Improved tool performance through metastability in hard coatings

As a basis for modeling fractural mechanics, a new concept of PVD coatings has been developed using an advanced cathodic are technology. In comparison with the well-known TiN and TiCN, tests in several applications show that this concept can be a new approach to optimize tool lifetime and wear resistance. The specific features of the applied PVD cathodic are technology allows the deposition of partially metastable coatings, The use of the concept leads to an increased fracture toughness of the coating without the need of reaching hardness values towards that of diamond. The metastability of a part of the grains in the coating allows absorption of the propagation energy of the microcracks and therefore reduces the mechanical wear. With such coatings, solutions for dry machining, for machining stainless steels and other difficult materials can be offered to manufacturers of tools and to end-users. The validity of this 'metastability' model will be discussed and must be studied through additional tests measuring the improved fracture toughness of the coatings. This type of PVD metastable coatings in combination with soft top layers like MoS2 appears to have a promising future. (C) 1997 Elsevier Science S.A.