A multilayer coating architecture to reduce heat checking of die surfaces

The primary reason for thermal fatigue cracking in die casting is the thermal load and its cycling during the operation. Conventional single and multiplayer coatings have been found to at best equal the thermal fatigue lives of hot working steels used for die casting dies. This paper presents a new approach to fatigue resistance that uses a three-layer coating architecture to reduce the heat transfer and chemical diffusion to the die steel substrate. In this, the outer layer consists of a thermal barrier coating of rare-earth oxide, the middle layer a TiAlN diffusion barrier coating and the inner layer a thin adhesive Ti layer. Thermal cycling tests in liquid aluminum up to 4000 cycles using this architecture and conventional commercial multi-layer PVD coatings confirm that the new coating significantly improves the thermal fatigue resistance of the substrate.