Resumo:
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
