指導老師：戴子堯 教授 姓名：周家源 班級：奈米四乙 學號：4A114004 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

Outline Introduction Experimental Result and discussion Conclusions 2015/12/22

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 . 鎳基超合金617，為固溶強化的鎳鉻鈷鉬合金，常被用來當成中間熱交換器的材料，可用來在非常高溫的氣體反應器中。中間熱交換器要求合金須具備能承受機械950度和在3-8Mpa。合金617最嚴重的損害將通過表面氧化和沿著晶界脫碳，晶界碳化物的融解再分配，晶界遷移與再結晶 2015/12/22

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

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

Results&Discussion 2015/12/22

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

Fig. 3. SEM micrographs showing longitudinal sections near the fractured surfaces after creep at 950 ℃ /30 MPa 2015/12/22

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

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. 在鋸齒形晶界TEM分析，無析出物指出在晶界鋸齒的根本動力，從降低界面自由能源於 每單位面積的晶界 鋸齒形晶界與精細/平穩晶粒內碳化物 保證2.8倍的抗蠕變性，由於其對晶界強化顯著的貢獻。 2015/12/22

Thanks for your attention ! 2015/12/22