In this study, a novel hybrid block copolymer containing POSS (BCP), poly(methacrylisobutyl-POSS)-b-poly(methylmethacrylate) (PMAiBuPOSS-b-PMMA) was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The structure and molecular weight were characterized via 1H NMR and GPC. BCP was creatively used as the compatibilizer to overcome the bad compatibility of epoxy and POSS in their blend system. SEM and dynamic mechanical thermal analyses (DMTA) were used to observe the surface morphology and thermal–mechanical behaviors of the resultant products. We found that the amount of microaggregation domains of POSS decreased, while the nano ones increased, when BCP content increased. All the aggregation domains were distributed in epoxy matrix uniformly at nanoscale with the addition of 10 phr BCP and 5 phr POSS monomers. The results indicated that BCP could effectively improve the compatibility between epoxy resin and POSS owing to its amphiphilicity in DGEBA. The fracture behavior of products transformed from brittle fracture to ductile fracture gradually with the increase of BCP, whereas the Tg and E′ decreased.

Poly(L-lactide)/poly(para-dioxanone) (PLLA/PPDO) (85/15 w/w) blends with 0, 1, 3, and 5 wt% poly(para-dioxanone-co-L-lactide) (PDOLLA) as a compatibilizer were prepared by solution coprecipitation. The in vitro hydrolytic degradation (HD) of blend bars with different contents of PDOLLA was studied by immersing the bars in a phosphate buffer solution (PBS) at pH 7.49. To estimate the degradation of blend bars, the weight loss, water absorption, thermal properties, surface morphology, and mechanical properties of blend bars, as well as the pH value changes of the PBS, were studied for 8 wk of HD. By adding 1 and 3 wt% PDOLLA, the weight loss of PLLA/PPDO (85/15 w/w) blends increased from 6.4 to 6.8 and 7.4% after 8 wk of HD, 6.2 and 15.6% increment, respectively, while, the average tensile strength of PLLA/PPDO (85/15 w/w) blends for 2–8 wk of HD increased from 25.8 to 29.0 MPa and 31.0 MPa, 12.4 and 20.2% increment, respectively. Considering their good mechanical properties and HD rate, the PLLA/PPDO (85/15 w/w) blends with 1 and 3 wt% PDOLLA are potential to be used as a medical implant material.

We report here the microstructural changes occurring in the zirconium alloy Excel (Zr–3.5 wt% Sn–0.8Nb–0.8Mo–0.2Fe) during heavy ion irradiation. In situ irradiation experiments were conducted at reactor operating temperatures on two Zr Excel alloy microstructures with different states of alloying elements, with the states achieved by different solution heat treatments. In the first case, the alloying elements were mostly concentrated in the beta (β) phase, whereas, in the second case, large Zr3(Mo,Nb,Fe)4 secondary phase precipitates (SPPs) were grown in the alpha (α) phase by long term aging. The heavy ion induced damage and resultant compositional changes were examined using transmission electron microscopy (TEM) in combination with scanning transmission electron microscope (STEM)-energy dispersive x-ray spectroscopy (EDS) mapping. Significant differences were seen in microstructural evolution between the two different microstructures that were irradiated under similar conditions. Nucleation and growth of <c>-component loops and their dependence on the alloying elements are a major focus of the current investigation. It was observed that the <c>-component loops nucleate readily at 100, 300, and 400 °C after a threshold incubation dose (TID), which varies with irradiation temperature and the state of alloying elements. It was found that the TID for the formation of <c>-component loops increases with decrease in irradiation temperature. Alloying elements that are present in the form of SPPs increase the TID compared to when they are in the β phase solid solution. Dose and temperature dependence of loop size and density are presented. Radiation induced redistribution and clustering of alloying elements (Sn, Mo, and Fe) have been observed and related to the formation of <c>-component loops. It has been shown that at the higher temperature tests, irradiation induced dissolution of precipitates occurs whereas irradiation induced amorphization occurs at 100 °C. Furthermore, dose and temperature seem to be the main factors governing the dissolution of SPPs and redistribution of alloying elements, which in turn controls the nucleation and growth of <c>-component loops. The correlation between the microstructural evolution and microchemistry has been found by EDS and is discussed in detail.

The present report presents results from the fabrication, structural, and optical characteristics of sub-100 nm thermal chemical vapor deposition-grown silicon-oxycarbide (SiCxOy) nanowire (NW) arrays fabricated by e-beam lithography and reactive-ion-etching. The composition of SiCxOy materials follows closely the silicon-oxycarbide stoichiometry [SiCxO2(1−x), (0 < x < 1)] as observed by compositional and structural analysis. The corresponding structural and bonding evolution of SiCxOy are well-correlated with changes in their optical properties, as demonstrated by the linear dependence of their optical gap and refractive index with [Si–C]/[Si–O] bond–area ratio. By virtue of these advantages, properly tailored SiCxOy NWs were fabricated, exhibiting strong room-temperature visible photoluminescence (PL) through engineering of [Si–C]/[Si–O] bonds. The current studies focused on the thermal-oxidation and excitation intensity behavior of SiCxOy NWs revealed their very good stability, as their luminescence characteristics remain unchanged upon annealing in oxygen ambient (250 °C), while the PL intensity dependence on the excitation power-density exhibited a linear increase up to ∼800 W/cm2.

In molecular dynamics simulations, the local stress state in the shear band is examined in six different model metallic glasses and one amorphous Si system (also has been perceived as a metallic glass analog) under different loading conditions. For all but the FeP and the amorphous Si systems, the running shear band (RSB) exhibits a liquid-like hydrostatic plus shear stress state. Our results suggest that the liquid feature of a RSB is not due to temperature rise or plastic confinement but due to the disorder driven by flow, which can be offset by strong directionality in bonding, phase segregation, or aging. The knowledge of the liquid-like stress state can be conveniently utilized in experiments to infer the local stress state of the RSB from the global tensile stress for metallic glasses.

With the increasing usage of Al alloys in vehicle manufacture, it is necessary to join dissimilar Al alloys with lap joint. However, hot cracking is a challenging issue due to the chemical composition and thermal tension, which greatly determines the reliability of automobile operation. Among different Al alloys, the series 5000 (Al–Mg) and 6000 (Al–Mg–Si) are widely used. To better understand the hot cracking behavior, various stack ups of AA5754 and AA6013 were laser welded to investigate the effects of process parameters on hot cracking formation. The chemical composition, microstructure, fusion ratio, and fracture morphology of the weld joint were also examined. The results showed that the order of material stacking affected weld's susceptibility to hot cracking significantly, and the critical process parameters were obtained for tested conditions which could effectively reduce hot cracking. The findings from this work provide guidance for hot cracking prevention in laser welding of dissimilar Al alloys.

A series of (HfN)1−x(TaN)x, ceramics with x representing the starting powder blend compositions of 0.0, 18.8, 28.1, and 46.7 at.%, have been fabricated by vacuum plasma spraying. During the plasma spraying, the mixture lost approximately 25 at.% nitrogen facilitating the precipitation of metallic and metal-rich nitride phases. These specimens underwent static air oxidation exposure up to 1700 °C. In general, it was found that the addition of tantalum nitrides to the hafnium nitrides resulted in poorer oxidation behavior. However, the 18.8 at.% specimen deviated from this trend and had the lowest observed mass change. This specimen formed a dark-colored oxide scale, indexed as Hf6Ta2O17, which acted as a passivation layer. Within the scale, hafnium oxynitride phases were observed. A transformation pathway in forming these rhombohedral oxynitride phases is proposed by the filling in of oxygen in the light element interstitial locations of the rhombohedral ε-Hf3N2 and ζ-Hf4N3 structures.

In cyclic nanoindentation of single-crystal silicon, an interesting phenomenon of a secondary pop-out event that closely follows the first pop-out event but with a larger critical load than the first is presented. Cyclic nanoindentation experiments under various loading/unloading rates and various maximum indentation loads were performed to verify the generality of the phenomenon of two pop-out events. Raman spectroscopy results indicate that the secondary pop-out does not induce any new phase, and the dominated end phases after the two pop-out events are still a mixture of Si-XII/Si-III phases. According to average contact pressure analysis, the phase transformation paths and the formation mechanism for the secondary pop-out event are discussed from the viewpoint of crystal nucleation and growth. The results indicate that phase transformations from the Si-I phase to Si-XII/Si-III phases are completed by two pop-out events in two adjacent indentation cycles, and the Si-XII/Si-III phases formed in previous indentation cycles strongly affect the phase transformations in subsequent loading/unloading processes.

The influences of parameters on the bubble size in aluminum alloy melt during the gas injection foaming process were studied. The four parameters were the orifice diameter (0.4–3.0 mm), the orifice numbers (1 and 4), the gas chamber volume (11–800 cm3), and the gas flux (10–282 L/h). It was found that the bubble size decreased with the decrease of the orifice diameter and the gas chamber volume, and with the increase of the orifice number. The effect of gas flux showed a dual-stage at different gas fluxes: the “metastable large bubble stage” and the “stable bubbling stage”. A modified semiempirical formula and a concept of “effective gas chamber volume,” which is the nominal chamber volume divided by the effective orifice number, were proposed. The bubble size calculated by the modified formula with the effective gas chamber volume agreed well with the experimental data.

The kinetics and morphology of oxides formed during in situ proton irradiation–corrosion experiment were analyzed. Experiments were conducted in 320 °C water with 3 wt ppm H2, while irradiated by a 3.2-MeV proton beam at a current density of 2 µA/cm2 producing a damage rate at 4.4 × 10−7 dpa/s. The resulting oxide was compared with reference samples corroded in an autoclave, and literature data found on in-reactor formed oxide. The corrosion rate of the sample irradiated in situ was 10 times faster than the in-pile corrosion rate. The cracked and porous irradiated oxide consisted of monoclinic equiaxed grains of zirconia with a preferential orientation of the oxide grains. Second phase particles (SPPs) consumed by the oxidation front were rapidly oxidized, but no SPPs were amorphized or dissolved in the metal matrix of the irradiated sample.

This work presented a study on the improvement of laser surface treatment on rolling contact fatigue resistance of gray cast iron. Sample surface covered with carbon powder was coupled with localized treatment by high-energy laser beam—a process defined as “laser cladding (LC).” With this method, the optimum precoating thickness was experimentally studied. Compared to the region treated by laser remelting, the crystal in LC region was finer, more compact, and uniform. Mechanical property testing showed not only high micro-hardness of LC region, but also improved tensile and compressive resistance of treated material. Fatigue wear tests and thorough analysis of fatigue detects suggested that LC treatment significantly improved fatigue wear resistance (FWR). Improved FWR was likely facilitated by delayed initiation and propagation of cracks, as well as the reduction of contact stress on substrate. Additionally, formations of fatigue defects on sample surface were thoroughly discussed.

Microstructural and property evolution of 1050 commercial pure aluminum subjected to high-strain-rate deformation (1.2–2.3 × 103 s−1) by split Hopkinson pressure bar (SHPB) and subsequent annealing treatment were investigated. The as-deformed and their annealed samples at 373–523 K were characterized by transmission electron microscopy (TEM) and microhardness tests. TEM observations reveal that the as-deformed sample is mainly composed of a lamellar structure, whose transverse/longitudinal average subgrain/cell sizes are 293 and 694 nm, respectively. The initial coarse grains are refined significantly. The initial lamellar grain structures are subdivided into pancake-shaped subgrains due to a gradual transition by triple junction motion at 473 K, and then a dramatic microstructural coarsening is observed at 523 K. It is suggested that annealing behavior of this dynamic loading structure is better considered as a continuous process of grain coarsening or continuous recovery.

The present study was conducted to predict the hot deformation behavior of the as-forged Nitinol 60 shape memory alloy by using the Arrhenius type, multiple-linear, and artificial neural network (ANN) models. The acquired flow stress data from isothermal hot compression tests in a temperature range of 650–850 °C under strain rate range of 0.01–1 s−1 were used to calculate the material constants for establishing the corresponding constitutive equations. Furthermore, a comparative study has been made on the capability of the aforementioned models to predict the high-temperature deformation behavior by comparing the prediction relative errors, average absolute relative error, and correlation coefficient. The results show that multiple-linear model predicts the flow behavior more accurately than the Arrhenius type model. The ANN model is much more efficient and has a better prediction power for the as-forged Nitinol 60 alloy than both the Arrhenius type and multiple-linear models.

Thermoelectric converters based on silicon nanostructures offer exciting opportunities for higher efficiency, lower cost, ease of manufacturing, and integration into circuits. This paper considers phonon transport in a broad range of nanostructured materials made from Si, Ge, and their alloys. Our model based on the phonon Boltzmann transport equation captures the lattice thermal transport in silicon–germanium (SiGe) nanostructures, including thin films, superlattices (SLs), and nanocomposites. In nanocomposites, the model captures the grain structure using a Voronoi tessellation to mimic the grains and their size distribution. Our results show thermal conductivity in SiGe nanostructures below their bulk counterparts and reaching almost to the amorphous limit of thermal conductivity. We also demonstrate that thermal transport in SiGe nanostructures is tuneable by sample size (thin films), period thickness (SLs), and grain size (nanocomposites) through boundary scattering. Our results are relevant to the design of nanostructured SiGe alloys for thermoelectric applications.

The magnetization behavior under temperature and magnetic field variation was investigated for La0.7Pb0.3MnO3 ceramics and ferromagnetic–ferroelectric 0.85(La0.7Pb0.3MnO3)–0.15(PbTiO3) composite. The second-order ferromagnetic phase transition in manganite is shifted to the tricritical point in composite material. Comparison of the intensive caloric effect and the difference between relative cooling powers (RCP) in both materials proves a significant role of intrinsic pressure in elevating caloric efficiency in composite induced by elastic coupling between the grains of LPM and PT components. No temperature change in composite under an electric field of 2 kV/cm associated with electrocaloric effect or indirect magnetoelectric coupling was observed. The effect of magnetic field on some peculiar temperatures is considered. A contribution from pressure generated by magnetic field to baric coefficient dT/dp of ferromagnetic transformation temperature in composite was suggested. The results obtained were analyzed in the framework of the magnetic equation of state and compared with the experimentally measured heat capacity.

The hot deformation behavior of X45CrSi93 valve steel was investigated by a series of compression and tensile tests by means of the Gleeble-1500 simulator and microstructural analyses. The experimental results show that the flow stress decreases with the increasing temperature between 850 and 900 °C followed by an abnormal increase with the increasing temperature between 900 and 1000 °C under the compressive conditions. A normal decrease of the flow stress is continued with the increasing temperature above 1000 °C. Meantime, the tensile specimen conducted at 1000 °C shows double necking effect. Further microstructural analyses show that the phase transition from α-ferrite to austenite and the solution strengthening caused by carbide dissolution are the main reasons for abnormal variation of flow stress for X45CrSi93. The negative temperature gradient in the tensile specimen results in the symmetrical microstructure and then the double necking phenomenon.