Effect of cathodic current density on performance of tungsten coatings on molybdenum prepared by electrodeposition in molten salt

Abstract

Smooth tungsten coatings were prepared at current density below 70mAcm−2 by electrodeposition on molybdenum substrate from Na2WO4-WO3 -melt at 1173K in air atmosphere. As the current density reached up to 90mAcm−2, many significant nodules were observed on the surface of the coating. Surface characterization, microstructure and mechanical properties were performed on the tungsten coatings. As the increasing of current density, the preferred orientation of the coatings changed to (200). All coatings exhibited columnar-grained-crystalline. There was about a 2μm thick diffusion layer between tungsten coating and molybdenum substrate. The bending test revealed the tungsten coating had –good bonding strength with the molybdenum substrate. There is a down trend of the grain size of the coating on molybdenum as the current density increased from 30mAcm−2 to 50mAcm−2. The coating obtained at 50mAcm−2 had a minimum grain size of 4.57μm, while the microhardness of this coating reached to a maximum value of 495HV.