Understanding the creep behavior of a 2.5D Cf-SiC composite.: III.: From mesoscale to nanoscale microstructural and morphological investigation towards creep mechanism

A multiscale microstructural and morphological investigation of the creep tested 2.5D C-f-SiC specimens has been conducted via scanning, transmission and high resolution electron microscopies (SEM, TEM and HREM) and automatic image analysis. Five modes of matrix microcracking together with two types of interfacial sliding have been identified. The combination of these seven elementary mechanisms leads to the macroscopic creep strain according to a time-dependent mechanism, which can be assimilated to slow crack growth. In HREM, the so-called 'nanocreep' of the carbon fibers has been evidenced, but its contribution to the macroscopic creep strain appears negligible. The major role of the pyrocarbon interphase has been clearly demonstrated through the two types of interfacial sliding. 'Step-creeping' tests were performed in order to identify the sequence of the elementary mechanisms in the global creep mechanism of the composite. In parallel, a promising approach of damage quantification has been achieved by automatic image analysis. This study stands as an illustration of the damage-creep concept, which corresponds to the mechanism that governs the creep behavior of the 2.5D C-f-SiC composite. (C) 2001 Elsevier Science B.V. All rights reserved.