Quasi-industrial accelerated testing of a HIPIMS deposited nano-layered CrAlYN/CrN coating for improving hot forging die life of nitrided H13 steel

Die life is a major concern in the hot forging sector because of ramifications for productivity and costs. Despite surface engineering technologies being an established route to protecting against die surface degradation, to the authors' knowledge there are no reports of a high-power impulse magnetron sputtering (HIPIMS) deposited coating having been trialled for this purpose. In this study, a 0.8 μm thick CrAlN base layer followed by a 9.0 μm CrAlYN/CrN nanoscale multilayer was deposited via HIPIMS onto a HIPIMS-pretreated nitrided H13 tool steel. The comparator was nitrided H13. An accelerated test method employed an industrial-scale screw press to forge 260 Inconel 718 billets onto a model die that was designed to exacerbate susceptibility to damage. Billets were preheated to 1000 °C and the tools were held at 250 °C. These conditions were sufficient to induce in the nitrided only die many of the damage mechanisms that variously determine real-world hot forging tool life. In contrast, the coating did not suffer abrasive wear or thermomechanical fatigue cracking and was considerably more resistant to oxidation and pick-up. Additionally, the coating provided excellent thermal insulation of the substrate and, hence, protection against thermal softening-induced plastic yield. It did not, however, protect against mechanical fatigue, with cracks occurring in the same single region of both dies. Although these led to localised complete loss of coating, the substrate was protected until such point and the onset of wear was significantly delayed.