Redox studies on dense zirconia-doped ceria pellets were carried out by thermogravimetric investigations and dilatometry. Up to 1600 K reduction parameters determined by both methods correspond to each other. At higher temperatures, however, thermogravimetry overestimates the degree of reduction since mass loss is not only due to oxygen exsolution but also to selective evaporation of CeO₂ whose vapour pressure is considerably higher than that of ZrO₂. As a consequence surface segregation of zirconia occurs in (Ce,Zr)O_2−δ pellets leading to a porous surface zone of Ce₂Zr₂O₇ pyrochlore which gradually grows in thickness. Surface enrichment of zirconia is detrimental for splitting CO₂ or H₂O since re-oxidation temperatures of (Ce,Zr)O_2−δ are known to be shifted towards lower temperatures with increasing ZrO₂ content. Thus, very harsh reduction conditions should be avoided for the (Ce,Zr)O_2−δ redox system. The kinetics investigations comprised the high temperature reduction step (T ≅ 1600 K) and the “low” temperature oxidation reaction with a carbon dioxide atmosphere (T ≅ 1000 K). The reduction kinetics (at around 1600 K and an oxygen activity of 7 × 10⁻⁴ in the gas phase) directly yield the (reduction) equilibrium exchange rate of oxygen in the order of 10⁻⁷ mol·O/(cm³·s) as the kinetics are surface controlled. The oxidation step at around 1000 K, however, occurs in the mixed control or in the diffusion control regime, respectively. From oxygen isotope exchange in combination with SIMS depth profiling oxygen exchange coefficients, K, and oxygen diffusivities, D, were determined for so-called equilibrium experiments as well as for non-equilibrium measurements. From the obtained values for K and D the (oxidation) equilibrium exchange rates for differently doped ceria samples were determined. Their dependency on the oxygen activity and the nature and the concentrations of a tetravalent dopant (Zr) and trivalent dopants (La, Y, Sm) could be semi-quantitatively rationalised on the basis of a master equation for the equilibrium surface exchange rate.

This paper shed light on the kinetics of transformation and the developed microstructure during wire arc additive manufacturing (WAAM). Three microalloyed alloys, two of them are high strength low alloyed steel (HSLA) grades and the third is a Ni-Cr-Mo steel, from which the welding wires are being produced, were investigated. Repeated cycles around varied temperatures from a reheating temperature of 1350 °C and down to a temperature 35 °C below the A_e1 are applied using dilatometer on samples from the steels. After applying the cycles, the dilatometric-samples were investigated metallographically and their macro- and microhardness values were measured. It is shown that the WAAM using HSLA steels produce softer structure than the steel of the welding wire. Combined microalloying with Ti and Nb can present a useful strategy for producing finer structure in the WAAM components due to the effect of Ti in inhibiting the prior austenite grain-growth and that of Nb in refining the final structure. Additionally, repeated heating near A_e3 refines the prior austenite grains and produced fine ferrite-pearlite structure in case of HSLA steels and a microstructure predominated by the granular bainite in case of welding wire alloy. The former microstructure was the softest one for the case of HSLA steels, whereas the softest structure in case of the welding wire alloy was the tempered martensite structure developed by reheating below A_e1. Idealized temperature curves were chosen for the heat treatment, which could be characterized in a well-defined manner. In future work such idealized curves together with temperature histories obtained in WAAM-process will be used to set up a database to train an AI-model for predicting structure and material properties.

High‐manganese steels containing 10 to 30 wt.‐% (weight‐%) Mn exhibit high strength and ductility. This study aims to improve the understanding of mechanisms determining the high‐temperature properties of such steels. A shear test equipment is developed, enabling mechanical testing in an as‐cast state after solidification from melt. This study covers four steel grades of about 13, 15, 17, and 21 wt.‐% Mn, 0.07 up to 0.8 wt.‐% C, and about 2.5 wt.‐% Al and Si each. The results are for 1000 °C and both for as‐cast and annealed states. Annealing is done for 1 h at 1020 °C, corresponding to a testing temperature of 1000 °C. For a better understanding of the material properties, micro‐segregation is investigated. Two types of micro‐segregation are found, type 1 resulting from solidification and type 2 from phase transformation from ferrite to austenite. Type 1 segregation is large, especially for Si and intermediate C‐contents. Type 2 segregation found for lower C‐ and Mn‐contents and predominately in the as‐cast state is associated with an increased ferrite content resulting in embrittlement. Increasing embrittlement is also found at elevated C‐contents mainly due to primary carbide formation. Annealing reduces micro‐segregation and the amount of ferrite and carbide precipitation.

The authors would like to add Stefan Beschnitt, who performed SIMS line scans, to the authors’ list in 5th position of their paper published in Inorganics