COMBINATIONS OF COATING AND HEAT-TREATING PROCESSES - ESTABLISHING A SYSTEM FOR COMBINED PROCESSES AND EXAMPLES

High resistance of metals against wear, fatigue and corrosion can be a chieved by several different treatments, like thermal, mechanical, the rmochemical and coating processes. Combining successful single process es into one treatment can result in an even higher resistance of mater ials against complex loads, e.g. superimposed wear, fatigue and corros ion, because of the addition of the single process advantages. For a s ubstantial choice of technical and economical promising combinations, a classification for combined processes was set up. The single process es were divided into five groups: thermal, mechanical, thermochemical, ion implantation and coating processes. A 5X5 matrix out of these fiv e groups was set up, which contains a large number of possible combine d processes. This matrix holds for steels as well as for non-ferrous a lloys. The potential of different combined processes was analyzed theo retically and experimentally. Several combined processes for steels an d non-ferrous metals were reviewed, popular combined processes for ste els are thermochemical treatment and coating as well as coating and th ermal treatment. Examples like carburizing and CVD, nitriding and PVD, CVD and quench hardening, and CVD and induction hardening will be pre sented. The combined process CVD and quench hardening illustrates the principle of combined processes: The high hardness of the thin CVD-coa ting is supported by the high strength of the quench hardened steel su bstrate. Examples for non-ferrous alloys are plasma nitriding and prec ipitation hardening of aluminum alloys and also nitriding and CVD of t itanium alloys. These examples will highlight the great potential of c ombined processes. (C) 1998 Elsevier Science S.A. All rights reserved.