Periodic Reporting for period 3 - ADVANCE (ADVANCE: Sophisticated experiments and optimisation to advance an existing CALPHAD database for next generation TiAl alloys)
Periodo di rendicontazione: 2021-09-01 al 2022-06-30
Reduction of aircraft CO2 and NOx emissions is achievable using lightweight materials such as TiAl alloys that are used in the design and manufacture of aircraft engines. A reduction in aeroengine weight directly contributes to a reduction in the airline industry’s global fuel consumption and thus its overall environmental footprint.
TiAl is stable at high temperatures with low weight and high strength, i.e. high specific strength, making it a good substitute for Ni-based alloys that have a lower specific strength and are traditionally the material used to make the rotating blades in the last stages of the low-pressure aero engine turbines. The next generation of aero engine designs aims to use TiAl alloys in at least one more stage of the low-pressure turbine because of TiAl alloys’ enormous weight saving potential. To cope with the higher operating temperatures of the more forward stages of the turbine, the temperature capability of TiAl alloys must be increased by 50–100 °C. This temperature requirement is a technical challenge requiring precise scientific data to determine the influence from chemistry on microstructure and its stability for this class of alloy. To be both precise and effective requires predictive simulation capabilities that will enable the evaluation of a large number of potential TiAl alloys in a very short time.
In the ADVANCE project an extensive and ambitious experimental program generated detailed and accurate phase equilibrium data for a series of homogeneous alloys of high purity in the ternary systems Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary systems Ti-Al-Nb-Z (Z = Mo, W). The new data available resolves some of the existing experimental controversies, adds missing data points, and allows for an accurate thermodynamic assessment of these individual subsystems. Furthermore, the new data has been used to extend an advanced CALPHAD database for TiAl alloys. The extended CALPHAD database is capable of rapid computational design and can facilitate the optimization of new TiAl alloys and the respective processing conditions with a high degree of confidence.
TiAl is stable at high temperatures with low weight and high strength, i.e. high specific strength, making it a good substitute for Ni-based alloys that have a lower specific strength and are traditionally the material used to make the rotating blades in the last stages of the low-pressure aero engine turbines. The next generation of aero engine designs aims to use TiAl alloys in at least one more stage of the low-pressure turbine because of TiAl alloys’ enormous weight saving potential. To cope with the higher operating temperatures of the more forward stages of the turbine, the temperature capability of TiAl alloys must be increased by 50–100 °C. This temperature requirement is a technical challenge requiring precise scientific data to determine the influence from chemistry on microstructure and its stability for this class of alloy. To be both precise and effective requires predictive simulation capabilities that will enable the evaluation of a large number of potential TiAl alloys in a very short time.
In the ADVANCE project an extensive and ambitious experimental program generated detailed and accurate phase equilibrium data for a series of homogeneous alloys of high purity in the ternary systems Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary systems Ti-Al-Nb-Z (Z = Mo, W). The new data available resolves some of the existing experimental controversies, adds missing data points, and allows for an accurate thermodynamic assessment of these individual subsystems. Furthermore, the new data has been used to extend an advanced CALPHAD database for TiAl alloys. The extended CALPHAD database is capable of rapid computational design and can facilitate the optimization of new TiAl alloys and the respective processing conditions with a high degree of confidence.
A series of experimental ternary Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary Ti-Al-Nb-Z (Z = Mo, W) alloys have been produced from elements of the highest available purity. To ensure homogeneity, alloys were primarily produced by levitation melting as well as using an advanced arc melting device. After casting the composition of all alloys and the content of the most prominent impurities have been determined by wet chemical analysis, which was complemented by electron probe microanalysis (EPMA). The majority of alloys produced by levitation or arc melting showed only minor deviations from the intended compositions and has little or no segregation, ensuring that those specimens can be considered as representing the intended overall chemical compositions to be investigated. In total 84 different alloys were successfully produced.
To generate samples for equilibrium heat treatment, a diamond wire was used to cut the cast alloys into slices of 2-10 mm thickness. These slice samples were encapsulated and annealed at a range of temperatures and at times sufficiently long to ensure equilibrium. At the end of the project, more than 360 different equilibrium heat treatments have been performed. Following equilibrium heat treatment the samples were subject to metallographic inspection and phase analysis using a range of techniques. These techniques include light optical and scanning electron microscopy (LOM, SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), electron probe microanalyzer (EPMA), differential thermal analysis (DTA), high-energy X-Ray diffraction (HEXRD) and transition electron microscopy (TEM). This work allowed the project team to accurately determine equilibrium phases and the composition, as well as phase transition temperatures, which is all important data needed to better understand the microstructure and chemistry of the chosen alloys. Results from these experimental studies has been disseminated at several scientific conferences, but also published in a series of open access publications.
With this information thermodynamic modelling of the studied ternary Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary Ti-Al-Nb-Z (Z = Mo, W) systems was made applying the Calphad approach. Updated Calphad descriptions for the individual ternary systems were integrated into a thermodynamic Calphad databases which has been validated against independent multicomponent data. This updated thermodynamic Calphad database will become commercially available for use with Thermo-Calc during end of 2022.
To generate samples for equilibrium heat treatment, a diamond wire was used to cut the cast alloys into slices of 2-10 mm thickness. These slice samples were encapsulated and annealed at a range of temperatures and at times sufficiently long to ensure equilibrium. At the end of the project, more than 360 different equilibrium heat treatments have been performed. Following equilibrium heat treatment the samples were subject to metallographic inspection and phase analysis using a range of techniques. These techniques include light optical and scanning electron microscopy (LOM, SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), electron probe microanalyzer (EPMA), differential thermal analysis (DTA), high-energy X-Ray diffraction (HEXRD) and transition electron microscopy (TEM). This work allowed the project team to accurately determine equilibrium phases and the composition, as well as phase transition temperatures, which is all important data needed to better understand the microstructure and chemistry of the chosen alloys. Results from these experimental studies has been disseminated at several scientific conferences, but also published in a series of open access publications.
With this information thermodynamic modelling of the studied ternary Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary Ti-Al-Nb-Z (Z = Mo, W) systems was made applying the Calphad approach. Updated Calphad descriptions for the individual ternary systems were integrated into a thermodynamic Calphad databases which has been validated against independent multicomponent data. This updated thermodynamic Calphad database will become commercially available for use with Thermo-Calc during end of 2022.
The experimental work performed in the project contribute to the detailed understanding of phase equilibrium present in ternary systems Ti-Al-X (X = Nb, Mo, W, O, B, Zr, C, Si) and quaternary systems Ti-Al-Nb-Z (Z = Mo, W). This experimental data has successfully be used to obtain an accurate Calphad thermodynamic database that has the necessary predictive capabilities to computationally study the state and properties for a large number of potential alloy compositions in a reasonably short analysis time. This functionality directly enables scientists and research and development teams in industry to become more efficient and innovative in their processes to develop and manufacture new and improved lightweight TiAl alloys. The short-term goal, to provide an accurate database that will aid in the design of a lightweight, high temperature tolerant TiAl alloy used to make aeroengines rotating blade parts, will likely be adapted in other transportation sectors where such materials are also beneficial.
This project belongs to the Clean Sky2 initiative and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820647.
This project belongs to the Clean Sky2 initiative and has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 820647.