Redeposition layer formation caused by shading effect during sputter cleaning and associated damage on rake face of TiN coated high-speed steel drills

Abstract

The degradation of protective hard coatings has a detrimental influence on the performance of metalworking tools like universal drills. Not only do the chemistry and structure of the coating have an influence on the tool damage behavior, but also the tool production steps can cause coating/substrate interface artifacts which weaken the adhesion of the coating to the tool surface. As the current paper will show, the given cutting edge geometry of a drilling tool made of high-speed steel (HSS) caused diminished visibility of the rake face and is referred to as shading. The shading of the rake face caused numerous artifacts, which negatively affected the wear behavior of the tool and the titanium nitride (TiN) coating. Examples of artifacts were (i) different surface roughness for flank and rake face, (ii) burr formation on the rake face, (iii) decreasing coating thickness from flank to rake face, and (iv) a redeposition layer of sputtered material on the rake face. This paper is focused on the failure behavior of a redeposition layer. The layer's occurrence was caused by the redeposition of sputtered substrate material during the sputter cleaning with Ti+ ions and was mainly limited to the area near the cutting edge. An additional local influence through the given rake surface waviness was present. The redeposition layer was an indication of an insufficient sputter cleaning process, whereby chromium oxides remained on the matrix surface. As a result, the layer adhesion of the given TiN/HSS system was lowered significantly, and delamination occurred at the rake face near the cutting edge. This led to increased overall wear velocity and diminished tool lifetime.