Elimination of Al₄C₃ phase in Al/SiC_P composites by HYSYCVD

This paper presents results of the microstructure characterization and evaluation of physical and mechanical properties of Al/SiC_p composites - intentionally containing the Al₄C₃ phase - prepared by pressureless infiltration, as well as results of treating the composites by the hybrid system chemical vapor deposition (HYSYCVD) route using Na₂SiF₆ as solid precursor. It also contains thermodynamic feasibility calculations (using the HSC 6.1™ program) of possible reactions between the SiF_x(x=1-4) gas species (produced during the thermal decomposition of Na₂SiF₆), Al₄C₃ and N₂ in the atmosphere. The composites were fabricated using an L4 Taguchi experimental design, infiltrating SiC_p porous preforms at 1100 and 1200 °C in ultra high purity (UHP) argon and nitrogen (Ar→N2) atmosphere for 90 and 120 min, with the Al-6Si-16Mg (wt. %) alloy. The specimens were characterized by XRD, SEM and EDS. Results show that the composites exhibit a surface hardness between 63.95 and 86.5 (HR30T) and Young ́s modulus up to 118.2 GPa. Application of a post-processing stage by HYSYCVD led to the elimination of Al₄C₃ and the formation of a coating of stable phases on the composites' surface. The experimental results confirm the thermodynamic feasibility of the proposed chemical reactions.