Resumo:
The advancement of technology has been the main reason for the production of new structural
materials combining excellent mechanical properties, low manufacturing cost and
applications in diverse environments. Among the most advanced materials, nickel-based
superalloys are the most prominent in applications involving high temperatures. For these
applications, an appropriate balance of properties is required, such as high mechanical
strength, high creep resistance, high fatigue resistance, high thermal conductivity, low
thermal expansion anisotropy and high oxidation resistance. Among these alloys are MarM246 and Mar-M247, which have Al and Cr in their composition, responsible for the
formation of Al2O3 and Cr2O3 oxide scale, useful of increasing resistance to oxidation and
corrosion at high temperatures. However, the use of these superalloys for a long period of
time can cause the fragmentation of these oxide scales or the evaporation of the Cr2O3,
interfering with the integrality of the material. One way to increase the useful life of these
alloys is to coating them with scales that are highly resistant to oxidation without interfering
with the properties of the substrate. The Halide Activated Pack Cementation (HAPC) process
is a very versatile, low-cost method used to coating many materials, regardless of their
geometry. In view of this scenario, the objective of this work was to study the deposition of
aluminum, one of the most used in the protection against oxidation and corrosion, for the
formation of coatings by the HAPC process on the Mar-M246 nickel superalloy, which until
now has not been reported in the open literature. The aluminization process was carried out
at four different temperatures, using NH4Cl as an activator and a powders mixture containing
pure Al and alumina. A thermodynamic study, with the aid of the HSC Chemistry 6.0
software, contributed to the choice of temperatures and activator, in addition to obtaining an
aluminum deposition mechanism in the formation of the coating phase for the process at
1000°C. The results showed, for all temperatures, coating without cracks, pores or adhesion
failures to the substrate and a layers with Ni2Al3 and/or NiAl3 in chemical composition. The
growth of the coating was evaluated by the growth kinetics in processes from 1 to 16 h,
obtaining the information of a parabolic growth and activation energy of 96.55 kJ.mol-1, for
the process of aluminization via HAPC, where these coatings were characterized by scanning
electron microscopy (SEM). All coatings formed in a period of 9 h, at all temperatures
studied, were characterized by optical microscopy (MO), SEM, dispersive energy
spectroscopy (EDS) and X-ray diffractometry (XRD), showing a layer thickness between 90 to
300 μm. These coated substrates were introduced 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, revealing a reduction in mass gain around 3.4 times for the layers formed in the
HAPC 900 and 1000°C processes.