Since the first application in the middle of 1970 in the space shuttle-program Metal matrix composites (MMCs) are commercially used in automotive and transportation systems as well as in power electronics and cutting tools. Their properties as lightweight materials combined with good wear resistance, thermal conductivity by at once low thermal expansion make MMCs perfectly for their use under creep conditions. The creep damage mechanisms in particle-reinforced Titanium- and Aluminium-based Metal Matrix Com¬po¬si-tes (MMCs) are analysed by in situ µ-tomography using synchrotron X-ray radiation. This 3D-method enables time and space resolved studies of the da¬ma¬ge mechanisms inside the volume during creep.
The analysis of the experimental data enabled the generation of illustrations visualizing the creep damage and failure as a function of time, stress and temperature. These illustrations con¬sider the microstructural damage mechanisms in the metallic matrix as well as fracture of reinforcements and matrix-reinforcement delamination. The detected micro¬struc¬tu¬ral damage me¬cha¬nisms are correlated to the macroscopic creep curve. To characterize the creep damage in the different creep stages existing models were used, which are specifying the phe¬no¬me¬no¬lo¬gy of the damage and give in¬for¬ma¬tion about damage formation and evolution. During the early creep stages surface diffusion dominates the creep damage through void formation and evolution regardless of the investigated MMC-materials Ti¬tan+15%(SiC)p, and AA6061+22%(Al2O3)p. In the later creep stages the damage mechanisms which lead to creep fracture are different: Void for¬ma¬¬tion and evo-lution in the matrix result in creep fracture at higher temperatures and low mechanical stresses. The main process in the Ti¬tan+15%(SiC)p-MMC is super-proportionally void growth by power-law creep in relation to creep strain. In contrast the surface diffusion determines void growth which remains pro¬por¬¬tio¬nal to creep strain in the AA6061+22%(Al2O3)p-MMC. However, at high mechanical stress and low temperature reinforcement fracture is observed.