Microstructure and fracture toughness of a β phase containing TiAl alloy

Microstructures and fracture toughness of Ti-45Al-2Nb-1.5V-1Mo-03Y alloy have been investigated. The alloy exhibits fine nearly lamellar microstructures, consisting mainly of fine lamellar grains, together with mixtures of gamma and residual beta phases along lamellar colony boundaries. Precipitation of both beta and gamma phases from alpha(2) lamellae was found after aging at 950 degrees C for 48 h. Phase transformations involving beta Phase both in alpha(2) laths and along colony boundaries are discussed. This TiAl alloy possesses a higher K(IC) value up to 23.5 MPam(1/2) at room temperature, compared with fully lamellar Ti-45Al-5Nb-0.3Y alloy. The toughening mechanism for current alloy is concluded as trans-lamellar fracture, ligament bridges and crack deflection, together with precipitation of beta and gamma phases. The precipitation of fine beta and gamma particles is considered as intrinsic toughening mechanism, because alpha(2)/beta and alpha(2)/gamma interfaces generating due to precipitation can restrict dislocation motion effectively. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.