Sliding wear evaluation of hot isostatically pressed thermal spray ceramet coatings

Abstract

The principal aim of this study was to compare the sliding wear performance of as-sprayed and Hot Isostatically Pressed (HIPed) thermal spray cermet (WC-12Co) coatings. Results indicate that HIPing technique can be successfully applied to post-treat thermal spray cermet coatings for improved sliding wear performance, not only in terms of coating wear, but also in terms of the total volume loss for test couples. WC-12Co coatings sprayed by a HVOF system were deposited on SUJ-2 bearing steel substrate and then encapsulated and HIPed at 850°C for one hour. A high frequency reciprocating ball on plate rig was used to measure the sliding wear resistance of these coatings in dry conditions under steel and ceramic contact configurations at two different loads. Results are discussed in terms of coating microstructure, microhardness, fracture toughness and residual stress evaluations. Microstructural investigations indicate fundamental changes in grain morphology, whereas x-ray diffraction revealed beneficial transformations in phase composition of these coatings during the HIPing post treatment. The effects of these microstructural changes on the physical properties and wear resistance are discussed.

Influence of Post-treatment on the Microstructural and Tribomechanical Properties of Suspension Thermally Sprayed WC–12 wt%Co Nanocomposite Coatings

“…The K IC of coating was approximated from a previous investigation by the authors [39], keeping in view the carbon deficiency of S-HVOF coatings; hence, a lower-bound values are used in this analysis. The difficulty in measuring the fracture toughness of brittle thermal spray coatings has previously been discussed [33,38]. The fracture toughness of the ball material was not directly included in this analysis as for the steel and WC-Co balls, fracture dominated wear mechanism was not observed.…”

Sliding Wear of Conventional and Suspension Sprayed Nanocomposite WC-Co Coatings: An Invited Review

“…Post-treatment of WC-Co coatings improves their wear performance by reducing porosity, and enhancing adhesion between splats and to the substrate (Ref 75, 76). Heat treatment, laser remelting and hot isostatic pressing (HIPing) are the main post-treatment methods used for thermal spray coatings ( Ref 15,75,102,[134][135][136]. Each of these methods has its respective benefits, as listed below.…”

“…The role of residual stress in the sliding wear process has been investigated ( Ref 54,134,166); however, it has not been included in the semiempirical mathematical models of sliding wear rate or numerical modelling. Note though that the numerical approach discussed in ''Computational Wear Modelling'' section can be adapted to include the throughthickness residual stress profile incorporated within the FEM of sliding wear.…”

An improved Vickers indentation fracture toughness model to assess the quality of thermally sprayed coatings

“…It should be noted that mismatch in the coating and substrate properties (e.g. hardness, elastic modulus) also influence the extent of coating failure [14][15][16]. The effect of the coating on the substrate deformation can be neglected where the indentation depth is considerably lower than the thickness of the coating.…”

“…The durability of thermal spray coating for wear and fatigue applications [13][14][15][16] is dependent upon a combination of coating and substrate properties including resistance to fracture within the coating (cohesive failure) or at the coating substrate interface (adhesive failure). Fracture toughness of the coating, both parallel and perpendicular to the direction of spraying due to its lamellar microstructure, ability of the substrate to support coating under indentation or contact stress, role of residual stress are some of the key design factors controlling the performance of coated components.…”