Role of laser scan strategies in defect control, microstructural evolution and mechanical properties of steel matrix composites prepared by laser additive manufacturing

Abstract

Steel matrix composites (SMCs) reinforced with WC particles were fabricated via selective laser melting (SLM) by employing various laser scan strategies. A detailed relationship between the SLM strategies, defect formation, microstructural evolution, and mechanical properties of SMCs was established. The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing. Particularly, the involved thermal cycling, which encompassed multiple layers, strongly affected the processing quality of SMCs. S-shaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs. However, due to large thermal stress, microcracks that were perpendicular to the building direction formed within the SMCs. By employing the checkerboard filling (CBF) hatching mode, the thermal stress arising during SLM can be significantly reduced, thus preventing the evolution of interlayer microcracks. The compressive properties of fabricated SMCs can be tailored at a high compressive strength (∼3031.5 MPa) and fracture strain (∼24.8%) by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode. This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input, e.g., laser power and scanning speed.