Abstract
Abstract In plastics industry molding tools are subjected to adhesive and abrasive wear as well as to corrosion. In this regard, (Cr, Al)N hard coatings deposited by physical vapor deposition (PVD) have a high potential to be used as protective coatings. The high power pulse magnetron sputtering (HPPMS) technology offers several advantages with regard to the deposition of hard coatings. Variation of the pulse length has a significant influence on the current–voltage-characteristic (I–U) of the cathodes, the chemical composition and the mechanical properties of the (Cr, Al)N coatings as well as on the reaction layer on the coating surface, which affect the interactions between the coated tool and the plastic melt in terms of adhesion. The present work deals with investigations of the influence of HPPMS pulse length at constant pulse frequency on the reactive gas N 2 in the deposition process and on the adhesion behavior of (Cr, Al)N coatings towards plastic melt. For this reason, the HPPMS plasma was analyzed at the substrate side via a retarding field energy analyzer (RFEA) and energy resolved mass spectrometer (MS). The RFEA was used to determine ion current densities at different HPPMS pulse length of t on = 40 μs, 80 μs and 200 μs. The MS was used to analyze the intensities of Cr + , Al + , N + and N 2 + in the HPPMS plasma. The results revealed that a decrease of the pulse length leads to an increased ion current density as well as an increased dissociation of molecular nitrogen, which has a significant influence on the chemical composition of the coating. Furthermore the adhesion behavior between coating and plastic melt is influenced by the pulse parameters via the changed chemical composition of the reaction layer on the coating surface. Based on these results, coatings with desirable mechanical properties with regard to wear resistance in plastics processing and a passive layer designed to ensure low adhesion of the plastic melt shall be developed.
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