The effect of interlayer time on the microstructure and mechanical properties of a Co-Cr alloy produced by laser powder bed fusion

In the laser powder bed fusion (LPBF) method, which is one of the metal additive manufacturing methods, the production quality is affected by many different parameters. One of these parameters is the interlayer time (ILT). The time between scanning two consecutive layers is an important aspect that determines the thermal history of manufactured parts. Depending on this parameter, the produced parts cool down to a certain extent and the microstructure of each layer is affected depending on the thermal history. As the microstructure of a material significantly affects its mechanical behavior, understanding the impact of ILT is crucial. This study investigates the microstructural and mechanical properties of Co-Cr alloy samples produced by LPBF using three different ILTs (22, 70, and 250 s). Modifications to ILTs were accomplished by altering the sample quantity (1, 5, and 20) generated in individual production runs. Additionally, it was examined whether the effect of ILT persists after heat treatment at 1100 °C for 30 min. As a result of the study, an increase in ILT has been observed to lead to reductions in microhardness and compressive yield strengths compared to the sample with the shortest ILT. Heat treatments led to decreased yield strengths and microhardness values across all samples. The obtained results were found to be directly linked with the varying cooling rates across ILTs, influencing phase distribution, residual stress, cell size and grain morphology. Moreover, the effect of ILT on microstructure remained significant post-heat treatment, continuing to influence mechanical properties.