Master of Science in Mechanical Engineering (MSME)
IN738LC is a nickel base superalloy, widely used in various applications in turbine engines at high temperatures. Its oxidation and nitriding characteristics were focused in this study. Oxidation kinetics of IN738LC in dry air was studied at selected temperatures, specially chosen depending on the chemical dynamics of the alloy at such high temperatures during annealing. Isothermal oxidation in dry air was carried out at 1000°C, 1090°C, 1140°C and 1190°C. XRD results indicated an interesting onset of preferred orientation in the ã’ depleted layer in all the samples. The XPS and XRD analyses revealed the main oxide phases present in the oxide layers. Volatilization of Cr2O3 was found to be the reason for the weight loss in the superalloy. Al2O3 formed a reliable and stable oxide layer above 1100°C. Above 1140°C two different FCC solid solutions were found to be formed and the superalloy oxidized heavily and lost weight. Intensified plasma-assisted nitriding (IPAN) is one of the most widely used surface nitriding techniques. The surface of the as-received IN738LC was nitrided using this technique. Preferred orientation was observed in the samples nitrided with 0.5, 1.0 and 1.5 mA of current density. The XPS analysis showed the formation of TiN and CrN along with TiO2. Nano precipitates of TiN were observed on the ã' precipitates. IPAN improved the microhardness value of the superalloy by about 70% and its wear resistance by about 10%.
Document Availability at the Time of Submission
Release the entire work immediately for access worldwide.
Pampana, Mary Shanti, "Study of characteristics of plasma nitriding and oxidation of superalloy IN738LC" (2004). LSU Master's Theses. 2709.