Fracture behaviour of TiAl intermetalics

Abstract

The role of microstructural parameters in fracture behaviour of TiAl intermetalics at room and increased temperatures will be in focus of interest. Based on experimental findings sampled in this field and arising from literature knowledge an overview of typical fracture micromechanisms acting in different microstructures of TiAl intermetalics will be presented. Where possible semi-quantitative evaluation of toughening effects will be presented. Tensile properties, flexural strength and fracture toughness have been evaluated mainly for Ti-40Al-2Cr- 2Nb-1B and Ti-46Al-0.7Cr-0.1Si-7Nb-0.2Ni alloys. For fracture toughness determination chevron-notch specimen technique have been applied except for standard pre-cracked samples. Positive effect of Nb on fracture resistance has been found; fracture toughness of the high Nb alloy increased at contemporary increase of flexural strength. Fracture surfaces have been evaluated using scanning electron microscopy showing the key role of mechanical twinning in deformation of both alloys followed. As a governing mechanism of crack nucleation microcrack formation at boundaries between mechanical twins and γ grains has been confirmed. © Springer Science + Business Media B.V. 2009.