Superliga de níquel sinterizada a partir de pós elementares com recobrimentos cerâmicos contra a carburização

Abstract

Nickel-based superalloys fabricated by centrifugal casting find application in high temperature services, particularly in highly carburizing atmospheres such as hydrocarbon pyrolysis furnaces. The demand for materials resistant to carburization underscores the importance of innovative and in-depth investigations in this area, aiming at alternatives with equal or superior performance through economically more attractive manufacturing processes. The primary objective of this research was the development of a sintered nickel-based superalloy from dissociated powders and the evaluation of ceramic oxide coatings produced by the sol-gel route and applied by static spin-coating as a barrier to the carburization process. The adopted methodology involved determining manufacturing parameters for the HP X superalloy through conventional powder metallurgy, evaluating its porosity and hardness according to the compaction pressure, and applying and assessing films of Al2O3, Nb2O5, SnO2, and ZnO before and after carburization tests. Techniques such as optical microscopy, SEM/EDS, XRD, XRF/EDX, hardness and microhardness tests were employed, along with regression analyses and variance analyses for statistical assessment of the obtained data. The results demonstrated that a compaction pressure of 800 MPa results in satisfactory properties for the sintered material, and statistically proved that porosity decreases with increasing compaction pressure, between 200 and 1200 MPa. Upon comparing the performances against carburization of the studied ceramic oxides, Nb2O5 stands out for its superior resistance. Statistically, samples coated with Nb2O5 exhibit a microhardness profile similar to that of non-carburized samples, indicating that, in the tested conditions, only this coating can be considered statistically effective as a barrier to carburization. The conclusions not only validate the initial hypotheses but also open new perspectives for future investigations. This work provides a solid foundation for significant advances in understanding the production of nickel-based superalloys by conventional powder metallurgy, as well as their protection against carburization through ceramic oxide coatings.