HPPMS (Cr1-xAlx)N WSy Coatings for the Application in Dry Cold Forging of Steel: Sythesis and Raman Characterization

Abstract

Lubricants are applied to reduce friction between workpieces and forming tools in cold forging processes. There is a strong demand to avoid lubricants due to economic, ecological and legislative aspects. PVD coatings took over the tasks of lubricants in numerous applications in the recent years. They may enormously reduce tool and workpiece wear in cold forging or deliver special functions even in the absence of lubricants. However, the abdication of lubricants goes along with the requirement that the dry tribological system has to withstand the increased tribological loads in dry metal cold forging of steel. The combination of (Cr1-xAlx)N and WSy within a PVD coating by means of high power pulsed magnetron sputtering (HPPMS) to gain outstanding tribological properties of WSy with increased abrasive wear resistance of (Cr1-xAlx)N is a promising candidate in order to replace lubricants on highly loaded tools in dry cold forging. HPPMS technology offers outstanding advantages in terms of dense morphology and high hardness. Using HPPMS-technology, complex-shaped forging tools with surfaces oriented non-parallel to the target can be coated as well. The aim of the current contribution is the investigation of the HPPMS (Cr1-xAlx)N WSy coatings by means of Raman spectroscopy. These coatings were deposited on 1.2379 tool steel using an industrial scale PVD unit. Tribological model tests were conducted using a Pin-on-Disc tribometer (PoD) which simulates dry contacts in cold forging. The analysis of tribological properties included the determination of friction coefficients and wear rates. The contact region was analyzed by Raman spectroscopy after the tribological tests. The investigated (Cr1-xAlx)N WSy coating is a promising candidate to avoid to use of lubricants for the application in dry cold forging process of steel.