Instabilities during superplastic deformation is more complicated than those during plastic deformation. Many valuable papers about mechanical analysis of instability have been published at home and abroad, which contributed much to the development of superplastic research. But their conclusions were different because of the diversity of the researchers’ thoughts and methods. Therefore, it is necessary to normalize these theories. In order to study the impact of material’s mechanical parameter on instability, tensile instability criterion of specimen without geometric defect at constant temperature, that is due to only material parameter, was analyzed based on state equation of deformation in this paper. The results not only coincided with those in some typical papers, but also proved theoretically that, during superplastic deformation, geometrical instability will happen after a period of uniform deformation which follows load instability, rather than in the mean time of load instability.

In-depth understanding of precipitation crystallography is very essential to the control of microstructure in many multi-phases materials. The present paper reviews the recent development of various crystallographic models. Each model was reviewed in terms of its hypothesis, applicable scope, basic idea, and especially its limitation. According to the comparison and contrast between different models, it is proposed that combining the O-line model and Near Coincidence Sites model may provide a more powerful tool to interpret the precipitation crystallography and morphology.

A thick ceramic film on SiC/2024 aluminum matrix composite was fabricated by plasma microarc discharge method. The growing curve of film was determined, and the morphology and phase composition of film were analyzed by scanning electron microscopy and X-ray diffraction. The morphology and distribution of reinforcement particles were emphatically observed, and then a growth model of microarc oxidation film on metal matrix composites was proposed. Under microarc discharge sintering, most SiC reinforcement particles have been oxidized, but only a few residual SiC particles still remain in the film close to the composite/film interface. Although the SiC particles hinder the film growth, the continuity of film has not been disrupted. That is completely different from conventional anodizing on metal matrix composites.

Al diffusion coatings were prepared on g-TiAl alloy by first arc ion plant Al then interdiffusion treatment processes. Al diffusion coatings have a good adherence with the substrate, and EDX and XRD show that the coatings composed of outer thick layer TiAl3 and inner thin layer TiAl2. For g-TiAl without coating under high temperature oxidation at 900oC in air, multilayer oxide scale is formed and consisted of mix of TiO2 and Al2O3, which exhibits relatively poor oxidation resistance. The high temperature oxidation resistance of the specimens coated with Al diffusion coatings is remarkably improved due to the formation of a dense and adherent Al2O3 scale. The oxidation and degradation mechanism of Al diffusion coatings also are discussed.

The solidification behavior and the morphological evolution of 316L stainless steel during laser rapid forming (LRF) were investigated. It was found that, there shows a complete  austenitic structure in the LRF sample within the processing parameters of this study, there was continued epitaxial growth of the g phase of the fine columnar dendrites from the substrate, with the <100> crystallographic orientation leaning to, even parallel to the deposition direction. There also exist a thin layer in which the dendrites grow along the laser scaning direction at the top of the LRF sample. Clad layer bandings were found in the samples; however, the continuity of the growth of the columnar dendrites was not upset. The growth morphology of primary  dendrites can be predicted by the microstructure selection models based on the maximum interface temperature criterion. The formation of the clad layer bandings and the epitaxial growth characteristic during LRF are also explained by the criteria for planar interface instability and dendritic growth theory and the columnar to equiaxed transition model. There shows an reasonable agreement between the theoretic analysis and the experimental results.

In situ observation of delayed propagation of unloaded indentation crack in humid air, as well as delayed domain change and delayed cracking induced by constant magnetic field in humid air for (Tb,Dy)Fe2 magnetostrictive alloy have been investigated using differential inference contrast microscope. The results showed that a residual stress during indenting could cause delayed propagation of unloaded indentation crack in humid air. A magnetic field exceeded a threshold field Hth caused instant propagation of indentation crack. A constant magnetic field below Hth could cause delayed change of domain configuration in humid air and delayed propagation of indentation crack in humid air.

The coefficients of the annealing and quenching critical unit cell of the stable element of the phase β in titanium alloy are defined and calculated, which is based on the basic constitute structural unit of the titanium alloy α+β and β i.e. their unit cell and atom coordinate. Attempt to bring forward a method to calculate the volume fraction of the phase α and β, which are in the annealed and quenched structure of titanium alloy α+β and β. With this method, the volume fraction of the phase a and b in the annealed and quenched structure of some common titanium alloy α+β and β are calculated, the calculated value is consistent with the experimental value.

A bulk metallic glass foam with a diameter of 8.1 mm and a length of 70 mm was fabricated by infiltrating Zr-based liquid metal into NaCl powder as a pattern in a few seconds and water quenching the pattern. Both the powders and the prealloyed charges were sealed in a U-turn quartz tube as a crucible and heated in two different temperature regions respectively in the electric resistance furnace. The sample fabricated is the largest in diameter up to now according to the literature. The X-ray diffraction and the scanning electron microscopy were used to check the amorphous nature and structure of the porous samples. The results show that the samples are consisted of amorphous phase and have good connectivity among the cells in the foam. The sizes of struts and the holes are largely smaller than 1mm. The density and porosity of the open-cellular bulk metallic glass are 3.63g/cm3 and 40.5% respectively. Porous bulk metallic glass is the most potential materials that will be used as biologic-transplant materials.

Size- and shape-controlled phase pure Ni nanoparticles were synthesized using nickel acetate as precursor, 1,2-propanediol as solvent and reducing agent, sodium hydroxide as pH adjusting agents, and surfactants as modifiers. The as-prepared Ni nanoparticles were characterized by transmission electron micrographs (TEM), selected area electron diffraction (SAED), powder X-ray diffraction (XRD) and Fourier transform infrared (FTIR). The presence of modifiers is crucial for the synthesis of size- and shape-controlled phase pure Ni nanoparticles. The modification effect of single modifiers such as PEGs and soidum dodeccanesulphonate, and their composites were investigated and analyzed. Among single modifiers, the presence of PEG-200 is beneficial to fabricating irregular snowflake-like crystals as well as the presence of PEG-600 does, PEG-2000 beneficial to synthesizing dodecahedra crystals, PEG-6000 beneficial to synthesizing triangular crystals, SDS beneficial to fabricating dodecahedra crystals and irregular snowflake-like crystals with smaller average particle size. Among the composite modifiers, the presence of SDS and PEG-600 is beneficial to fabricating irregular snowflake-like crystals with bigger average particle size of 140nm, as well as the presence of SDS and PEG-6000 does. The effects of the eletrostatic attraction and steric barrier of the modifiers play an important role in the synthesis of Ni nanoparticles certified by Fourier transform infrared (FTIR).

TiN/TaN multilayers with same period and different modulation ratios have been fabricated using reactive magnetron sputtering methods. X-ray diffraction and high-resolution transmission electron microscopy were used to determine the structural characterization of the multilayers and their mechanical properties were measured by a nanoindentation method. The results show that modulation structure affects both the growth rate and preferred growth direction. With the increase of layer thickness (TiN or TaN), the growth rate of the layer decreases. We also find that two kinds of grains with (111) and (100) normal to the films grow epitaxtially with slightly different modulation periods. The hardness and moduli of TiN/TaN multilayers increase by about 50% and 30%, respectively. The maximum values appear at the modulation ratio of 3:1, hardness is 34.2 GPa and modulus is 344.9 GPa. Based on the structure analysis and the mechanical properties, the hardening mechanism in TiN/TaN multilayers are discussed in the paper.

Abstract: A general finite-element software program, Marc/Mentat, has been used to develop a coupled thermo-mechanical model of rotary swaging process of pure magnesium. Distributions and transitions of stress and strain are clarified and the critical conditions predicting two deformation defects are obtained. The deformation zone can be divided into three parts: Ⅰis the bulging head-end, Ⅱthe formed zone and Ⅲ the reduction zone. In the formed zone, the equivalent strain distributes inhomogeneously along the radial direction. The equivalent strain in the center is not more than half of that at the edge. The critical conditions preventing insufficient forging and edge-crack are εc≥ε0,εe<εb, respectively. The residual stresses are between 18MPa and 30MPa. Temperature-rising owing to the heat translateded from plastic deformation energy is not notable.

Five single activating fluxes, TiO2, Cr2O3, CdCl2, ZnCl2, AlF3, were used to investigate the effects of the coating quantity of active fluxes on TIG welding penetration of magnesium alloy. The distribution of active flux element in the weld-pool was measured by EPMA analysis. The results showed that the above activating fluxes all increased the weld penetration. Each flux has a saturation point in penetration increment. The distributions of Mg and Al elements in the weld-pool are changed in different degrees after welding with flux. No active flux element was found in the weld-pool after welding with CdCl2 and ZnCl2 fluxes, however, the elements Ti, Cr and O were observed in the weld-pool after welding with TiO2 and Cr2O3 fluxes, By the analysis, the chlorides increased weld penetration mainly due to the effect of flux on the arc, the oxide increased weld penetration mainly due to the reaction of flux with the fusion zone metal.

This paper presents a novel method for predicting the Jominy curve of structural steels. An analytical function containing the undetermined parameter was used to calculate the Jominy hardness distributions. This undetermined parameter was defined as the hardenability coefficient of steel, which is different from the conventional element coefficient and depends on the descending velocity of the Jominy curve. Therefore, the problem predicting the Jominy curve changes to one calculating the hardenability coefficient. It was demonstrated that the hardenability coefficient depends on the chemical composition under the condition of the standard Jominy test. An empirical relationship between the hardenability coefficient and the chemical composition of structural steels has been established using a subsection approach. Substituting the obtained hardenability coefficient into the distribution model of the hardness, the predicted Jominy curves exhibited very good agreements with the experimental data.

Ductility exhaustion theory premises that material flow caused by loads under fatigue-creep conditions can be described by dynamic viscosity, and the criterion of failure is that dynamic viscosity equals material toughness. A new fatigue-creep life prediction method has been put forward based on ductility exhaustion theory with the assumption that ductility consumption only relates to plastic strain and creep strain caused by tensile stress, and plastic strain occurs only when tensile stress equates with σmax-(σmaxσa)^1/2. The method given is applicable for stress control mode, and includes effects of stress ratio, stress rate, tensile hold time, and mean strain velocity. Applicability of the new method is assessed with fatigue, creep, and fatigue-creep data on 1.25Cr0.5Mo under stress control at 540℃, and the prediction is found to be very satisfactory with a factor of ±×1.25.

NiTi shape memory alloy is widely used as a biomaterial for the good compatibilities of its surface titanium oxide. Oxygen adsorption on NiTi surface is important for the formation of titanium oxide. In this work, first principle pseudopotential plane wave calculations based on density functional theory and the generalized gradient approximation (GGA) have been used to study the electronic structure of NiTi (100) surface, molecular O2 and adsorption of O2 on the NiTi alloy (100) surface. The results show that Ti-terminated surface is more reactive than Ni-terminated surface. O2 is activated and will decompose upon adsorption. Among several possible adsorption configurations considered, the most stable one corresponds to bridge configuration and the top configuration is unstable. Structural and density of state (DOS) analysis shows the interaction of O atom and surface is the total contribution of valance orbital of O atom and hybridized surface orbital of NiTi alloy.

Image recognition was used to study the corrosion morphology of LC4CS aluminum alloy samples with periodic rain tests, and the concept of image feature δ was introduced. The effects of each orthogonal experiment factor on acceleration were analyzed by image feature δ, the best combination of factor lever for accelerated corrosion test was also obtained. The conclusion was consistent with the result based on the corrosion weight loss.

In this paper, preparation of composites Al2O3/ZrO2(Y2O3) by vacuum sintering was studied. The effects of the contents of ZrO2(3Y) and ZrO2(2Y) on the sintering densification, microstructure and transformation behavior in detail were analyzed. The effect of the content of ZrO2(Y2O3) on the microstructure of the composites was also investigated, and it was found that there is a critical value of the content. The results also show that when the contents of ZrO2(Y2O3) were 15vol% and 20vol%, the relative densities of the composites Al2O3/ZrO2(Y2O3) were 99.6% and 98.5%, respectively, and the corresponding average grains of ZrO2(Y2O3) were 1.1μm and 1.8μm. In addition, the transformation quantities of the samples before and after their fracture were ＝43.8vol% and =18.4vol%.

ABSTRACT Grain structure modeling of Ti- (45~48) at% Al alloy ingots has been carried out by using a new cellular automaton method coupled with macroscopic heat transfer calculation. Cells are divided into primary and peritectic ones. Different cells take the different solidification path. By the new method, the formation of peritectic phases can be shown graphically throughout solidification. The formation of shrinkage cavity at the top of the ingot is included in the calculation. A special-moving-allocation technique is designed to minimize the computation costs and memory size associated with a large number of cells. The potentiality of the present model is demonstrated by comparing the simulated results with the experimental one. The influences of convection and initial alloy composition on the grain structures are studied. The mechanisms producing these results are discussed. The simulated results indicate that the size of equiaxed zone increases with increasing the convection coefficient and alloy composition. And the number of peritectic phases decreases as the alloy composition decreases.

The effect of cerium addition on the microstructures of AZ91 magnesium alloy has been studied. It was found that a small amount of cerium addition to AZ91 magnesium alloy produced a large decrease in the α-Mg grain size. With increasing Ce addition, the amount of β-Mg17Al12 phase was decreased, and its size became dispersed fine. In addition, the rod-shaped or needle-like Al4Ce phases mainly distributed at grain boundaries have been observed in the AZ91 alloys with Ce addition. The grain refinement mechanism was investigated using EDS analysis and water-quenched microstructural observation. The results showed that the grain refinement of the AZ91 alloys containing Ce was mainly attributed to the addition of Ce generated constitutional undercooling at solidification interface front, consequently, increase in the number of nucleation. In addition, its restricting growth effect on the α-Mg crystals can result in the further grain refinement.