A technique is presented for accurate and time-resolved quantification of chromium volatilization from alloys at high temperature. A denuder tube which is coated with Na2CO3 is placed downstream of the samples. CrO2(OH)(2) that evaporated from the samples is collected on the denuder and converted to the thermally stable Na2CrO4. The chromate is then dissolved in water and determined quantitatively. Three commercially available ferritic 22% Cr steels intended for use as solid oxide fuel cell interconnect materials (Sanergy HT, Crofer 22 APU, and ZMG 232) have been investigated with respect to chromium volatilization and oxidation rate. The effect on chromium volatilization of a submicrometer cobalt coating on the steel surface is reported. Comparisons are made with a conventional thick ceramic coating. The experiments are carried out at 850 degrees C in N-2 - 20% O-2 - 3% H2O atmosphere. The submicrometer Co coatings proved to be very efficient, reducing Cr volatilization by 1 order of magnitude. Microscopic studies show that both uncoated steel and steel coated with a submicrometer cobalt film develop two-layered oxide scales with the bottom part consisting of a Cr-rich corundum-type oxide. The uncoated samples develop a top layer consisting of (Cr, Mn)(3)O-4 oxide, whereas the Co-coated samples exhibit a top layer consisting of Co-rich spinel oxide. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3462987] All rights reserved

The coarsening behavior of three-phase materials, such as eutectic material systems, is of high technological interest. Microstructure evolution simulations can help to understand the effect of different magnitudes of the diffusivities in the different phases. In this study, the evolution of a 3D three-phase morphology was modeled with equal interfacial energy and volume fraction and similar thermodynamic properties for the three phases, but the diffusion mobilities were taken different. It was observed that the phase with the lowest mobility has the highest growth rate and, on average, a larger number of grain faces, while the other two phases have a nearly equal growth rate and average number of grain faces. The simulation results are compared with results from experiments and simulation studies for single-phase and two-phase materials.

The coarsening behavior of three-phase materials, such as eutectic alloys, is of high technological interest. In this study, 3-D ternary three-phase polycrystalline materials were modeled to study the effect of bulk diffusion and phase arrangement on the coarsening kinetics. The diffusion mobilities were defined to be different in the three phases. By varying the phase boundary and grain boundary energies, microstructures with different phase arrangements were obtained, in which the different types of grains had a tendency to alternate or cluster. In all cases, a regime was reached where the average grain size follows a power growth law with growth exponent n = 3, indicating bulk diffusion controlled coarsening. The overall growth rate and that of the individual phases were clearly affected by the phase arrangement, the magnitude of the phase boundary energy and the diffusion mobilities of the different phases. In all cases, the phase with the lowest diffusion mobility showed the highest growth rate and on average a larger number of grain faces. While the average number of grain faces became constant in time in systems with constant grain boundary energy, the average number of grain faces continued to increase during the whole simulation time when the grain boundary energy was misorientation dependent.

A 3-dimensional phase-field model is implemented to simulate the grain evolution in the final stage of liquid-phase sintering. The model considers a liquid phase and a polycrystalline solid phase. Results for varying ratios of the solid-solid interface energy to solid-liquid interface energy and varying solid volume fractions are presented. A variety of microstructures, from fully connected grain structures with liquid pockets at the grain junctions to individual grains fully wetted by the liquid matrix, is seen. The 3 main mechanisms for particle shape accommodation, namely, contact flattening, Ostwald ripening and particle bonding, are reproduced in the simulations. The solid volume fraction, particle size distribution, contiguity, connectivity, particle-particle contact areas and the number of particle contacts per particle are measured as a function of time. The exponent in the power growth law varies between 2.4, for the fully connected grain structures, and 3, for the completely wetted grains.

Equiatomic FeCoCrNi (Zr 0 ) and non-equiatomic FeCoCrNiZr 0.4 (Zr 0.4 ) high-entropy alloys (HEAs) Received 25 May 2018 were synthesised by mechanical alloying and spark plasma sintering. XRD analysis verified the Revised 24 August 2018 formation of FCC and BCC solid solution phases in both alloys after 30 h of ball milling. While the SPS FeCoCrNi alloy contains both FCC and BCC solid solution phases, the FeCoCrNiZr 0.4 presents an FCC solid solution. The thermodynamic analysis showed that FeCoCrNiZr 0.4 is more stable with respect to the FeCoCrNi alloy. The phase stability of FeCoCrNiZr 0.4 was revealed up to ∼800°C. The shear strength and hardness of the FeCoCrNi HEA improved with Zr addition. plasma sintering; thermal Failure analysis of the shear punch tested samples revealed a ductile fracture with dimple stability; mechanical structure for FeCoCrNi and a brittle fracture with a smooth featureless surface for FeCoCrNiZr 0.4 .