Study of innovative coatings for hot working tools

Thermal spraying processes have many advantages that help improve the performance and extend the life of materials and components. In the present paper the properties and wear behaviour of plain carbon specimenscoated with Ni or Co based alloy powders have been studied for the coating of tools employed in hot working applications, e.g. rolls in a rod mill plant. The morphologies of the different coating layers were very similar, showing the presence of porosity and inclusions, especially at the interface with the coated material, however their influence on the wear behaviour of the specimens was negligible. All the Ni based alloysshowed similar behaviour and satisfactory wear resistance, although small changes in chemical composition induced different hardnesses in the coating layers. The best wear resistance was observed with harder specimens. The Co based powder did not allow the formation of layers with hardnesses high enough to provide good wear resistance. When the Co based powder was mixed with a Ni based powder, the wear behaviour proved disappointing in applications involving rolling and sliding.