Modelling of the Ductile Damage Behaviour of a Beta Solidifying Gamma Titanium Aluminide Alloy during Hot-Working

Abstract

Gamma titanium aluminides are innovative materials for high temperature and light weight applications [1]. On the other hand, their hot workability can be limited by failure during hot deformation processes. The prediction of ductile damage in metallic materials can be performed by macromechanical ductile damage criteria [2-4]. If the calculated damage D parameter exceeds a critical value Dc, the material fails. Some macromechanical ductile damage criteria are shown in Table 1, with σ as effective stress, ε as effective strain, σmax as maximum principal stress, σm as hydrostatic stress (mean stress) and εf as equivalent fracture strain. The damage responds to strain localization and thus, to multiaxial stress concentration that increases fracture probability.

Studies on Ductile Damage and Flow Instabilities during Hot Deformation of a Multiphase γ-TiAl Alloy

“…While brittle damage by the occurrence of tensile stresses at the bulge of the sample could be well described in previous work [10], micro-damage in the forging cross could be described by the α parameter as a consequence of softening effects (thermal and strain) combined with low restoration, which is experimentally validated.…”

“…At low temperatures, cracks (highlighted) appear at the surface, parallel to the compression axis and are mainly present in the bulged area of the deformed samples. These cracks occur due to the tensile circumferential stresses during compression, which is normally seen in forging of brittle materials as explained in [10]. The specimen deformed at 1340°C does not reveal any cracks at the surface (Fig.…”

“…The cracks at the bulged area of the deformed samples occur due to the occurrence of tensile stresses during compression as discussed using models of brittle cracking in [10]. The macro-crack formation is temperature dependent, and at higher temperatures the intensity for macro-crack formation decreases (see Fig.…”

Influence of process parameter variation during thermo-mechanical processing of an intermetallic β-stabilized γ-TiAl based alloy

“…Extensive surface cooling leads to surface crack initiation and/or part rupture, identified in [13]. Effective strain within the billet was comparable for both low and high ram speed (see Figure 2b and Figure 2d).…”