Functionally graded A6061-TiB2 in-situ nano-composites by high shear dispersion mixing assisted centrifugal casting technique

Abstract

Functionally graded metal matrix composites (FGMMCs) are the subject of extensive research due to their potential to provide position-specific properties for advanced engineering structural components. The study presents the processing and characterization of FG A6061-5 wt% TiB₂ in-situ nano-composites, processed using three different techniques: manual stirring (MS)/continuous impeller stirring (CI)/high shear mixing (HS), followed by solidification through centrifugal casting. High-shear mixing (HS) significantly improved TiB₂ dispersion, resulting in smaller clusters (10 nm to a few microns) compared to CI (9 µm) and MS (3 µm). Moreover, primary α-Al grain size was reduced by 59% in HS, 33% in CI, and 19% in MS, relative to the cast alloys. Consequently, the hardness variation from inner to outer regions was also greater in heat-treated samples, with HS composites exhibiting a 34% increase, compared to 28% for CI and 24% for MS, indicating superior performance in the HS-processed composites. An increase of compressive yield strength from 170 to 185 MPa was observed for different composite samples (MS, CI, and HS-outer regions) between as-cast and heat-treated conditions. The heat-treated HS-processed composite exhibited the highest tensile yield strength of 259 MPa, ultimate tensile strength of 372 MPa, and a strain of 3.7%, representing substantial improvements over both the alloy and other composites. In terms of wear resistance, the heat-treated HS-processed composites showed a 56% reduction in wear rate compared to the alloy, outperforming CI (44%) and MS (38%). The improved properties are attributed to mechanisms such as Hall–Petch, Orowan’s, and CTE mismatch strengthening.