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.
