Oxidation behaviour of SiC/SiC ceramic matrix composites in air

Oxidation of silicon melt infiltrated SiC/SiC ceramic matrix composites (CMC) was studied in air at 1200–1400 °C for 1, 5, 24 and 48 h. Weight gain and oxide layer thickness measurements revealed the oxidation follows parabolic reaction kinetics with increase in temperature and time. XRD showed the extent of oxide layer (SiO2) formation was greatest after 48 h at 1400 °C: an observation confirmed by X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM) analyses. Oxide layer thickness varied from 1 μm after 48 h at 1200 °C to 8 μm after 48 h at 1400 °C. Oxidation of SiC/SiC composites is both temperature and time dependent with an activation energy of 619 kJ mol−1. BN coatings around SiC fibres showed good resistance to oxidation even after 48 h at 1400 °C

Effect of barium on the structure and characteristics of Mg2Si reinforced particles Al–Mg2Si–Cu in situ composite

Addition of barium (Ba) in various concentrations is susceptible to cause changes on Mg2Si reinforced particles in Al–Mg2Si–Cu in situ composite. In this study, six samples of the composite with different concentrations of Ba (0.1–0.8 wt%) were prepared. The alteration of Mg2Si structure, phase reaction characteristics and cooling curves behaviour of the composite were investigated via optical microscope, scanning electron microscope (SEM), and computer aided cooling curve thermal analysis (CACCTA). The results depicted that 0.2 wt% exhibit the appropriate concentration of Ba added in order to modify and refine the Mg2Si particles. The skeleton and dendrite shape of Mg2Si particles have been transformed into fine polygonal shape accompanied with decreased in average size from 1178.5 µm of the unmodified particles to 289.1 µm. In fact, the refinement of Mg2Si particles is associated with the increased of nucleation temperature, TN of the respective phase together with the least undercooling, ΔU correspond to the easiness of the particles to be formed prior to its growth. Meanwhile, the decrement of TN respective to other concentrations of Ba indicates the opposite refinement effect of the particles as it became coarser. Besides, the refinement of Mg2Si has induced more nucleation of the particles resulting the increment of the density of particles and better distribution over the composite area. Therefore, the corresponding mechanical and tribological properties of the composite are believed to be improved accordingly