Tribological characteristics of WC-based claddings using a ball-cratering method

Tungsten carbide-based thick coatings are used as wear resistant claddings or surface overlays in industrial applications to counter erosive and/or abrasive wear problems. Three-body abrasive wear behaviour of infiltration brazed tungsten carbide (WC) claddings was investigated using a ball-cratering method, a version with a free ball, with slurry containing 150-300 µm silica sand particles. Three WC claddings tested had different volume fractions and size distribution of carbides that resulted in their different bulk hardness and the matrix was a Ni-Cr based alloy. It was found that the wear rates of all WC claddings were almost constant with testing time or distance travelled by a rotating ball. The wear rates were independent of the slurry delivery rate and did not increase with increasing rotating ball roughness. The wear rates were affected by the material characteristics of WC claddings such as the volume fraction of carbides, directly related to bulk hardness, and carbide size distribution. SEM examination found that three-body rolling wear was a dominating wear mechanism. The softer matrix was worn out preferentially, leaving behind protruding and weakly-supported carbides. Small solid carbides were then dislodged and larger cemented WC/Co carbides were gradually worn out by a combination of microcracking and attrition. The abrasive characteristics of WC claddings in the ball-cratering tests were then compared to the characteristics of nominally identical materials in the standard ASTM G65 and G76 tests, as reported in the literature, and similarities and differences found are reported. Also, the in-field wear mechanisms found in the WC cladding were compared to the mechanisms observed in the ball-cratering tests

Three-body tribocorrosion of high-chromium cast irons in neutral and alkaline environments

Two high-chromium cast irons (HCCIs) with different microstructure and Cr:C ratio of 9 and 6 were tested using a new three-body abrasion-corrosion rig incorporating electrochemical techniques. Coarse garnet particles acted as abrasive grits and the effect of mechanical parameters (i.e. load, sliding distance) was investigated. Electrolytes with different pH, neutral and alkaline were used and the effects of chloride ions and elevated temperature were also tested. SEM and optical profilometry were used to analyse the extent of abrasion-corrosion damage and the surface morphology.In the corrosion-only tests it was found that the corrosion rate increased with increasing pH, and both the chloride ions and elevated temperature had a detrimental effect. Increasing alkalinity has shifted the anodic behaviour from the matrix to the carbides. The influence of key alloying elements on the corrosion behaviour is also addressed.Electrochemical measurements revealed that the concurrent three-body abrasion had accelerated corrosion for both HCCIs in most environments tested. The following abrasion-corrosion mechanism for HCCIs in highly alkaline solutions is proposed: (i) removal of a thin oxidized layer from the carbide phase; (ii) plastic deformation and extrusion of the Fe-Cr matrix over the carbide-depleted regions. SEM images revealed repeated plastic deformation with the wear morphology similar to the three-body abrasion of ductile materials, and carbides were not visible. In neutral environments the carbide/matrix interface was the most vulnerable to corrosion initiation, with the matrix dissolving preferentially and the unsupported carbides fracturing. The influence of materials characteristics on the abrasion-corrosion synergistic action is also described in this paper

The effects of particle angularity on low-stress three-body abrasion-corrosion of 316L stainless steel

© 2016 Elsevier Ltd This study investigates the effects of particle angularity on the tribo-electrochemical behaviour of 316L stainless steel under low-stress three-body abrasion–corrosion conditions. Different angularity particles were delivered to the interface between the samples and a rotating rubber counterface, while changes in current with time were potentiostatically monitored. Based on a linear relationship existed between tribological factors (load and speed) and the average current evolved, an empirical correlation is proposed and possible underlying mechanisms are discussed. The effects of particle angularity on the surface and sub-surface damage are also demonstrated. It was found that increasing particle angularity improved their depassivation efficiency

In vivo imaging of the human eye using a 2-photon-excited fluorescence scanning laser ophthalmoscope

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