Isothermal Oxidation Behavior Of DZ792Superalloy

DZ792alloy is a directionally solidified Ni-base superalloy by directional solidification technology, which is based on IN792alloy after the little changing of the alloy elements. DZ792alloy is mainly applied to the gas turbine blades. Comparing with the servicing condition of aeroengine, the gas turbine for the heavy industry is undergoing more severely condition and longer time. At the same time, since it usually used without any coating, the oxidation resistance will be more and more important. So, not only the mechanics performance but also both the excellent oxidation and corrosion resistance at high temperatures are asked. Therefore, it is very important for safety servicing to accurately evaluate the oxidation resistance of an alloy, and it is also useful for the developing new alloy and improving the same kind of alloys.In the present study, the oxidation characteristics of DZ792alloy were system estimated under static atmosphere at750～950℃up to500h, according to the commen working condition of the alloy. The microstructure, morphologies and components of the oxidized scales were synthetically examined by an optics microscope (OM), an X-ray diffraction (XRD) and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer (SEM/EDX). The oxidation rules of DZ792and the main effect factors of the oxidation characteristics were summarized, and the oxidation mechanism was also discussed.It has been found that the oxidation kinetics curves of DZ792follows parabolic law in a temperature range of750～950℃during isothermal oxidation under static atmosphere. The diffusion activation energy O is to be about244.86kJ·mol-1fitted from the kinetics curve, so it can be considered that the oxidation within this temperature ranger is mainly controlled by Cr3+diffusion among Cr2O3oxidation scale. Based on the calculation results of oxidation velocity constant K, it can be estimated that the oxidation resistance grade of DZ792alloy is complete anti-oxidation within750～850℃, and anti-oxidation within900～950℃. Considering of the integrative performance of the alloy, it is suggested that the optimal servicing temperature is in the range of750～850℃. The oxidation products are mainly consist of Cr2O3, TiO2, TiTaO4and NiCr2O4as well as the Al2O3and TiN which is the inside oxidation products. The oxidation scale can be divided into several zones in the order of TiO2, CrO3+TiTaO4+NiCr2O4, Al2O3and TiN, from the surface to inside. During the oxidation, the surface, the carbides, grain boundaries and eutectic of the hypo-surface can be easily oxidized, whose priority oxidation accelerated the oxidation behavior of the alloy. The oxidation of Ti element and the depletion of Cr element led to the inside oxidation of Al element, which will influence the steady growth of the oxidation scales, so that the oxidation resistance decrease.