Search

The structure, elastic properties and electronic structure of VC and V 4 C 3 have been studied by the first-principles pseudopotential plane-wave method based on density functional theory. Compared with VC, V 4 C 3 has lower values of 13.3%, 19.2% and 17.7% in bulk modulus, shear modulus and Young modulus, respectively. The total density of states (DOS) of VC and V 4 C 3 were calculated. The higher shear modulus of VC is due to the differences of DOS for VC and V 4 C 3 . The overlap populations of the V–C bonds in VC and V 4 C 3 were analyzed and the hardnesses of VC and V 4 C 3 were calculated. The calculated hardness of V 4 C 3 is 15.8 GPa, which is lower than that of VC. The calculated hardness of VC is 28.5 GPa, which matches fairly the experimental one.

The microstructural evolution of the coexistence ofspinodal decomposition and ordering ischaracterized by metallographic microscopy andtransmission electron microscopy in aged Fe-23Al(i.e. Fe-23at%Al) alloy. This paper discusses aphase transition mechanism of the microstructureevolution. The obtained results indicate that the asquenchedFe-23Al alloys with equiaxed grain sizeof about 500μm comprise two kinds of the orderedphase in nano-scale, i.e., B2-FeAl and DO3-Fe 3Alphases. The average size of B2-FeAl orderingphases is about 15nm, while the size of DO3-Fe 3Alordering phases is extreme fine in the as- quenchedFe-23Al alloys. The as-quenched Fe-23Al alloypresents characteristics of the coexistence ofspinodal decomposition and ordering during thesubsequent age ing at 565°C and 520°C. Thedomain size of B2-FeAl ordered phase rapidlyincreases while the one of DO3-Fe 3Al orderedphase slowly develops with the increase in agingtime/with increased ageing time. A conclusion isreached that the coarsening process of both B2-FeAl and DO3-Fe 3Al ordered phase is controlledby the spinodal decomposition mechanism.

Functional gradient material (FGM) of the ZrO2-Ni system was developed by a powder metallurgical process, and investigated for its microstructure by means of X-ray diffractometry (XRD), electron probe microanalysis (EPMA), transmission electron microscopy (TEM) and optical microscopy. It was shown that the sintered body of ZrO2-Ni FGM is almost fully densified, and its chemical composition and microstructure have the expected gradient distribution. With composition variation, the microstructure changes gradually from zirconia particles dispersed in a nickel matrix to the converse with nickel particles dispersed in a zirconia matrix, with network structures in the intermediate composition range. Therefore, no distinct interfaces appear in the FGM due to the gradient change of components, that is, both zirconia and nickel are present everywhere in the microstructure. In phase composition, the sintered ZrO2-Ni FGM consists of nickel, tetragonal zirconia and a little monoclinic zirconia. No reaction between nickel and zirconia has been detected. The substructure of nickel and monoclinic zirconia are twins, and strain fringes can also be found in zirconia.

We investigate the surface plasmon resonances (SPRs) behavior of silver niobate (AgNbO3) experimentally and theoretically. Result shows that the localized SPRs (LSPRs) of AgNbO3 combining with its interband transitions enlarge the absorption band across the whole ultraviolet-visible range. The LSPRs behavior in visible-light is mainly ascribed to the metal-like state of silver ion and self-assembled microstructures of AgNbO3 microcrystal. The ab initio density functional theory calculations are carried out to obtain the further insight of the SPRs behaviors. Theoretical study indicates that the Ag atoms are weakly bound in the perovskite structure, leading to a metal-like state, which was the key factor to SPRs behavior of AgNbO3.

A Mo/Si slurry was coated onto the surface of Al/Si-coated carbon fiber reinforced carbon (C/C) composites and vacuum-sintered to form a fused double-layered coating. The effect of the Al content (6 and 10 mass%) in the Al/Si layer on the oxidation resistance of the composites was investigated. Results indicate that the presence of Al effectively prevents liquid Si infiltration into the composites. The composite with the 10 mass% Al has a much lower oxidation resistance than that with the 6 mass% Al. It is revealed that when the Al content is 10 mass% an Al phase dispersed around MoSi2 grains is found in the Mo/Si layer, which decreases the oxidation resistance of the composite at 1370 ° C. This can be ascribed to voids generated within the Mo/Si layer due to the outward diffusion of Al and pores in Al2O3 formed during oxidation, which provide paths for oxygen diffusion. [New Carbon Materials 2013, 28(3): 222–227]

The mechanical performance of a ZrO2-Ni functionally graded material (FGM) developed by powder metallurgy was investigated by means of three-point bending test. It was shown that the mechanical behavior of ZrO2-Ni system strongly depends on constitutional variation, exhibiting typical behavior of elasto-plastic deformation similar to metallic material in the Ni-rich composition and typical behavior of elastic deformation and macroscopic brittle fracture in the ZrO2-rich composition. The mechanical properties of ZrO2-Ni system also display various gradient distributions corresponding to constitutional change. With the rise of Ni content, Vickers hardness decreases, but fracture toughness increases remarkably. Young’s modulus changes corresponding to the distribution of porosity. Bending strength is quite sensitive to microstructural factors, and its peak and valley point are relevant to the dispersion strengthening of ZrO2 particles and the distributional transition of components, respectively.

The plasma sprayed ZrO 2 /NiCoCrAlY graded coating exhibits excellent gradually compositional distribution. The relative density of the graded coating is 90% or so, and contains a few pores inevitably. ZrO 2 component contains some c, t and t’ phases, as well as a little m phase, and the NiCoCrAlY component is mainly consists of γ(Ni) and γ' (Ni 3 Al), as well as a little α-Cr phase and e-Co phase. During spraying process, NiCoCrAlY reacts with oxygen in air, and some NiO, Cr 2 O 3 , Alssss 2 O 3 film formed on the particles surface.

The hot flow stress of as-quenched Al - Cu - Mn alloy was modeled using the constitutive equations. The as-quenched Al - Cu - Mn alloy were treated with isothermal hot compression tests in the temperature range of 350–500°C, the strain rate range of 0.001–1 s-1. The hyperbolic sine equation was found to be appropriate for flow stress modeling and prediction. Based on the hyperbolic sine equation, a constitutive equation is a relation between 0.2 pct yield stress and deformation conditions (strain rate and deformation temperature) was established. The corresponding hot deformation activation energy (Q) for as-quenched Al - Cu - Mn alloy was determined to be 251.314 kJ/mol. Parameters of constitutive equation of as-quenched Al - Cu - Mn alloy were calculated at different small strains (≤ 0.01). The calculated flow stresses from the constitutive equation are in good agreement with the experimental results. Therefore, this constitutive equation can be used as an accurate temperature-stress model to solve the problems of quench distortion of Al - Cu - Mn alloy parts.

The self-diffusion process in B2 type intermetallic compound AlCo has been investigated by the first-principles calculations within the frame work of density functional theory (DFT). The obtained mono-vacancy formation, migration and activation energies for four self-diffusion mechanisms, the next-nearest-neighbor (NNN) jump, [110] six-jump cycle (6JC), straight [100] 6JC and bent [100] 6JC diffusion show that the NNN jump mechanism of Co vacancy requires the lowest activation energy (Q = 6.835 eV ) in these diffusion mechanisms, which indicates that it is the main way of self-diffusion in AlCo . The electronic structure including the electron density difference on (-1 1 0) plane as well as atomic Mulliken populations were calculated, and the change of bonding behavior during the [110] 6JC process was discussed in detail. Finally, the self-diffusion coefficients of NNN jump and 6JC mechanisms for AlCo were also studied via the first-principles calculations and semi-empirical predictions, which indicates that the self-diffusion coefficients for NNN jump of Co vacancy show the highest value than the others.