研究亞穩態β鈦合金Ti-10V-2Fe-3Al (Ti-1023)於雙相區(α+β相)與單相區(β相) 熱壓縮變形下之塑流行為與顯微結構演變，使用Gleeble-3500熱加工模擬試驗機在變形溫度700-900 ℃與應變速率0.01-1 s-1進行單軸熱鍛加工，取得不同應變量下之真實應力-應變曲線及微觀結構。並基於應力-應變圖數據，繪製製程加工圖(Processing map)，確認良好加工區間無論位於雙相區還是單相區皆為低應變速率0.01-0.1 s-1區間。進而計算出Ti-1023合金之變形活化能，700 ℃(α+β相)為333.2 kJ/mol，900 ℃(β相)為 212.4 kJ/mol，且建立本構方程式以描述熱鍛壓過程中之變形行為，驗證本構方程預測結果與實驗數據之間的準確性。另一方面，透過背向散射電子技術(Electron backscatter diffraction, EBSD)，觀察不同相區間之微觀結構變形演化；掌握Ti-1023於高溫變形下之應變硬化及動態軟化機制，α+β相為連續動態再結晶與不連續動態再結晶作為主要的軟化機制，且隨著不連續動態再結晶比例上升，微觀結構呈現出局部流動特徵，而β相主要的軟化機制為動態回復。最後，藉由顯微硬度測試建立機械性質與晶粒尺寸之關聯(Hall-Petch method)，明顯得知β相之顯微硬度對於平均晶粒尺寸有高度敏感性。

A study on flow behavior and microstructure evolution of near β titanium alloy Ti-10V-2Fe-3Al (Ti-1023) in two-phase region (α+β phase) and single-phase region (β phase) during hot upsetting was presented. The Gleeble-3500 thermal processing machine was employed to perform uniaxial hot upset forging at temperatures of 700 ℃ to 900 ℃ and strain rates of 0.01 s-1 to 1 s-1, the true stress-strain curves and microstructural evolution under different strains were carried out in this present study. Based on the true stress-strain curves, processing maps were performed to confirm that the great processing window in the range of low strain rates 0.01 s-1 to 0.1 s-1 whether forming in α+β phase region or β phase region. Besides, the average deformation activation energy of Ti-1023 alloy held 333.2 kJ/mol in α+β phase region and 212.4 kJ/mol in β phase region were calculated, accordingly the constitutive equations were also established for describing the hot deformation behavior as well as the prediction of experimental true stress-strain curves were verified. On the other hand, the deformation evolution of the microstructures in different phase regions were observed through electron backscatter diffraction (EBSD) technique, the strain hardening and dynamic softening mechanism of Ti-1023 under elevated deformation temperature were comprehended, in which the mainly softening mechanism occurred with continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) in the α+β phase region, thus the proportion of discontinuous dynamic recrystallization (DDRX) increased and the more characteristics of local flow were found in the texture, however, the major softening mechanism in the β phase region dominated with dynamic recovery. Subsequently, the relationship between mechanical properties and grain size was established by using microhardness test (Hall-Petch method), hence the microhardness with highly sensitivity to the average grain size in the β phase region relatively.

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