Effect of cyclic infiltrations on microstructure and mechanical behavior of porous mullite/mullite composites

A porous mullite fiber/mullite matrix composite was cyclically infiltrated in an AlCl3 solution to introduce alumina into the pore space. It is shown that the matrix porosity decreases with the number of infiltration cycles. Moreover, the microstructural observations indicate that the distribution of residual pores within the infiltrated composites is heterogeneous, with a lower porosity in the surface region relative to the interior region. Beyond 4 cycles of infiltration, surface embrittlement occurs due to a significant enhancement of the interparticle bonds and the fiber/matrix interfaces in the surface region, leading to a notable reduction in fracture energy.