Heat and Mass Transfer Phenomena in the Application of Wire-Based Nickel/Tungsten Carbide Overlays
One of the main areas of research at the Canadian Centre for Welding and Joining is the measurement of droplet heat content in free-flight metal transfer in GMAW and related processes. The technique is based on calorimetry of multiple droplets, together with high-speed video, image recognition, and data acquisition. A novel set-up involving a cathode with a hole enables the operation of welding machines using standard settings because the arc attaches to the cathode, yet the molten metal falls through the hole and is captured by the calorimeter. The water-cooled cathode also acts as a secondary calorimeter, discriminating the heat input provided by droplets from that of the arc acting on the cathode. Among the findings from this line of research are the direct measurement, for the first time, of a droplet temperature minimum at the transition between globular and spray transfer. This insight has been used to explore the existence of a temperature minimum in tubular Ni/WC wires for wear protection overlays for the oil sands. These overlays are extremely sensitive to degradation if the molten metal temperature is excessive during application. Wire based processes show much promise for practical applications, but are seldom used because of high degradation problems. At this time, the experimental results show a minimum of temperature using Ni/WC tubular wire. Based on this result, a selected set of promising process conditions are being used to make a set of prototype overlay welds and to analyse the microstructure and volume fraction of WC in the Ni.
This project is in partnership with: Syncrude Canada Ltd.