Microstructure evolution of laser directed energy deposition process prepared CNTs/WE43 composites during solution and aging treatment

Solution and aging treatment were conducted on the laser directed energy deposition (LDED)-prepared carbon nanotubes (CNTs)-reinforced WE43 (CNTs/WE43) layers to optimize their microstructure and surface properties in this study. The microstructure of the WE43 and CNTs/WE43 layers was systematically compared. The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment. The spot segregation composed of Mg₂₄Y₅, CNTs, and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content. The grain growth of both types of layers underwent three stages: slow, rapid, and steady-state. The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature, resulting in a 47% increase at 510 ℃ and a 35% increase at 540 ℃ in the grain growth exponent compared to the WE43 layers at 510 ℃. During the subsequent aging treatment at 225℃, the precipitation sequences from plate-shaped β″ to plate-shaped and globular β′ were observed in both types of layers. CNTs can facilitate an increase in the nucleation rate of precipitates, but without accelerating precipitation hardening rate. The long and short diameters of the precipitates in peak-aged state were decreased by 48.5% and 43.1% by addition of CNTs, respectively. The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment. The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.