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Gamma titanium aluminides are very interesting for their use in high-performance applications such as aircraft engines due to their low density, high stiffness and favorable high-temperature properties. However, the pronounced brittleness of these intermetallic alloys is a major challenge for their processing through conventional fabrication methods. Additive manufacturing by means of electron beam powder bed fusion (EB-PBF) significantly improves the processability of titanium aluminides due to the high preheating temperatures and facilitates complex components. The objective of this study was to determine a suitable processing window for EB-PBF of the TNM-B1 alloy (Ti-43.5Al-4Nb-1Mo-0.1B), using an increased aluminum content in the powder raw material to compensate for evaporation losses during the process. Design of experiments was used to evaluate the effect of beam current, scan speed, focus offset, line offset and layer thickness on porosity. Top surface roughness was assessed through laser scanning confocal microscopy. Scanning electron microscopy, electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDX) were used for microstructural investigation and to analyze aluminum loss depending on the volumetric energy density used in EB-PBF. An optimized process parameter set for achieving part densities of 99.9% and smooth top surfaces was derived. The results regarding microstructures and aluminum evaporation suggest a solidification via the β-phase.

Due to their high strength-to-weight-ratio, magnesium alloys are very attractive for use in automotive engineering. For application at elevated temperatures, the alloys must be creep-resistant. Therefore, the influence of the operating temperature on the material properties under quasistatic and cyclic load has to be understood. A previous study investigated tensile-tensile fatigue behavior of the magnesium alloys DieMag422 and AE42 at room temperature (RT). The aim of this study was the comparison of both alloys regarding compression, tensile, and compression-compression fatigue behavior. The quasistatic behavior was determined by means of tensile and compression tests, and the tensile-compression asymmetry was analyzed. In temperature increase fatigue tests (TIFT) and constant amplitude tests (CAT), the temperature influence on the cyclic creeping (ratcheting) behavior was investigated, and mechanisms-relevant test temperatures were determined. Furthermore, characteristic fracture mechanisms were evaluated with investigations of the microstructure and the fracture surfaces. The initial material was analyzed in computed tomographic scans and energy dispersive X-ray (EDX) analyses.

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Due to their high specific strength and temperature resistance, γ-titanium aluminides (γ-TiAl) have a growing importance for automotive and aerospace applications. However, conventional processing is very challenging due to the inherent brittleness of the material. Therefore, new manufacturing techniques and methods have to be established. Additive manufacturing techniques such as electron powder bed fusion (PBF-EB/M) are favored, since they enable near net shape manufacturing of highly complex geometries. The high preheating temperatures, which typically occur during PBF-EB/M, can significantly improve the processability of TiAl and facilitate the fabrication of complex parts. In this study, a previously optimized material condition of the β-solidifying TNM alloy TNM-B1 (Ti-43.5Al-4Nb-1Mo-0.1B) was manufactured by PBF-EB/M. The resulting microstructure, defect distribution and morphology, and mechanical properties were characterized by means of characterization methods, e.g., CT, SEM, light microscopy, hardness measurements, and tensile tests. A special focus was on the mechanical high-temperature behavior. The pronounced sensitivity of the material to defects and internal notches, e.g., due to lack of fusion defects (misconnections) which were found in the as-built condition, was identified as a main cause for premature failure below the yield point due to the low ductility. This failure was analyzed and potential improvements were identified.