Abstract
In order to improve thermo-mechanical processing 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 intermetallic titanium aluminide alloys using a deformation dilatometer modified for working in the HZG synchrotron radiation beamline HEMS at DESY, Germany. This class of alloys was recently established as lightweight high-temperature material for turbine blades in aero engines. Conventional binary titanium aluminides consist of tetragonal gamma phase plus hexagonal alpha-2 phase whereas advanced ternary alloys can show an additional amount of cubic beta-o phase.
We determined the diffraction elastic moduli of the different phases in the elastic region. During deformation of a ternary alloy (Ti-42Al-8,5Nb) at a temperature of 900 °C and a strain rate of 0.001 1/s 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 alpha-2 phase was observed. Especially the hexagonal alpha-2 shows a pronounced difference between soft and hard orientations and at the beginning of the elastic-plastic region a significant load transfer onto the alpha-2 phase was observed.
