Process optimization of melt growth alumina/aluminum titanate composites directed energy deposition: Effects of scanning speed

Abstract

Directed energy deposition (DED) has developed rapidly in recent years as a new material-structure integration manufacturing technology for preparing melt-growth ceramics. However, the influence of process conditions on the forming quality has not been systematically studied. Alumina/aluminum titanate composite ceramics were directly prepared using DED technology with an extensive process window. The effects of the scanning speed on the typical defects, microstructure, and mechanical properties of prepared samples were systematically investigated, and the optimized process parameters were determined. Results show that the scanning speed has a significant effect on the macroscopic defects, such as cracks and pores, microstructure characteristics, such as grain morphology and size, and mechanical properties, such as flexural strength. Slow-speed scanning achieved a longer retention time of the liquid molten pool, which was beneficial to pore suppression. Rapid scanning reduced the temperature gradient at the bottom of the molten pool to obtain crack-free samples. The directional growth tendency of α-Al2O3 cellular dendrites that were discretely distributed in the Al6Ti2O13 matrix phase weakened, and the secondary dendrites gradually developed by increasing the scanning speed. This phenomenon was attributed to the change of the heat-dissipation direction and the solidification rate of solid/liquid interface caused by the scanning speed. Moreover, the fracture toughness of the prepared samples gradually increased as the scanning speed increased, while the flexural strength showed a parabolic law behavior. The trend of the properties was due to microstructure refinement and macroscopic defects. Generally, the optimal forming quality was achieved at a scanning speed of 300−500 mm/min. Within this process window, the sample had up to 98 % densification, 1640 Hv hardness, 3.75 MPa m1/2 fracture toughness, and 212 MPa flexural strength.