Impact of duplex plasma nitriding and AlCrN coating on mechanical, tribological, and corrosion properties of H13 tool steel

This study examines the impact of a duplex surface treatment, combining plasma nitriding and AlCrN coating, on the mechanical, tribological, and corrosion properties of H13 hot-work tool steel. The substrate was plasma-nitrided at 480 °C for 12 h in a N 2 /H 2 atmosphere (1:7 ratio) and subsequently coated with AlCrN using cathodic arc physical vapor deposition. Surface characterization included adhesion testing (VDI 3198), pin-on-disc wear testing (5 N load, 500 m sliding distance), XRD, FE-SEM, and electrochemical evaluation in 3.5 wt.% NaCl solution. The surface hardness increased from 1224 HV (AlCrN) to 1602 HV (duplex), and after the Johnson–Högmark modification remained around 1710 HV, confirming that plasma nitriding strengthened the substrate without degrading the coating microstructure. Adhesion improved markedly from HF4 to HF1. The specific wear rate decreased by approximately 68%, from 1.28 × 10 -4 to 4.10 × 10 -5 mm 3 ·N -1 ·m -1 , while the friction coefficient dropped from 0.672 to 0.396. Electrochemical studies indicated that both coatings significantly enhanced corrosion resistance compared with the bare substrate. Potentiodynamic polarization results showed that the corrosion potential shifted from –0.52 V (AlCrN) to –0.60 V (duplex), and the corrosion current density reached 2.21 × 10 -6 A·cm -2 . Qualitative EIS analysis revealed a single capacitive loop for all samples, with the AlCrN coating exhibiting a slightly larger semicircle and thus higher polarization resistance than the duplex-treated sample. Nevertheless, the duplex coating maintained a high impedance magnitude (|Z| > 10 4 Ω·cm 2 ), confirming that the nitrided diffusion layer remained an effective barrier against corrosion propagation. Overall, the duplex process simultaneously enhanced hardness, improved wear resistance, and preserved a satisfactory level of corrosion stability, making it suitable for die and mold applications subjected to severe wear conditions.