Thermal fatigue resistance of plasma duplex-treated tool steel

Thermal fatigue represents one of the most important stresses encountered i n technical applications like aluminum pressure die casting and hot forging . The resulting damage is the well-known heat checking phenomenon, characte rized by nucleation of a fine cracks network on die and insert surfaces. Us ually, many other detrimental stresses, i.e. wear, erosion -corrosion by th e molten aluminum and oxidation act during service, thus suggesting the int roduction of protective surface treatments. The beneficial effect of nitrid ing, PVD-coating and, more recently, of their combination in duplex systems , in counteracting these stresses has been proved. On the contrary, the coa ting influence on thermal fatigue resistance is not yet clearly established . in this paper the influence of plasma nitriding, multi-layer PVD coating (i.e. CrN, ZrN) and duplex treatment (plasma nitriding and PVD) on the ther mal fatigue resistance of AISI H11 hot work tool steel was studied. For thi s purpose a specific experimental apparatus, based on induction heating and water cooling, has been realized. Particular attention was given to plasma nitriding, used as pre-treatment in duplex plasma surface engineering. The role of compound layer, diffusion layer and coating(s) is discussed on the basis of the damage observed during the test. (C) 2001 Elsevier Science B. V. All rights reserved.