The paper concerns the deposition and high temperature oxidation behavior of simple aluminide and SiAl coatings on the TiAl-based alloy TNB-V5. The coatings were produced using pack cementation method with varying content of Si and Al in the pack. The samples were thermally cycled at 850 °C in 23 h cycles up to 131 cycles (total of 3013 hours) in order to obtain mass change curves. The results of cyclic oxidation tests were related to the microstructure of the as deposited coatings. Special effort has been done in order to study the growth of protective oxide scales as well as the evolution of the metal-scale interfaces in detail using analytical high resolution Scanning Transmission Electron Microscopy (STEM).
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.
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