The Use of Acoustic Emission to Characterize Fracture Behavior During Vickers Indentation of HVOF Thermally Sprayed WC-Co Coatings

Abstract

This paper describes how acoustic emission (AE) measurements can be used to supplement the mechanical information available from an indentation test. It examines the extent to which AE data can be used to replace time-consuming surface crack measurement data for the assessment of fracture toughness of brittle materials. AE is known to be sensitive to fracture events and so it was expected that features derived from the AE data may provide information on the processes (microscale and macroscale fracture events and densification) occurring during indentation. AE data were acquired during indentation tests on samples of a WC-12%Co coating of nominal thickness 300 lm at a variety of indentation loads. The raw AE signals were reduced to three stages and three features per stage, giving nine possible indicators per indentation. Each indicator was compared with the crack profile, measured both conventionally and using a profiling method which gives the total surface crack length around the indent. A selection of the indents was also sectioned in order to make some observations on the subsurface damage. It has been found that reproducible AE signals are generated during indentation involving three distinct stages, associated, respectively, with nonradial cracking, commencement of radial cracking, and continued descent of the indenter. It has been shown that AE can give at least as good a measure of cracking processes during indentation as is possible using crack measurement after indentation.

Structure Property Relationship of Suspension Thermally Sprayed WC-Co Nanocomposite Coatings

“…Industrially optimized coating process parameters were used for the conventional coatings. The fracture response of these conventional HVOF coatings has previously been reported by the authors [36].…”

Sliding wear investigation of suspension sprayed WC–Co nanocomposite coatings

“…Industrially optimized coating process parameters were used for these conventional HVOF coatings. The fracture response of the HVOF-JK coatings has previously been reported by the authors [43]. HVOF-JK is a first generation HVOF spray gun which is gas-fuelled.…”

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

“…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.…”

“…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.…”