Revolutionary Approach to Develop Novel TiAl Alloys for Powder Processed LPT Blades in Jet Engines

An integrated inverse design approach to accelerate the development of novel titanium aluminides for LPT blades in jet engines, specifically focusing on powder processing, such as MIM (Metal Injection Molding) and AM (Additive Manufacturing), has been undertaken, in collaboration with industries and universities, under the project of “<i>Materials Integration for Revolutionary Design System of Structural Materials</i>” in <i>Cross-ministerial Strategic Innovation Promotion Program</i> (SIP) in Japan. We have successfully developed a novel TiAl alloy with mechanical properties superior to the currently existing alloys and fabricated into 200 mm LPT blade by both MIM and AM processes. Our integrated computational materials design system is composed of three modules: “Mechanical-property Prediction Modules (MPM)”, “Microstructure Design Module (MDM)”and “Process Design Module (PDM)”. For example, the system works as follows: specific values of the properties required by industries, say, tensile strength and fracture toughness, are at first input into the MPM, and the MPM calculates and outputs the volume fraction of the most important microstructure constituent to meet the required properties, based on our mechanical property database (DB). Then, the volume fraction value is input into the MDM, and the MDM optimizes alloy composition and heat treatment condition to have the microstructure, based on our multi-component phase diagram DB. The proposed alloy with the composition is then cast into bar ingots and powdered by EIGA by industries. All of the powders are used for MIM (&lt;45μm) and for AM-EBM (&gt;45 μm) without any waste and fabricated into LPT through each PDM. Tokyo Tech is in charge of the integrated system of MPM and MDM, so that this talk focuses on some points to integrate the modules to the system. For MPM, the key is the digitalization of β/γ cellular microstructure because the bcc β-Ti phase introduced by the cellular transformation (α₂+γ -&gt; β+γ) significantly affects the mechanical properties. For MDM, the most critical point is the reliable knowledge on the phase diagram with oxygen. We found that oxygen tremendously affects the phase equilibria among β-Ti, α-Ti (α₂-Ti₃Al) and γ-TiAl phases and eventually changes the transformation pathways to control the microstructures. Without this information, thus it is impossible to build up the system since a large amount of oxygen is picked up in MIM process in comparison with AM process. The details of MPM and MDM including the calculation methods will be independently presented by our co-authors in this symposium. <br/>A part of this study has been carried under the research of SIP II in JST (Japan Science and Technology Agency).