The electrical conductivity of laser-remelted and plasma-sprayed Ni and Cr coatings

The effect of various coatings on busbar joint resistance has been studied as this is where the majority of problems in busbar circuits appear. Nickel and chromium coatings were applied to copper busbar surfaces by plasma spraying and some of these coatings were subsequently laser remelted. The resistance and temperature rise of busbar joints have been investigated for the cases where the joint surfaces were nickel-coated, chromium-coated or left untreated, and where the coatings were either laser remelted or not. Cross-sections through the coatings were examined by a scanning electron microscope (SEM) and showed that the laser remelting produced much better bonding between coating and substrate, which showed itself in lower joint resistance. Increased interfacial pressure reduced the joint resistance for both the coatings, almost to the values for the bare copper joints, in the case of nickel. Hardness measurements along the cross-section showed the coating thickness clearly, and that little mixing had taken place during the laser remelting. The current was varied and produced little change in the joint resistance but increased the joint temperature, the increase being proportional to the power dissipated in the joint.