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

A multiscale microstructural and morphological investigation of the creep t ested 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 seve n 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. T he major role of the pyrocarbon interphase has been clearly demonstrated th rough the two types of interfacial sliding. 'Step-creeping' tests were perf ormed 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. Th is study stands as an illustration of the damage-creep concept, which corre sponds 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.