Joint second prize - Significance of Y and Cr in TiAlN hard coatings for dry rich speed cutting

High speed cutting of die steels (A2, HRC58 15 000 rev min(-1), 385 m min(- 1)) demands high wear and oxidation resistant and extremely well adherent c oatings. PVD is the preferred deposition technique to tailor a coating for this application. With the development of TiAlN based hard coatings, an imp ortant step in the direction of improved cutting performance has been achie ved. TiAlCrYN is a state of the art coating, which has proven to be very su ccessful in demanding dry high speed cutting operations. A special feature of this coating is a double layered overcoat consisting of a lower fine mul tilayered TiAlYN/CrN with a periodicity of 1.6 nm graded into an upper glas sy amorphous TiAlY oxynitride. The incorporation of Y leads to an enhanced oxidation resistance, whereas the most important effect of the double layer ed overcoat is the reduction of the friction coefficient. To confirm the be neficial effects of Y and Cr, sophisticated TEM has been employed with an X -ray resolution of approximately 3 nm. Segregation of Y and other elements in this system (tool/coating) were detected along the column boundaries in the TiAlCrYN coating at 900 degreesC. Y is acting like a 'plug' against bot h inward and outward diffusion of foreign elements. The oxidation behaviour has been further quantified using highly sensitive thermogravimetric analy sis and glancing angle X-ray diffraction. The successful impact of the inco rporation of Y into TiAlCrN and the use of a Cr containing nanostructured o xynitride sputter deposited overcoat is shown by coated two flute ball nose d solid carbide cutters at a cutting speed of 385 m min(-1). (C) 2001 IoM C ommunications Ltd.