MULLITE ALUMINA PARTICULATE COMPOSITES BY INFILTRATION PROCESSING .4. RESIDUAL-STRESS PROFILES

Residual stress profiles through mullite/alumina bodies prepared by an infiltration process were determined. In one approach, residual stress profiles were predicted by obtaining concentration profiles and treating the bodies as laminates. In a second approach, a strain gage technique in which part of the sample was ground away while recording the resulting strain was used. The results showed that residual compressive stresses existed in the surface region of all composite samples. The strain gage approach indicated values of surface compression in the range of 176 to 291 MPa, which were higher than those predicted using the laminate approach. The results were compared with changes in the mechanical properties and found to be consistent with the increases in the strength and indentation fracture toughness which resulted when mullite was added to alumina by the infiltration technique.