The structural features of an electron‐beam‐melted titanium aluminide alloy are presented. The microstructure consisting of γ‐TiAl, α2‐Ti3Al, and βo‐TiAl reveals inhomogeneous phase and Al distributions, which are quantified by electron probe microanalysis. Electron backscatter diffraction is utilized to indicate a solidification via the β‐phase preferably along the <001> direction, resulting in a {001}βo fiber texture parallel to the building direction. These findings are correlated to a calculated isopleth section of the Ti‐Al‐Nb‐Mo system and the corresponding phase fraction diagram. The investigated β‐solidifying γ‐TiAl‐based alloy, therefore, combines both the characteristics of electron‐beam‐melted Ti and TiAl alloys.

The global economic network, increasing mobility and wealth have a significant impact on energy consumption and environmental degradation, creating a serious social and political pressure on climate protection issues and a sustainable use of limited natural resources. In this context, a variety of programs are launched worldwide on a political and scientific / technical level to reduce aviation as well as automobile emissions. To meet these requirements, apart from new and improved design and lightweight construction concepts, high-temperature lightweight structural materials and their processing technologies play a key role. Due to their high specific (creep) strength and low density, intermetallic titanium aluminides have a particularly great potential, which is already being used industrially. While in the last decades, predominantly ingot metallurgical processes have been developed for the production of pre-material, which have subsequently been processed by casting and hot-working, the introduction of powder-based manufacturing technologies (e. g. additive manufacturing), with the availability of high-quality alloy powder, opens up new ways of material processing and component design. The basis of this work is the process-adapted 4th generation TNM-alloy, which was developed at the Chair of Physical Metallurgy and Metallic Materials. Due to its reactivity, manufacturing methods used are electron beam melting and laser powder-bed fusion as well as spark plasma sintering. Furthermore, high demands are placed on the production of the powder, in particular with regard to its purity. The chemical composition of the project alloy is designed and optimized so that it is “resistant” to the characteristics of the different manufacturing processes and their physical conditions. The starting powders and the manufactured specimens are subjected to a comprehensive characterization involving microstructural investigations on several length scales as well as the examination of the mechanical properties. Moreover, in order to further optimize the mechanical properties at elevated temperatures, it is an essential goal to develop suitable heat treatments. This work will show how conventional and high-resolution metallography can be used to combine innovative alloys with new processing technologies.

The formation mechanism of banded microstructures of an electron beam melted engineering intermetallic Ti–48Al–2Cr–2Nb alloy, the solidification behavior, and the heat treatment response are investigated via a process parameter study. Scanning electron microscopy, hardness testing, X‐ray diffraction, electron probe microanalysis, thermomechanical analysis, electron backscatter diffraction, heat treatments, as well as thermodynamic equilibrium calculation, and numerical simulation were performed. All specimens show near‐γ microstructures with low amounts of α2 and traces of βo. Fabrication with an increased energy input leads to an increased Al loss due to evaporation, a lower α‐transus temperature, and to a higher hardness. Banded microstructures form due to abnormal grain growth toward the bottom of original melt pools, whereas α2 in Al‐depleted zones enables a Zener pinning of the γ‐grain boundaries, leading to fine‐grained areas. Via numerical simulation, it is shown that increasing the energy input leads to larger maximum temperatures and melt pool sizes, longer times in the liquid state, and more remelting events. Solidification happens via the α‐phase and increasing the energy input leads to an alignment of (111)γ in building direction. Furthermore, banded microstructures respond heterogeneously to heat treatments. Heat treatment is introduced based on homogenization via phase transformation to obtain isotropic microstructures.

The properties of intermetallic titanium aluminides, such as the so-called TNM alloy, which is, owing to its high specific strength and low density, already used in the aviation and automotive sector in the temperature range from 600–800 °C, are highly dependent on the fractions and nature of the present phases. Reliable options of quantitative phase analysis are therefore indispensable. Against this background, samples of an additively manufactured TNM alloy with the composition Ti-42.1Al-4.1Nb-1.0Mo-0.1B (at. %) were metallographically analyzed and the phase fractions of the α2-, β0 and γ phases were quantitatively determined by image analysis, electron backscatter diffraction, and Rietveld analysis in the course of X-ray diffraction experiments performed in this work. With regard to the fractions of the α2 and γ phases, different results were obtained for the three methods applied which can be attributed to the characteristics of additive manufacturing and the quantitative phase analysis of multiphase samples.

Due to the unique combination of low density and their excellent properties-profile at elevated temperatures, intermetallic γ-titanium aluminide based alloys are a promising structural material for applications in aviation and the automotive industry. Additive manufacturing of a TiAl alloy of nominal composition Ti-48Al-2Cr-2Nb (in at. %), using electron beam melting, resulted in a banded and anisotropic microstructure. In this work, the present microstructure was examined by means of visible light and scanning electron microscopy with regard to morphology and phase distribution. Furthermore, a three-dimensional representation of the microstructure was generated based on differently oriented metallographic specimens. Phase analysis was performed using high-energy X-ray diffraction in order to quantitatively determine present phase fractions and to relate them to findings from microstructural analysis.