Interface engineering through TiC blending and interlayer approaches for defect mitigation in hybrid PBF-LB/M aluminium parts

Modern industrial applications demand a combination of structural strength and design complexity in components. To achieve this, a hybrid in-situ multimaterial PBF-LB/M process was proposed, combining high-strength aluminium bulk parts produced through conventional manufacturing routes with complex AM-built regions made from AM-suitable alloys. However, the components manufactured combining AA 2017 as the conventional substrate and AlSi10Mg as the AM material resulted in defects including non-spherical porosity and hot cracking at the interface region due to epitaxial grain growth. In this study, material-based interventions to reduce defect formation to produce a high-integrity interface were investigated. Feedstock modifications to promote grain size reduction involved adding pure Ti, and introducing TiC nanoparticles through two methods: (i) blending 1 wt.% TiC with AlSi10Mg powder, and (ii) applying a pure TiC interlayer between AlSi10Mg and AA2017. The approach with TiC interlayer achieved over a 60% reduction in defect area, compared to just 13% for TiC blended powder. Furthermore, all TiC-modified samples exhibited a decrease of more than 70% in defect count, confirming the effectiveness of TiC modification in significantly reducing the number of defects. EBSD analysis revealed a 35% reduction in interface grain size with the TiC interlayer, versus 10% with the blended powder. The TiC interlayer promoted grain nucleation, thereby restricting epitaxial growth and inhibiting crack propagation at the interface through a uniform dispersion of unsintered TiC particles. Nonetheless, agglomerates and sintering of TiC particles were observed in all modified samples. The extent of TiC particle sintering was significantly higher in the samples printed with blended powder, likely due to direct laser exposure on TiC agglomerates. Additionally, TiC modification could have extended the melt pool lifetime, facilitating bubble degassing and reducing spherical porosity. Overall, the TiC interlayer approach demonstrated significantly superior performance compared to powder blending in enhancing the integrity of hybrid AM interfaces.