|Abstract: ||本研究主要係針對Ti-6Al-6V-2Sn合金，藉由不同的熱處理溫度與冷卻方式，經不同時效溫度後，進行室溫與高溫(450oC)之缺口拉伸試驗，探討溫度效應對顯微結構與機械性質之影響。 結果顯示Ti-6Al-6V-2Sn 於β轉換溫度(945oC)之上965oC進行固溶熱處理，空冷後得到針狀α相與殘留β相，水淬後得到α相；若是在低於β轉換溫度下900oC進行固溶熱處理，空冷後得到針狀α相與Primary α相及殘留β相，水淬得到α相與α相及Primary α相。固溶水淬後時效，α相會分解成α相與細小的β相，使得時效後硬度增加，在965oC固溶水淬後經482oC時效得到最大硬度值約為460Hv。 對Ti-6Al-6V-2Sn於室溫環境下進行缺口拉伸試驗，900oC固溶水淬後的試片經593oC時效，破裂形貌呈現出伴隨塑性變形產生之延性破裂而有抗缺口脆化的現象，引發缺口強化，以致於有最佳的抗缺口脆化的表現，缺口拉伸強度為最大值1425 MPa，破斷特徵為延性的窩穴狀破裂。當在450oC環境下拉伸，延性金屬的缺口強化有效提高缺口拉伸強度，965oC固溶水淬後經482oC時效之試片，缺口拉伸強度值約為1300 MPa，破斷特徵為穿晶破裂伴隨著晶界剪變，而隨著時效溫度的增加，α相與β相晶粒持續成長粗大，而使缺口拉伸強度遞減。|
The main subject of this research is focused on the study of temperature effects on microstructures and mechanical properties for the dual phase titanium alloy, Ti-6Al-6V-2Sn. By using different solution heat treatment processes, it will show the different morphology and microstructure. When the titanium alloy is carried out solution heat treatment above β transus temperature (945oC), i.e. at 965oC, the resultant microstructures would show the acicular α and retained β products after air cooling, and show the α martensite product after water quenching, respectively. If the solution heat treatment temperature is below the β transus temperature, i.e. at 900oC, the resultant microstructures would show the primary α, acicular α and retained β products after air cooling, and show the primary α, α and αmartensite products after water quenching, respectively. Moreover, the further aging process after solution heat treatment process with water quenching would result in the transformation of α phase. Here, α phase decomposed into α and tiny β phase, these would cause the enhancement of hardness. Consequentially, the maximum hardness would be obtained after solution heat treatment (965oC) with water quenching, and then 482oC aging. It is about 460 Hv. The notched tensile test of Ti-6Al-6V-2Sn with several conditions was carried out at room temperature and 450oC, respectively. After the notched tensile test at room temperature, the fracture surface of Ti-6Al-6V-2Sn specimen, carried out solution heat treatment (at 900oC), water quenching, and 593oC aging, showed the spherical dimples characteristic of ductile fracture. It caused notch strengthening, and got the best resistance to the notched embrittlement phenomenon. Accordingly, the maximum notched tensile strength is about 1425 MPa. When the notched tensile test was carried out at 450oC, the temperature effect would enhance ductile behavior and effectively cause notch strengthening. The tensile strength of Ti-6Al-6V-2Sn specimen, carried out solution heat treatment (at 965oC), water quenching, and 482oC aging, is approximate to 1300 MPa. Besides, the fracture surface showed the transgranular fracture with shear deformation of grain boundary. However, the notched tensile strength decreased progressively with aging temperature increasing as results of grain coarsening of α and β phases.