Laser-structured high performance PVD coatings

Abstract

Structured plastic components, which are used for flow-optimization, self-cleaning surfaces and optical applications, are usually produced by injection molding using structured tools. A suitable technique for structuring these tools on macro and nanometer scales is laser ablation, which offers a high level of accuracy and flexibility. The influence of laser treatments for the fabrication of nanostructures on the surface properties of steel has been extensively investigated. In contrast, there are only few studies dealing with the cause-effect mechanisms between a corresponding laser treatment and PVD (physical vapor deposition) hard coatings.This work deals with the influence of a laser nanostructuring on the properties of different CrAl-based PVD hard coatings. For this purpose, three coatings, one nitride (Cr,Al)N and one oxynitride (Cr,Al)ON, as well as one CrN/AlN nanolaminate were deposited on steel AISI 420 (X42Cr13, 1.2083) using a PVD process. The coatings were structured by means of an ultra-short pulsed (USP) laser with a varying laser pulse energy (Ep) ranging from Ep1=0.005mJ over Ep2=0.011mJ to Ep3=0.018mJ. On the one hand, an increasing laser pulse energy leads to significantly greater structural depths. This was quantified by confocal laser scanning microscopy (CLSM). On the other hand, it has been found that, in excess of a certain laser pulse energy, the universal hardness of the coatings decreases. By means of microstructural investigations, such as X-ray diffraction (XRD) and transmission electron microscopy (TEM), this effect was investigated and characterized. It was found that thermal effects induced during laser structuring lead to an increasing ratio of amorphous to crystalline domains of the PVD coating, causing the reduction in hardness. Finally, suitable combinations of PVD hard coatings and laser structuring parameters are recommended.