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Abstract: Thermal residual stress analysis and failure simulation of particle-reinforced composites are performed based on thermomechanics and the finite element method (FEM) to investigate the effects of particles on strength and toughness. It is discovered that the residual stresses in matrix are controlled mainly by adjacent particles via stress superposition, and an expression for the residual stress is derived. The size of the residual stress zone in the matrix is found to increase with the particle size. The FEM failure simulation in uniaxial tension reveals two features: (i) the residual stress caused by the second phase particles in ceramic matrix would lead to strength degradation due to the weakest link theory; (ii) the second phase particles in the composite may enhance the fracture toughness because of the crack arrest and crack-deflection caused by residual compressive stress. These features have been confirmed by experimental results of TiN/Si3N4 composite. [Copyright &y& Elsevier]

An abstract of the article "Effect of Sample Size and Testing Temperature on the Fracture Toughness of Ti3SiC2" by Yi-Wang Baa and Yan-Chun Zhou is presented.

Abstract: The microstructure, mechanical and thermal properties, as well as oxidation behavior, of in situ hot-pressed Zr2[Al(Si)]4C5–30vol.% SiC composite have been characterized. The microstructure is composed of elongated Zr2[Al(Si)]4C5 grains and embedded SiC particles. The composite shows superior hardness (Vickers hardness of 16.4GPa), stiffness (Young''s modulus of 386GPa), strength (bending strength of 353MPa), and toughness (fracture toughness of 6.62MPam1/2) compared to a monolithic Zr2[Al(Si)]4C5 ceramic. Stiffness is maintained up to 1600°C (323GPa) due to clean grain boundaries with no glassy phase. The composite also exhibits higher specific heat capacity and thermal conductivity as well as better oxidation resistance compared to Zr2[Al(Si)]4C5. [Copyright &y& Elsevier]

Abstract: In this work, the dry sliding friction and wear properties of Ti3AlC2 and Ti3AlC2/Al2O3 composites against AISI52100 steel ball were investigated using a reciprocating ball on flat configuration under different normal loads. The results indicated that the friction/wear processes of both Ti3AlC2 and the composites against AISI52100 steel experienced two different stages with an abrupt transition between them under all test conditions. The first stage was characterized by low coefficient of friction (μ) and neglectable wear rate. While the second stage was of much higher wear rate and μ. When the transition occurred, μ increased dramatically accompanied with formation of a mass of debris. In Ti3AlC2, the main wear mechanisms during the first stage involved surface materials transfer and oxidation accompanied with subsurface damages by grains kinking, delamination as well as transgranular and intergranular cracks. Accumulating of such contact damages under repeated sliding contact finally leaded to surface and subsurface microfracture of Ti3AlC2. Then microfracture controlled severe wear started. Incorporation of Al2O3 in Ti3AlC2 not only improved wear resistance of Ti3AlC2 but also extended the first mild friction/wear stage, because Al2O3 particles borne load and restrained large-scale deformation and microfracture of Ti3AlC2. [Copyright &y& Elsevier]

The synergistic effect of triple ion beams is investigated by simultaneous and sequential irradiations of gold, hydrogen and helium ions on the low activation martensitic steel (CLAM) developed in China. The depth profile measurements of the positron annihilation Doppler broadening S parameter are carried out as a function of slow-positron beam energy to examine the produced radiation damage. The synergistic effect of displacement damage and hydrogen and helium on the formation of radiation damage is clearly observed. In the preset case, this effect suppresses the radiation damage in the CLAM steel due to the helium and/or hydrogen filling of vacancy clusters. [ABSTRACT FROM AUTHOR]

The thermal expansion of as-prepared and annealed silver nanowires embedded in anodic alumina membranes with different diameters was studied by in situ x-ray diffraction in the temperature range from 25 to 800 °C. For both the as-prepared and annealed samples, the coefficients of thermal expansion have “V” shape change as the diameters increase; and the minimum values of the coefficients of thermal expansion do not correspond to the same diameters of nanowires. The collective effects of the surface tension, the limit effects of anodic alumina membrane, and the vacancies incorporated into the silver lattice were responsible for the thermal expansion. [ABSTRACT FROM AUTHOR]

Thermal expansion of as-prepared and annealed ordered arrays of silver nanowires embedded in anodic alumina membranes (AAMs) was studied by in situ x-ray diffraction measurement in the temperature range from 25 to 800 °C. The axial thermal expansion coefficient (TEC) for the as-prepared nanowires is 6.35×10-9/°C and 6.02×10-6/°C below and above 650 °C, respectively. However, the TEC of the annealed sample turns from 2.32×10-6/°C to 12.06×10-6/°C when the temperature is above 350 °C. The collective effects of the intrinsic expansion, surface pressure, the limit effect of AAM, and the vacancies incorporated into the silver lattice were responsible for the thermal expansion. [ABSTRACT FROM AUTHOR]

The CS/PVA/Fe3O4 nanocomposite membranes with chainlike arrangement of Fe3O4 nanoparticles are prepared by a magnetic-field-assisted solution casting method. The aim of this work is to investigate the relationship between the microstructure of the magnetic anisotropic CS/PVA/Fe3O4 membrane and the evolved macroscopic physicochemical property. With the same doping content, the relative crystallinity of CS/PVA/Fe3O4-M is lower than that of CS/PVA/Fe3O4. The Fourier transform infrared spectroscopy (FT-TR) measurements indicate that there is no chemical bonding between polymer molecule and Fe3O4 nanoparticle. The Fe3O4 nanoparticles in CS/PVA/Fe3O4 and CS/PVA/Fe3O4-M are wrapped by the chains of CS/PVA, which is also confirmed by scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The saturation magnetization value of CS/PVA/Fe3O4-M obviously increases compared with that of non-magnetic aligned membrane, meanwhile the transmittance decreases in the UV-visible region. The o-Ps lifetime distribution provides information about the free-volume nanoholes present in the amorphous region. It is suggested that the microstructure of CS/PVA/Fe3O4 membrane can be modified in its curing process under a magnetic field, which could affect the magnetic properties and the transmittance of nanocomposite membrane. In brief, a full understanding of the relationship between the microstructure and the macroscopic property of CS/PVA/Fe3O4 nanocomposite plays a vital role in exploring and designing the novel multifunctional materials. [ABSTRACT FROM AUTHOR]

Doppler broadening and coincidence Doppler broadening of annihilation radiation experiments have been performed in three kinds of polyethylene glycol (PEG) membrane formed with different average molecular weight using the tunable monoenergy slow positron probe as a function of implantion energy. The obtained positron annihilation parameters are interpreted from two aspects: surface effect and differences in micro-structure or chemical environment of positron annihilation. The experimental results show that the regulation of densification of PEG molecular packing and distribution uniformity from the near surface layer to the bulk region in the film forming process can be well realized by changing its molecular weight. Combining a variable monoenergetic slow positron beam and these two positron annihilation spectroscopy methods is a powerful tool to study positron annihilation characteristics and for polymeric thin-film fine structure analysis. [ABSTRACT FROM AUTHOR]

Doppler broadening spectroscopy in the positron annihilation technique (DBS-PA) has been employed to investigate the defect properties in argon-damaged tungsten exposed to low-energy and high flux deuterium plasma. Argon ion irradiations with energy 500 keV are performed for tungsten samples with various levels of damage. The remarkable increment of the S parameter in DBS-PA indicates the introduction of vacancy-type defects in argon irradiated tungsten. An increase of ion fluence results in a continuous increase of the S parameter until saturation. Unexpectedly, a much higher fluence leads to a decrease of the S parameter in the near surface, and the (S,W) slope changes greatly. This should be associated with the formation of argon-vacancy complexes in the near surface produced by the excessive implanted argon ions. With deuterium plasma exposure, a significant decrease of the S parameter occurs in the pre-irradiated tungsten, suggesting the sharp reduction of the number and density of the vacancy-type defects. The thermal desorption spectroscopy results demonstrate that the argon-damaged tungsten, compared to the pristine one, exhibits an enhanced low-temperature desorption peak and an additional and broad high-temperature desorption peak, which indicates that deuterium atoms are trapped in both low-energy and high-energy sites. All these observations directly indicate the deuterium occupation of irradiation-induced vacancy defects in damaged tungsten, which is responsible for the remarkable increase of the deuterium retention in comparison with the pristine one. [ABSTRACT FROM AUTHOR]

The magnetic properties and defect types of virgin and N-doped TiO2 single crystals are probed by superconducting quantum interference device (SQUID), X-ray photoelectron spectroscopy (XPS), and positron annihilation analysis (PAS). Upon N doping, a twofold enhancement of the saturation magnetization is observed. Apparently, this enhancement is not related to an increase in oxygen vacancy, rather to unpaired 3d electrons in Ti3+, arising from titanium vacancies and the replacement of O with N atoms in the rutile structure. The production of titanium vacancies can enhance the room temperature ferromagnetism (RTFM), and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering. [ABSTRACT FROM AUTHOR]

Yttria-stabilized zirconia (YSZ) is irradiated with 2.0-MeV Au2+ ions and 30-keV He+ ions. Three types of He, Au, Au + He (successively) ion irradiation are performed. The maximum damage level of a sequential dual ion beam implanted sample is smaller than single Au ion implanted sample. A comparable volume swelling is found in a sequential dual ion beam irradiated sample and it is also found in a single Au ion implanted sample. Both effects can be explained by the partial reorganization of the dislocation network into weakly damaged regions in the dual ion beam implanted YSZ. A vacancy-assisted helium trapping/diffusion mechanism in the dual ion beam irradiated condition is discussed. No phase transformation or amorphization behavior happens in all types of ion irradiated YSZ. [ABSTRACT FROM AUTHOR]