IMPROVED FRACTURE TOUGHNESS IN METAL MATRIX COMPOSITES

MODEL METAL MATRIX COMPOSITE MATERIALS WILL BE FABRICATED AND TESTED IN A STUDY OF THE INFLUENCE OF MICROSTRUCTURAL PARAMETERS ON FRACTURE TOUGHNESS. MICROSTRUCTURAL PARAMETERS TO BE VARIED AT TWO LEVELS IN A STATISTICALLY DESIGNED EXPERIMENT INCLUDE THE DEGREE OF CHEMICAL BONDING BETWEEN THE MATRIX AND REINFORCING PHASES, THE HOMOGENEITY OF DISPERSION OF THE REINFORCING PHASE, THE MEAN SIZE OF THEREINFORCING PHASE PARTICLES, THE RESIDUAL DISLOCATION DENSITY OF THE MATRIX PHASE, AND THE DEGREE OF HOT WORKING OF THE CONSOLIDATED COMPOSITE. THE MODEL SYSTEM USED WILL BE A 2124 ALUMINUM ALLOY MATRIX WITH A SIC PARTICULATE REINFORCING PHASE. DETAILED EVALUATIONS WILL BE MADE TO CORRELATE MICROSTRUCTURE, PROCESSING CONDITIONS, TENSILE PROPERTIES AND FRACTURE TOUGHNESS OF THE MODEL COMPOSITES. SUPPORTING STUDIES WILL TREAT THE EFFECTS OF MATRIX/REINFORCING PHASE INTERFACIAL CHEMISTRY ON FRACTURE TOUGHNESS. RECOMMENDATIONS FOR CONSTIUENT PHASE SELECTION AND MICROSTRUCTURAL DESIGN FOR IMPROVED TOUGHNESS COMPOSITES WILL BE FORMULATED.