Response to thermal cycling of CAPVD (Al,Cr)N-coated hot work tool steel

The principle failure mechanism in thixoforming dies is thermal fatigue as the mechanical loading on the tooling is modest owing to a mushy feedstock. X32CrMoV33 hot work tool steel samples coated with (Al,Cr)N via Cathodic Arc Physical Vapour Deposition were submitted to thermal cycling under conditions which approximate thixoforming of steels. The PVD AlCrN coating provides adequate protection against oxidation of the hot work tool samples, shown to be one of the predominant mechanisms leading to thermal fatigue cracking. However, it does not last very long due to the extensive softening of the tool steel substrate and the thermal expansion mismatch between the hot work tool steel and the nitride coating.