Failure analysis of anti-friction coating for cylinder blocks in axial piston pumps

The present study deals with the wear behaviour and failure analysis of cylinder blocks belonging to an axial pistons pump. An anti-friction coating made of high-lead bronze was joined on the blocks by a casting process. The production parameters, in terms of cooling rate and casting temperature, were changed to optimize the performance of the coating by obtaining different microstructures. The blocks were subjected to full-scale wear tests by simulating the worst operative conditions in a test-bench. During the tests, the coating of some cylinder blocks failed after few hours. In order to obtain a correlation among such behaviour, wear performance and microstructure, failure analysis was carried out by means of optical and scanning electron microscopy with energy dispersive spectrometry (SEM/EDS). Confocal topography has been carried out to analyse wear tracks after the tests and to evaluate wear mechanism. The experimental tests showed that the failure of the coating was mainly due to the inhomogeneity in the distribution of lead segregations depending to the cooling rate of the casting process.