New multilayered coatings for high speed cutting
High speed cutting technology has traditionally been the best way to increase both the efficiency and precision of metal cutting processes. However, new alloys now exist which are particularly difficult for machining. Furthermore, important environmental and health concerns have precipitated a reduction in the use of cutting fluids as lubricants and refrigerating agents during the cutting process. Cutting fluids are a significant source of waste and are expensive to dispose of; they are also linked to respiratory illnesses and cancer. The HIPERCUT project developed a new generation of tools for use in high speed machining. The work undertaken by Tekniker focussed on multiple layers based on chromium nitride (CrN), alternating with aluminium titanium nitride (AlTiN) and interlayers of chromium aluminium titanium nitride (CrAlTiN) to improve adhesion. Scratch tests determined the level of coating adhesion, showing a critical load of 60N for TEK011 samples and about 80N for TEK012 samples. In neither case was delamination or flaking of the coating observed. The coating also demonstrated excellent oxidation behaviour at temperatures in the range of 700°C to 900°C. Plastic hardness was around 50GPa for the multilayer, taking into account plastic recovery. Young's modulus, used for determining stiffness, was 450GPa with 66% elastic recovery. Researchers selected different AlTiN and AlTiN/CrN based multilayer processes in order to investigate the reliability of coating procedures with regard to adherence, hardness and thickness. The process was then scaled up for an industrial sized physical vapour deposition (PVD) chamber. The PVD chamber deposited a thin film through the condensation of a vaporised form of the material onto a surface. Scientists used the chamber to determine the variation in chemical composition, the thickness of each monolayer period, the total thickness, and hardness.
