Comparative study of microstructural characteristics of electrospark and Nd:YAG laser epitaxially growing coatings

As low-heat input welding processes, electrospark deposition and pulsed Nd:YAG laser cladding can be commonly used to prepare epitaxially growing coatings. However, these two processes have quite different characteristics in the energy input, the amount of materials involved, and the temperature gradient, and hence might result in dissimilar microstructural characteristics. In this paper, a comparative study has been made between microstructural characteristics in epitaxial growth coatings prepared by electrospark deposition and pulsed Nd:YAG laser cladding. Some interesting results have been achieved. Firstly, epitaxial growth coatings can be commonly achieved by these two techniques. Secondly, microstructural morphologies of these two epitaxial growth coatings are obviously different, cellular columnar structure prevails in the electrospark coating while columnar dendritic structure occupies most of the laser coating thickness, more importantly, electrospark coating remains fully columnar in the whole layer whereas laser coating tends to change from columnar to equiaxed at the top of the layer. Thirdly, electrospark coating possesses finer and more homogeneous microstructure than laser coating.