AN INVESTIGATION OF SHEAR DEFORMATION IN A SEMISOLID STATE OF A HIGH-STRAIN RATE SUPERPLASTIC SI3N4P AL-MG-SI COMPOSITE/

Shear deformation behavior in a wide temperature range of 683-893 K an d at 2 x 10(-3)-3/s for a high strain rate superplastic Si3N4p/Al-Mg-S i composite is described. The dominant deformation mechanism was dislo cation creep at 683-773 K, superplasticity containing no liquid phase at 813-823 K, superplasticity containing a liquid phase at 833-863 K a nd deformation related to the liquid Bow at 873-893 K, respectively. I n the superplasticity region, the shear strain to failure was signific antly increased by the presence of a discontinuous liquid phase. At 87 3-893 K, high m of about 1 was attained. The deformation in this tempe rature range is likely to be the lubricated how in a semi-solid state containing a continuous liquid phase. However, ductility was low in th is region. This is probably because of decohesion at boundaries with a thick liquid phase, (C) 1998 Acta Metallurgica Inc. Published by Else vier Science Ltd All rights reserved.