Laser Surface Engineering of composite titanium diboride coating on steel : synthesis and characterization

The aim of the present study was to identify and develop an unique combination of coating technique and material, which could target its properties similar to that of an "ideal coating". In the present study, Nd:YAG laser was used as a tool to deposit ultrahard TiB² ceramic on AISI 1010 steel within a fixed envelope of processing parameters such as laser power and traverse speed. The thrust of the present study is on the material properties and behavior of the TiB² coating within the fixed envelope of these processing parameters. A uniform, continuous and crack free coating with metallurgically sound interface is obtained. Coating is “composite” in nature, comprising TiB² particles and the Fe from steel trapped in the laser melt zone. Such coating has been evaluated for various properties such as mechanical (hardness, elastic modulus,interfacial energy, fracture toughness and fracture morphology), chemical and structural(x-ray diffraction, SEM, TEM and HRTEM) and high temperature oxidation and corrosion properties. Coating is hard and tough in nature. A semi-quantitative model has been developed to estimate the elastic modulus of TiB² coating using nanoindentation technique. It also has been concluded that TiB² coating has a high interfacial energy suggesting a stronger and adherent interface. Composite TiB² coating has a significant oxidation resistance up to 800°C. Also, it has shown improved high temperature corrosion resistance against liquid aluminum. Such features contribute significantly towards the goal of achieving an ideal coating.