In order to improve hot forming of multiphase alloys a better understanding of deformation and load partitioning mechanisms is required. High-energy synchrotron sources in combination with advanced sample environments provide the possibility to study hot forming processes in situ and time resolved. Thereby, the evolution of phase fractions, crystallographic texture and lattice strain can be directly observed by X-ray diffraction while simultaneously recording the process parameters.
We studied the hot compressive deformation of an intermetallic titanium aluminide alloy using a deformation dilatometer modified for working in the Hereon beamline HEMS at DESY. This class of alloys was recently established as lightweight high-temperature material for turbine blades in aero engines. In addition to conventional binary titanium aluminides, which consist of tetragonal \gamma\ phase plus hexagonal \alpha₂ phase, advanced ternary alloys can also show an additional amount of cubic \beta_o phase.
During deformation of a ternary alloy (Ti-42Al-8.5Nb) at a temperature of 900 °C and a strain rate of 0.001 s^-1 plastic deformation starts in the \beta_o phase at applied stress levels of 300-350 MPa followed by \gamma\ phase at levels between 450-590 MPa. Load partitioning between differently oriented grains of the \gamma\ and the \alpha₂ phase was observed. Especially the hexagonal \alpha₂ shows a pronounced difference between soft and hard orientations and at the beginning of the elastic-plastic region, a significant load transfer onto the \alpha₂ phase was observed. Additionally, we determined the diffraction elastic moduli of the different phases in the elastic region.