Microstructure Design Module for the Development of Powder Processed LPT Blade in TiAl Alloys

In order to reduce the cost and time required to develop the TiAl low-pressure turbine blade for jet engines, we have built an inverse problem approach using two modules: one is the mechanical properties prediction module (MPM) to predict the microstructures that satisfy the required properties, and the other is the microstructure design module (MDM) to specify the composition range and heat treatment conditions for tailoring the microstructures. In this presentation, the MDM is highlighted. In this module, the two-step heat treatment of the lamellar formation and subsequent aging is assumed. The temperature and composition dependence of the volume fraction of each phase, as well as the supersaturation for the discontinuous precipitation of α₂-Ti₃Al + γ-TiAl → β-Ti + γ, are calculated in the framework of CALPHAD method. Furthermore, the effects of oxygen on the phase equilibria and kinetics are considered aiming at its application to powder processes such as metal injection molding. Therefore, the key is to understand the effects of oxygen experimentally and to construct a thermodynamic database that accurately reproduces them. Two series of quaternary Ti-Al-M-O alloys (M: transient metal elements) with various oxygen levels were studied at the temperature range between 1573 K and 1273 K using the combination of wavelength dispersive spectroscopy and soft X-ray emission spectroscopy. Then, thermodynamic parameters for two quaternary systems as well as the constituent sub-systems were assessed. Selected important interaction parameters and their composition dependence were optimized based on the <i>ab-initio</i> calculation using KKR-CPA method. The newly assessed database reproduces phase boundaries in multi-component systems with an accuracy of 1% for metal elements and 0.2% for oxygen concentrations. In the presentation, we will demonstrate an alloy design based on this module.