Aluminum metal matrix hybrid composites were synthesized through powder metallurgy route from ball milled powders to yield the compositions: Al + 0% TiO2, Al + 2.5% TiO2, Al + 2.5% TiO2 + 2% Gr, and Al + 2.5% TiO2 + 4% Gr. The densification and deformation properties of sintered Al–TiO2–Gr composites during cold upsetting were investigated experimentally. The powder preforms are compacted using suitable punch and die in 40 kN hydraulic press and the initial percentage theoretical density was maintained as 85%. Sintering was done in an electric muffle furnace at the temperature of 590 °C for a period of 3 h. The sintered preforms were subjected to incremental compressive loading of 10 kN until cracks were found at the free surface. The true axial stress (σz), true hoop stress (σθ), true hydrostatic stress (σm), and true effective stress (σeff) were calculated for all the preforms and all these stresses are correlated with the true axial strain (εz). The densification behaviors of the composites were studied against true axial strain (εz) and lateral strain. Better densification and deformation property were obtained for pure aluminum preforms compared with other composite preforms. Addition of TiO2 to the pure Al and Gr reinforcements increases the strength coefficient of the Al–TiO2 composite.

The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer- or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C++ programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.

This study presented a novel fabrication process for TiNi thin films by vacuum diffusion technology using reactive Ni/Ti/Ni multilayer thin films. The sandwiched thin films were prepared by chemical nickel plating. Ni/Ti/Ni multilayer films were heat treated for various diffusion times and temperatures and the influences of the temperature and diffusion time on the interdiffusion behavior of the Ti–Ni system were researched in detail. The results showed that a homogeneous TiNi thin film was obtained at 1173 K with a diffusion time of 4 h. Moreover, the formation sequence of the intermetallics in the Ti–Ni diffusion system was investigated by thermodynamic analysis and experiment. It was found that three compounds – TiNi3, Ti2Ni, and TiNi – formed in the diffusion process at the Ti/Ni interfaces. More importantly, the nucleation of TiNi3 and Ti2Ni was prior to that of TiNi because of the lower reaction Gibbs free energy and increasing interface energy of TiNi3 and Ti2Ni.

To prepare hydrogels with ultrarapid response rate and excellent mechanical properties, the poly(N-isopropylacrylamide)/clay nanocomposite hydrogels were synthesized by freezing polymerization technique. The start freezing time, as an important parameter determining the properties of gels, was designed and investigated. The results showed that the properties of gels including mechanical properties, swelling ratio, and swelling/deswelling rate were closely dependent on the freezing polymerization time. Comparably, the gels synthesized with earlier freezing time exhibit a faster swelling rate and an ultrarapid deswelling rate due to the integral interconnecting porous structure, while the swelling ratio, tensile strength and modulus decrease considerably. With the delay of start freezing time, the response rate decreases while the mechanical properties improve. Through the analysis of scanning electron microscope, differential scanning calorimetry, x-ray diffraction, dynamic rheological tests, and mechanical tests, the relevance of gels' structure with the freezing time was explored. It is reasonably presumed that freezing process impacts the effective crosslink of polymer chains by clay significantly, the earlier the freezing started, the more chains with free end existed in gels.

Gadolinium-based transparent polycrystalline ceramic garnet scintillators are being developed for gamma spectroscopy detectors. The scintillator light yield and energy resolution depend on many of the ceramic characteristics, including composition, homogeneity, and presence of secondary phases. To investigate phase stability dependence on composition, three base compositions – Gd3Ga2.2Al2.8O12, Gd1.5Y1.5Ga2.2Al2.8O12, and Gd1.5Y1.5Ga2.5Al2.5O12 were studied, and for each composition the rare earth content was varied according to the formula (Gd,Y,Ce)3(YXGa1−X)2(Ga,Al)3O12; where −0.01 < X < 0.05. We have found that yttrium and gallium help to stabilize the garnet crystal structure in the ceramics by allowing interionic substitution among the cationic garnet sites. Specifically, a composition of Gd1.49Y1.49Ce0.02Ga2.5Al2.5O12 can accommodate approximately 2 at.% excess rare earth ions from the perfect garnet stoichiometry and remain a phase pure transparent ceramic with optimal performance as a radiation detector. This expanded phase stability region helps to enable the fabrication of large transparent ceramics from powder with tolerance for flexibility in chemical stoichiometric precision.

Reduced graphene oxide–nickel ferrite (RGO–NiFe2O4) has been successfully synthesized by the hydrothermal method in the presence of poly(diallyldimethylammonium chloride) (PDDA). PDDA is used both as a reducing agent and as a stabilizer. The prepared RGO–NiFe2O4 nanocomposites have been thoroughly characterized by spectroscopic (Fourier-transform infrared spectroscopy, Raman spectroscopy, and x-ray diffraction) and thermogravimetric analysis. Microscopy techniques (scanning electron microscopy, atomic force microscopy, and transmission electron microscopy) were used to probe the morphological structures as well as to investigate the exfoliation of RGO sheets. It is interesting to find that RGO–NiFe2O4 nanocomposites exhibited much better electrochemical capability than NiFe2O4. In addition, the as-prepared RGO–NiFe2O4 nanocomposites can effectively remove methyl orange from water under ultraviolet light irradiation, which can be used as novel photocatalysts for environmental protection.

To provide insight into the influence of the length scale on the kinetics of phase evolution during severe plastic deformation, we studied the microstructure evolution of cryomilled Al and Ti mixture, which is further subjected to high-pressure torsion (HPT). The cryomilled microstructure consisted of elemental Al and Ti, and the subsequent HPT deformation at ambient temperature led to the solid state formation of Al-rich intermetallics. X-ray diffraction peaks originating from TiAl2 and TiAl3 were observed after one revolution of HPT, suggesting a shear strain-assisted formation of the intermetallics. A high resolution transmission electron microscope confirmed the formation of TiAl2 following HPT for one revolution. Further HPT straining led to microstructure refinement and a mixing of the Ti and Al, as well as of any phases formed initially. The solid state formation of the intermetallics and the overall evolution of the microstructure are discussed based on the generation of a high density of lattice defects that evolve under the strain conditions present during HPT.

The grain size dependence of the radiation response of silicon carbide (SiC) has been studied under 1.0 MeV Kr2+ ion irradiation. It was found that radiation resistance decreased with grain refinement, in contrast to previous studies on the same nanocrystalline (nc) SiC material using Si ion and high voltage electron irradiation. The effect of grain size on radiation response may depend upon the ion species used due to a potential change in amorphization mechanism. It was also determined that temperature had a strong effect on the grain size dependence of the radiation response in SiC due to the activation temperatures of critical recombination and migration reactions. This work explores the possible impacts of irradiation species, temperature, and experimental design on the radiation response of SiC.

The influence of predeformation and stress on the isothermal bainite transformation has been investigated in G55SiMoV steel via microstructure observation and kinetic analysis. It was found that the bainite transformation became faster and at the end of isothermal holding the bainite fraction increased under the applied stress condition. When the stress increased to 150 MPa, the bainite distribution became to be nonrandom in G55SiMoV steel. Different deformation conditions, in which both promotion and inhibition occurred in the same steel, were created. The promoting and inhibiting factors affected bainite transformation comprehensively. 20% deformation could promote the bainite transformation when it deformed at 900 °C, but prevent bainite transformation when it deformed at 750 °C. Increase of ferrite nucleation rate caused by distortion and dislocation, would suppress the growth of bainite carbides and make most carbides without full growth be finer and shorter.

High strength aluminum (Al) alloys were prepared by rapid solidification method in the Al–Ni–La system. Microstructural characterizations show that all the investigated Al–Ni–La alloys are comprised of Al, rod-like Al3Ni, and blocky Al11La3 phases, of which the size and volume fraction are composition-dependent. The Al85.5Ni9.5La5 (at.%) alloy shows the finest microstructure, which contributes to the highest strength along with considerable plasticity. The experimental analysis and finite element simulation (FES) show that the distribution of the intermetallic phases greatly affects the mechanical properties of the alloys. The rod-like Al3Ni phase precipitated with the locally uniform direction prevents the propagation of cracks and benefits the plastic deformation, whereas the blocky Al11La3 phase exhibits the nature of brittleness and acts as the origin of the microcrack initiation. These findings suggest a new method to design high strength Al alloys.

Aluminum matrix fly ash (AMFA) cenosphere composites were fabricated using the stir casting technique. The used type of fly ash cenosphere, which accounted for over 60% in all fly ash particles, was in narrow and small size (2–30 μm). During synthesis, effects of several key technological parameters on microstructure and properties were investigated using orthogonal experimental design. The optimal technological parameter was achieved as: melt temperature of 700 °C + stirring rate of 1200 r/min + stirring time of 6 min + fly ash cenosphere content of 13 wt%. With this optimal technological parameter, as-cast and forged composites were manufactured. Their tensile strengths were measured and improved maximally by 50% when the cenosphere content is 13 wt%. Such size and content of fly ash cenosphere and technological parameter could largely improve the properties of composites, which should be introduced into the production process of AMFA composites.

Nanosized Eu2+-doped AlN phosphor was successfully synthesized by a metal-organic precursor method for the first time. Aluminum and europium chlorides were simultaneously reacted with triethylamine in acetonitrile media to yield solid precipitates, which were transformed into nanosized AlN:Eu2+ phosphor powders upon calcination in an ammonia gas atmosphere. The possible reaction mechanism was proposed, which is in good agreement with the experimental results. The direct formation of Al–N bonds through a coordination reaction in solution is a key factor in the formation of well-crystallized AlN:Eu2+ grains at a moderately low temperature (1200 °C), which significantly suppresses abnormal grain growth and favors the formation of nanocrystalline (∼15 nm) particles with a homogeneous particle size distribution. Due to the homogeneous distribution of a relative high amount of Eu incorporation (2 wt%), the nanophosphors were effectively excited by UV light and featured an intense green emission band with a peak at 506 nm.

Vertically aligned graphene was grown by plasma-enhanced chemical vapor deposition using methane feedstock. Optical emission spectroscopy (OES) was used to monitor the plasma species, and Raman spectroscopy was used for characterizing the properties of as-grown vertically aligned graphene. OES-derived information on plasma species, such as C, C2, CH, and H, are correlated with the properties of the vertically aligned graphene. Graphene grown at 250 W and 15 sccm exhibited the lowest amount of defects. Although OES peak intensities occurred at the highest power and lowest flow conditions, the OES peak ratios of plasma species had a greater dependence on flow rate and exhibited a saddle point in the atomic C/H ratio corresponding to optimal growth involving the lowest amount of overall defects. Plasma diagnostics provides a valuable approach to optimize growth characteristics and material properties.

Superelasticity of shape memory alloy (SMA) results from the reversible thermoelastic martensitic transformation. Although this property has been studied extensively at the macroscale, the study of this superelastic behavior at the micro/nanoscale is relatively new. In this work, we processed TiNi-based SMAs with different compositions and different phase transformation temperatures. Nanoindentations were performed with different peak loads and at various temperatures to systematically characterize the degree of localized stress-induced martensitic transformation at the nanoscale for each SMA. Micropillar compression tests were also performed to study the global superelastic behavior at the microscale. The physics of stress-induced martensitic transformation versus the phase transformation temperature, the testing temperature, and the peak load relations was explored and the difference between the localized and the global superelastic behaviors was discussed. Our results demonstrate the potential of integrating TiNi-based SMAs into functional micro- and nanodevices.