| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 97 === Hot Isostatic Pressinng (HIP) is widely used in the casting industry to remove the internal porosity generated during the casting process. It combines higher pressure and temperature to produce materials and parts with substan- tially better properties than other methods. These results in the improved strength, ductility and fatigue life of castings. Inconel 718 is the most widely used superalloys for aerospace applications. The Inconel 718 niclkel-base superalloy has decent corrosion resistance high of temperature and ambient temperature, and excellent creep and fatigue strengths at high temperature.
However, the unsuitable heat treatments will give to the precipitation of detrimental phases.
The aim of this paper is to discuss the heat treatment, including solution temperature and aging heat treatment time paramters after HIP process, and ultimately to reach proper microstructural control and mechanical properties.
Experimental results show that the reduced mechanical strength of Inconel 718 is due to Laves and δ phases on the grain boundary. The Laves and δ phases dissolve completely in the 1020oC, 1hr solution treated condition, and show the ultimate tensile strength (UTS) of 1331.5 MPa. NbC carbides dissolve partly under 1060oC, 1hr solution treatment, will precipitate with thin film shapes after aging treatment, and the UTS reduces to 1298.8 MPa.The optimized solution treatment condition is 1020oC, 1hr.
γ〞has the diameter of 30.41 nm under the double aging at 720oC, 8hrs and furnace cooling to 620oC followed by 620oC, 4hrs and air cooling. It shows the largest UTS of 1407.2 MPa, will be a peakaging theatment. Besides if the purpose of the UTS is to reach the casting superalloy basic standards, the commercial treatment of aging treatment is 720oC, 2hrs and furnace cooling to 620oC followed by 620oC, 8hrs and air cooling, show the UTS of 1185.4 MPa.
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