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版權所有 翻印必究 指導老師：戴子堯 教授 姓名：周家源 班級：奈米四乙 學號：4A114004 2015/12/22 1 版權所有 翻印必究 Outline Introduction Experimental Result and discussion Conclusions 2015/12/22 2 版權所有 翻印必究 Introduction • The operation condition of IHX requires the alloy to withstand mechanicaldegradation at 950℃and 3–8 MPa in He impurities for a period of more than 60 years . • most damage would be primarily focused on grain boundaries of Alloy 617 through the surface oxidation and decarburization along GBs , the dissolution and redistribution of GB carbides , GB migration and recrystallization . 2015/12/22 3 版權所有 翻印必究 Experiments • The investigated material was a commercially available Alloy617 in a hot-rolled plate form of 19.5 mm thickness. • The proprietary heat treatment was designed to produce serrated GBs with a proportion of over 80%. The samples weresolution-annealed at 1200 ℃ for 10 min and slow-cooled to 80 ℃ at a cooling rate of 5 ℃/min. 2015/12/22 4 版權所有 翻印必究 • A cylindrical specimen of 6 mm gauge diameter and 25 mm gauge length was employed for creep test with thecondition of 960 ℃ /30 MPa in air. • Cold work treatment was carried out by loading the heat-treated specimen to a tensile strain of 5% at room temperature with a strain rate of 5 × 10−4 /s before creep tests. 2015/12/22 5 版權所有 翻印必究 Results&Discussion 2015/12/22 6 版權所有 翻印必究 Fig. 2. Creep curves of Alloy 617 at 950 1C and 30 MPa for the various microstructures: (a) creep strain with time and (b) creep strain strain rate with time. 2015/12/22 7 版權所有 翻印必究 Fig. 3. SEM micrographs showing longitudinal sections near the fractured surfaces after creep at 950 ℃ /30 MPa 2015/12/22 8 版權所有 翻印必究 Fig.4. Distribution of dislocations and M23C6 carbides in the subgrain structures after creep at 950 ℃/30 MPa for the various microstructures 2015/12/22 9 版權所有 翻印必究 Conclusions • TEM analysis on the serrated GB without precipitates indicated that the fundamental driving force for the GB serration stems from lowering interfacial free energy of GB per unit area. • The serrated GBs with fine/stable intragranular carbides ensured 2.8 times better creep resistance due to their significantcontribution to GB strengthening. 2015/12/22 10 版權所有 翻印必究 Thanks for your attention ! 2015/12/22 11