本研究目的為藉由觀察機械性質、電性與微結構，探討較低溫度通電對Ti-6Al-4V合金性質變化之機制。本實驗對Ti-6Al-4V薄帶以4000-8500A/cm2電流密度通電2-60分鐘，量測不同電流密度下微硬度變化；後續以7000A/cm2電流密度條件觀察通電時間對材料微硬度、電阻率影響，並藉由微結構變化瞭解電流影響材料性質之機制。掃描式電子顯微鏡與能量散射光譜儀分析結果顯示通電後因溫度較低而無相變化、亦無固溶析出現象，X光繞射結果顯示電流在短時間內使材料內部產生應變，並對結晶面造成破壞使繞射峰積分面積下降。以穿透式電子顯微鏡觀察發現材料結晶面受電子風力與焦耳熱共同作用影響，造成此材料的α與β兩相在不同通電時間下的差排產生與消除。藉由電子背向散射繞射分析結果顯示，通電後α與β相優選取向皆無改變，但通電短時間內α(0001)與β(111)取向比例有變化，而兩相高低角度晶界比例不變顯示通電後無明顯再結晶現象，α相晶粒尺寸些微上升。低溫通電微硬度變化與通電時間關係由α(0001)取向比例變化主導，電阻率變化行為則與晶粒尺寸變化有較大關聯性。

This study investigated the mechanism of the properties and microstructure variation on Ti-6Al-4V alloy after current stressing at lower temperature. The strip specimens were subjected to 4000-8500 A/cm2 direct current stressing for 2-60 minutes. The variation in microhardness, electrical resistivity, and microstructure were discussed with different stressing time at 7000 A/cm2. SEM and EDS results showed that no observable phase transformation, solid solution and precipitation occurred due to the low current stressing temperature. XRD results indicated that electric current induced lattice strain in short time and the decrease in integral peak intensities as resulted from lattice disruption. TEM observation showed that the lattice structure was affected by the cooperation of electron wind force and Joule heat, resulting in the formation and annihilation of α and β phase at different stressing time. According to EBSD analysis, the preferred orientation of α and β phase remained the same, but the fraction of α(0001) and β(111) orientation changed after current stressing for a few minutes. Besides, the fractions of HAGBs (high angle grain boundary) and LAGBs (low angle grain boundary) of both phases did not vary much, indicating that the recrystallization behavior was not obvious after current stressing. A slight increase in α phase grain size can be observed. The major mechanism of microhardness variation was the change in the fraction of α(0001) orientation, and the variation in electrical resistivity was highly related to the change in grain size.

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