While repair is mainly used to restore the original part geometry and properties, hybrid manufacturing aims to exploit the benefits of each respective manufacturing process regarding either processing itself or resulting part characteristics. Especially with the current implementation of additive manufacturing in the production of TiAl, turbine blades for both hybrid manufacturing and repair new opportunities are enabled. One main issue is the compatibility of the two or more material types involved, which either differ regarding composition or microstructure or both. In this study, a TNM^TM-alloy (Ti-Nb-Mo) was manufactured by different processes (casting, forging, laser additive manufacturing) and identically heat-treated at 1290 °C. Chemical compositions, especially aluminum and oxygen contents, were measured, and the resulting microstructures were analyzed with Scanning Electron Microscopy (SEM) and High-energy X-ray diffraction (HEXRD). The properties were determined by hardness measurements and high-temperature compression tests. The comparison led to an overall assessment of the theoretical compatibility. Experiments to combine several processes were performed to evaluate the practical feasibility. Despite obvious differences in the final phase distribution caused by deviations in the chemical composition, the measured properties of the samples did not differ significantly. The feasibility of combining direct energy deposition (DED) with either casting or laser powder bed fusion (LPBF) was demonstrated by the successful build of the dense, crack-free hybrid material.

Temperature-time cycles are essential for the formation of microstructures and thus the mechanical properties of materials. In additive manufacturing, components undergo changing temperature regimes because of the track- and layer-wise build-up. Because of the high brittleness of titanium aluminides, preheating is used to prevent cracking. This also effects the thermal history. In the present study, local solidification conditions during the additive manufacturing process of Ti-48Al-2Cr-2Nb with laser metal deposition (LMD) are investigated by both simulation and experimental investigations. Dependencies of the build-up height, preheating temperatures, process parameters and effects on the resulting microstructure are considered, including the heat treatment. Solidification conditions are found to be dependent on the build height and thus actual preheating temperature, process parameters and location in the melt pool. Influences on both chemical composition and microstructure are observed. Resulting differences can almost be balanced through post heat treatment.

Within the scope of this study, basic research was carried out on laser micro polishing of the tool steel 1.2379 (AISI D2) using a square, top-hat shaped intensity distribution. The influence of three different quadratic laser beam sizes (100 µm, 200 µm, 400 µm side length) and fluences up to 12 J/cm² on the resulting surface topography and roughness were investigated. Surface topography was analyzed by microscopy, white light interferometry, spectral roughness analysis, and 1D fast Fourier transformation. Scanning electron microscopy and electrical discharge analyses indicate that chromium carbides are the source of undesired surface features such as craters and dimples, which were generated inherently to the remelting process. Particularly for high laser fluences, a noticeable stripe structure was observed, which is typically a characteristic of a continuous remelting process. Although the micro-roughness was significantly reduced, often, the macro-roughness was increased. The results show that smaller laser polishing fluences are required for larger laser beam dimensions. Additionally, the same or even a lower surface roughness and less undesired surface features were created for larger laser beam dimensions. This shows a potential path for industrial applications of laser micro polishing, where area rates of up to several m²/min might be achievable with commercially available laser beam sources.

Lightweight titanium aluminides (TiAl, ρ = 3.9 – 4.1 g/cm3) gain in importance as high temperature structural material. The known properties like high strength and creep resistance combined with high corrosion and wear are of continuous interest for turbomachinery applications like low pressure turbine blades. Additive manufacturing (AM) provides the possibility for near-net-shape production of functional complex parts and can contribute to reduce consumption and costs of material, tooling and finishing. The typical high brittleness and oxygen affinity of TiAl cause special requirements for processing this material with AM. In this work, recent progress in Additive Manufacturing of the TiAl alloys of the nominal compositions Ti-43.5Al-4Nb-1Mo-0.1B (at.-percent, TNM™-B1), Ti-48Al-2Cr-2Nb (at.-percent, GE4822) and Ti-45Al-2Nb-2Mn-0.8B (at.-percent, 4522XDTM) is presented. Microstructures resulting from both Laser Powder Bed Fusion (LPBF) and Direct Laser Deposition (DED) are compared with respect to the characteristics of the manufacturing processes. Hardness measurements according to Vickers are performed, and pressure strength tests are performed on selected samples. The crack-free additive manufacturing of complex geometries made of TiAl is demonstrated as well as an approach for manufacturing hybrid parts combining DED and LPBF.