Structure and texture evolution of the metal matrix composite PM2014 Al-20%Al2O3 during superplastic deformation

Grain structure and texture evolution during superplastic deformation were studied on the PM2014-20%Al2O3 metal matrix composite produced via a powder technology method. Samples were deformed in tension at different strains in the range of true strain rates 10(-4)-10(0) al at temperature T=500 degrees C. It was shown that in the initial stage of superplastic flow deformation bands are formed in the aluminum matrix along the tension direction. Initial <111> fibre texture is broken and formation of <110> fibre texture takes place. Further strain up to epsilon=50% leads to dynamic recrystallization occurrence inside the deformation bands. This yields the formation of a fine-grained structure. The <111> fibre texture is restored. Both at low strain rates in region I and at high strain rates in region III no microstructural band formation is observed and <111> fibre texture is retained during plastic deformation. These experimental results are caused by the fact that a character of cooperative grain boundary sliding (CGBS) is strain rate dependent. Examination of surface shows that in region II the CGBS is highly non-uniform while at lower and higher strain rates grain boundary sliding is much more homogeneous. The effect of reinforcements on uniformity of CGBS and, consequently, on structure and texture evolution is discussed.