Laser vitrification processing of thermally sprayed enamel coatings

Over the last decade, the use of vitreous enamel for industrial applications has increased due to its excellent technical properties such as corrosion resistance, dirt resistance and non-flammability. Traditional enamelling on steel consists of applying enamel frit powder by electrostatic charging followed by heating and fusing in a furnace at 800°C. This process is limited by the size of the furnace and has a huge impact on the structural properties of the steel base material.

In this paper, thermal spraying with powders and suspension spraying, and laser sintering have been applied to produce enamel glazed ceramic coatings on steel substrates. The main advantage of laser sintering compared to conventional oven treatment is its higher process speed of about 3 mm/s for larger parts, a lower thermal impact and savings in terms of costs energy. The influence of the enamel formulation, the spraying method and the laser parameters on the coating properties, microstructure, topography, phase composition, mechanical stability and coating vitrification were investigated. The laser-treated enamel coatings were characterised by smooth, glossy surfaces with an average roughness Ra below 1 μm. Dense coating layers with closed porosity ("bubble structure"), similar to those obtained by conventional oven enamelling, could be achieved.