Recently, significant progress in the field of grain boundary segregation was achieved, for example, in better understanding and modeling the stabilization of nanocrystalline structures by grain boundary segregation, searching for more advanced approaches to theoretical calculation of segregation energies and development of the complexion approach. Nevertheless, with each progress, new important questions appear which need to be solved. Here, we focus on two basic questions appearing recently: How can be the experimental results on the grain boundary segregation compared reliably to their theoretical counterparts? Is the preferred segregation site of a solute in the grain boundary core substitutional or interstitial? We also show that the entropy of grain boundary segregation is a very important quantity which cannot be neglected in thermodynamic considerations as it plays a crucial role, for example, in prediction of thermodynamic characteristics of grain boundary segregation and in the preference of the segregation site at the boundary.

In this study, Au-based nanoglasses in the form of thin films deposited by magnetron sputtering are comparatively dealloyed. The films have either nanograined or nanocolumnar microstructure, depending on the working pressure of Ar in the sputtering chamber. Nanocolumnar thin films exhibit much higher dealloying rate reducing effectively the dealloying time with respect to nanograined and homogenous thin films. Electrocatalysis experiments indicate that the resulting nanoporous films are active for the methanol electrooxidation, with promising results in term of stability especially for the dealloyed nanocolumnar film.

We developed a facile hydrothermal method to synthesize gold nanoplates with the assistance of surfactant cetyltrimethylammonium chloride (CTAC). Gold nanostructure shapes from triangular, truncated triangular to hexagonal morphology with different sizes can be obtained by accommodating the molar ratios of the surfactant to the gold precursor ([CTAC]/[HAuCl4]). The edge width of gold nanoplates could also be adjusted from tens to hundreds of nanometers, and even several microns. The growth mechanism analysis reveals that the surfactant CTAC directs and promotes the growth of the tabular {111} facets to form nanoplate structures with the size and shape variations. The structure-dependent localized surface plasmon resonance of different gold nanoplates was theoretically and experimentally explained by finite element method simulation and surface-enhanced Raman scattering (SERS) enhancement, respectively. Based on the Raman spectrum analysis of the marker molecule 4-mercaptobenzoic acid (4-MBA) labeled with different gold nanoplates, it demonstrates that the enhanced SERS performance relies on the different plasmonic properties of the gold nanoplates. Therefore, the gold nanoplates may have potential applications in SERS-based sensing and imaging field.

Porous TiAl3 intermetallics were synthesized by the thermal explosion (TE) reaction from TiH2–75 at.% Al elemental powders combining with carbamide as the space holder. The results showed that the space holder particles were removed completely by dissolving in water before sintering and the violent exothermic reaction occurred from the temperature of 672–1193 °C within a few seconds. After TE, TiAl3 was the dominant phase in sintered products and the open porosity of 60.8% was obtained without space holder, while the porosity considerably increased to 81.4% with the addition of 60 vol% carbamide particles. The pore-forming mechanism can be concluded as follows: the sphere large pores replicated from carbamide particles and the small pores generated by the TE reaction. Moreover, porous TiAl3 intermetallics possess the excellent oxidation resistance at 650 °C in air, which enabled them good candidate materials for improving the service life and the accuracy of filtration under special conditions.

Nanosize SiCp (n-SiCp) reinforced Mg–9Al matrix composites (Mg–9Al–xSiC, x = 2.5, 5, 7.5, 10 wt%) with nearly full densification are fabricated by the semisolid powder hot pressing technique assisted with ultrasonic. The effect of SiC nanoparticle contents on microstructures and mechanical properties of the composites is systematically investigated. Grain size and density of Mg–9Al–xSiC composites and morphology of bonding interfacial between the n-SiCp and matrix are found to be greatly dependent on the n-SiCp contents, resulting in the strength and ductility of the composites increase first and then decrease as the increase of n-SiCp contents. As the SiCp content increasing to 7.5 wt%, superior mechanical properties with the yield strength of 191 MPa, ultimate tensile strength of 248 MPa, and elongation to failure of 5.3% are achieved. The improved mechanical properties could be attributed to grain boundary strengthening, Orowan strengthening, and load transfer strengthening.

This report summarizes a recent study demonstrating simple and rapid synthesis of a new Al–Mg alloy system and ultimately synthesizing a metal matrix nanocomposite, which was achieved by processing stacked disks of the two dissimilar metals by conventional high-pressure torsion (HPT) processing. The synthesized Al–Mg alloy system exhibits exceptionally high hardness through rapid diffusion bonding and simultaneous nucleation of intermetallic phases with increased numbers of HPT turns through 20, and improved plasticity was demonstrated by increasing strain rate sensitivity in the alloy system after post-deformation annealing. An additional experiment demonstrated that the alternate stacking of high numbers of dissimilar metal disks may produce a faster metal mixture during HPT. Metal combinations of Al–Cu, Al–Fe, and Al–Ti were processed by the same HPT procedure from separate pure metals to examine the feasibility of the processing technique. The microstructural analysis confirmed the capability of HPT for the formation of heterostructures across the disk diameters in these processed alloy systems. The HPT processing demonstrates a considerable potential for the joining and bonding of dissimilar metals at room temperature and the expeditious fabrication of a wide range of new metal systems.

Carbon nanotubes (CNTs) and silicon carbide nanoparticle (nano-SiCp)-reinforced magnesium (Mg) matrix hybrid composites were prepared through a three-step melt spinning process (ball milling, mechanical stirring, and ultrasonic vibration processing). The hybrid nanoreinforcements showed high strengthening efficiency by which the yield and tensile strength of the hybrid composites experienced 46.7 and 15.2% increment, respectively, compared with the matrix alloy. Obviously, the mixed ball-milling process of SiC nanoparticles and CNTs promoted the dispersion of each other, and both the uniformly distributed SiC nanoparticles and CNTs contributed to the enhanced mechanical performance of the hybrid composites. Besides, the addition of the hybrid nanoreinforcements induced the precipitation of nanosized rod-like MgZn2 phases in the as-extruded composites which also made a contribution to the enhanced performance of the composites. Investigations on the strengthening mechanisms of the hybrid composites show that it originates from grain refinement, load transfer, precipitation enhancement, and Orowan reinforcing. More importantly, the contribution made by each part was analyzed in detail.

TiB2 particulates were formed in situ in an aluminum matrix via chemical reactions between an aluminum melt and the mixture of K2TiF6 and KBF4 salts. Different effects of Sc addition on the formation of the TiB2 particulates were revealed depending on the participation of Sc at different stages of the formation of the particulates. The metal–salt reactions resulted in boride layers along the α-Al grain boundaries in the presence of Sc, while the addition of Sc after the metal–salt reactions broke up the boride layers improving the dispersion of the TiB2 particulates to a limited degree. Sc promoted the growth of the TiB2 particulates, resulting in the coarsening of TiB2 particulates. The participation of Sc in the formation of TiB2 particulates altered the coarsening of the TiB2 particulates, resulting in different morphologies of the TiB2 particulates depending on the participation of Sc in the formation of the TiB2 particulates at different stages.

The powder thixoforming method was used to fabricate 10 vol% silicon carbide particle (SiCp) reinforced 6061 Al matrix composites with high mechanical performances successfully. Here, we demonstrated with proof that proper solution treatment could not only enhance tensile strength of the composite: its ultimate tensile strength and yield strength increased from 230 to 128 MPa in the as-fabricated state to 275 and 212 MPa solutionized at 808 K for 6 h but also improve composite’s tensile elongation significantly with an increment of 161.5% from 2.6% to 6.8%. Corresponding toughening mechanisms are mainly investigated from the perspective of both microstructure examination and total strain to failure calculation through a modified model. The theoretical predictions are in reasonably good agreement with the experimental data. This work may provide a practical way to alleviate the inverse strength–ductility relationship of particulate reinforced metal matrix composites and provide reference for the SF calculation of similar composites subjected to solution treatment.

In this paper, mechanical characteristics of the aluminum layer coated with graphene are investigated by performing numerical tensile experiments through classical molecular dynamics simulations. Based on the results of the simulations, it is shown that coating with graphene enhances the Young’s modulus of aluminum by 88% while changing the tensile behavior of aluminum with hardening–softening mechanisms and significantly increased toughness. Furthermore, the effect of loading rate is examined and a transformation to an amorphous phase is observed in the coated aluminum structure as the loading rate is increased. Even though the dominant component of the coated hybrid structure is the aluminum core in the elastic region, the graphene layer shows its effects majorly in the plastic region by a 60% increase in the ultimate tensile strength. High loading rates at room temperature cause the structure transforms to an amorphous phase, as expected. Thus, effects of loading rate and temperature on amorphization are investigated by performing the same simulations at different strain rates and temperatures (i.e., 0, 300, and 600 K).

In this research, heat transfer analysis was operated by simulation to investigate the influence of carbon nanotubes (CNTs) on laser absorption and molten pool characteristic as well as the vaporization porosity of a typical magnesium alloy of AZ31B in the selective laser melting (SLM) process. It is concluded that the laser absorption is enhanced by 7.9% through mixing 1.5 wt% CNTs into AZ31B alloy powders. The full melting state of molten pools for CNTs/AZ31B composites was achieved by laser input energy densities (LIEDs) larger than 42 J/mm3. However, vaporization porosity has an ascendent tendency with LIED increasing, which leads to poor densities of manufactured parts. As a result, the optimal relative density and mechanical properties of composites are obtained by an LIED of 42 J/mm3. It may solve the problem of low laser absorption in laser processing for magnesium alloys and provide a referenced method to evaluate the vaporization porosity of the material in the SLM process.

The elastic properties and solid-solution strengthening (SSS) of the binary Ni–Co and Ni–Cr, and ternary Ni–Co–Cr alloys were investigated by the first-principles method. The results show that both Co and Cr increase lattice parameters of the binary alloys linearly. However, nonlinearity is found in compositional dependence of lattice parameters in the ternary Ni–Co–Cr alloys, that is, Co increases but decreases the lattice parameter at low and high Cr concentrations, respectively. Co increases the bulk, shear, and Young’s moduli (B, G, and E), while Cr increases B but decreases G and E in the binary alloys. In the ternary Ni–Co–Cr alloys, G and E have a similar compositional dependence to those in the binary alloys, except for B. Based on the Labusch model, the SSS parameter of Ni–Cr is larger than that of Ni–Co. The SSS effect increases significantly with Cr addition, especially at low Co concentrations in the ternary Ni–Co–Cr alloys. Meanwhile, it increases mildly with Co addition at low Cr concentrations but decreases with Co addition at high Cr concentrations.

Positron annihilation spectroscopy and differential scanning calorimetry were used to evaluate the changes of the atomic configurations in Zr-based metallic glasses (MGs) due to alloying and plastic deformation. The correlation between the atomic configurations of MGs and the amorphous-to-icosahedral phase transition due to heating was investigated. The results indicate that the free volume frozen in the as-cast Zr60Al15Ni25, Zr65Al7.5Ni10Cu17.5, and Zr65Al7.5Ni10Cu17.5Ag5 MGs substantially decreases in sequence. More excess free volume is introduced in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling. The annihilation of free volume due to alloying considerably stabilizes the icosahedral structure of MGs, which enhances the nucleation and growth of quasicrystals upon heating. However, the nucleation and growth of quasicrystals are considerably suppressed in Zr65Al7.5Ni10Cu17.5Ag5 MG due to cold rolling and milling, during which the more introduced excess free volume results in substantial destruction of short-range order with 5-fold symmetry. The present work further provides direct evidence for the prevalence of icosahedral short-range order in MGs.

In this work, differential scanning calorimetry (DSC) was used to characterize and analyze the precipitation/dissolution kinetics of second phase particles during the cooling/reheating process in a vanadium microalloyed steel. The results indicated that three obvious exothermic peaks were detected on the cooling DSC curve. Furthermore, three corresponding endothermic peaks were also detected on the heating DSC curve. Combined with thermodynamic calculation and transmission electron microscopy analysis, these three exothermic peaks along cooling DSC curve were defined as the precipitation reaction of V(CN), the reaction of austenite transformation into ferrite and the precipitation reaction of VC, respectively. Meanwhile, three corresponding reverse reactions for cooling were also defined along the reheating DSC curve. The linear regression result revealed that the precipitation activation energies for V(CN) and VC were identified as 311.2 kJ/mol and 167.6 kJ/mol, respectively. The dissolution activation energies for VC and V(CN) were identified as 255.4 kJ/mol and 592.6 kJ/mol, respectively.

The effects of misorientation on the quasi-static and dynamic mechanical behaviors of a second generation Ni-based single crystal superalloy DD5 were investigated. A Split-Hopkinson pressure bar system was used to perform dynamic compression. The crystallographic misorientation between the stress axis and the [001] direction was characterized through rotating orientation X-ray diffraction. The results demonstrated that the flow stress was closely related to the misorientation. It decreased first and consequently increased as the misorientation increased from 0° to 45°. The dynamic flow stress was significantly higher than the quasi-static stress. Moreover, the flow stress under dynamics was more sensitive to the misorientation. A constitutive model was used to illustrate the misorientation effect on the mechanical behavior. Finally, the effect of strain rate on the crystal orientation was also investigated. It was discovered that the orientation deviation change following quasi-static compression could be neglected. By contrast, the orientation changed by 3–9° subsequently to dynamic compression.

In this work, three Mg–Zn–Y–Ca alloys reinforced by icosahedral quasicrystal phase through trace Y addition were extruded at a low temperature of 503 K. With increasing the contents of Zn and Y, the grain size of the as-extruded alloy was significantly reduced while both the size and volume fraction of nanosized precipitates were increased. The grain refinement in the Mg–Zn–Y–Ca alloy was related to dynamical recrystallization during extrusion and the pinning effect of nanosized precipitates on the grain boundaries. After extrusion, the yield strength (YS) and ultimate tensile strength (UTS) of the three alloys were significantly increased. The YS of 294.0 MPa, UTS of 337.5 MPa, and elongation of 10.6% were obtained in the case of Mg–2.09Zn–0.26Y–0.12Ca (at.%) alloys. The improvement in the mechanical properties could mainly be due to the grain boundary strengthening and Orowan strengthening. The as-cast alloy exhibited a typical cleavage fracture while the as-extruded alloy possessed a mixture fracture of dimple fracture and cracking along the twinning.

The hot deformation behavior and processing characteristics of Mg–3Zn–0.3Ca–0.4La (wt%) alloys were investigated by hot compression deformation. The results suggested that deformation parameters had significant effects on deformation behavior and dynamic recrystallization of the Mg–Zn–Ca–La alloy. The average activation energy of deformation was calculated to be 188.9 kJ/mol. The processing map was constructed and analyzed based on the dynamic material model, and the optimum hot working window of the alloy was determined to be the temperature of 350 °C and the strain rates between 0.001 and 0.01 s−1. Furthermore, the DRX kinetic model of the Mg–3Zn–0.3Ca–0.4La (wt%) alloy was established, which implied that incomplete dynamic recrystallization occurred for the Mg–Zn–Ca–La alloy in the present work. Microstructure analysis indicated that deformation parameters played a critical role on the microstructure optimization. The dynamically recrystallized (DRXed) region fraction and the DRXed grain size were increased with the increase of deformation temperature and decrease of deformation rates.

Multi-pass warm rolling with falling temperature was proposed and investigated to obtain AZ31 Mg alloy sheets with a fine-grained microstructure. The results indicated that the grain microstructure of AZ31 alloy sheets was successfully refined from 22.1 to 4.5 μm after multi-pass warm rolling with falling temperature and annealing. Compared to the as-received sheet, the multi-pass warm rolled sheets in annealed condition exhibited weaker (0001) basal texture intensity, which resulted in the significantly increased Schmid factor of 〈a〉 basal slip. After multi-pass warm rolling with falling temperature, the rolled sheets in annealed condition also exhibited much better mechanical properties, e.g., higher tensile strength, larger fracture elongation, and higher Erichsen value, especially the IE of 8-pass warm rolled sheet in annealed condition was significantly increased by ∼33% under the same thickness, which could be attributed to the refined grain microstructure and the weakened basal texture.

Monosized spherical Cu–20% Sn (wt%) alloy particles with diameter ranging from 70.6 to 334.0 μm were prepared by the pulsated orifice ejection method (termed “POEM”). Fully dense without pores and bulk inclusions, the cross-sectional micrographs of the spherical alloy particles indicate an even distribution of Cu and Sn. These spherical Cu–Sn alloy particles exhibit a good spherical shape and a narrow size distribution, suggesting that the liquid Cu–Sn alloy can completely break the balance between the surface tension and the liquid static pressure in the crucible micropores and accurately control the volume of the droplets. Furthermore, the cooling rate of spherical Cu–20% Sn alloy particles is estimated by a Newton’s cooling model. The cooling rate of the Cu–20% Sn alloy particle decreases gradually with the particle diameter increasing. Smaller particles have higher cooling rates and when the particle diameter is less than 70 μm, the cooling rate of particles can reach more than 3.3 × 104 K/s. The secondary dendrite arm spacing has strong dependence on particle diameter which increases gradually with the increase of particle diameter. The results demonstrate that POEM is an effective route for fabrication of high-quality monosized Cu–20% Sn alloy particles.

Ti–Al alloys are established as promising candidates for aerospace applications due to their lightweight, good elevated temperature strength, and decent corrosion resistance. In this study, a Ti–51Al (at.%) alloy is fabricated by spray deposition. The effects of temperature and strain rate on the deformation behavior of the spray-deposited Ti–Al alloy are investigated. The microstructural evolution of the Ti–Al alloy with different deformation temperatures is discussed in detail. A strain-dependent constitutive equation was proposed to predict the flow stresses at the elevated temperatures for the spray-deposited Ti–Al alloy. The microstructure of the as-deposited Ti–51Al alloy exhibits a α2/γ lamellar-structure with average size 25 ± 2 μm, due to the high cooling rate observed during solidification. The lamellar structure is embedded on a γ matrix. The amount of the α2/γ lamellar-structure reduces gradually with increasing the hot deformation temperature. After hot isostatic pressing at 1523 K, the microstructure is mainly comprised of the γ matrix.