Multi-scale finite-element modelling of fatigue-crack growth in TiAl intermetallic matrix TiNb and Nb platelet composites Original Research Article

A multi-scale finite-element (FE) model of a fatigue specimen for an intermetallic matrix/platelet composite is developed to investigate the crack growth micromechanisms and interactions between the matrix, platelets and interfaces in the crack-tip microstructure under repeated cyclic loading. The outer macroscopic region of the FE model is sufficiently large, with respect to the inner microstructural region, for the cyclic loading to be applied as a single variable point load. On the other hand, the inner microstructural region is sufficiently refined to allow detailed microstructural modelling of the effects of repeated cyclic loading on the matrix, platelets and matrix/platelet interfaces. Two cases are considered; the case of a strong interfacial bond, where the increased resistance to fatigue crack growth comes from crack-tip shielding due to the elastic mismatch, and a weak interfacial bond where interfacial sliding provides an additional contribution. The multi-scale FE model is compared to experimental data from γ-TiAl matrix TiNb and Nb platelet composite systems, where comprehensive fatigue data are available for both the composite and the individual constituents. The model accurately predicts the threshold stress intensity range for the well-bonded TiAl matrix/TiNb platelets system, but is shown to be inapplicable to the TiAl matrix/Nb platelets system for which an LCF treatment would be more appropriate.