Improved Plasma Etching and Nitriding Technology for Enhanced PVD Coating Performance using Advanced Arc Enhanced Glow Discharge

Abstract

Plasma etching plays an essential role for the vacuum-based cleaning of tools and components to remove native oxide films and volatile contaminations on the surface of substrate materials. The pretreatment prior to PVD processes directly influences the adhesion and consequently the overall performance of the coating system. Therefore, different approaches such as bias based glow discharges (GD) and metal ion etching (MIE) methods are commonly conducted, which are however on the one side strongly limited in their etching rate as well as in their adaptability and on the other side lead to macro defects on the surface of the substrate reducing the performance of the coated tools. To overcome these challenges an improved etching process, which combines the high plasma density of cathodic arc evaporation with a noble gas-based glow discharge called advanced Arc Enhanced Glow Discharge (AEGD) is used. In this context, the unique possibility to independently control the bias potential and freely modulate the pulse pattern with a simultaneous scalable plasma density for the etching process open new possibilities in terms of pretreatments for PVD coated tools.

The resulting current on the handling system I_Bias was found to be an indicator for the intensity of the plasma activity and could be directly linked to etching rate and therefore was proving the independency and scalability of the AEGD process from the applied bias voltage. Compared to conventional glow discharge, advanced AEGD significantly increases the current on the handling current caused by an intensified ion bombardment, which leads to higher etching rates without negatively affecting the surface integrity of submicron-grained cemented carbide substrate materials, resulting in a better adhesion of AlTiN coatings. Additionally, for tool steels an adjusted composition of the plasma allows the nitriding of the surface near region, which leads to a graded hardness increase without forming a compound layer. The adhesion of the subsequently deposited coating was improved by the diffusion process due to the higher load carrying capacity. Thus, the advanced AEGD technology is effective in increasing the ionization degree of both the noble gas ion etching and plasma nitriding, allowing to significantly improve the performance of coated tools and components.