| Summary: | 碩士 === 中正理工學院 === 兵器系統工程研究所 === 87 === The purpose of this research is aimed at evaluating the relationship between microstructures and mechanical properties of the INCONEL X-750 nickel-based superalloy. The microstructures developed both based on some typical heat treatment programmes that designed specifically for commercial X-750 alloys and on some modified thermal procedures in our laboratory were investigated using optical and electron microscopy techniques. Some room temperature mechanical properties of this alloy including hardness, strength, and ductility were also examined. One of the intense efforts was conducted on the evaluation of ductile/brittle fracture characteristics in the absence of corrosive testing environment.
It was found that the mechanical properties were affected significantly by the various metallurgical factors such as phase morphology, composition and crystal structure of various carbides presented heat-treated alloys. Normally, microstructures in which grains enclosed with a carbide film that usually found in alloys after solid solution treatment are ductile and have a typical dimple fracture appearance. However, the ductility would always decrease, more or less, by increasing the aging temperature and/or extending the soaking duration of aging treatments. The intergranular fracture mode found in some aged specimens with a limited ductility were also examined in some detail, and the possible fracture mechanisms were discussed.
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