Internal stress superplasticity in directionally solidified Al-Al3Ni eutectic composite

Thermal cycling creep behavior in fiber-reinforced composites was investiga ted using a directionally solidified Al-Al3Ni eutectic composite. A superpl astic elongation of 120% was obtained during a ther mal cycling tensile cre ep test. Compression creep tests were performed under an external stress ap plied either parallel or perpendicular to the growth direction. The average strain rates for the two directions exhibited the characteristics of inter nal stress superplasticity: those at low stresses were much higher than the corresponding isothermal creep rates and were proportional to the applied stress. In the case of transverse loading, the thermal cycling creep rate w as explained quantitatively using the previously reported internal stress s uperplasticity model for particle-dispersed composite. In the case of longi tudinal loading, it was much lower than that predicted using the model beca use of the difference in the stress state and the relaxation process. Howev er, thermal cycling creep had very low activation energy, which is a unique characteristic of internal stress superplasticity. (C) 1998 Acta Metallurg ica Inc. Published by Elsevier Science Ltd. All rights reserved.