We have studied the effects of focused-ion-beam (FIB) irradiation and prestraining on the mechanical properties of nearly defect-free Au microparticles on a sapphire substrate. The Au microparticles, which were produced by a solid-state diffusion dewetting technique, were FIB-irradiated and/or prestrained, the latter using a nanoindenter with a flat ended punch operating under a nanohammering mode. Also, the prestrained Au microparticles were exposed to FIB to examine the effects of ion-beam damage on the properties of crystals containing mobile dislocations. We found that both FIB irradiation and prestraining reduced the yield strength of pristine Au microparticles significantly and made the stress–strain curves jerky. However, FIB irradiation does not affect the mechanical properties of prestrained Au microparticles very significantly. Once a microparticle contains mobile dislocations, its mechanical properties are not influenced much by the defects generated by FIB irradiation, even at the submicrometer scale.

We demonstrate that the size and crystallinity of grains in individual ZnO nanofibers greatly influence their sensing properties for CO. The sensing properties, including sensitivity, response and recovery times of a sensor fabricated with ZnO nanofibers composed of large grains are much superior to those of a sensor fabricated with nanofibers of small grains. The crystallinity, improved by the longer calcination time, is likely to be responsible for the higher sensitivity in the large-grained nanofibers. The facilitated occupancy and desorption of CO molecules at grain boundaries in the large-grained nanofibers are the most probable causes of the shorter response and recovery times in detecting CO, respectively. This work suggests not only that electrospinning-synthesized ZnO nanofibers hold promise for realizing sensitive and reliable gas sensors but also that the size as well as the crystallinity of the grains existing in individual nanofibers need to be optimized to obtain the best sensing properties.

We investigate the collective effect of a high volume fraction of ∑3 twin boundaries on the response of nanotwinned Cu to high dose He implantation near room temperature and find that they do not curtail the formation of vacancy and interstitial clusters. This result is rationalized through atomistic modeling, which shows that point defects at these boundaries have nearly identical properties to those in pure fcc Cu.

A dislocation-density grain–boundary (GB) interaction scheme for face-centered cubic bicrystals with three coincident site lattice boundaries was developed to account for the interrelated dislocation-density interactions of GB emission, absorption, and transmission. The proposed GB scheme was coupled to a dislocation-density multiple-slip crystalline plasticity formulation and specialized finite-element algorithms to account for behavior on the microstructural scale. A conservation law for dislocation densities was also used to balance dislocation-density absorption, transmission, and emission within the GB region. The predictions indicated that GB absorption increases are due to increases in immobile dislocation densities in high-angle GBs without coplanar slip planes and collinear slip directions, such as Σ17b. Low-angle GBs with coplanar slip planes and collinear slip directions are characterized by high transmission rates and insignificant GB dislocation-density accumulations. GB processes such as emission, absorption, and transmission are directly related to microstructural behavior and can be potentially controlled for desired material response.

Effect of a low-voltage pulsed magnetic field (LVPMF) on the solidified microstructure of Mg–Al–Zn alloy has been investigated. Experimental results show that the solidified structure of Mg–Al–Zn alloy can be remarkably refined and that the morphology of α-Mg is transformed from developed dendrite to fine rosette with the application of LVPMF. Magnetization of the solute and solvent in the diffusion layer cannot account for the formation of the rosette α-Mg under LVPMF. A model for the formation of rosette α-Mg under LVPMF has been developed by analyzing the growth behavior of α-Mg dendrite. Morphology change of α-Mg dendrite under LVPMF is caused by Joule heat concentrated on the dendrite tip. Accumulation of Joule heat on the dendrite tip melts the local dendrite tip and increases the radius of curvature. The increased radius of curvature at the dendrite tip lowers the growth rate and results in the formation of rosette α-Mg.

Static electropulsing-induced phase transformations of a cold-drawn ZA27 alloy wire were studied by using x-ray diffraction, backscattered scanning electron microscopy, and electron backscattered diffraction (EBSD) techniques. By using EBSD, phases with close microstructure are discriminated, based on transmission electron microscopy determined lattice parameters of phases. Thus, it was quantitatively detected that electropulsing tremendously accelerated phase transformations in two stages: (i) η′S and ε′T decomposed sequentially (in a way of quenching) and (ii) ε′T and η′S formed via reverse decompositions (in a way of up-quenching).

The compositional dependence of phase formation, thermal stability, and mechanical properties of (Cu0.5Zr0.5)100−x(Al0.5Ag0.5)x (x = 2, 4, 6, 8, 10, 12, 14, 16) bulk metallic glasses was studied. The Young’s modulus (85 ± 1 to 95 ± 1 GPa) and Vicker’s hardness (585 ± 7 to 627 ± 8 Hv) increased with increasing Al + Ag content from 8 to 16 at.%, respectively. The liquidus temperature decreased from 1210 ± 2 to 1110 ± 2 K with increasing Al + Ag content from 2 to 16 at.%. The starting temperature of the endothermic event related with transformation of the low-temperature equilibrium phases to CuZr parent phase increased from 997 ± 2 to 1043 ± 2 K, whereas the electronegativity difference for the (Cu0.5Zr0.5)100−x(Al0.5Ag0.5)x (x = 2, 4, 6, 8, 10, 12) alloys decreased from 0.2838 to 0.2713. The martensitic transformation temperatures decreased with increasing Al and Ag content for the (Cu0.5Zr0.5)100−x(Al0.5Ag0.5)x (x = 2, 4, 6, 8) alloys.

Effects of the precipitated phase and the ordered phase domain of an Fe-6.5 wt%Si alloy before and after heat treatment on the bending properties were investigated in this study. The results showed that original needle-like phases were spheroidized after the heat treatment at 900 °C for 1 h followed by slow or rapid cooling. Compared with the directional solidified sample, the slow cooling sample had a higher order degree, whereas the rapid cooling samples had a lower order degree. After rapid cooling heat treatment, the fracture deflection of the sample was increased by 73.8%. Fracture analysis showed that transition from quasi-cleavage fracture to tear pit-like fracture took place in the rapid cooling sample. The bending properties of the Fe-6.5 wt%Si alloy were improved mainly due to the changes in morphology and amount of the precipitated phase as well as the reduction of order degree.

Al–AlN composite powders containing 9–55 vol%AlN were fabricated in situ by nitriding a powder mixture of AA6061–2% Mg–1% Sn at 560 °C. Transmission electron microscopy (TEM) revealed that the in situ formed AlN reinforcements are present as nanoscale AlN whiskers on each powder particle. The composite powder was consolidated by hot extrusion at 450 °C with an extrusion ratio of 11:1. This produced an AlN-free and an AlN-containing lamellar structure along the extrusion direction. The nanoscale AlN is dispersed in the AlN-containing lamella and shows excellent bonding with the Al matrix, free of decohesion and voids. The lamellar composite containing 9 vol%AlN has an ultimate tensile strength of 332 MPa and tensile elongation of 3%. Composites containing ≥17.5 vol%AlN achieve much higher tensile strengths (538 MPa) but zero tensile elongation. However, they show a low coefficient of thermal expansion up to 450 °C and may therefore have potential for selected elevated temperature applications.

During the mechanical alloying of a prealloyed Fe–Mo and Mn powder, a large amount of energy is involved because of continuous collisions between the grinding media and the powder. The energy is transformed into massive plastic deformation and solid solution formation. Both phenomena increase in the hardness of the milled particles. To quantify the contribution of both effects to the hardening, nanoindentation experiments were performed on the as-milled powder and after an annealing treatment, based on the assumption that the thermal process would eliminate the lattice distortions due to plastic deformation. When the indentation profile was measured, a significant pileup around the perimeter of the indentation track was observed; therefore, it was necessary to measure the actual amount of contact area by atomic force microscopy. Thus, parameters of mechanical powders can be determined, giving to the conclusion that 40% of the hardening induced can be attributed to the plastic strain.

For evaluating the effects of ultrafine nanograins (UFNGs) on the fracture toughness of conventional nanocrystalline (nc) materials, we developed a composite model composed of UFNGs (with a grain size d between 2 and 4 nm) evenly distributed in the conventional nc matrix (20 nm ≤ d ≤ 100 nm). The UFNGs could be treated as a part of triple junctions, denoted as super triple junctions. In the framework of our model, stress concentration near crack tip initiates intergrain sliding that leads to the generation of edge dislocations at super triple junctions. The dependence of critical crack intensity factors on grain size was calculated. It was demonstrated that the existence of the UFNGs approximately doubles the critical crack intensity factors.