Influence of process parameters on micro-defects and structure of K418B superalloy in laser powder bed fusion

The K418B superalloy is fabricated utilizing laser powder bed fusion (LPBF) technology, and an analysis is conducted to examine the impact of process parameters on microdefect, density, microstructure, and hardness by OM, SEM and hardness tester. This is achieved by varying the laser power (ranging from 140 W to 220 W) and scanning speed(between 600 mm/s and 1400 mm/s). The findings reveal that both laser power and scanning speed significantly influence the relative density and defect distribution of the samples. Specifically, low energy density leads to the formation of irregular pores, whereas high energy density is associated with the emergence of spherical pores and solidification cracks. Excessive or insufficient volume energy density (VED) results in decreased density and impaired performance. The optimal processing conditions are identified as a laser power of 180 W and a scanning speed of 1400 mm/s, under which the sample density exceeds 99.95%, with minimal surface defects and only a small quantity of solidification cracks. Microstructure reveals distinct melt pool boundaries and cellular structure, accompanied by a Vickers hardness of 366.8 HV_0.2. Notably, the grains at the melt pool boundaries are coarse, with cellular columnar crystals spanning multiple melt pools, indicating rapid solidification. The hardness initially increases and then decreases with VED, aligning with changes in pore content and density. The study attributes cracks primarily to thermal stress and provides a foundational basis for optimizing LPBF processing parameters of K418B alloy, holding potential engineering applications for enhancing the manufacturing quality of critical aero engine components.