Elimination of Al4C3 phase in Al/SiCp composites by HYSYCVD

This paper presents results of the microstructure characterization and evaluation of physical and mechanical properties of Al/SiCp 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 (TM) program) of possible reactions between the SiFx(x=1-4) gas species (produced during the thermal decomposition of Na2SiF6), Al4C3 and N-2 in the atmosphere. The composites were fabricated using an L4 Taguchi experimental design, infiltrating SiCp porous preforms at 1100 and 1200 degrees C in ultra high purity (UHP) argon and nitrogen (Ar -> N-2) 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.