| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 100 === In this study, the hot cracking susceptibility of the Incoloy 800H and 825 nickel-base alloy substrate was discussed with filler and without filler. And later nickel alloy of filler 52 and 82 Tungsten inert gas shielded arc welding in the specimen. Observation of nickel based superalloy at high temperature by the critical strain for crack. On the other hand by using a stereoscopic microscope, optical microscope observation of the crack surface type of organization, as well as X-ray diffraction analysis of the weld structure, observed by scanning electron microscopy. The maximum crack length, amount of cracks, and total cracks length were recorded. The difference of liquid and solid (ΔT) was analyzed in nickel-based superalloy using differential thermal analysis (DTA) and then examine the relationship between cracks and the hot cracking sensitivity.
The results showed that the hot cracking sensitivity of the nickel-based super-alloys with filler at high temperature was lower than that without filler base metal. The hot cracking sensitivity had a slight effect with the Inconel 82 filler addition. According to experimental data, the relationshop between the hot cracking susceptibility and the liquid-solid two-phase range can be obtained. When the crack total length was increased, the liquid-solid two-phase range is higher and then the hot cracking susceptibility was raised. The morphologies of cracks included the intergranular crack in the molten pool, the molten pool solidification cracking, the weld heat-affected zone of intergranular cracks, and the transgranular crack in the heat-affected zone. The occurrence of cracking in materials under high temperature can be inferred according to the morphologies of cracks. The results showed that no low temperature precipitates under high temperature incoloy nickel-based alloys. This was because that a critical strain increased to the range of the brittle temperature range rature in base metal during the varistraint test. When the brittle temperature range was higher under high temperature, hot cracking sensitivity was more obvious. The results displayed the hot cracking sensitivity was most evident in Incoloy 800H alloys of all the nickel-based alloys.
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