THE EFFECT OF TEMPERATURE ON THE FRACTURE MECHANISM IN 2014AL/15VOL-PERCENT-AL2O3 COMPOSITE

The tensile fracture strain, stress and fracture mode for a discontinuously reinforced aluminum matrix composite, 2014Al/15vol.%Al2O3, were determined and compared with those of the unreinforced matrix material, 2014Al, at various temperatures. Tests were conducted under uniaxial tension at elevated temperatures with a strain rate of 0.1 s-1. It was found that the tensile fracture strain as well as fracture stress of the composite were lower than those of the matrix material. The tensile fracture mode changed from transgranular fracture to intergranular fracture between 400-degrees-C and 500-degrees-C for both materials. For the composite, at temperatures below 400-degrees-C the growth and coalescence of voids occurred via a dislocation creep process primarily along the Al-Al2O3 interface. Above 400-degrees-C voids initiated and grew at the Al-Al2O3 interface and grain boundaries via a diffusion creep process. The void growth was found not along the tensile direction but along the Al-Al2O3 interface and grain boundaries, and this resulted in a low fracture strain. A method for determining quantitatively the characteristics of the void initiation and growth is discussed.