Multi-Dimensional Revealing the Influence Mechanism of the δ Phase on the Tensile Fracture Behavior of a Nickel-Based Superalloy on the Mesoscopic Scale

As the key materials of aircraft engines, nickel-based superalloys have excellent comprehensive properties. Mircotensile experiments were carried out based on in situ digital image correlation (DIC) and in situ synchrotron radiation (SR) technique. The effects of the δ phase on the grain orientation, surface roughening, and strain localization were investigated. The results showed that the average kernel average misorientation (KAM) value of the fractured specimens increased significantly compared with that of the heat-treated specimens. The surface roughness decreased with an increasing volume fraction of the δ phase. The strain localization of specimens increased with the increasing ageing time. The size and volume fraction of voids gradually increased with the increase in plastic strain. Some small voids expanded into large voids with a complex morphology during micro-tensile deformation. The needle-like δ phase near the fracture broke into short rods, while the minor spherical δ phase did not break. The rod-like and needle-like δ phases provided channels for the propagation of the microcrack, and the accumulation of the microcrack eventually led to the fracture of specimens.

Simulation of the Peritectic Phase Transition in Fe-C Alloys

In this work, a multi-phase cellular automaton (CA) model is extended for the quantitative simulation of peritectic phase transition. First, the effects of cooling rate/supersaturation and temperature on the peritectic transformation kinetics in Fe-C alloys are investigated by utilizing the present CA model. The CA simulations show that supersaturations in the parent phases (liquid and δ-ferrite) increase the L/γ interface growth velocity remarkably, but tinily for the δ/γ interface migration velocity. There exists a transition supersaturation for isothermal transformations, at which the growth rates of the two interfaces are equal. The transition supersaturation is found to increase with decreasing temperature. Microstructural evolution at different cooling rates during peritectic transformation is simulated using the experimental conditions. At low cooling rates, the δ/γ interface propagates at a higher velocity than the L/γ interface. At high cooling rates, however, the γ-phase grows more into the L-phase with a cellular morphology. Then, the proposed CA model is applied to simulate the microstructural evolution during peritectic reaction. It is observed that the γ-phase propagates along the L/δ interface and finally encircles the δ-phase. Meanwhile, the intervenient γ-phase grows in thickness through peritectic transformation. The CA simulations are compared reasonably well with the experimental data and analytical calculations.

The Effect of the Multi-doping Strategy on Stabilization of the Cubic δ-phase in the Bi2O3-based Solid Electrolyte Systems in Terms of the SOFC Applications

In this study, the effects of multi-doping strategy on phase stabilization and electrical conductivity for the doped Bi 2 O 3 system were investigated. All solid mixtures were created by solid state reactions according to a certain stoichiometric ratio in atmospheric conditions. The structural, electrical, thermal and surface characterizations of the created samples were performed by x-ray diffraction method (XRD), four point-probe technique (4-PPT), differential thermal analysis/thermo gravimetric analysis (DTA/TGA) and scanning electron microscope (SEM), respectively. From XRD results, it was seen that the fcc δ-phase could be stabilized by using only 1:1:1:2 or 2:2:2:1 dopant content ratio (in here, “1:” is corresponds to” 5%” mole). The other compounds prepared out of this ratios were mixed phase because of the containing both α-phase peaks and δ-phase peaks on their XRD pattern. When the all samples were compared in terms of electrical conductivity at 750 °C, it was observed that the fcc δ-phase stabilized samples exhibited higher conductivity than that of other compounds as expected. The highest electrical conductivity was for the sample, dopant content ratios of which are 1: 1: 1: 2, with 0.014 S.cm -1 at 750 °C and also it had the lowest activation energy (0.51 eV) among all samples. On the other hand, according to the thermal analysis results, it was concluded that phase transition occurred only on the DTA curve of the sample given with dopant content ratios 1:1:1:1 due to presence of endothermic peak on its DTA curve at 729°C during the heating process. Also, for this sample, it was clearly predicted from the electrical conductivity graphs depending on temperature that the phase transition occurred at just that temperature (729 °C) due to the sudden increase in conductivity by indicating phase transition from the α-phase to the cubic δ-phase. The SEM analysis pointed out that grain size decreased as total dopant ratio increased and also the grain boundary changed sharply with the increase in the total dopant ratio.

Phase evolution of all-inorganic perovskite nanowires during its growth from quantum dots

All-inorganic lead-halide perovskites have emerged as an exciting material owing to their excellent optoelectronic properties and high stability over hybrid organometallic perovskites. Nanowires of these materials, in particular, have shown great promise for optoelectronic applications due to their high optical absorption coefficient and low defect state density. However, the synthesis of the most promising alpha-Cesium lead iodide (α-CsPbI3) nanowires is challenging as it is metastable and spontaneously converts to a non-perovskite δ-phase. The hot-injection method is one of the most facile, well-controlled, and commonly used approaches for synthesizing CsPbX3 nanostructures. But the exact mechanism of growing these nanowires in this technique is not clear. Here, we show that the hot-injection method produces photoactive phases of quantum dots (QDs) and nanowires of CsPbBr3, and QDs of CsPbI3, but CsPbI3 nanowires are grown in their non-perovskite δ-phase. Monitoring the nanowire growth during the hot-injection technique and through detailed characterization, we establish that CsPbI3 nanowires are formed in the non-perovskite phase from the beginning rather than transforming after its growth from perovskite to a non-perovskite phase. We have discussed a possible mechanism of how non-perovskite nanowires of CsPbI3 grow at the expense of photoactive perovskite QDs. Our findings will help to synthesize nanostructures of all-inorganic perovskites with desired phases, which is essential for successful technological applications.

Characterization of Ni-Cr-Mo alloy phase structures under DLD process

Direct laser deposition of Ni-Cr-Mo alloy has been carried out to study the phase structure transformation under various operating parameters. To assess the phase composition SEM, TEM and XRD analysis were performed. It clearly seen that the precipitation of straightening phases (γ' and γ") depends on the temperature gradients caused by different laser power. The nucleation of γ' phase starts at 750 W while γ" phase at 1000 W. The changes in temperature gradients lead to different diffusion condition across all the stage of laser power variation and formation of δ-phase, primary MC carbides and Laves phase. δ-phase of all samples did not change the shape and characterized only by plate-like shape.