Tribology of NiCrAlY+Al2O3 composite coatings by plasma spraying with hybrid feeding of dry powder+suspension

Abstract

NiCrAlY layers containing different amounts of Al2O3 (0, 3, 6, 12, 18 wt.%) were deposited onto stainless steel substrates by a “hybrid” plasma spray process whereby the NiCrAlY powder was fed in dry form whilst fine Al2O3 powder, dispersed in ethanol, was injected through a suspension feeding system.\ud The Al2O3 reinforcement, consisting of fine, rounded particles interspersed within larger NiCrAlY lamellae, only causes marginal changes in hardness, due to the limited particles-matrix cohesion. Nonetheless, at room temperature, ball-on-disk dry sliding wear rates against sintered Al2O3 counterparts decrease from ≈5⁎10−4 mm3/(Nm) for pure NiCrAlY to ≈5⁎10−6 mm3/(Nm) with 18 wt.% Al2O3 addition. Pure NiCrAlY indeed suffers adhesive wear, whereas, on the composite coatings, the pull-out of some Al2O3 particles triggers the formation of a tribo-layer of smeared oxide fragments, which mediates the contact with the counterbody.\ud At 400 °C and at 700 °C, all wear rates are levelled to ≈8⁎10−5 mm3/(Nm) and ≈2⁎10−5 mm3/(Nm), respectively. An oxide layer grows on the NiCrAlY matrix upon high-temperature exposure, resulting in a tribo-oxidation wear mechanism, which makes the addition of Al2O3 irrelevant. At 700 °C, coatings are further strengthened by partial healing of interlamellar defects and by fine-grained β-NiAl precipitating within the metal matrix

Sliding and abrasive wear behaviour of HVOF- and HVAF-sprayed Cr3C2–NiCr hardmetal coatings

“…Ball-on-disk tests (ASTM G99) were performed using a High Temperature Tribometer (Anton Paar Tritec, Peseux, Switzerland). Sintered Al 2 O 3 spheres (nominal hardness HV E 1900) were employed as counterparts, since (as explained by the authors in a previous paper [46]) alumina is chemically inert and therefore not prone to produce additional tribochemical interactions, which would confuse the interpretation of wear mechanisms. Alumina is also suitable to simulate the occurrence of wear due to sliding against hard asperities, such as foreign particles, in-situ developed debris, hard phases contained in the counterbody (e.g.…”

Mechanical, Tribological, and Oxidation Resistance Properties of NiCrAlY Coating by Atmospheric Plasma Spraying

“…After 1,100 • C heat treatment, the NiAl phase is substituted by the Ni 3 Al phase. This result, probably due to the NiAl phase, would be expected in thermodynamic equilibrium conditions (Bolelli et al, 2015) and solidified in the matrix. Figure 3 shows the cross-sectional microstructures of coatings at different heat treatment temperatures.…”

Tribocorrosion Properties of NiCrAlY Coating in Different Corrosive Environments

“…To meet this requirement, the protective coatings are applied to protect the mechanical parts without changing the external structure. MCrAlY (M = Cobalt and/or Nickel) alloys with excellent oxidation resistance, corrosion resistance and wear resistance performance have been widely used in nuclear power, automotive and marine industries acting as the protective coatings [1,[7][8][9][10][11][12][13][14][15]. J. Chen et al investigated the tribocorrosion behavior of NiCoCrAlYTa coating in corrosion.…”