RESIDUAL-STRESS IN ALUMINA MULLITE COMPOSITES

Lattice strains have been measured by neutron diffraction from the alumina matrix in alumina-mullite composite cylinders. Infiltration processing results in a macroscopic variation of mullite concentration and residual stress throughout the samples. At the midheight of the cylinder, the stress component parallel to the cylinder axis is in a compression of -130 +/- 30 MPa with respect to the value near the top surface. At the surfaces, the stress component parallel to the surface is in a compression of -130 +/- 30 MPa with respect to values near the midheight of the cylinder. An overall tensile shift of the macroscopic stress profile in a fully infiltrated specimen is interpreted as a grain interaction effect between the alumina and mullite constituents. The positional dependence of the mullite phase concentration is also determined by neutron diffraction.