Obtenção de camadas com alta resistência a oxidação na superliga de níquel mar-m246 a partir da co-deposição de alumínio e silício utilizando o processo “halide activated pack cementation”

Abstract

Nickel-based superalloys are the ones that stand out the most in applications involving high temperatures. They contain a combination of desired properties for such applications: high mechanical strength, high creep resistance, high fatigue resistance, high thermal conductivity, low anisotropy of thermal expansion and high resistance to oxidation. Among them there is the MAR-M246 alloy that has Al and Cr in its composition, elements responsible for the formation of layers of Al2O3 and Cr2O3, oxides that are capable of increasing the resistance to oxidation and corrosion at high temperatures. However, if the material were used for a long period of time, these layers may defragment (or in the case of chromium oxide, evaporate) which would interfere with the material's properties. One of the ways to prevent this degradation is to coat these alloys with oxidation-resistant layers and, among the coating methods, the process known as Halide Activated Pack Cementation (HAPC) is a very versatile method, low cost, used to cover different materials regardless of their geometry. Thus, this work proposed to coat the MAR-M246 alloy by co-deposition of Aluminum and Silicon using HAPC. For this purpose, three different powder coating mixtures (MPR) were created, with 75% Al2O3 powder, 25% of a mixture of Si and Al powders, in the ratios 90:10 (MPR I), 50:50 (MPR II) and 27.5:72.5 (MPR III) and 0.015mg NH4Cl. The coating process on the 3 samples was carried out at 1000°C for 9 hours in a vacuum sealed quartz reactor. The coated samples were characterized by Scanning Electron Microscopy (SEM), energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) before and after oxidation tests. The results showed that there was a layer creation in the 3 MPR's, with thickness varying from 130 to 180 µm. Then, the coated substrates were placed in an oxidation test at 1000°C for 240 hours, revealing an optimization in the oxidation resistance by the formation of the Al2O3 oxide layer with a mass gain reduction of up to 2x for the layer formed by MPR III