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In the present study, a commercial Fe-based metallic glass (MG) powder was deposited by laser cladding on 304 stainless steel substrates. The main purpose of this work is to study a range of processing conditions that allow the fabrication of well-established deposits. Experiments were conducted to evaluate the effect of the main processing variables on the mechanical properties and phases obtained in the coatings. XRD and SEM characterization was also performed to evaluate the phases and morphology of the deposits obtained. The results suggest that dense Fe-based MG cladded coatings require high thermal energy for deposition, and high dilutions were obtained in final deposits; however, the cooling rate is not enough to obtain 100% amorphous deposits. Although the MG structure observed in the precursor powders was not kept in the final deposits, the precipitation of crystalline phases resulted in very high hardness (> 700 HV0.1), which improved wear resistance against the substrate material. The processing of this alloy by laser cladding is promising when coatings with high hardness and wear resistance are required and can be a good alternative to the thermal sprayed process in which these alloys are conventionally processed. [ABSTRACT FROM AUTHOR]

This work aimed to evaluate the effect of V addition into TiSiN coatings deposited by an industrial-scale cathodic arc evaporation system on the structure and mechanical-tribological properties. X-ray diffraction patterns and Raman spectra confirm the formation of a solid solution presenting the fcc NaCl-type structure without a preferred orientation for both TiSiN and TiSiVN coatings. The addition of V did not affect the coating's hardness but induces a half-reduction in the coefficient of friction during the dry sliding tests. The wear mechanism changed from abrasive to mild-adhesive due to the inclusion of V, suggesting a reduction in the wear rate that might be of interest for dry cutting tools. [ABSTRACT FROM AUTHOR]

Ni-Al coating alloys, which are commonly used in gas turbine engines operating in marine environments, are highly susceptible to hot corrosion attack. The effect of alloy composition and exposure conditions on the development of a protective alumina scale, which is important for the hot corrosion resistance of the alloy, and how they affect the transition of alumina from the θ to the α polymorph have been evaluated. A series of Ni-Al model alloys with a base composition of Ni-36 at.% Al, and 5 at.% additions of Cr, Pt and Si were exposed in dry air and in air-10%HO at 900 °C. The presence of water vapor in the gas led to higher oxidation rates and retarded the θ- to the α-AlO transformation. The oxidation behavior of the alloys and the alumina polymorph which formed differed depending on the alloying element considered. Additions of Cr accelerated the θ to α transformation, while Pt and Si retarded it. [ABSTRACT FROM AUTHOR]

The effect of pre-oxidation treatment and surface preparation of optimized NiCoCrAlY coatings deposited by high-velocity oxygen fuel (HVOF) spraying and exposed to a low-temperature corrosive environment is reported herein. Coatings with two surface finish conditions (as-sprayed and ground) were heat treated under two different oxygen partial pressures (air and argon). The electrochemical corrosion behavior was evaluated in CO-saturated brine via potentiodynamic polarization, polarization resistance, and electrochemical impedance measurements. The results show that the grinding process and pre-oxidation treatment in argon enhanced growth and formation of α-AlO scale. The potentiodynamic polarization results show that both pre-oxidation and surface treatment had a positive influence on the corrosion resistance of the coating. The reduction of the porosity and the formation of a dense, uniform, and adherent oxide scale through pre-oxidation treatment led to an increase of the corrosion resistance due to a decrease in active sites and blocking of diffusion of reactive species into the coating. However, according to the results, complete transformation from metastable alumina phases to α-AlO in addition to formation and growth of dense α-AlO is required to ensure full protection of the coating and base material over long periods. [ABSTRACT FROM AUTHOR]