本研究藉由微拉伸試驗和微結構分析探討冷加工Ti6Al4V合金以高電流密度直流通電對性質變化之機制探討，將狗骨頭形狀微拉伸試片結合風扇散熱進行1×104 - 1.4×104A/cm2電流密度通電1~30分鐘以及進行1.2×104、1.4×104A/cm2電流密度通電30分鐘的熱對照組，並量測微拉伸性質，後續進行微結構分析了解微拉伸性質變化機制。利用掃描式電子顯微鏡觀察破斷面，破斷機制皆屬延性破斷而未受微拉伸強度與伸長率影響。電子微探儀定量分析兩相固溶原子比例未受通電或熱對照組影響。X光繞射分析未觀察到析出物繞射峰，此外應變分析β相(200)結晶面於短時間通電造成應變，且增加電流密度導致微應變速率提升。X光繞射分析所得的差排密度變化趨勢為通電短時間內明顯下降，並於通電長時間維持穩定。電子背向散射繞射分析觀察拉伸方向的晶粒取向未有明顯變化，而通電導致α相轉變成β相，並且β相隨通電時間增加有晶粒成長，表示GOS分析隨通電時間增加生成的無應變β相晶粒應為相變化形成，並非再結晶現象。針對彈性模數、降伏強度、伸長率探討微拉伸性質的變化機制，彈性模數變化受相轉變機制影響；降伏強度變化於1.2×104A/cm2電流密度主要受應變硬化機制主導，1.4×104A/cm2電流密度則受應變硬化和相轉變機制共同主導；伸長率變化於通電前期(1.2×104A/cm2 1~5分鐘、1.4×104A/cm2 1~10分鐘)以應變硬化和相轉變機制共同主導，但目前已知機制對通電長時間的伸長率變化未能解釋，需進一步實驗探討。

This study investigated the mechanism of micro-tensile properties and microstructure variation of cold-worked Ti6Al4V alloy under electromigration at high current densities. The dog bone-shaped specimens were subjected to 1×104-1.4×104A/cm2 direct current stressing for 1-30minutes. Fan cooling incorporated for removing excess joule heat during the current stressing. The SEM analysis revealed that all specimens exhibit ductile fracture mechanism despite the variations in micro-tensile properties. XRD analysis showed that short-time current stressing induced strain in β phase (200). The strain variation rate increased at larger current densities. Dislocation density calculated by XRD initially decreased after current stressing while stabilized at a certain value in 30-minute stressing. EBSD analysis did not show changes in grain orientation along the tensile direction, but showed phase transformation and grain growth of β phase. The study investigated the effect of current stressing on elastic modulus, 0.2% yield strength, and elongation. Elastic modulus variation was likely attributed to phase transformation, while 0.2% yield strength was influenced by strain hardening and phase transformation at different current densities. The mechanism of elongation variation under long-time current stressing requires further investigation, although the behavior at short-time current stressing can be explained by strain hardening and phase transformation.

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