Topographic evolution of balls used in microabrasion tests

Abstract

This work aims to contribute to the understanding of the topographic modification of the surface of the counter-body during micro-abrasion and its complex relationship with specimen wear. The topographic evolution of the surface of five different balls (Ø25.4 mm) was monitored: one ceramic (Si3N4), one metal (AISI 52100 steel), and three thermoplastic polymers (polypropylene, polyacetal and polyamide 6.6). AISI 304 austenitic stainless steel specimens were tested in a fixed-ball micro-abrasion test rig using a silica slurry (10%wt. in water), rotation speed of 150 rpm, and total test time of 90 min (in 15 min intervals). The topographic evolution of the ball topography was monitored by laser interferometry of the abrasive tracks at each measurement interval, always in the same region. The parameters Sq, Sz, Ssk, Sku, λq, Sdq and Str were computed. Significant wear and changes of the surface topography of the balls were observed along the tests. Harder balls underwent evident grooving, while the softer polymeric balls showed fibrillation characteristics, alignment of polymeric chains and transfer film. For the initial 15 min of test, before reaching a steady-state wear regime, the softer balls (polypropylene, polyamide 6.6 and polyacetal) showed, in general, an increase in Sq, λq and Sdq, possibly by the generation of a transfer film on the surface, which was not observed for the harder balls. After the steady-state regime was achieved, all balls reduced their values of Sq, λq and Sdq. Plots of Sku x Ssk identified non-Gaussian height distribution curves (mostly with high kurtosis and negative asymmetry) for all balls. Sq and Sdq presented a linear relationship with the wear coefficients of the specimens (k) dependent on the material of the ball, whereas an overall linear relationship between λq and k was observed independently of the ball material. Str was a good indicator of aligned grooving abrasion, but showed a linear relationship with k only for the steel ball.