Microstructural development and solidification cracking susceptibility of Cu deposits on steel: Part I

The tool and die industry is interested in depositing Cu onto steel using direct metal deposition techniques in order to improve thermal management of mold dies manufactured from steel alloys. However, Cu is a known promoter of solidification cracking in steel. The goal of this work was to identify the range of Cu compositions in steel that cause cracking and understand the cracking susceptibility through analysis and modeling of microstructural development. A wide range of steel-Cu deposits, from approximately 3 to 97 wt% Cu, were fabricated using the gas tungsten arc welding (GTAW) process with cold wire feed. The deposits were found to be crack free when the concentration of Cu was below approximately 5 wt% or above approximately 52 wt%. Cracking was observed in deposits with Cu concentration between approximately 5 and 43 wt%. Thus, to ensure crack free deposition of Cu onto Steel, the concentration of the first layer must be about 52 wt% Cu or greater. The corresponding volume fraction of terminal Cu in samples that cracked was between approximately 0.1 and 27%. The resultant microstructures were characterized by various microscopy techniques to understand the influence of Cu on solidification cracking. Additionally, solidification modeling was undertaken to determine the amount of terminal Cu rich liquid that would form under equilibrium and non-equilibrium solidification conditions.