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Temperature effect on microstructure and mechanical behavior of Ti-15V-3Cr-3Al-3Sn
|Authors: ||Wen-Han Chen|
|Contributors: ||NTOU:Institute of Materials Engineering|
|Issue Date: ||2011-11-23T03:13:05Z
|Abstract: ||本研究主要先對Ti-15V-3Cr-3Al-3Sn單相(β)鈦合金(BCC結構，以下簡稱Ti-15-3），經不同溫度之時效熱處理之後，探討溫度效應對顯微組織及機械性質影響，之後再利用熱氫製程細化晶粒來改善合金機械性質。結果發現，經426 oC時效處理之後，第二相析出物(α-相，HCP結構)會先由晶界處析出，而後往晶粒內成長，其顯微組織呈現纖細交錯分佈，相對應量測到極高的硬度值(420 Hv)。再者，析出物之顯微組織隨時效溫度上升而呈粗大化，然而，其體積分率下降，亦即，α-相體積分率下降而β-相體積分率提高。實驗之Ti-15-3合金經540oC時效熱處理後，量測得最高室溫缺口拉伸強度。此外，亦於不同環境溫度下(150~450 oC)對其進行缺口拉伸試驗，結果發現，在450 oC高溫環境下，經426 oC時效熱處理之合金試樣，由於環境溫度效應消弭缺口脆化現象，而此環境溫度呈現最高缺口拉伸強度(1160 MPa)，至於其他環境溫度下缺口拉伸試驗，仍以經540 oC時效熱處理後之合金試樣表現較佳缺口強度。 再者，本研究亦發現，氣態充氫後經760 oC持溫5小時之共析反應，細小針狀的δ相(FCC結構)氫化物會於α-相邊界析出往β-相晶粒內成長。再者，經780 oC持溫1.5小時脫氫處理後，可明顯觀察到晶粒細化現象，其顯微組織中細長型α第二相析出物在晶界處析出。此時表面硬度值高達499 Hv，室溫缺口拉伸強度可達到959 MPa，其未因高硬度而導致缺口脆化現象發生，結果顯示Ti-15-3合金經熱氫製程後不僅可細化晶粒亦可提升機械性質。|
Ti-15V-3Cr-3Al-3Sn, -phase titanium alloy (so-called Ti-15-3 with BCC structure), is subjected to study the temperature effects on microstructure and mechanical behavior by using different aging temperature (426600 oC). Moreover, Ti-15-3 is also further manipulated to improve the mechanical properties by using thermohydrogen processing (THP). It follows that the secondary phase (α-phase with HCP structure) could first segregate on the grain boundary and then grow toward the interior of an adjacent grain, where the fine and interlaced-phase precipitates were formed in the grains after 426oC aging treatment and resulted in the maximum hardness (420 Hv). Besides, the morphologies of -phase precipitates were coarsening with increasing the aging temperature, but its volume ratio was decreasing, i.e., the -phase volume was decreasing and the -phase volume was increasing with increasing the aging temperature. The as-received Ti-15-3 specimen after 540oC aging treatment was showed the highest measured tensile strength of notched tensile test. However, the test was also carried out at different environment temperatures (150 ~ 450 oC). It followed that the as-received Ti-15-3 specimen after 426oC aging treatment showed the notched tensile optimum strength at 450 oC environment temperatures due to the temperature effect kept from notched embrittling and resulted in the high notched tensile strength performance (1160 MPa). As for the tests at other environment temperatures, the notched tensile optimum strength was still got from the as-received Ti-15-3 specimen after 540 oC aging treatment. Regarding to the study coupling with thermohydrogen processing,the Ti-15-3 raw matrix after filling hydrogen processing was first performed a eutectic reaction at 760oC for 5 hours. Consequentially, the fine hydride, δ-phase with FCC structure, would segregate at the α-phase boundary and grow toward the interior of -phase grain. Moreover, the as-received specimen after eliminating hydrogen treatment at 780 oC for 1.5 hours, was clearly achieved the grain size reduction, where the narrow secondary phase precipitated on the grain boundary. Accordingly, the surface hardness is high up to 499 Hv, and the notched tensile strength at room temperature could get up to 959 MPa. The notched embrittlement has not been occurred due to high hardness performance. It demonstrates that Ti-15-3 alloy could not only be accomplished the grain size reduction, but also enhanced the mechanical properties by using the thermohydrogen processing.
|Appears in Collections:||[材料工程研究所] 博碩士論文|
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