Study on the organization and properties of Ti-6Al-4 V fabricated by laser powder bed fusion based on the thickness of the gradient layer

Intelligent additive manufacturing is the future direction, and changing parameters during manufacturing process is an effective measure to adjust the quality of parts. In this study, the stability behavior of the manufacturing process under three process strategies, low layer thickness fabrication (LLTF), high layer thickness fabrication based on the interval of the powder layer thickness (IPLT), and changing of layer thickness strategy (CLTS), was comparatively investigated. Multilayer experiments and mechanical properties experiments were performed during laser powder bed fusion, and the correlation between manufacturing quality and powder layer thickness was compared. By optimizing the process parameters, the surface quality of CLTS is similar to that of LLTF, and the value of minimum surface roughness can be between 22 and 23 mu m. Only balling effect due to spattering and a small amount of porosity were found in the cross-section of CLTS. The relative density of most of the fabricated parts is higher than 99%, and the highest relative density is up to 99.99%. IPLT has longer and thicker martensite than LLTF, and the beta-grain of CLTS is also coarser than LLTF. The tensile properties of CLTS are similar to those of LLTF, and the ultimate tensile strength, yield strength and elongation of CLTS are 1205 MPa, 1107 MPa and 6.8%, respectively. Due to the anisotropy of the LPBF, the horizontally constructed Ti-6Al-4 V specimens yielded higher strengths, while the vertically constructed specimens obtained better elongation. The fracture of the part is characterized by a mixture of brittle fracture, ductile fracture and quasi-dissociative fracture. The surface quality, relative density and mechanical properties of CLTS are similar to those of LLTF, while the forming efficiency is much higher than that of LLTF, which can reach 7.35 mm(3)/s.