Inhibiting sensitivity of microstructure and properties to heat input in DED-arc of 7075 aluminum alloys: The role of TiC-nanoparticles

Abstract

Achieving high-quality 7075 high-strength aluminum alloy manufactured via directed energy deposition-arc (DED-Arc) remains challenging due to its sensitivity of microstructures and properties to heat inputs. This study examines how TiC nanoparticles can effectively reduce the adverse effects of high heat input from the arc on the surface morphology, microstructure, and properties of 7075 aluminum alloy deposits. The surface morphology, defects, microstructures, and mechanical properties of the deposited alloy parts were characterized. The analysis revealed that reducing the heat input results in smoother surface morphology but has little effect on the number of defects, grain morphology, grain size, and tensile strength. Even under various heat inputs, all deposited samples containing TiC nanoparticles exhibit equiaxed grain structures with an average grain size of approximately 8.98 ± 0.27 μm and possess a tensile strength exceeding 500 MPa with minimal variance. Further studies involving microstructures and computational fluid dynamics suggest that the incorporation of TiC nanoparticles mitigates the impact of thermal dynamic conditions within the molten pool. It was discovered for the first time that there is a significant lattice mismatch of about 18% between the crystal planes of TiC and the Al-matrix in the deposited samples. This mismatch increases the free energy of the growth phase, effectively creating a pinning effect for the growing grains. Consequently, this nanoparticle-induced physical barrier disrupts the conventional control of grain growth dictated by thermodynamic conditions, effectively limiting grain size under various heat inputs by arc. This work demonstrates a promising strategy to reduce the sensitivity of microstructure and properties to heat input during DED processes.