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

Abstract

This study presents an improved approach to the quality assessment of thermally sprayed coatings. Measurements were carried out on five different coatings. Since it is the overall extent of surface cracking during Vickers indentation that is indicative of the volumetric damage, the surface crack length was measured, including the radial cracks, edge cracks, and other cracks around the indentation. It is concluded that the proposed model provides a way forward for determining the fracture toughness (K 1c ) of brittle materials where no radial cracks are developed. An elastic-plastic finite element simulation of the Vickers indentation test was conducted to locate the stress fields.

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

“…Another reason for the relative increase in hardness is the densification of the coating (i.e., solidstate diffusion at high temperature). Although porosity was not quantified in the current study due to pullout of loose particles, the mechanism of densification or collapse of porosity during HIPing can be seen in the published literature [39]. Previous studies on WC-based hardmetal coatings have indicated a similar trend of hardness after the HIPing post-treatment [15,16].…”

“…In terms of coating wear rate, the trend is similar to that of total wear rate except for steel ball couples where HIPing post-treatment of S-HVOF coatings shows an increase in wear rate. Previous research has shown that the increase in elastic modulus after HIPing post-treatment also results in an increase in fracture toughness of WC-Co coatings [15,16,39]. There was also an increase in hardness after HIPing due to crystallization and densification.…”

“…The deposition efficiency was slightly lower than that obtained from conventional HVOF spray process. In order to compare performance against standard HVOF coatings, HVOF-JK (Jet Kote) coating was deposited using WC-12 wt%Co agglomerated and sintered powder using industrially optimized coating process parameters [38,39]. All coatings were deposited on AISI440C steel disks of 31 mm diameter and 6 mm thickness.…”

“…Tables 8 and 9 provide the physical parameters for coating and ball material for establishing the semiempirical models of wear rate. 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].…”

Particle in-flight behavior and its determining the microstructure and mechanical properties of zirconia based thermal barrier coatings

“…The Vickers indentation were performed on the polished cross section of the coating, which were measured at least 20 times in random different areas with a load of 2.94 N and 10 s holding time and keeping at least five times greater than the diagonal length of indentation between consecutive indentations. The Weibull statistical analysis was used to analyze the scatter of micro-hardness data, which distribution characteristic of the mechanical property can reflect the microstructural characteristic of the as-sprayed coatings [17][18][19].The fracture toughness of as-sprayed coatings was determined by [20],…”