The influence of post heat treatment processes on thermal fatigue resistance of thermally sprayed coatings

Die-casting moulds are subjected to severe conditions of cyclical thermal and mechanical loads, as well as chemical and mechanical wear. Dies mostly fail due to a combination of wear mechanisms. Heat checking, erosion, melt corrosion and soldering often lead to complete die failure. Ceramic plasma-sprayed coatings have a great potential for die protection, since they are chemically inert, and show high form stability at elevated temperatures. Furthermore, they show good resistance against thermal shock due to the porous state of the coated layer and low young's modulus. In the present study, the influence of hot isostatic pressing on thermal fatigue resistance of plasma spraying coatings is investigated. Thermal and thermo-mechanical tests were applied to characterise their ability to protect dies. The coatings were evaluated by residual stress measurements, metallography, hardness test and X-ray diffraction.