Super- and ultrahard nanacomposite coatings: generic concept for their preparation, properties and industrial applications

The generic concept for the design of novel superhard (and ultrahard) nanocomposites is based on a thermodynamically driven (spinodal) segregation in binary (and ternary or quaternary) systems which leads to a spontaneous self-organization of a stable nanostructure. Such a nanostructure and the related mechanical properties are stable up to high temperatures of greater than or equal to 1000degreesC. The unusual combination of mechanical properties, such as the superhardness of 40-100 GPa, a high elastic recovery of 80-95% upon a strain of greater than or equal to10% and a high resistance against crack formation are associated with that nanostructure. They can be understood in terms of conventional fracture mechanics scaled down to dimensions of 3-5 nm sized nanocrystals. We shall also discuss other so called "nanocomposite" coatings in which the enhanced hardness is not due to a nanostructure but due to a high compressive stress in these coatings and therefore decreases upon annealing at T greater than or equal to 450degreesC (e.g. MnN/M', M = Zr, Cr, etc., M = Ni, Cu, etc.). In the second part of the talk we shall give a brief overview of the recent industrial applications of the superhard nanocomposite coatings which became available on the market recently. (C) 2002 Elsevier Science Ltd. All rights reserved.