- Evaluation of Creep Reliability of Powder Metallurgy and Cast-type Ni-based Superalloy by Using Ultrasonic Wave
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Chan-Yang Choi, Jin-Hun Song, Se-Ung Oh, Chung-Seok Kim, Sook-In Kwun, Sung-Tag Oh, Chang-Yong Hyun, Jai-Won Byeon
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J Korean Powder Metall Inst. 2012;19(3):215-219.
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DOI: https://doi.org/10.4150/KPMI.2012.19.3.215
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 Abstract
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- An attempt was made to evaluate creep reliability of two commercial Ni-based superalloys by using ultrasonic wave. The materials include fine-grained PM alloy fabricated by mechanical alloying and subsequent hot isostatic pressing, and IN738LC cast alloy with a grain size of a few cm. Microstructural parameters (fraction of creep cavity and size of gammaprime precipitates) and ultrasonic parameters (velocity, attenuation) were measured to try to find relationships between them. Ultrasonic velocity decreased with creep cavity formation in PM alloy. On the other hand, no distinct changing trend of ultrasonic velocity was observed for IN738LC alloy. Ultrasonic attenuation was found to have a linear correlation with the size of gammaprime precipitates and was suggested as a potential parameter for monitoring creep reliability of IN738LC alloy.
- Variation of Tensile Strength by Addition of Y2O3 and Effect of Aging Treatment in Ni Base Alloy Fabricated by MA Method
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Il-Ho Kim, Won-Sik Lee, Se-Hyun Ko, Jin-Man Jang, Sook-In Kwun
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J Korean Powder Metall Inst. 2008;15(1):23-30.
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DOI: https://doi.org/10.4150/KPMI.2008.15.1.023
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Abstract
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- Ni-20Cr-20Fe-5Nb alloy with or without Y_2O_3 was manufactured by mechanical alloying process and consolidated by spark plasma sintering (SPS). The grain size of the alloy with Y_2O_3 was smaller than that of alloy without Y_2O_3 which results from the effect of Y_2O_3 suppressing grain growth. The tensile strength at room temperature was increased by the addition of Y_2O_3 but decreased abruptly at temperature above 600°C. It seems to result from the change of deformation mechanism due to fine grain size, that is, grain boundary sliding is predominant at above 600°C while internal dislocation movement is predominant at below 600°C. After conventional heat treatment process of solution treatment and aging, a small amount of delta(Ni_3Nb) phase was formed in Ni-20Cr-20Fe-5Nb alloy while a large amount of gamma"(Ni_3Nb) was formed in Inconel 718 in the previous report. This is due to exhaustion of Nb content by the formation of NbC during consolidation.
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