This study presents a short-time reactive Al-melt treatment that simultaneously enhances hardness and corrosion resistance in liquid-metal-dealloyed Mg–Ti composites. A three-dimensional bicontinuous Mg–Ti composite is first fabricated by immersing a Ti30Cu70 precursor in a pure Mg melt, followed by immersion in a pure Al melt at 750 °C for 10 s. The initial Mg–Ti composite consists of a co-continuous α-Mg/α-Ti matrix–matrix structure. After Al-melt treatment, the interconnected morphology is preserved, while the phase constitution is reconstructed into a multiphase α-Ti/TiAl3/Al3Mg2 structure. TiAl3 forms along the residual α-Ti ligaments, whereas the original Mg-rich regions transform into Al3Mg2. The average effective grain size of the residual α-Ti decreases from 3.7 to 0.8 µm, accompanied by increased local misorientation and a higher density of {11–22} compression twin boundaries. As a result, the surface hardness increases from 106 to 378 HV, while remaining above 260 HV at a depth of 260 µm. The Al-treated Mg–Ti composite also exhibits a markedly reduced corrosion rate in 3.5 wt.% NaCl solution, decreasing from 13.2 to 0.5 mm/year based on hydrogen evolution measurements and from 17.2 to 0.7 mm/year based on weight-loss measurements. Scanning Kelvin probe force microscopy reveals that the initial direct α-Mg/α-Ti interface, with a Volta potential difference of approximately 635 mV, is replaced by α-Ti/TiAl3 and TiAl3/Al3Mg2 interfaces with lower potential differences of approximately 271 and 285 mV, respectively. Overall, the short-time Al-melt treatment enables simultaneous hardness increase and corrosion mitigation through rapid interfacial reconstruction and phase transformation while preserving the bicontinuous structure.
High-entropy alloys (HEAs) are multicomponent systems that have attracted significant attention due to their superior mechanical properties as compared to conventional alloys. Among these properties, hardness plays a vital role and is strongly influenced by the selection and concentration of principal alloying elements. However, predicting the hardness of HEAs is challenging due to the complex and nonlinear relationship between composition and mechanical behavior. In this study, an artificial neural network (ANN) model was developed using experimentally reported hardness data for HEAs composed of Fe, Co, Ni, Cr, V, Mn, Al, Nb, and Cu. The model achieved high prediction accuracy, with adjusted R2 values of 0.9592 and 0.9023 for the training and testing datasets, respectively. A user-friendly graphical interface was also developed to support the practical application of the model. The model was further employed to evaluate the effect of individual alloying elements on hardness using the Index of Relative Importance (IRI). Results showed that Al had the highest positive influence on hardness, while Fe exhibited the most negative impact. Elements such as Al, Cr, Nb and V were found to enhance hardness, whereas Co, Cu, Mn, Ni, and Fe tended to reduce it. Finally, the developed model proposed HEA compositions 30Co–10.5Ni–21.1Cr–7Mn–25Al and 16Fe–27.54Co–47.1Cr–6Mn–13.65Nb with a predicted hardness of 733.67HV and 963.8HV, respectively. The predicted hardness was found near to experimental values.
The continued scaling of semiconductor devices toward high-aspect-ratio architectures necessitates increasingly aggressive plasma etching conditions, which in turn accelerate the degradation of plasma-facing chamber components. Consequently, there is an urgent need to develop alternative materials that surpass conventional candidates, such as Al2O3 and YAG, by offering both cost-effectiveness and superior erosion resistance. In this study, polycrystalline MgO ceramics were fabricated via hot pressing with the incorporation of Al2O3, Y2O3, and SiO2 additives. The effects of additive composition and sintering temperature on the resulting microstructure and plasma etching resistance were systematically investigated. The synthesized MgO ceramics exhibited a dense, fine-grained microstructure and achieved an etching rate significantly lower (12–33
This study presents three-dimensional unsteady computational fluid dynamics simulations, under the assumption of local thermodynamic equilibrium, conducted in OpenFOAM to examine how varying the outlet diameter and throat length of a plasma spray torch affects its internal arc behavior and exit jet characteristics. Voltage and attachment-point temperature diagnostics show a restrike cycle driven by an imbalance between Lorentz and drag forces. These attachment dynamics are consistent across downstream geometries. Outlet observations reveal that Lorentz-driven off-axis motion produces crescent-shaped temperature and velocity fluctuations. When time-averaged, these yield a flat-topped parabolic radial temperature profile with a 15 kK centerline peak and an M-shaped mean velocity with a central dip. The hot-core thickness is geometry-insensitive because the sharp drop in thermal conductivity imposes the conductive bottleneck while elevated kinematic viscosity suppresses shear-layer mixing. In contrast, the velocity responds predictably to geometry: Larger outlets reduce overall jet speed and flatten the core, whereas longer throats increase centerline velocity nearly linearly by extending the acceleration region. These results supply compact, physics-based heat-source and inflow boundary conditions for thermal spray simulations.
This study investigates the interplay between composition-dependent phase stability and deformation mechanisms in Co-Cr-Ni medium-entropy alloys (MEAs) of equiatomic and non-equiatomic compositions. Co-rich (Co2CrNi), Cr-rich (CoCr2Ni), and Ni-rich (CoCrNi2) MEAs were designed with each composition determined by selecting a constituent element present in the highest proportion compared to the equiatomic CoCrNi system, which served as the master composition. The composition tuning resulted in distinct microstructure evolution, influencing the mechanical properties and flow mechanisms, closely correlated with variations in stacking fault energy (SFE). Notably, the results highlighted the superior formability, attributed to the distinct deformation mechanisms present in single-phase MEAs (i.e., Co2CrNi, CoCrNi2, and CoCrNi). On the other hand, the introduction of similar to 50 at% Cr thermodynamically triggered the formation of sigma-phase upon homogenization treatment, negatively affecting the stability of the face-centered cubic (FCC) matrix and the alloy's mechanical behavior. Macro-to-nanoscale hierarchical microstructure analyses confirmed the progression of deformation via deformation-induced twinning (CoCrNi) and epsilon-martensite formation (Co2CrNi) in low-SFE alloys. In contrast, the higher-SFE CoCrNi2 alloy exhibited highly dense dislocation walls (HDDWs) with fewer planar dislocation arrays despite the presence of numerous annealing twins. This research provides a systematic alloy design strategy, integrating theoretical analyses with experimental observations to achieve an in-depth comprehension of composition tuning in the Co-Cr-Ni system.
