STRAIN-RATE EFFECTS ON HIGH-TEMPERATURE FRACTURE-BEHAVIOR OF A 2124AL-SIC(W) COMPOSITE

Abstract

The high-temperature fracture behavior of a 2124Al-SiC(w) composite compared with a 2124Al alloy was investigated in this study. Axisymmetric tensile tests were carried out over a temperature range from 25-degrees-C to 550-degrees-C and at strain rates from 5 x 10(-5) s-1 to 0.3 s-1. Detailed fractographical observations and cross-sectional microstructure analyses were also made to identify local micromechanical processes of cavity initiation at high temperature. One of the important results is that the cavity initiation sites of the composite are strongly influenced by the strain rate at high temperatures: cavities initiate at whisker ends at low strain rates and at whisker sides at high strain rates. Furthermore, the favored direction of cavity growth is also dependent upon the strain rate, being approximately 45 deg at low strain rates and perpendicular to the tensile axis at high strain rates. Such different local fracture processes at different strain rates are interpreted in terms of the role of the SiC whiskers on the load carrier in the composite at high temperatures.