Studies of Erosion Resistance of Protective Coats on the Surfaces of Machine Elements Washed with Fluids

Abstract

This article indicated at erosion as one of the causes of degradation of surfaces washed by fluids and conditions of its occurrence. Corrosive – erosive theory of metal surface degradation has been discussed linking it with an instance of destructive processes taking place in cylinder liner blocks of combustion engines. Physics and conditions influencing processes on liquid – washed operational surface phase boundary have been justified. Out of the contemporary hypotheses explaining the physics of cavitation erosion, the bubble theory has been considered. A mathematical model of erosion has been presented in the context of cavitation implosion energy determining crash interactions of liquid cumulative fluxes on the washed surface. Occurring plastic deformations have been graphically explained linking them with the occurrence of fatigue micro-cracks and later with erosive pits. Influence of initial steel hardness on intensity of cavitation erosion has been checked. Discussion of ways to increase metal surface resistance to cavitation erosion has been carried out.

Studies on resistance to erosion of nickel and its alloys to be used in elements of fluid - flow machines

“…At present the theory of corrosive -erosive damage to cylinder liners of diesel engines has been widely acclaimed [1,2]. Practically all researchers believe that the pre-cause of damage to the cooled surfaces of liners and cylinder blocks is the turbulent interaction of liquid with the metal surface being the result of cavitation bubble implosion.…”

“…The change of pressure at any point of the liner surface washed by liquid may be evaluated with a dimensionless coefficient of local discharge [2]:…”

“…Their subsequent development leads to the formation of erosive pits in the form of craters. Figure 1 shows a diagram of metal damage caused by cumulative flux [2].…”

“…Frequently, in order to prevent erosive damage, technical literature suggests not very effective methods of increasing the hardness of the surfaces undergoing cavitation erosion. However, in the study [2] cavitation erosion intensity was defined by:…”

“…An important characteristics of metals from the point of view of their erosive resistance is their plasticity, which is shown in formula (7). Study [2,3] notes that plasticity of metals with hexagonal lattice is higher than those with face-centred lattice. Deformation of these metals appears as a slide along the [001] plane, which does not lead to strengthening of the surface layer, that is to work-hardening.…”