Comparative study of surface modification techniques through average flank wear in high speed steel tools coated with thin TiN film

Abstract

Hard coatings are usually applied to improve high speed steel (HSS) tools performance. However, to achieve this aim, a good adhesion between coating film and substrate is necessary. The coating failure, associated to the lack of adhesion to the substrate, can lead to tool premature wear, reducing its efficiency. The surface modification can improve the coating film adhesion levels by modifying substrates surface roughness, and then, ensuring better anchorage of the deposited layer. In this research two techniques of superficial modification, planar sputtering and chemical polishing, were compared. The sputtering uses plasma application, where cations formed in the reactor collide with samples surface, removing material from it. For chemical polishing, it was used acid and alkaline solutions. After surface treatments, all roughness levels were measured using a roughness tester. The Cathodic Cage Plasma Nitriding (CCPN) technique was used to deposit a TiN film on tools surface. Then, X-ray diffraction, Vickers microhardness and SEM tests were carried out to verify the presence of deposited film, as well as its thickness and mechanical properties, and then, machining tests with SAE 1045 steel where performed, applying the coated tools. Optical microscopy was carried out to track average flank wear up to 0.3 mm, characterizing the end of tool life. It can be observed that all the coated tools obtained an increase in its life, registering the variances according to the different roughness profiles. The best results were verified for chemical polishing with acid solution treatment condition, as it allowed longer machining time with less flank wear.