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Effect of PVD films wet micro-blasting by various Al2O3 grain sizes on the wear behaviour of coated tools

Micro-blasting on PVD films has been documented, among others, as an efficient method for inducing
compressive stresses, thus for increasing the coating hardness and potentially tool life of coated tools. Since
contradictory results have been registered concerning the efficiency of wet micro-blasting on coated tools for
improving the wear behaviour, the paper aims at explaining how this process can be successfully applied for
post-treatment of PVD films. In this context, the employed conditions such as pressure and grain size affect
significantly the wear resistance of the micro-blasted coated tools.
In the described investigations, TiAlN coatings were post-treated through wet micro-blasting by Al2O3
abrasives of various grains' diameter. Abrasion mechanisms after micro-blasting were investigated by
roughness measurements. Nanoindentations on micro-blasted film surfaces at various pressures revealed the
influence of this process on coating superficial hardness. The related residual stress changes were estimated
considering the film yield stress alterations, which were analytically determined, based on nanoindentation
results. Nano-impact tests were conducted for investigating the effect of the developed film compressive
stresses at certain micro-blasting pressures and grain sizes on the film's brittleness. To monitor film thickness
and cutting edge radius changes of coatings subjected to micro-blasting, ball cratering tests and white light
scans were carried out respectively. In this way, micro-blasting conditions for improving the film hardness,
without revealing the substrate in the cutting edge region, were detected. Finally, the wear behaviour of
coated and variously wet micro-blasted tools was investigated in milling of hardened steel.