Effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by DED method

The additive material built-up by the directed energy deposition (DED) method is affected by the melting and solidification reaction with the substrate material. This work investigated the effect of line energy on microstructures and mechanical properties of Co-Cr-Mo alloy single-track fabricated by the DED method. The line energy is a function of scanning speed and laser power, which are the main process parameters for the DED method. The Co-Cr-Mo alloy single-track with low line energy has a columnar grain microstructure with a strong (0 0 1)γ texture parallel to the build direction. As the line energy increased, the single-tracks had mixed microstructure, including fine columnar grains and coarse equiaxed grains with random texture. In addition, the secondary dendrite arm spacing of the single-track depends on the line energy due to the rapid cooling rate. The ε-Co phase in Co-Cr-Mo alloy single-track increased with increasing line energy throughout the isothermal γ → ε martensitic transformation. The effect of the ε-Co phase on the mechanical properties of the Co-Cr-Mo alloy single-track is insignificant. The diffusion of alloying elements from the substrate material throughout the fusion zone occurred and influenced the mechanical properties of the Co-Cr-Mo alloy single-track. The elastic modulus and nano hardness decreased with increasing line energy because of the diffusion of alloying elements from the substrate material. •The role of the fusion zone in DED’ed Co-Cr-Mo alloy single-track was studied.•Columnar grain microstructure changed to mixed microstructure with line energy.•Diffusion of alloying elements throughout the fusion zone occurred and affected the hardness.•Isothermal γ→ε phase transformation occurred at high line energies above 200 J/mm.