Investigation of Ti alloying for microstructural evolution and strengthening mechanism: Avoiding Al4C3 formation in SiCp/Al composites via laser directed energy deposition

Abstract

The near-net-shape characteristics of Additive Manufacturing offer significant advantages in fabricating SiCp/Al composite components. However, the high-temperature melt pool during the deposition process promotes an interface reaction between SiC and Al, forming Al4C3. Al4C3 shortens the service life of SiCp/Al composite structural components, so it is critical to avoid its formation when preparing SiCp/Al composites via laser-directed energy deposition. This study prepared SiCp/Al composite components through coincident wire powder laser-directed energy deposition with Ti alloying, effectively preventing the formation of Al4C3 in AMC. Furthermore, it investigated the effect of Ti atoms on the microstructural evolution and strengthening mechanism. The results showed that the formation of large flake-like Al4C3 was avoided without generating excess Al3Ti only when using an appropriate amount of Ti (Ti: SiC = 3: 10). After introducing Ti, Ti atoms in the melt pool migrated towards the SiC surface and reacted with C atoms (from the dissolution of SiC) and formed TiC. The resulting TiC enclosed the SiC particles in a thin film, preventing the further dissolution of SiC and inhibiting the generation of Al4C3. Additionally, some TiC nanoparticles dispersed within the matrix, serving as heterogeneous nucleation sites for Al, reducing the average equivalent circular grain radius from 38.10 µm to 7.20 µm. After Ti alloying, the average modulus and yield strength of AMC both increased. This increase was attributed to the load transfer energy of SiC particles, grain refinement of the matrix, and the dispersion-strengthening effect of TiC nanoparticles. An intrinsic relationship between the SiC-Al-Ti interfacial reaction and the mechanical properties of SiCp/Al composites has been established to provide theoretical guidance for eliminating Al4C3 phases in SiCp/Al composites prepared by laser-directed energy deposition, ensuring performance comparable to traditionally fabricated products.