Experimental and numerical investigation of cavitation-induced erosion in thermal sprayed single splats

Abstract

Hydraulic components are coated by thermal spraying to protect them against cavitation erosion. These coatings are built up by successive deposition of single splats. The behavior of a single splat under mechanical loading is still very vaguely understood. Yttria-stabilized zirconia (YSZ) and stainless-steel splats were obtained by plasma spraying onto stainless steel substrates. The velocity and temperature of particles upon impact were measured and the samples were subsequently exposed to cavitation erosion tests. An acoustic cavitation simulation estimated the water jet velocity and hammer stresses exerted by bubble collapse on the surface of the specimen. Although the results suggested that high stress levels resulted from cavitation loading, it was clear that weak adhesion interfaces played a crucial role in the accelerated cavitation-induced degradation.

In-situ observations and acoustic measurements upon fragmentation of free-floating intermetallics under ultrasonic cavitation in water

“…Therefore, delamination followed by further crack formation and growth (as seen in Fig. 5 b) explains the observed ‘peeling off’ of layers governing the micro-fragmentation behaviour of Al 3 Zr primary crystals, similar to the mechanism discussed elsewhere for thermal-sprayed coatings [74] .…”

An equivalent method of jet impact loading from collapsing near-wall acoustic bubbles: A preliminary study

“…As seen in Fig. 9 , the instantaneous hammer pressure is about 1.3 GPa, which is of a similar order of magnitudes to the calculation values in the literature [46] , [47] , [48] .

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Ultrasonic Cavitation Treatment of Metallic Alloys

“…A jet of streaming flow during solidification could significantly affect solute diffusion, convection and transport phenomena at the solid-liquid interface, which in turn is associated with dendritic fragmentation, grain growth, instabilities and the morphological features of grains [55,56]. The flow pattern induced by the acoustic stream can be tracked visibly using transparent analogues such as water, glycerine and ethanol [57]. In the case of liquid melts, it is difficult to directly observe the flow pattern induced by acoustic streaming, however, with reference to the transparent analogues, numerical solvers can be used to predict acoustic streaming and its effect on temperature gradient, flow velocity and acoustic pressure gradients [37,38,[58][59][60][61][62].…”

“…The additional factors (temperature range, time duration and alloying elements) that contribute to deliver grain refinement when UST is applied below the melting or liquidus temperature in alloys are: (i) Increased number of nucleation events on heterogeneous potent particles compared to UST terminated above liquidus temperature [6,44,47,53]; (ii) Reduction in the temperature gradient of the bulk liquid under the action of acoustic streaming promoting nucleation on potent particles and assists the survival of grains [45,52,57,77];…”