AlPO_4-coated mullite/alumina fiber reinforced reaction-bonded mullite composites

摘要

A precursor for reaction-bonded mullite (RBM) is formulated by premixing Al_2O_3, Si, mullite seeds and mixed-rare-earth-oxides (MREO). An ethanol suspension thereof is stabilized with poly ethyleneimine protonated by acetic acid. The solid in the suspension is infiltrated into unidirectional mullite/alumina fiber-preforms by electrophoretic infiltration deposition to produce fiber-reinforced, RBM green bodies. Crack-free composites with <= 25 percent porosity were achieved after pressureless sintering at 1300 deg C. Pre-coating the fibers with AlPO_4 as a weak intervening layer facilitates significant fiber pullout on composite fracture and confers superior damage tolerance. The bend strength is approx 170 MPa at 25 deg C <= T <= 1100 deg C. At 1200 deg C, the composite fails in shear due to MREO-based, glassy phase formation. However, the A1PO_4 coating acts as a weak layer even after thermal aging at 1300 deg C for 100 h.