| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 93 === Abstract
Inconel 718 Ni-base superalloys are mainly strengthened by precipitates and solute additions, and are produced in various forms suitable for application at high temperature, where creep and fatigue are important mechanisms of deformation. Based on its good strength combined with an excellent resistance to oxidation at elevated temperatures, alloy 718 is most widely used in aerospace , nuclear and petrochemical industries.
Hot Isostatic Pressing via main function to reduce Inconel 718 inside porosity rate, strengthen Inconel 718 inside structure, reduce fatigue starting point, and prevent the transmission of crack, control Hot Isostatic Pressing via three main parameters of temperature、pressure , time, try to get and make a parameter bestly.
In the research finding, Reduce the influence that the mechanical intensity of Inconel 718 is leant segregation and Laves phase on the grain boundary, in order to reduce segregation and Laves phase gathering on grain boundary, reduce the mechanical intensity, this research utilizes HIP via to control temperature and reach more than 1100℃,dispel unfavorable precipitate phase, and utilize the homogenizing of HIP via, make the alloying element distributed evenly, in addition, even application of force because of HIP via, originally regarded as δ of bad precipitate phase, take shape and distribute discontinously in grain boundary, have function of suppressing grain growth, improve the mechanical intensity indirectly, make HIP via result different in other via.
The coherent precipitation of γ' andγ" are the main phases that strengthen the Inconel 718, especially theγ'. By the control of parameters during HIP Processes, massive and uniform precipitation ofγ' will be available. As we know that the niobium is a key element needed to precipitate the strengthen phaseγ' andγ". During a HIP process, high temperature will cause harmful phases that contain niobium to be dissolved and more strengthen phases can be formed. Thus the strength of Inconel 718 can be further improved.
In this study, HIP can be used to enhance the mechanical properties of Inconel 718 effectively, reduce the porosity and defects, and suppress the growth in gain size is reported. The best parameter of HIP process found in this paper was 1180℃, 1750bar and kept in 4 hours.
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