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Abstract As an alternative to WC-CoCr and Cr 3 C 2 -NiCr coatings for wear and corrosion protection, a TiC – 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder, free from hazardous and/or supply-critical elements (Ni, Co, W), was produced by high-energy ball-milling and processed by High Velocity Oxygen-Fuel (HVOF) spraying, obtaining dense (<1 vol% porosity), hard (H IT > 12 GPa) layers with reasonably good deposition efficiency of ≈ 54%. Tribological testing revealed that the TiC-FeCrAl coatings are particularly promising for sliding contacts, as their ball-on-disc wear rates against an Al 2 O 3 counterpart were lower than those of an HVOF-sprayed Cr 3 C 2 -NiCr reference, both at room temperature and at 400 °C, although they could not match the performance of WC-CoCr. At room temperature, brittle fracture along oxidized lamellar boundaries caused localized spallation, releasing debris in the contact region, but, in the incubation period before spallation cracks could propagate, remarkably low friction (≈0.27) was recorded. At 400 °C, spallation was largely suppressed by thermal softening, whilst coarser abrasive grooving became the dominant wear mechanism. TiC-FeCrAl coatings appeared less suited to high-stress abrasion, since extensive brittle fracture resulted in higher wear rates than HVOF-sprayed Cr 3 C 2 -NiCr, and to (acidic) corrosive environments. Electrochemical polarisation tests in 0.1 M HCl indeed revealed limited corrosion resistance of the FeCrAl matrix. Highlights • A TiC – 25 vol% (Fe-20 wt%Cr-5 wt%Al) powder was produced by high-energy ball-milling. • HVOF-sprayed coatings have < 1% porosity, H IT > 12 GPa and deposition efficiency ≈ 54%. • The coatings resist ball-on-disc sliding wear better than Cr 3 C 2 -NiCr at ≈ 25 °C and 400 °C. • Brittle cracking reduces their resistance to high-stress particle abrasion conditions. • Degradation of the FeCrAl matrix limits their electrochemical corrosion resistance. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive characterisation of HVOF- and HVAF-sprayed Cr 3 C 2 –25 wt.% NiCr hardmetal coatings. One commercial powder composition with two different particle size distributions was processed using five HVOF and HVAF thermal spray systems. All coatings contain less Cr 3 C 2 than the feedstock powder, possibly due to the rebound of some Cr 3 C 2 -rich particles during high-velocity impact onto the substrate. Dry sand-rubber wheel abrasive wear testing causes both grooving and pull-out of splat fragments. Mass losses depend on inter- and intra-lamellar cohesion, being higher (≥70 mg after a wear distance of 5904 m) for the coatings deposited with the coarser feedstock powder or with one type of HVAF torch. Sliding wear at room temperature against alumina involves shallower abrasive grooving, small-scale delamination and carbide pull-outs, and it is controlled by intra-lamellar cohesion. The coatings obtained from the fine feedstock powder exhibit the lowest wear rates (≈5x10 −6 mm 3 /(Nm)). At 400 °C, abrasive grooving dominates the sliding wear behaviour; wear rates increase by one order of magnitude but friction coefficients decrease from ≈0.7 to ≈0.5. The thermal expansion coefficient of the coatings (11.08x10 −6 °C −1 in the 30–400 °C range) is sufficiently close to that of the steel substrate (14.23x10 −6 °C −1 ) to avoid macro-cracking. [ABSTRACT FROM AUTHOR]

A Cr3C2-NiCr coating ( 5 y 106 μm.), was thermal-spray projected using different procedures (plasma, HVOF and HFPD) onto stainless steel specimens. This type of coating is normally used as protection against heat, corrosion and erosion actions encountered in superheater and reheater tubes in power plant boilers. The microstructures, porosities, oxide contents and microhardnesses of the coatings were determined. Thermal fatigue tests under simulative power plant service conditions were conducted in an experimental combustion chamber and, finally, the adhesion between the substrate and the coating layer was evaluated by means of tensile tests. The obtained results are discussed, and special attention was paid to the specific characteristics of the different spraying procedures.El material tipo cermet Cr3C2-NiCr fue empleado como recubrimiento con una granulometría entre 5 y 106 μm., siendo proyectado térmicamente por tres técnicas distintas : proyección por arco plasma no transferido (plasma), proyección mediante llama a elevada velocidad (HVOF) y la proyección por detonación a elevada frecuencia (HFPD) .Este tipo de recubrimiento es empleado como elemento protector frente al desgaste en elementos de calderas de vapor como son los sobrecalentadores y recalentadores de vapor, en donde las condiciones de servicio tan severas (alta temperatura, erosión por cenizas volantes, etc.) acortan notablemente la vida útil de los materiales convencionales empleados.Se determinan las microestructuras, porosidades, contenidos en óxidos y microdurezas de los distintos recubrimientos obtenidos. También se llevaron a cabo ensayos de fatiga térmica similares a las condiciones imperantes en el interior de una caldera mediante el empleo de un combustor experimental. Finalmente fue determinada la adherencia de las capas a los sustratos receptores mediante ensayos de tracción. Los resultados obtenidos son discutidos en función de las características específicas de los diferentes sistemas de proyección utilizados.

Cermets based cutting tools remain widely used in machining processes for their wear resistance. WC–Ni 3 Al cermets are potential replacements of WC–Co cermets in titanium machining due to their superior mechanical and chemical properties, especially at elevated temperature. In present study the reciprocating sliding wear behavior of WC–10Ni 3 Al was investigated using a ball-on-flat tester, with the Ti6Al4V sphere as the counter-face material. Meanwhile, the diffusion test between WC–10Ni 3 Al cermet and Ti6Al4V was conducted for further study of the reciprocating sliding wear mechanisms of WC–10Ni 3 Al. The WC–8Co was utilized as the reference material. The experimental results show that WC–10Ni 3 Al has a higher wear resistance than WC–8Co, for all the examined contact loads. Adhesive wear is the main wear mechanism for both WC–10Ni 3 Al and WC–8Co. The severer adhesion and element diffusion leads to the serious wear of WC–8Co surface, while WC–10Ni 3 Al can maintain the lower wear due to its low chemical affinity and element diffusion with Ti6Al4V, even under the high contact load. [ABSTRACT FROM AUTHOR]

Abstract: The aim of the current study was to investigate the effect of oxidation on abrasive wear behaviour of TiC based cermets at temperatures ranging from 20 to 900°C. Three types of material performance maps were constructed: oxidation rate maps, wear rate maps and maps showing the effect of oxidation on abrasion. Discussion on the performance of different cermet grades is supported by the SEM images combined with EDS and XRD analysis. The results should facilitate the selection of TiC-based cermets providing optimum composition of cermets for high temperature applications. [Copyright &y& Elsevier]

TiC-based hardmetal coatings containing 25 or 40 vol% Ni-20 wt%Cr matrix (hereafter TiC–25NiCr and TiC–40NiCr) were obtained by High Velocity Oxygen-Fuel (HVOF) and High Velocity Air-Fuel (HVAF) spraying, starting from high-energy ball milled feedstock powders. These coatings are intended as critical raw materials-free solutions against wear and corrosion. HVOF-sprayed coatings contain some more oxide inclusions than do HVAF ones, but, irrespective of the deposition conditions, TiC–40NiCr coatings are usually somewhat harder (800–900 HV 0.3) than TiC–25NiCr ones. They also exhibit lower wear rates in ball-on-disc sliding tests against Al 2 O 3 at room temperature. A hard asperity can indeed penetrate slightly deeper into TiC–25NiCr, as it deforms inelastically through microcracking. Bigger abrasive grooves are thus produced. The wear resistance of TiC–40NiCr coatings compares favourably to that of a Cr 3 C 2 -25% (NiCr) reference, and even approaches that of WC-10 wt%Co-4wt.%Cr. TiC–40NiCr coatings are also more corrosion resistant than both reference materials when tested by electrochemical polarization in a 3.5% NaCl solution. At 400 °C, to the contrary, TiC–25NiCr coatings exhibit better sliding wear resistance, whilst more severe abrasive grooving and adhesive tearing affect TiC–40NiCr samples. TiC–NiCr coatings are also unaffected by the transverse macro-cracking that was found to compromise the usefulness of WC-CoCr at 400 °C. • High energy ball-milled TiC–NiCr powders are suitable as thermal spray feedstock. • HVAF TiC–25NiCr and TiC–40NiCr coatings have lower oxidation levels than HVOF ones. • Despite different oxide contents, HVOF and HVAF coatings exhibit similar performances. • TiC–25NiCr has better sliding wear resistance than Cr 3 C 2 –NiCr at 400 °C. • TiC–40NiCr can substitute WC-CoCr against wear and corrosion at room temperature. [ABSTRACT FROM AUTHOR]