A duplex treatment consisting of plasma nitriding (PN) and physical vapor deposition (PVD) significantly improves the thermal, tribological, and corrosion resistance of forming tools, and especially if they are intended for applications subject to high mechanical loads. This study investigates the influence of nitriding on the properties of a conventionally heat‐treated AISI D2 tool steel, coated with a Cr‐Al‐Ti‐B‐N layer, while the effect of the presence or absence of a compound layer is discussed. PN is performed at 510–520°C using different N2‐H2 gas mixtures. The Cr‐Al‐Ti‐B‐N layers are deposited at 480°C using a combination of cathodic arc evaporation and magnetron sputtering. The samples are characterized using electron probe microanalysis with wavelength‐dispersive X‐ray spectroscopy, optical and scanning electron microscopy, glancing‐angle X‐ray diffraction, surface hardness measurements, profilometry, Rockwell indentation, and scratch tests. These techniques reveal relationships between the depth gradient of the chemical composition and microstructure of the nitrided interlayer, the adhesion of the PVD coating, and the hardness of the tool steel. Although the PVD process induces a structural transformation in the compound layer, this transition does not have a negative influence on the adhesion of the PVD coating.

The dry sliding wear behavior of AISI D2 tool steel is investigated under different heat treatment states in hardened, plasma nitrided, and duplex layer conditions. Plasma nitriding (PN) is performed at 510-520 • C with varying N 2 -H 2 gas mixtures, and Cr-Al-Ti-B-N layers are deposited at 480 • C by means of physical vapor deposition (PVD). This work investigates the influence of the nitride layer and, in particular, the presence of a compound layer on the tribological behavior of the duplex layer system. Therefore, as-nitrided conditions both without and with a compound layer -as well as with a mechanically removed compound layer -are subsequently hard coated. Comparative ball-on-disc wear tests in linear-reciprocating sliding motion against WC-Co counterbody balls are conducted at a load of 120 N. Compared to sample states without a compound layer, the as-nitrided states with a compound layer exhibit improved wear coefficients. In contrast, all duplex layer states exhibit comparably low friction coefficients and low wear coefficients independently of the presence of a compound layer.Removal of the compound layer prior to PVD coating leads to a significant reduction in wear resistance due to reduced surface roughness before the hard coating and the associated change in the bonding between the nitride layer and hard coating. K E Y W O R D Scompound layer, duplex surface engineering, friction and wear, plasma nitriding, PVD hard coating INTRODUCTIONTool steels are the preferred materials for most fields of application with demanding tribological working conditions -such as die casting, forging, stamping, cutting, and rolling. [1][2][3] One widely used representative of this group of steels is X155CrVMo12-1 (AISI D2), which is applied in complex applications involving, for example, high normal loads and sliding speeds. 4,5 In order to counteract the associated reduction in tool life, hard coatings produced by surface treatment techniques such as plasma nitriding (PN) and physical vapor deposition (PVD) hard coating are commonly applied. PN affords significant improvements in surface hardness, fatigue strength, corrosion, and wear resistance 3,4,6 compared to conventional steels. However, nitrided layers do not provide sufficient resistance in highly aggressive environments or under heavy mechanical stresses. [2][3][4]6,7 PVD hard coatings are mainly used because of their high hardness and excellentThis is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

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