Influence of Impact on the Mechanical Behaviour of the Gamma-Based TiAl Alloy TNBV3B

Abstract

The quasi-static and fatigue behavior after impact of the TiAl alloy TNBV3B produced via three different processing routes—cast, forged and extruded—has been studied on flat and airfoil-like shaped specimens making use of ballistic impact experiments. For impacts resulting in cracks the behaviour can be described using a linear-elastic fracture mechanics approach. The residual strength is described on the basis of the fracture toughness. The residual fatigue strength of impact-cracked specimens is estimated on the basis of the threshold for crack growth of the TNBV3B alloys. However, when there is no visible crack or when the crack length is below the size of the deformed impact area, residual stresses and micro-damage play a dominating role making the linear-elastic fracture mechanics approach invalid. The deformation hardened zone in TiAl has been studied making use of micro-hardness tests showing their extension and the degrees of deformation for different impact energies.