The metadynamic recrystallization (MDRX) behavior of a medium carbon Cr–Ni–Mo alloyed steel 34CrNiMo was investigated using two-stage hot compression test on a Gleeble thermal-mechanical simulator in the temperature range of 1273–1423 K, strain rate range of 0.1–5.0 s−1, and interval times of 0.5–5 s. The softening of the flow stress at the second stage of compression and microstructure observation confirm the occurrence of MDRX at the elevated temperatures within very short interval time. Then the MDRX softening fraction was calculated based on the flow stress curves. The results indicate that the MDRX softening fraction increased with increasing interval time, deformation temperature, and strain rate. The kinetics of MDRX softening behavior was established using Avrami equation and the apparent activation energy of MDRX for 34CrNiMo steel was evaluated as 93 kJ/mol. The predicted results show good agreements with the experimental ones, indicating the efficiency of proposed kinetics equation.

A systematic analysis of the correlation between the valence electrons and the transformation temperatures of Ti–Ni-based shape memory alloys has been carried out by Zarinjad and Liu. They have shown that the valence electron theory can be successfully applied to estimate these temperatures, although the mechanisms of the temperature shift during alloying remains not completely understood. Other important shape memory alloy systems with technological importance are the Cu–Al based, which deserve a thorough analysis concerning the composition influence on the transformation temperatures and the valence electron theory. In this paper, the valence electron concentration, valence electron density (VED), enthalpy of reaction, and crystallographic compatibility were analyzed to understand the mechanisms, which control the transformation temperatures of Cu–Al-based alloys. It was observed that the larger the VED, the more energy is used in the transformation. The same tendency is present when the crystallographic compatibility is smaller. These results show that the valence electron theory based on the VED plays an important role in the prediction of the temperature transformation and the energies involved in the reaction.

The effect of aluminizing and Cu electroplating of the steel insert in fabrication of Al-matrix bimetal on the microstructure and mechanical properties of the interface layer was investigated. Compound casting process was used to fabricate Al-matrix bimetals reinforced with coated steel insert. The microstructures at the interface region were studied using light optical and scanning electron microscopes and energy dispersive X-ray spectroscopy. The interfacial shear strengths of the fabricated bimetals were compared using push-out test. The results showed that electroplating with copper and aluminizing of steel insert in aluminum matrix led to significant improvement of metallurgical bonding between the steel and aluminum cast matrix. Cu-coated insert contained a thicker and uniform reaction layer formed at the interface between the steel insert and aluminum matrix compared to aluminized coated insert. The results of push-out tests indicated higher interfacial shear strength for the bimetal with Cu-coated insert despite possessing a larger thickness.

Metal working tools are generally exposed to hard conditions, and the control of their excessive wear is of a crucial importance for the metal working process. Indeed, tribo-layers as mechanically mixed layers and wear debris are completely involved in the wear behavior. This paper undertakes the study of the frictional behavior and wear of X40CrMoV5 (AISI H13) tool steel as a function of speed rotation at room temperature. The utmost objective of this research work is to assess some wear mechanisms of this tool steel used at room temperature. The tribological experiments were accomplished on high temperature pin-on-disc tribometer with an open sliding contact. The pin material was X40CrMoV5 steel and the disc material was Fe360B steel. The investigations were accomplished for different rotatory speeds of the disc ranging from 25 rpm to 100 rpm, and different nominal pressure. SEM and EDS explored the development surface damage and oxides tribo-layers. It was concluded that the increase of the rotation speed of the disc and the nominal pressure reduce the friction coefficient by the creation of a wear protective layer.

Polymer nanocomposites are being considered as future materials to effectively attenuate high energy radiations. The present work addresses effects of neutron radiation on the mechanical properties of lightweight multifunctional polymer composite which were fabricated by dispersing nanoparticles with radiation shielding properties in an epoxy polymer. Three different types of nanoparticles including boron nanopowder, gadolinium, and boron carbide, which are known for excellent radiation absorbing characteristics, were dispersed into epoxy resin to form core sheets for final hybrid sandwich structure. The neutron radiation shielding performance of nanocomposites and their mechanical and thermophysical properties were investigated. The study indicates that the neutron shielding efficiency increased significantly by introduction of nanoparticles. Moreover, the mechanical testing and thermophysical analysis showed that the core materials can retain the structural integrity after they are exposed to the highly thermalized neutron radiation in steady-state mode with a flux of 3 × 1013 n/cm2/s.

Cs2LiYCl6 (CLYC) is a commercial scintillator material having good energy resolution and dual gamma/neutron detection capabilities. CLYC crystals currently used in detectors are grown by the vertical Bridgman method. Boules grown from stoichiometric melts, however, often contain secondary phases, Cs3YCl6 and LiCl, at the beginning and end of the crystal, respectively, suggesting that this composition is incongruently melting. Since no phase diagram containing CLYC existed in the literature prior to this study, the Cs2YCl5–LiCl phase diagram was explored. Several crystals were then grown from various melt compositions. As predicted from the phase diagram, a starting composition of around 60 mol% LiCl did not produce Cs3YCl6 and maintained a low concentration of LiCl.

In this work, we reported the growth of cadmium-free Ag-doped Zn–In–S nanocrystals (NCs) with effective photoluminescence (PL) via a hot-injection strategy. The effects of the nucleation temperatures, reaction times, and Ag-doping concentrations on the PL properties of Ag-doped Zn–In–S NCs were investigated systematically. The as-synthesized NCs exhibit color-tunable PL emissions covering a broad visible range of 472–585 nm. After being passivated by a protective ZnS shell, the PL quantum yield (QY) of the resultant NCs was greatly improved up to 33%. With the increase of the Ag-doping level, the PL is significantly intensified due to the improved concentration of Ag ions which provides more holes to recombine with electrons from the bottom of the conduction band. This also makes the emission via the dopant energy level become a powerful, competitive advantage for the NCs with higher Ag-doping levels, resulting in a longer lifetime and higher PL QY. These results suggest that tailoring the Ag-doping level can be a powerful strategy to control the optical properties of Ag-doped Zn–In–S NCs.

We report the structure and synthesis approach for obtaining a ceramic nanocomposite pellet comprising ∼50 nm-sized TaC nanoparticles. A mixture of Ta metal powder and the carbon precursor 1,2,4,5-tetraphenylethynyl benzene, pelletized by vacuum pressing at 131 MPa, on further thermal treatment with Ar at 1400 °C yields such a ceramic composite. On air oxidation, the TaC nanoparticles are converted to Ta2O5 nanoparticles at 760 °C. Hardness measurements revealed that the composite exhibited a global hardness in the range of 1.23–1.57 GPa. However, nanoindentation studies showed that, locally, hardness of the TaC nanoparticles (∼15 GPa) approached that of the densified TaC ceramic. Superconducting studies of the pellet consistently exhibited two transitions with T c values of 10 K and 8.5 K, respectively, that corresponded to bulk TaC and to a component of unknown origin. The results discuss the morphological and constitutional characterizations of the TaC nanoparticle-containing composite.

A series of self-assembled WO3–BiVO4 nanostructured thin films with 17, 25, 50, 67, and 100 mol% WO3 were grown on the (001) yttria-stabilized zirconia (YSZ) substrate by pulsed laser deposition method. The microstructures including crystalline phases, epitaxial relationship, interface structures, and chemical composition distributions were investigated by a combination of various electron microscopy techniques including scanning electron microscopy, transmission electron microscopy, and X-ray energy dispersive spectroscopy. The monoclinic BiVO4 formed the matrix, in which WO3 nanopillars were embedded with specific epitaxial relationships. In BiVO4-rich sample, orthorhombic Bi2WO6 was formed. However, metastable hexagonal WO3 phase and orthorhombic WO3 phase coexisted in other composite samples. The thin amorphous layer at the film/substrate interface indicated that the mismatch strain between films and substrate is released. The hydrostatic tensile strain due to thermal expansion mismatch between BiVO4 and WO3 as well as the diffusion of Bi into the WO3 stabilized the metastable h-WO3. A WO3–BiVO4 pseudobinary phase diagram was proposed based on the magnitude of the thermal expansion mismatch and the distance of Bi diffusion, which can be applied to design the microstructures of WO3–BiVO4 heterojunctions and optimize their photoelectrochemical properties.

In this study, the density functional theory (DFT) and Monte Carlo (MC) simulations were conducted to determine the equilibrium conformation of Pt2Ru3 nanoparticles with diameters 1.0–3.5 nm at finite temperature. DFT calculations were carried out to estimate the binding energy using slab configurations and energy could be correlated with some structural descriptors and multilinear regression equations to calculate the binding energy from descriptors related to the number of a specific bond to neighboring atoms. MC simulations were carried out to obtain the equilibrium conformation of atoms in Pt2Ru3 at 150–363 K. MC simulations’ result shows that atoms of the same element tend to segregate each other, and Pt/Ru ratio on the surface increases with increasing particle size; also, most of the Pt are located on the surface whereas most of the Ru are located on the subsurface or at the core sites. It is qualitatively exhibited that the Pt/Ru ratio on the surface decreases with increasing temperature.

The hot deformation behavior of Nb–V–Ti microalloyed ultra-high strength steel was investigated by isothermal compression at 900–1200 °C with strain rates from 0.01 to 10 s−1. The microstructure evolution and precipitation behavior were studied using an optical microscope and a transmission electron microscope Results indicate that the peak stress of experimental steel increases with increasing the strain rate and decreasing the deformation temperature. The constitutive equation of hot deformation was developed with the activation energy Q being about 407.29 kJ/mol. The processing maps were also obtained to identify the instable regions of the flow behavior and to evaluate the efficiency of hot deformation. The size of dynamically recrystallized grains increases gradually with a decrease in the strain rate. Three types of carbides were identified, namely M3C, rich-Ti MC, and rich-Nb MC. With the increase of the deformation rate, the amounts of carbides increase, and the average sizes of the carbides decrease gradually.

Using in situ transmission electron microscopy, we report the observation of the melting behavior of one-dimensional nanostructures of Sn with different length/width aspect ratios. The melting of small aspect-ratio nanowires (nanorods) results in the expansion of liquid Sn along both axial and radial directions with the tendency to form an isometric or spherical particle, thereby minimizing the total surface area. For nanowires with the length/width aspect ratio of ∼10.5, perturbation along the liquid stream causes an unstable necking phenomenon and the whole wire tends to shrink into a spherical particle. In contrast, Rayleigh instability sets in for the melting of the nanowires with the length/width aspect ratio as large as ∼21, which gives rise to necking and fragmentation of the wire into particles. The amorphous native surface oxide (SnO x ) layer serves as a confinement tube and plays an important role in the melting induced morphological evolution of Sn nanowires. A thin SnO x layer is flexible with the ability to shrink or expand upon the flow of molten Sn. The increased rigidity for a thick SnO x surface layer kinetically suppresses bulging and necking formation in molten Sn nanowires.

In this paper, we report on the microstructural evolution and mechanical properties of a 5052 Al alloy processed by rotationally accelerated shot peening (RASP). A thick deformation layer of ∼2 mm was formed after the RASP process. Nano-sized grains, equiaxed subgrains, and elongated subgrains were observed along the depth of the deformation layer. Dislocation accumulation and dynamic recrystallization were found primarily responsible for the grain refinement process. An obvious microhardness gradient was observed for all of the samples with different RASP processing parameters, and the microhardness in the top surface of 50 m/s-5 min RASP-processed sample is twice that of its coarse-grained (CG) counterpart. The yield strengths of the RASP-processed 5052 Al alloy samples were 1.4–2.6 times that of CG counterparts, while retaining a decent ductility (25–84% that of CG). The superior properties imparted by the gradient structure are expected to expand the application of the 5052 Al alloy as a structural material.

Thermal transport in materials used for energy applications is a physical process directly tied to performance and reliability. As a result, a great deal of effort has been devoted to understanding thermal transport in materials whose ability to conduct heat is critical. Here, our objective is to discuss the utility of laser-based thermoreflectance (TR) approaches that provide microscale measurement of thermal transport. We provide several examples that implement the TR technique to investigate thermal transport in materials used in nuclear energy applications. First, we discuss utility of this technique to measure thermal conductivity in ion irradiated ceramic materials during investigations where the primary objective is to understand the impact of radiation induced crystalline structure defects on thermal transport. We also present the capability of TR approach to resolve thermal conductivity of each layer in tristructural isotropic fuel, silicon carbide fiber composites, and 2nd phase precipitates in uranium silicide. Finally, the ability to measure interface thermal resistance between adjacent layers in composites is demonstrated.

Plastic deformation of small metallic single crystals has focused a lot of attention because of their enhanced or specific mechanical properties. Here, submicron beryllium wires, obtained from selective etching of an Al/Be eutectic alloy, were deformed in tension in situ using a transmission electron microscope. Our observations indicate that wires oriented parallel to their 〈c〉 axis and containing almost no dislocations present a fragile-like behavior associated to a high stress level. $\left\{ {10\bar 12} \right\}$ 〈1011〉 twins were also frequently observed near fractured wires, indicating that this deformation mode is important in small-scale Be. In a twinned area, a locally ductile behavior was observed due to the favorable orientation for prismatic slip. We also stress out the importance of a remaining outer layer, made of Al oxide, in the plastic deformation. On the basis of finite element modeling, we show that the deformation of the wire may involve dislocations moving along the wire axis, in or close to the Be/Al oxide interface, in agreement with in situ observations. Thus, even in naturally oxidized wires, the outer layer is supposed to play an important role in the deformation, not only in modifying a stress/strain field but also presumably in facilitating diffusional processes, such as dislocation climb or dislocation nucleation.

Wear and corrosion properties of AM70 magnesium alloy subjected to equal channel angular pressing (ECAP) were investigated using pin-on-disc dry sliding wear test and electrochemical impedance spectroscopy (EIS), respectively. Wear test was conducted with 30 and 40 N loads with sliding distance of 5000 m and at a constant speed of 3 m/s. Reduced coefficient of friction (COF) and wear mass loss of ECAP processed samples showed increased wear resistance. Worn surface analysis by scanning electron microscope (SEM) showed the presence of delamination, wear debris, and plowing. Energy dispersive X-ray spectrometer (EDS) revealed the occurrence of oxidation, and the wear mechanism was identified as abrasion and oxidation wear. EIS plots showed the improvement in corrosion resistance of ECAP processed magnesium alloy compared to initial condition due to grain refinement and homogeneous distribution of secondary particles.

The surfacing welding has been widely utilized in the industrial equipment manufacturing and repairs. The wear properties of surfacing alloys have an important effect on the whole performance of repaired components. The solution treatment (T4) and solution treatment followed by aging (T6) effects on the dry sliding wear behavior of surfacing AZ91 magnesium alloys with tungsten inert gas welding were investigated in this work. The results demonstrated that the surfacing alloy without treatment exhibited poor wear resistance, due to the massive intermetallic β-phases (Mg17Al12). These phases were believed to produce stress concentrations in the particle-to-matrix interface and tended to generate cracks during friction. The T4 alloy had more improved wear resistance than the as-received alloy. The T6 treatment improved the wear resistance further, resulting from the high density dispersed fine β-phase precipitation in the α-Mg matrix, which enhanced the alloy strength and hardness and decreased the subsurface metal deformation degree caused by friction.

Nanoindentation testing of compliant materials has recently attracted substantial attention. However, nanoindentation is not readily applicable to softer materials, as numerous challenges remain to be overcome. One key concern is the significant effect of adhesion between the indenter tip and the sample, leading to larger contact areas and higher contact stiffness for a given applied force relative to the Hertz model. Although the nano-Johnson–Kendall–Roberts (JKR) force curve method has demonstrated its capabilities to correct for errors due to adhesion, it has not been widely adopted, mainly because it works only with perfectly spherical tips. In this paper, we successfully extend the nano-JKR force curve method to include Berkovich and flat indenter tips by conducting numerical simulations in which the adhesive interactions are represented by an interaction potential and the surface deformations are coupled by using half-space Green’s functions discretized on the surface.