The contour scan strategies in laser powder bed fusion (LPBF) of Ti-6Al-4V were studied at the coupon level. These scan strategies determined the surface qualities and subsurface residual stresses. The correlations to these properties were identified for an optimization of the LPBF processing. The surface roughness and the residual stresses in build direction were linked: combining high laser power and high scan velocities with at least two contour lines substantially reduced the surface roughness, expressed by the arithmetic mean height, from values as high as 30 µm to 13 µm, while the residual stresses rose from ~340 to about 800 MPa. At this stress level, manufactured rocket fuel injector components evidenced macroscopic cracking. A scan strategy completing the contour region at 100 W and 1050 mm/s is recommended as a compromise between residual stresses (625 MPa) and surface quality (14.2 µm). The LPBF builds were monitored with an in-line twin-photodiode-based melt pool monitoring (MPM) system, which revealed a correlation between the intensity quotient I₂/I₁, the surface roughness, and the residual stresses. Thus, this MPM system can provide a predictive estimate of the surface quality of the samples and resulting residual stresses in the material generated during LPBF.

Intermetallic Al-Si-based coatings can greatly increase the oxidation resistance of γ-TiAl alloys. However, the effects of the Si addition are not fully understood. Therefore, it is difficult to determine the Si content that is optimal for oxidation resistance. Therefore, pure Al and several Al-Si coatings with varying Si contents between 1 and 81 at.% were studied. The coatings were produced using a combinatorial magnetron sputtering process. Scanning electron microscopy and energy dispersive X-ray spectroscopy were used for structure and chemical analysis. The phases were identified by X-ray diffraction. Cyclic oxidation tests at 900 °C were conducted up to 5000 cycles of 1 h each and subsequently evaluated by thermogravimetric analysis. Si addition in the range of 1 to 12 at.% did not deteriorate the oxidation resistance compared to a pure Al coating up for 1000 cycles (1 h) of oxidation at 900 °C, while higher Si contents led to a high mass gain. For oxidation times up to 5000 cycles (1 h), a sufficient thickness of the coatings is crucial for good oxidation resistance. The main effect of Si addition is to enhance the transformation speed of the deposited Al and Si to the high temperature stable Ti(Al,Si)₃ phase during the heat treatment. Si additions of up to 12 at.% led to increased initial mass gains and a decrease in the oxidation rates during subsequent exposures compared to pure Al coatings.