下，大部分的應力值要比單道次小，而二道次製程圖之峰值效率要比單道次製程圖大。兩者雖皆有三個不穩定區域，但在低溫α+β相區裡，以二道次的溫度區間較大，溫度也較高。此外，製程圖的方法也與實際的微結構相符合。在真應變為0.5下，單道次製程圖之效率最大值為50％，主要在900-960℃，應變率0.001-0.003s-1；二道次製程圖之效率最大值為60％，分佈在940-975℃，應變率0.001-0.002s-1。因此採用多道次製程圖，在實際加工上，將有助對製程條件更精確地判別，進而選擇更穩定區域之參數。

Titanium is one of the worthful and high-performance materials. Several special characteristics are obtained through appropriate processing parameters of hot working during forming. Because most processes need multi-pass hot working, the major parameters such as temperature and strain rate have to be controlled strictly. This research was to explore the single-pass and two-pass hot compression of Ti-6Al-4V (ELI) using Gleeble. The experimental conditions included five temperatures and five strain rates with ten seconds unloading time. The difference of the two processes were compared and analyzed through the simulation of processing map. The results of this study show that most of the stresses with two-pass are higher than that with single-pass at high strain rate. And the peak efficiency of power dissipation for the two-pass is higher too. There are three unstable regions in both processing maps. The temperature range in two-pass processing map is wider, and its temperature was higher around α+β phase field. The developed processing map is well consistent with the observed microstructure. In the single-pass processing map with a true strain of 0.5, 50％ peak efficiency can be obtained around 900-960℃ and 0.001-0.003s-1. While 60％ peak efficiency can be obtained in the two-pass processing map around 940-975℃ and 0.001-0.002s-1. Thus, it is helpful to choose more accurate parameters of process around the stable region by using multi-pass processing map at the actual working