Cracking and microstructure formation in laser cladded Ni۶۰ coatings fabricated by circular and annular lasers: a comparative study

Laser cladding of Ni۶۰ hard-facing coatings were fabricated using isogenous circular and annular lasers. The microstructure and cracking susceptibility of these laser-deposited coatings were examined, along with the analysis of temperature and stress fields through finite element simulation. The comparative study revealed that the coatings deposited by the annular laser, at laser power inputs ranging from۱۵۰۰ to ۲۰۰۰W, exhibited significantly lower cracking susceptibility than those deposited by the circular laser. The microstructural analysis identified that the formation of chromium borides was reduced in the annular laser-deposited coatings, whereas the formation of chromium carbides was enhanced compared to those deposited by the circular laser. Additionally, the crystal orientation was improved and crystal growth type was more dendritic in the annular laser-deposited coatings, which in turn reduced the grain boundary misorientation and refined the formation of chromium carbides. This structural arrangement led to a decrease in hardness and stress concentration, substantially lowering the cracking susceptibility. A cracking-free coating with acceptable hardness loss was successfully achieved using the annular laser at ۲۰۰۰W laser power input. This study underscores the potential of laser beam shaping technology in improving the cracking resistance of hard-facing coatings fabricated by laser cladding.