Analysis of incubation period versus surface topographical parameters in liquid droplet erosion tests

A novel approach to identifying the incubation time in liquid droplet eroded materials/coatings was explored by using metrological methods. Links were investigated between surface texture characteristics and the ending of the incubation period. The usual practice within erosion testing is to record the change in mass of the sample or to observe the appearance of the sample to establish an estimate of the time to failure. The primary objectives of this work were to: (1) measure and compare surface topographical parameters of eroded surfaces in both two dimensional (2D) and three dimensional (3D); (2) identify parameters that could be used consistently and were robust in terms of noise filtering; and (3) analyze the relationship between the incubation period and the variation of the surface topographical parameters. The failure mode of the coating was the most important aspect in the relationship between the two factors investigated. AA2024-T3 clad was shown to have a progressive damage mechanism, due to its ductile nature. The relationship between the PS_a (arithmetic mean surface area primary profile) values and the mass loss values was seen to be linear after the incubation period. However, the analyses of the erosion protection coatings showed different failure mechanisms that were not generally preceded by significant changes to the surface condition. The 2D data was seen to be relevant when compared to the 3D areal surface parameters. The incubation period can be identified in certain liquid droplet eroded materials by using the surface topographical data and comparing to experimental results.