Functionally Gradient H13 Tool Steel/Oxygen-Free High Thermal Conductivity Cu Composites Manufactured by Laser-Directed Energy Deposition

Abstract

H13 tool steel and copper (Cu) functionally gradient materials (FGMs) have been manufactured using laser-directed energy deposition (L-DED). Differential scanning calorimetry analysis of H13-Cu blends shows clear separation of the Fe-rich and Cu-rich liquids due to the Fe–Cu miscibility gap. Also, in the analysis, it is determined that there is a large solidification range that will promote solidification cracking. A compositional gradient is produced by changing the powder feed rates in situ within the L-DED system, to create six different compositions, beginning with 100% H13 at the substrate and ending at 100% Cu. Single-track clads and three-layer clad tracks of various H13-Cu blends are successfully printed onto a wrought H13 substrate. The cross section of the clad samples containing Cu experiences vertical cracking, indicative of solidification cracking. Rectangular FGM samples of H13-Cu are successfully printed onto a wrought H13 substrate using two different laser powers, namely 400 and 460 W; however, these samples experience major porosity and detrimental transverse cracking issues situated in the ≈25 and ≈45 wt% Cu sections. This is attributed to the Fe–Cu miscibility gap, difference in coefficient of thermal expansion, and Cu being known to promote cracking in steels. Some potential solutions to these issues are discussed.