A bulk NbCr2 Laves phase matrix composite toughened with ductile Cr phase has been fabricated by spark plasma sintering (SPS) using pre-alloyed NbCr2 and Cr powders. The sintering behaviour and phase morphological evolution of the sintered alloy were investigated. The results show that a series of microstructure evolutions along the sintering temperature occurred: elongated Cr phase with uniform dispersion of fine NbCr2 and Cr phase → coarse Cr phase with matured fine NbCr2 and Cr → coarse Cr and Nb phases with lamellar eutectics. The microstructural evolution and phase transformation along the sintering temperature are analyzed by considering the inhomogenous temperature distribution and the accelerated atomic diffusion due to the pulsed electric current applied during SPS. The room temperature fracture toughness of the sintered samples is expected to be markedly improved due to the absence of lamellar or the occurrence of ductile Cr and Nb phases.

In an attempt to introduce a novel approach to formulate carbon black (ketjen black) suspension with enhanced colloidal stability, improved flowability, and higher conductivity, ketjen black was dispersed in microemulsion systems composed of a non-ionic surfactant (Triton X100), decanol, and water. Rheo-electric and rheo-microscopy proved to be very powerful techniques that are able to elucidate the microstructure evolution with the composition and under shear flow. Interestingly, the carbon black slurries at low decanol/water ratio are weak gels (flowable) with higher electrical conductivity than those at higher ratio, which shows strong-gel viscoelastic response. In addition, the slurries show recoverable electrical behavior under shear flow in tandem with the viscosity trend. It is likely that the oil-in-water microemulsion enhances slurries’ stability without affecting the percolating network of carbon black. On the other hand, the oil-in-water analogous and bilayer structure of the lamellar phase makes the slurries less conductive as a consequence of losing the network percolation.

CALPHAD databases have traditionally been developed for investigation of single-principal component alloys. With the advent of batch processing capability, engineering teams have proposed using these models to systematically explore compositional space for multiprincipal element systems. However, the uncertainty of phase equilibria predictions outside of traditional compositional bounds has yet to be evaluated. This study assesses the current capabilities of commercially available CALPHAD databases to predict phase equilibria within ternary phase space as a function of the number of full binary system descriptions contained within the thermodynamic databases, the spatial location in compositional space relative to subsystem descriptions, and the specific database used. A strong correlation was observed between the fraction of subsystem descriptions available for the free energy calculation and the accuracy of phase predictions in undefined ternary space. The accuracy of equilibria predictions degraded with increased compositional extrapolation from defined subsystems.

AZ31 magnesium alloy sheets were A-TIG-welded through a coating of flux, which contained different ratios of Ce powder and nano-sized SiC as reinforcement particles and equal mass of TiO2 as activating fluxes. The microscopic analysis results illustrated that relatively low content of Ce in the reinforcement particles caused the formation of Al3Ce precipitates and refined the grains of α-Mg phase together with β-Mg17Al12 and SiC particles. The increase in microhardness and ultimate tensile strength of the joints was 6.2% and 19.2%, respectively, when reinforcement particles contain 20 wt% Ce compared to the joints coated without Ce. By studying the electrochemical test results, when using 20 wt% Ce + 80 wt% SiC as reinforcement particles, the corrosion current density was the lowest and the corrosion resistance reached the largest value, reflecting the improvement of corrosion property of the joint affected by Ce element.

Biodegradable poly(lactide acid) (PLA) has been well-studied as a shape memory polymer in recent years, but the brittleness and relatively high Tg limit its applications. In this study, a series of PLA/poly(ethylene glycol) (PEG) blends were manufactured by using the solvent evaporation method. The thermal behaviors, morphology, hydrophilicity, and mechanical properties of the samples with different contents of PEG have been experimentally studied by differential scanning calorimetry, scanning electronic microscopy, water contact angle, dynamic mechanical analysis, and tensile test. Furthermore, the influence of PEG on the shape memory properties under different loading conditions including the stretch strain, recovery temperature, deformation temperature, and tensile rate were explored systematically. Experimental results reveal that introduction of appropriate contents of the plasticizer PEG into the PLA/PEG systems results in the significant improvement of morphology, hydrophilicity, and mechanical properties while the high shape memory properties are still retained.

A set of embedded atom method model interatomic potentials is presented to represent a high-entropy alloy with five components. The set is developed to resemble but not model precisely face-centered cubic (fcc) near-equiatomic mixtures of Fe–Ni–Cr–Co–Cu. The individual components have atomic sizes deviating up to 3%. With the heats of mixing of all binary equiatomic random fcc mixtures being less than 0.7 kJ/mol and the corresponding value for the quinary being −0.0002 kJ/mol, the potentials predict the random equiatomic fcc quinary mixture to be stable with respect to phase separation or ordering and with respect to bcc and hcp random mixtures. The details of lattice distortion, strain, and stress states in this phase are reported. The standard deviation in the individual nearest neighbor bond lengths was found to be in the range of 2%. Most importantly, individual atoms in the alloy were found to be under atomic strains up to 0.5%, corresponding to individual atomic stresses up to several GPa.

Among various methods used for the reduction of graphene oxide (GO) into a purer form of graphene, the thermal reduction method provides a simpler, safer, and economic alternative, compared to other techniques. Thermal reduction of GO causes significant weight loss and volume expansion of the material. Current work investigates the onset temperature where reduction in terms of exfoliation takes place, which is determined to be 325 °C at standard atmospheric pressure. Reduction temperature plays the most crucial role as it controls the quality of reduced graphene oxide in terms of weight percentage of carbon and lattice defect. The study leads to achieving highest content with a minimum defect in the graphene lattice at the optimum temperature, which is found to be 350 °C at standard atmospheric pressure. The thermal reduction process has been analyzed with the help of Fourier transform infrared spectroscopy, thermogravimetric analysis, and thermal degradation kinetics. From thermal degradation kinetics of GO, the rate of reaction has been found to be independent of concentration and is a sole function of temperature.

For thixoforming, it is necessary to have a good microstructure of fine, uniform, and globular grains in a semisolid range. In this study, the nano-Al2O3(Al2O3np)/Al7075 composites with a high solid fraction were fabricated by specially made Al2O3np containing Mg powders and semisolid ultrasonic vibration (SSUV) process. The influence of SSUV technology on primary α-Al grain and second phase in the composites was investigated. Microstructural studies revealed that a good semisolid slurry with an average grain size of 73 μm, a shape factor of 0.84, and a solid fraction of 0.715 could be obtained. Also, it could be shown that SSUV affected largely the size and type of the second phase as well as growth and nucleation of the primary α-Al grain. TEM analysis revealed that there are well-defined crystallographic orientation relationships between the second phases and α-Al, suggesting enhanced heterogeneous nucleation in Al7075 alloys. Moreover, mechanisms involved in the development of microstructure were discussed.

Fused-filament-fabrication (FFF) is a commonly used and commercially successful additive-manufacturing method for thermoplastics. Depending on the FFF process parameters, the internal-strains along print direction, thermal-gradient across layers, and anisotropy introduced during layer-by-layer build-up can significantly affect the macroscopic properties, dimensional stability, and structural performance of the final part. Conversely, these factors can be optimized to result in unique, controllable thermally actuated shape-transformations. This work aims at quantifying and understanding the underlying mechanisms that drive the thermally actuated shape-transformation in three commonly used thermoplastics fabricated by the FFF method namely, poly-lactic-acid (PLA), high-impact-polystyrene (HIPS), and acrylonitrile-butadiene-styrene (ABS). Initially, the release of internal-strains is analyzed for unidirectionally printed samples experimentally and computationally, employing a thermoviscoelastic-viscoplastic constitutive model. Subsequently, two basic initial (as-printed) configurations, namely, a beam and a circular-disc are chosen to study the 1D to 2D and 2D to 3D shape-transformations, respectively. The effect of process parameters such as the printing speed, print path, and infill density on the shape transformation behavior is investigated systematically. Finally, the results are applied to demonstrate shape-transformations for application in morphing-structures and/or as an alternative, simplified process in fabricating curved-components.

To overcome the limited feasibility of various refractory high-entropy alloys (HEAs) due to the presence of (i) very dense elements (W and Ta), (ii) costly elements (Hf and Ta), and (iii) oxidation prone elements (V) in them, AlxCryMozNbTiZr HEAs were prepared via arc-melting. Considering the critical nature of oxidation resistance in high-temperature applications, HEAs were characterized to form a combinatorial library of microstructural and oxidation behavior. AlxCryMozNbTiZr HEAs revealed multiphase microstructures consisting of intermetallic phases along with BCC matrices. Mass loss and porous microstructures were obtained in Mo-rich HEAs after oxidation at 1000 °C for 1 h. The presence of Al enhanced the oxidation resistance and developed a protective oxide layer on the HEAs. Al30Cr10-NTZ exhibited promising potential for use in high temperature applications, as it showed an oxidation time exponent of ∼0.5 and a dense and continuous oxide layer.

Magnesium is a biodegradable material that has potential application in cardiovascular stent development: its excellent mechanical properties and blood compatibility make it highly useful in interventional therapy. Nevertheless, the following shortcomings restrict its further application: antihyperplasia function and promoting surface endothelialization. In this study, we immobilized a specific link peptide of endothelial cells, Arg-Glu-Asp-Val (REDV), onto polydopamine (PDA)-deposited Mg–Zn–Y–Nd alloy surface via covalent reaction to improve the growth of the endothelial cells. The PDA/REDV coating with optimized parameters maintained the good blood compatibility of the Mg–Zn–Y–Nd alloy at the biomimetic speed of the blood flow and significantly inhibited the growth of the vascular smooth muscle cells and macrophage attachment/activation, which indicated its better functions in antihyperplasia and anti-inflammation. In particular, the PDA/REDV coating not only showed consistent results in promoting the attachment of endothelial cells as reported elsewhere, but also displayed the ability of enhancing the viability of endothelial cells (or inhibiting apoptosis), suggesting its pro-endothelialized function through different pathways. In summary, this PDA/REDV coating addressed the above-mentioned shortcomings of the magnesium alloy, which may promise its wider application.

Refractory high-entropy alloys (RHEAs) have recently attracted much attention, primarily due to their mechanical properties at elevated temperatures. However, the equilibrium phase-stability of these alloy systems is not well established. The present investigation focuses on the phase stability of Al0.5NbTa0.8Ti1.5V0.2Zr RHEA at temperatures ranging from 600 to 1200 °C. The detailed phase characterization involves coupling of scanning electron microscopy, transmission electron microscopy, and atom probe tomography. The stable phases present at these temperatures are (i) 1200 °C—body-centered cubic (BCC) matrix with nano-B2 precipitates; (ii) 1000 °C and 800 °C—a BCC matrix phase with Al–Zr rich hexagonal closed packed intermetallic precipitates and, (iii) 600 °C—a BCC + B2 microstructure, comprising a continuous BCC matrix with discrete B2 precipitates. These results highlight the substantial changes in phase stability as a function of temperature in RHEAs, and high-entropy alloys in general, and also the importance of accounting for these changes especially while designing alloys for high temperature applications.