In this work, we present a detailed investigation of the growth of palladium-seeded GaAs nanowires. Nanowires grown on GaAs (111)B substrates consist of three different morphologies, denoted as curly (containing multiple kinks), inclined (relative to the substrate, such as 〈001〉), and vertical. We show that the relative yield of the different types is controllable by a combination of V/III ratio and temperature, where vertical and inclined nanowires are promoted by a high temperature and low V/III ratio. These growth conditions are expected to promote a higher Ga incorporation into the Pd particle, which is confirmed by energy dispersive x-ray analysis. We propose that the observed relationship between particle composition and nanowire morphology may be related to the particle phase, with liquid particles promoting straight nanowire growth. In addition, particles at the tips of nanowires are sometimes observed to be smaller than the initial particle size, suggesting that Pd has been lost during the growth process. Finally, we demonstrate the importance of initial particle size-control to interpret diameter changes after growth.

Device quality CdS/CdTe heterostructures and completed solar cells (∼12% efficient) have been studied using photoluminescence (PL) as a function of temperature and laser excitation power. The CdS/CdTe junctions were grown on transparent conducting oxide covered soda lime glass using radio frequency sputter deposition. In the current work we found that the PL spectra of sputtered and thermally evaporated CdTe absorber films share common features. It was found that the luminescence shifts from being dominated by sub-gap defect-mediated emission at lower excitation powers to near band edge excitonic emission at higher excitation powers. It was found that the presence of Cu suppresses the sub-band gap PL emissions. This effect was concluded to be due either to Cu occupying cadmium vacancies (VCd) or forming acceptor complexes with them. This points to a potential role of Cu in eliminating sub-band gap recombination routes and hence increasing the charge separation ability of the device.

The co-doped ZnB2O4:Eu3+, Tb3+ phosphor was prepared by a thermal conversion method using Zn[B3O3(OH)5]·H2O:Eu3+, Tb3+ as the precursor, which was characterized by energy dispersive x-ray spectrometer, x-ray powder diffraction, infrared, scanning electron microscopy, and photoluminescence. The effects of doped concentration, calcining temperature, and calcining time of precursor on the luminescence property of ZnB2O4: Eu3+, Tb3+ phosphor were investigated. The results showed that the ZnB2O4: Eu3+, Tb3+ phosphor with maximum luminescent intensity was obtained by calcining the precursor at 900 °C for 6 h. It is found that the ZnB2O4: Eu3+, Tb3+ phosphor prepared by this method exhibits much stronger emission intensity than that synthesized by conventional high temperature solid-state method. Meanwhile, ZnB2O4: Eu3+, Tb3+ also has stronger emission intensity and higher red to orange ratio than those of ZnB2O4: Eu3+.

The ground state properties of γ-Fe4X (X = B, C, N, and O) were studied by means of the density functional theory. The calculations were performed using the linearized augmented plane wave method as implemented in the Wien2k code. From the equilibrium cohesive energy point of view, all the compounds are ferromagnetic and the stability increases in the following sequence: γ-Fe4O, γ-Fe4N, γ-Fe4B, γ-Fe4C. The electron density suggests that the chemical bonding in γ-Fe4X (X = B, C, N, and O) is a mixture of covalent and ionic character that vary in intensity with the X atom. The magnetic moments and hyperfine interactions are clearly and differently affected by the nature of the X atom. The results indicated that there is not a linear relation between the 2p electron number of the X atom and the magnetic properties of the compounds.

Effect of a transverse magnetic field on macrosegregation and growth of primary Al2Cu dendrites in directionally solidified Al–40 wt% Cu alloys was investigated experimentally. The experimental results indicated that the magnetic field caused the formation of channel-like and freckle segregations. It was also found that the application of the magnetic field benefited the growth of primary Al2Cu dendrites and the axial segregation. Moreover, the magnetic field decreased the primary dendrite spacing and the mushy zone length; however these effects weakened with the increase of the magnetic field intensity. The above experimental results should be attributed to the formation of the thermoelectric magnetic convection during directional solidification under the transverse magnetic field.

Rapid solidification of Al30Si70 alloy was studied via electromagnetic levitation technique. The solidification kinetics and the morphology of the solidification front of the Si phase were analyzed in situ by using a high-speed video camera and subsequent microstructural analysis of as-solidified samples. It shows that solidification of the sample always starts from one point. After that, nucleation continues to proceed at the interface front during growth. The morphology of primary Si transforms from faceted wafer to nonfaceted equiaxed grain and the grain size decreases with increase of undercooling. At small undercooling, the growth velocity of primary Si decreases with time and the floated Si wafers have a trend to agglomerate, while at large undercooling, the nucleation rate decreases with time, which are explained by the fact that silicon content, undercooling and density at the solid–liquid interface change with time in solidification. Finally, the nucleation rate and growth velocity were discussed in combination of classical theory.

Multilayered thin films of Al/Cu/Fe have been prepared by magnetron sputtering and annealed into quasicrystalline and approximant phases on Al2O3 and Si substrates, respectively. The nanomechanical and nanotribological properties, such as hardness, elastic modulus, friction, and toughness, have been measured using a triboindenter and analytical methods. The approximant phase was proved to be slightly harder than the quasicrystalline phase with a hardness of about 15.6 GPa, and with a similar elastic modulus of about 258 GPa. These values however decreased rapidly with an increasing amount of Si in the approximant. The indentation toughness of the approximant, <0.1 MPa/m½, was however inferior to that of the quasicrystals with 1.5 MPa/m½. Friction coefficients were measured in a range of 0.10–0.14 for both the quasicrystalline and approximant thin films.

Aln Si12−n N12 (n = 0, 1, 2, and 4) are electron redundant systems. The calculations show that the stabilities of Aln Si12−n N12 and Al12N12 are very close. One Si atom in each Si2N2 square protrudes obviously and the cages are distorted. The excess electrons reside at the outside of the protrudent Si atoms as lone pair electrons. They occupy antibonding orbitals and form the highest occupied band. The Si–N bonds are covalent bonds with strong polarity. The overlap integral is 0.38 per Si–N bond and is 17% stronger than the overlap in Al12N12. The atoms in molecule charge on the in-plane and protrudent Si atoms are 3.13e and 1.65e, respectively. The lone pair electrons form large local dipole moments enhance the electrostatic interaction between the protrudent Si and N atoms. The energy gaps of the electron redundant cages Aln Si12−n N12 (n = 0, 1, 2, and 4) are about 1 eV smaller than the gap of Al12N12. As the lone pair electrons are loosely bond, the SiN-based cages have large hyper-polarizabilities and so have potential applications, such as nonlinear optical materials.

The effect of 0.5 wt% Mn addition on the microstructure and mechanical properties of cast Al–2Li–2Cu–0.8Mg–0.4Zn–0.2Zr (wt%) alloy was investigated. Results showed that the grain size of Mn-containing alloy was smaller than that of Mn-free alloy in both the as-cast and solution treated state. Al20Mn3Cu2 dispersoids were formed during solution treatment in the Mn-containing alloy. After aging at 175 °C for 32 h, a large volume fraction of coherent Al3Li/Al3(Li, Zr) particles were precipitated in both Mn-free and Mn-containing alloys, while more Guinier–Preston–Bagaratsky zones were observed in the Mn-free alloy. Mn addition improved the elongation significantly, which was 1.7% for Mn-free alloy and 3.3% for the alloy with 0.5 wt% Mn addition.

This paper proposes a method for determining the mechanical properties (Young's modulus, Poisson's ratio, yield strength, and work hardening factor) of a material at a specific point using an indentation technique that utilizes a specially designed indenter in conjunction with an inverse problem and finite element analyses. The specially designed indenter combines the characteristics of spherical and conical indenters and can be used to produce multiple indentations at a single point. The feasibility of the proposed method for determining the local mechanical properties of a material was confirmed by detailed precision verifications in the ideal case and the worst case.

The microstructural evolution of spray-formed high speed steel during hot deformation was investigated as well as the effects of spray forming parameters on the porosity formation. Four distinct zones are identified in the as-deposited material, and interstitial porosity is present in the bottom and peripheral zones, while gas-related porosity is mainly found in the central zone. It can keep the porosity at a minimum value by using the optimum parameters, e.g., the average porosity of central zone is 3.7% for a superheat of 170 °C and a gas-to-metal flow rate of 0.7. During hot deformation at 1150 °C, the amount of porosity can be obviously decreased by increasing the height reduction which also plays a key role in breaking up eutectic carbides. The critical height reduction for the breakdown of the eutectic carbides is 50%, the dominant mechanism being mechanical fragmentation.

Carbon nanotubes (CNTs) reinforced Ti matrix composites with tailored microstructures and properties were fabricated by direct metal laser sintering (DMLS). A relationship of processing conditions, distribution characteristics of CNTs, and properties was established. The appearance of balling phenomenon and micropores at relatively low laser energy input reduced the densification level of DMLS CNTs/Ti composites. As a η of 700 J/m was properly settled, the composite part with a near-full 96.8% density was obtained. On increasing the laser energy input, the distribution states of CNTs in Ti matrix changed markedly from agglomeration to homodisperse. The optimally prepared fully dense CNTs/Ti composite with uniform distribution of CNTs had significantly enhanced H d of 9.4 GPa and E r of 328 GPa, which showed respectively ∼2.5- and ∼3.4-fold increase upon that of unreinforced Ti, and resultant a relatively low friction coefficient of 0.23 and reduced wear rate of 3.8 × 10−5 mm3/(N m).

Narrow gap submerged arc welding method accompanied with multilayer and multipass technology was used to manufacture advanced 9Cr and CrMoV dissimilarly welded joint used as a newly developed turbine rotor. The aim of this investigation was to evaluate the high cycle fatigue (HCF) behavior of the welded joint at room temperature. Uniaxial-stress controlled HCF tests at stress ratio R = −1 were performed with specimens chipped from the welded joint of mockup and the S–N curve up to 1.0 × 108 cycle lifetime was obtained. It was found that the fracture location transferred from heat affected zone (HAZ) of CrMoV side to weld metal (WM) with decreasing stress amplitude. The microstructure of the welded joint was characterized and microstructure diversity was found to be responsible for the failure locations both in the CrMoV–HAZ and WM. Fracture morphology of failure samples were also investigated by a scanning electron microscope. It is detected that the stress amplitude required to drive the inclusion to be the crack initiation of the CrMoV–HAZ lies behind the transition. With decreasing stress amplitudes, void in the WM more easily tends to be the initiation of a fatigue crack than inclusion.

The aim of this study is to prevent cracks in large foam bodies prepared by thermo-foaming of alumina powder dispersions in molten sucrose. Cracks initiate in the binder burnout stage during which the bodies undergo shrinkage in the range of 32–49 vol% depending on sucrose content. Intermediate pyrolysis of the sucrose polymer binder prevents the cracking of large foam bodies as the carbon produced by pyrolysis binds the alumina particles during the initial stage of shrinkage and provides adequate strength to withstand the internal stresses produced during the pyrolysis and subsequent carbon burnout. The carbon bonded alumina foam bodies obtained after pyrolysis do not show any visible cracks during subsequent carbon burnout and sintering because the alumina particles establish a firm network with each other due to particle drag and rearrangement during pyrolysis of the sucrose polymer binder as evidenced from microstructure analysis. The carbon bonded alumina foam bodies show high compressive strength (2–1.3 MPa) and are amenable to machining operations such as milling and drilling without cracking.