Impact of ion modification of HSS surfaces on the wear resistance of cutting tools with surface engineered coatings

The paper considers some ways to improve surface engineered coatings for cutting tools. These coatings were formed by two stages: diffusion saturation with nitrogen (ion nitriding) and application of the (Ti, Cr)N hard coating by means of the cathode arc plasma deposition process (CAPDP). The coating includes also an additional ion alloyed layer applied to the previously nitrided surface of HSS. Such multilayered coating makes it possible to significantly increase (in 2.1-2.4 times) the wear resistance of a cutting tool by extending the stage of normal wear. There were studied 16 chemical elements implanted into the base surface and those of four antifunctional materials effecting on the life of a HSS cutter with a surface engineered coating. It was shown that leading positions in wear resistance are taken by coatings with a modified sublayer of elements with high antifunctional properties. A compromise between the high wear resistance and reliability of a coating, which is characterized by a high adhesion to the substrate, is observed in the multilayered coating that contains a sublayer enriched with indium. Indium is present in the sublayer both in metal and bound states (In-N). The positive effect of indium on wear resistance appears to be tied with two types of phenomena developing on the friction surface. Acting as a liquid lubricant, indium in metal state leads to reducing the friction coefficient. At the same time, when heated at cutting, indium is partly oxidized with developing of oxygen-containing phases protecting the surface when passing from the normal stage of tool wear to the avalanche-like one. This is beneficial for prolongation the stage of normal friction, considerably enhancing the tool life. (C) 2001 Elsevier Science B.V. All rights reserved.