Nanocomposite (Ti,Al,Cr,Si)N HPPMS coatings for high performance cutting tools

Abstract

During the machining of high-speed steels, thermal and mechanical loads occur. This can influence the cutting performance and cause damage to the tools. Due to their high hardness, wear resistance and toughness, hard coatings are used to improve productivity. The development of a complex coating (Ti,Al,Cr,Si)N for cutting tools and a comprehensive analyses of the tools are objectives of the current research. The coating deposition was conducted in an industrial scale coating unit using a hybrid technology consisting of direct current and high power pulse magnetron sputtering (dcMS/HPPMS). Tungsten carbide was used as substrate material. To enhance the cutting performance, a nanocomposite architecture was developed which consists of crystalline (Ti,Al,Cr)N phases in an amorphous SixNy matrix. The oxide reaction layer that is formed on the coating's surface upon exposure to the atmosphere has a significant influence on the tool performance. Thus, the design of a diffusion-resistant coating system was proceeded by the synthesis of a thin oxynitride toplayer (Ti,Al,Cr,Si)ON. This has received little attention in the literature so far. The oxidation behavior of the coated samples under atmospheric conditions and the phase stability in a vacuum atmosphere were comprehensively analyzed at high temperatures up to T = 1300 °C. Under both conditions, detailed analyses on the diffusion between the workpiece material AISI M2 and the coatings were additionally performed. Furthermore, the influences of the pulse duration of the HPPMS cathodes and the bias voltage on the coating properties were investigated. A higher oxygen content in (Ti,Al,Cr,Si)ON compared to (Ti,Al,Cr,Si)N is achieved without changing the content of the remaining elements except for nitrogen. This allows the chemical composition of the reaction layer to be adjusted for specific purposes. The coated samples possess a high oxidation resistance and diffusion resistivity. Moreover, the coating systems exhibit a significant phase stability.