Microstructural characterisation of fatigue crack growth fracture surfaces of lamellar Ti45Al2Mn2Nb1B

Investment cast Ti45Al2Mn2Nb1B with fine lamellar microstructures was subject to fatigue crack propagation testing at 650 degrees C and a stress ratio of R = 0.1. The fracture surfaces were examined under SEM and the observed features are correlated with both stress intensity range (Delta K) and lamellar orientation. Translamellar fracture is primary fracture mode for most of the lamellar orientations. Interlamellar fracture is influenced by a combination of the Delta K and lamellar orientation. At low Delta K only the lamellar colonies with their lamellar interfaces almost perpendicular to the stress axis fractured via interlamellar fracture mode. At high Delta K interlamellar fracture can occur in lamellar colonies with any orientations. (C) 2013 Elsevier Ltd. All rights reserved.