Influence of D-gun coating on the thermomechanical, corrosion, and metallurgical behaviour of 1.2709 tool steel fabricated by the LPBF technique

In this study, a novel approach is used to study the effect of D-gun deposited 86WC-10Co-4Cr cermet coating of 100 µm thickness on the 1.2709 tool steel substrate fabricated by the Selective Laser Melting process. Results are compared between as-built, heat treated (500°C, 750°C, 1000°C for 6 h), and coated samples. The thermomechanical study using dilatometry analysis revealed lowest average coefficient of thermal expansion in coated sample than heat treated and as-built samples. The as-built microstructure exposed non-equiaxed formation with elongated columnar boundaries along the build direction with lack of fusion and porosity defects which was further refined through subsequent heat treatment process. The coated sample microstructure confirms the cermet formation. The macrostructure and SEM with EDS studies align with the microstructure results and exposed defects in as-built sample. The Tafel plot in potentiodynamic polarisation study revealed less corrosion rate, higher corrosion potential and lesser corrosion current density in coated sample than as-built and heat treated samples. Nyquist and Bode plots revealed that heat treatment improved corrosion resistance, while coating offered the highest protection by effectively blocking electrochemical activity.