Superhard i-C coatings used in complex processes of surface strengthening of tools and machine parts

Abstract

A study of the mechanical properties of i-C coatings deposited onto substrates of different materials indicated that the plastic strain of the substrate had a considerable effect on the measured values of microhardness and elastic modulus, and on the fracture toughness, fatigue strength and other mechanical properties of the coatings. These characteristics determine the efficient use of i-C coatings on tools and on friction surfaces of machines. A greater effect of i-C coatings on the increase in wear resistance of tools and machine parts can be achieved at the expense of hardening the surface layer between the base of the machine part and the i-C coating. At the same time the surface strains are reduced and the contact resistance increases. To ensure complex strengthening of tools and machine parts, a “Thermion” installation was developed. The automated modular complex allows ion-diffusion alloying (nitriding, carbonitriding and others) of metal substrates to a depth of up to 100 μm, the deposition of multilayer cermet coatings of up to 10 μm in thickness, and the deposition of a superhard i-C coating at both low ( T ≲ 600 °C) and high ( T ≳ 900–1000 °C) substrate temperatures. The installation is the result of developments of a team including specialists from the Ukraine, Estonia, Belorussia, R.S.F.S.R., Poland, Romania and East Germany. The “Thermion” installation comprises a vacuum electric arc device in combination with a magnetron or electron-beam source used for evaporation, ionization, destruction and excitation of the substances deposited. In the process of ion-vacuum treatment, an r.f. voltage is applied to the substrate holder which ensures additional stimulation of plasma-chemical processes owing to a rise in electron temperature and a degree of discharge unbalance, and excludes break-through of the surface of the machine part treated by plasma. The potentials of the installation are shown by examples.