Epitaxial growth of TiO2 (rutile) thin films by halide CVD

Thin films of TiO2 have been deposited on α-Al2O3 (0 1 2) substrates from TiI4 and O2 using low pressure chemical vapour deposition. The TiO2 films were iodine-free and both the anatase and the rutile phase TiO2 could be deposited. The rutile phase was found to grow with a strong [1 0 1] orientation at deposition temperatures down to 490 °C. The rocking curve FWHM value for the (1 0 1) reflection was as low as 0.43°. The in-plane orientational relationship between the rutile film and the substrate was determined by φ-scan measurements to be [0 1 0]rutile//[1 0 0]α-Al2O3 and [1 0 1-]rutile//[1- 2- 1]α-Al2O3

Elemental segregation in an AlCoCrFeNi high-entropy alloy - A comparison between selective laser melting and induction melting

Additive manufacturing of a high-entropy alloy, AlCoCrFeNi, was studied with selective laser melting from gas atomized powder. A wide process parameter window in the SLM process was investigated but it was impossible to produce crack-free samples, attributed to stresses that originate during the building processes. The microstructure and elemental segregation in the SLM samples were compared with induction-melted AlCoCrFeNi. The induction-melted sample crystallizes in randomly oriented large grains (several hundred microns). Dendritic and inter-dendritic areas with slightly different chemical composition can be observed. Within these areas a spinodal decomposition occurs with a separation into FeCr- and NiAl-rich domains. Further spinodal decomposition within the FeCr-rich regions into Cr- and Fe-rich domains was observed by atom probe tomography.In contrast, the SLM-samples crystallizes in much smaller grains (less than 20 μm) with a dendrite-like substructure. These dendrite-like features exhibit distinct chemical fluctuations on the nm-scale. During annealing more pronounced chemical fluctuations and the formation of Cr-rich and Cr-poor regions can be observed. The difference in microstructure and spinodal decomposition between the induction-melted and SLM samples is attributed to the significantly higher cooling rate for SLM. This study shows that, by using different synthesis pathways, it is possible to modify the microstructure and segregation of element within alloys. This can be used to tune the materials properties, if the cracking behavior is handled e.g. by change of alloy composition to minimize phase transformations or use of a heating stage