To reveal the electron and phonon transport mechanism in bismuth nanowire (BiNW), the electronic structure, the lattice dynamics, and the thermoelectric properties of bismuth bulk (BiB) and BiNW were investigated in this paper through first-principles calculation and the Boltzmann transport theory. The results suggest that BiNW possesses an increased electrical conductivity and Seebeck coefficient, while its thermal conductivity, especially phonon thermal conductivity, is reduced significantly as compared to BiB. As a consequence, a largely enhanced figure of merit (ZT) at 300 K of 2.73 is achieved for BiNW. The enhancement in electrical conductivity and Seebeck coefficient of BiNW is originated from its high density of states and large effective mass of carriers. Such significant suppression in phonon thermal conductivity of BiNW is ascribed to the reduced phonon vibration frequency, the decreased phonon density of states, and the shortened mean free path of phonons. So BiNW should be viewed as an excellent candidate for a thermoelectric material with a high figure of merit. Moreover, we have provided a complete understanding on the relationship between the electronic structure, the dynamics, and the thermoelectric properties of BiNW.

The oxidation behavior of nonstoichiometric Ti2AlCx (x = 0.69) powders synthesized by combustion synthesis was investigated in flowing air by means of simultaneous thermal gravimetric analysis-differential thermal analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscope/energy dispersive spectroscopy, with an effect of powder size. The oxidation of the fine Ti2AlC powders with the size of about 1 μm starts at 300 °C and completes at 980 °C, while with increasing the powder size around 10 μm the corresponding temperature increases to 400 and 1040 °C, respectively. The oxidation of nonstoichiometric Ti2AlCx (x = 0.69) powders is controlled by surface reaction in 400–600 °C, and mainly diffusion in 600–900 °C, with the corresponding oxidation activation energy of 2.35 eV and 0.12 eV, respectively. In other words, the critical temperature of changing oxidation controlling step is around 600 °C. The oxidation products were mainly rutile-TiO2 and α-Al2O3. The tiny white flocculent particles of α-Al2O3 appeared on the surface of fine Ti2AlC powders and increased with increasing the oxidation temperature.

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.

Magnesium alloy has great potential for bone implantation. However, its corrosion rate is fast in physiological environment. In this paper, biological Mg–Zn–Ca alloy was processed by high pressure torsion (HPT) and subsequently annealed at 90–270 °C for 30 min. The microstructure and corrosion resistance in simulated body fluid were investigated. The results revealed that with the rise of the annealing temperature, the grain size of the HPT alloy gradually increased and the relative diffraction peak intensity of (0002) grain orientation decreased. The amount of second phases increased first and then decreased, while the surface stress decreased first and then increased. All of these changes affected the corrosion rate simultaneously. The corrosion resistance of the HPT alloy increased first and then decreased with the rise of annealing temperature. After annealing at 210 °C for 30 min, the corrosion resistance was the best. Therefore, it was feasible to control the corrosion rate via annealing treatment.

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.

Magneto polymer matrix composites (MPMC) is a new class of magnetic polymer materials which are being developed and under investigation as potential materials for tomorrow’s aircraft structures. It encompasses magnetic, particulate strengthening (dispersion strengthening) as well as fiber reinforcement/strengthening characteristics which are sought out to be utilized toward making efficient future aerospace composite materials. Various types of ferrites including barium, cobalt, iron, and strontium were explored for being used in making new composites. Here a comprehensive review of the synthesis, structure, properties, thermodynamics, surface chemistry, and phase transformations of individual ferrites and clusters of ferrites as fillers is presented. In particular a discussion about the rational control of the mechanical, physical, thermal, electrical, and magnetic properties of magneto polymer matrix composites through surface functionalization, modification, emulsification/compounding/blending, heat treatment (phase transformation and separation), and control of processing conditions (temperature, pressure and geometry of mold) is provided. These smart materials have a wide range of potential applications in medicine, drug delivery, bio imaging, bio marking, tissue engineering, electromagnetic interference (EMI) and electromagnetic force (EMF) shielding, and as competent materials for aerospace structural applications.

Al–Zn–Mg–Cu–Zr alloys are very important aeronautical materials because of their low density, high strength, and high ductility. Corrosion failure is a significant factor causing aviation accidents, which should be investigated to develop an aeronautical material but has not been done yet. In this work, the effects of aging mechanisms on the exfoliation corrosion behavior of a spray deposited Al–Zn–Mg–Cu–Zr alloy were investigated. Natural aging (NA), single-stage aging (SA), and retrogression and re-aging (RRA) were treated on specimens before exfoliation corrosion testing. Corrosion attacks were evaluated using the optical microscope (OM) and scanning electron microscope (SEM). Corrosion mechanisms were deduced on the basis of polarization curve results and an equivalent circuit. The RRA sample exhibited the smallest corrosion attack among the three samples, while the NA sample showed the largest corrosion attack. Intergranular corrosion on grain boundaries was discussed to understand the exfoliation corrosion process in the RRA sample. The amount and size of precipitates in grain interior and grain boundary of RRA samples are larger than those in SA and NA samples, leading to the low corrosion susceptibility of the RRA sample.

Bragg coherent X-ray diffraction imaging has been used to determine the structure of the initial clusters of α-Fe nano crystals which form upon annealing of an iron-based amorphous alloy or metallic glass. The method is able to identify the shapes and strain of these crystallites without any need for cutting the sample, so can visualize them in three dimensions in their intact state. In this way, the delicate dendritic structures on the exterior of the crystallites can be seen and its density versus radius relationship identifies a fractal dimension of the porous region that is consistent with diffusion-limited aggregation models. The crystal sizes were found to be around 60 nm after annealing at 700 °C growing to about 330 nm after annealing at 750 °C. This article introduces the BCDI method and describes its application to characterize previously recrystallized samples of iron-based amorphous alloys. It paves the way for a possible future in situ nucleation/growth investigation of the relationship between kinetics and nanostructure of metallic glass.

The constitutive equation was established based on the consideration of strain compensation to describe the hot deformation behavior of low carbon reduced activation ferritic/martensitic (RAFM) steels at the temperatures of 850–1050 °C and the strain rates of 0.01–10 s−1. The result indicates that the flow stress is increased with the increase of strain rate but decreased with increase of deformation temperature. During the hot deformation process, the increase of temperature is beneficial to attain the complete dynamic recrystallization (DRX). However, excessively high temperature leads to grow up of dynamic recrystallized grain. Higher strain rate leads to finer recrystallized grains. The material constants (α, n, A) and deformation activation energy (Q) are calculated by the regression analysis. The increase of strain caused the decrease of Q, indicating the DRX occurred more easily. In addition, the developed constitutive equation could accurately predict the hot deformation behavior of the low carbon RAFM steel.

Thermal stability of pulsed laser deposited (PLD) nanocrystalline tantalum was explored through in situ transmission electron microscopy (TEM) annealing over the temperature range of 800–1200 °C. The evolution of the nanostructure was characterized using grain size distributions collectively with electron diffraction analysis and electron energy loss spectroscopy (EELS). Grain growth dynamics were further explored through molecular dynamics (MD) simulations of columnar tantalum nanostructures. The as-deposited grain size of 32 nm increased by only 18% at 1200 °C, i.e., 40% the melting point of tantalum, conflicting with the MD simulations that demonstrated extensive grain coalescence above 1000 °C. Furthermore, the grain size remained stable through the reversible α-to-β phase transition near 800 °C, which is often accompanied by grain growth in nanostructured tantalum. The EELS analysis confirmed the presence of oxygen impurities in the as-deposited films, indicating that impurity stabilization of grain boundaries was responsible for the exceptional thermal stability of PLD nanocrystalline tantalum.