Shortlisted laser surface coating of TiC on H13 die steel: effects on corrosion and errosion behaviour

Abstract

Coatings and surface treatments are being extensively used to increase the service life of die casting dies by reducing molten metal corrosion and erosion of the die. Owing to their excellent corrosion and abrasion resistance, refractory ceramic coatings are particularly suitable for coating die casting dies, and titanium carbide can provide significant resistance to molten aluminium corrosion and erosion. Technologies currently in use for applying such coatings include physical vapour deposition, plasma spraying, and ion implantation. Laser surface engineering is a very attractive technique because of its flexibility, non-equilibrium processing capabilities (involving high solidification rates in the range 103–108 K s-1), and ability to produce metastable phases and increase the solid solubility limit beyond the equilibrium phase diagram. Coatings thus produced are metallurgically bonded, which provides better substrate adhesion. The effects of the grain size of laser coated TiC coatings and of laser surface treatment itself on corrosion and erosion behaviour of H13 die steel in molten Al casting alloy A390 were investigated in the present study. The corrosion rate is accelerated by turbulence and by an increase in melt temperature. A significant improvement in corrosion resistance was achieved for H13 steel coated with TiC. Finer grain size and use of laser shock processing contribute to improved corrosion and erosion resistance of steel in molten aluminium. Based on metallographic and energy dispersive spectrometry studies, the effectiveness of the coatings along with possible reasons for their behaviour are discussed.