IN-713LC超合金細晶製程及機械性質之研究

Abstract

摘 要 本實驗係以IN-713LC超合金為材料，以變化澆鑄溫度及離心鑄造等方式，澆鑄出不同晶粒大小之試桿，並進行熱均壓處理，以研究晶粒大小及熱均壓處理對機械性質之影響。 實驗結果顯示，控制澆鑄溫度及離心鑄造法具有細化晶粒之效果，分別可得到晶粒大小約為65 mm及25 mm等軸細晶。熱均壓處理可消除細晶鑄件中的微縮孔，改善其對機械性質的影響。經過熱均壓處理之試桿，其硬度及室溫拉伸降伏強度、抗拉強度、延伸率與晶粒大小之關係均符合Hall-Petch方程式。在拉伸破斷面部分，熱均壓處理並不影響3 mm 柱狀晶及90 mm等軸晶的破裂模式，其破裂主要起源為骨架形碳化物；無熱均壓處理之離心鑄造等軸細晶試桿(25 mm)裂紋主要分佈在晶界及微縮孔附近；經過熱均壓處理後等軸細晶試桿破裂模式為沿晶及穿晶混合破裂。在927℃/158 MPa的潛變測試條件下，粗晶之破斷壽命較細晶佳；但離心鑄造所得的25 mm超細晶其破斷壽命反較降低澆溫所得的90 mm細晶佳。

Abstract The IN-713LC superalloy employed in this study was prepared by various pouring temperature and centrifugal casting , and then casted into standard test bars with dif-ferent grain size. The bars were followed by HIP treatment. Thus , the effects of grain size and HIP treatment on mechanical properties of IN-713LC superalloy were in-vestigated. The results showed that the effects of fine grain were obtained by control of pouring temperature and centrifugal casting . Grain size of the fine equiaxial grain was about 65 mm and 25 mm by controling 20℃ superheat and centrifugal casting , respectively. Besides , HIP treatment eliminated micro-shrinkage porosity in the casting , and have improved mechanical behavior . After the test bars treated by HIP , their mechanical properties , such as hardness , yield strength , tensile strength and elongation , were in agreement with Hall-Petch equation . Furthermore , for the fractographs , HIP treatment did not affect fracture modes in 3 mm columnar and 90 mm equiaxial grain test bars, whereas the fracture evidently arised form script carbide .The cracks , in the test bars of finer equiaxial grain by centrifugal casting dealed with no HIP treatment , were distributed at grain boundary and micro-shrinkage porosity nearby . The fracture mode of finer equiaxial grain test bars by HIP treatment was a mixture mode of transgranular and intergranular fracture at room temperature. For a creep-tested under 927℃/158 MPa , the specimen of the coarse grain(3 mm) possessed more prolonged rupture life than the specimen of the fine grain , but the rupture life for the ultra-fine grain specimen (25 mm) , obtained by centrifugal casting was higher than that the fine grain specimen (90 mm) obtained by lower pouring temperature.