Leng Chen

Characteristics of Hot Compressed Magnesium Alloy AZ31 with Initial Textures Analyzed by Orientation Mapping

Orientation mapping based on EBSD technique was applied to reveal the orientations of new grains and their relationships to the surrounding matrices, to analyze Kikuchi band contrast and the influence of strain rates on local orientation evolution. This information is used to understand the dynamic recrystallization mechanism and the relative contribution of plastic slip versus grain boundary glide or grain rotation related with super-plasticity. For this purpose samples with different initial textures were deformed by (quasi-)plain strain compression at two strain rates. It is suggested that the dynamic recrystallization in this alloy proceeds in continuous way by progressive subgrain rotation. No evident non-basal slip of was observed by referring texture evolution in the sample with initial basal texture. A high strain rate promotes more contribution of plastic slip accompanied by fast orientation changes. The fact that groups of grains with very similar orientations in basal oriented samples is discussed in terms of viscous flow.

Relationship between texture and residual macro-strain in CVD diamond films based on phenomenological analysis

Abstract The relationship between texture and elastic properties of chemical vapor deposition (CVD) diamond films was analyzed based on the phenomenological theory, which reveals the influence of crystalline orientation and texture on the residual macro-strain and macro-stress. The phenomenological calculations indicated that the difference in Youngs modulus could be 15% in single diamond crystals and 5% in diamond films with homogeneously distributed strong fiber texture. The experimentally measured residual strains of free-standing CVD diamond films were in good agreement with the correspondingly calculated Youngs modulus in connection with the multi-fiber textures in the films, though the difference in Youngs modulus induced by texture was only around 1%. It is believed that texture should be one of the important factors influencing the residual stress and strain of CVD diamond films.

Residual Stress Analysis of Microwave Plasma CVD Diamond Films

The residual stress and crystallographic texture of diamond films were investigated in the present work. The diamond films were synthesized on (100) silicon wafer by Microwave Plasma Chemical Vapor deposition (MPCVD). Then the residual stresses of the films were measured by X-ray diffractometer equipped with the two-dimensional detector. The residual stresses can be classified into two categories, i.e., the intrinsic stresses and the thermal stresses. It was shown that the thermal stresses were compressive in the temperature range studied and the intrinsic stresses were tensile. The crystallographic textures of the films were measured by X-ray diffractometer with the method of pole figure and orientation distribution function (ODF). The experimental results suggest that the crystallographic textures of the films depend upon the deposition temperature and methane flow rates, and the components and intensity of crystallographic textures have effect on the residual stresses in diamond films to a certain extent.

Microstructure and Texture in Free-Standing CVD Diamond Films

Free-standing CVD diamond films were prepared under the substrate temperature in the range of 850-1050oC. Macro- and micro-textures of the films were investigated based on the SEM observation as well as on the ODF and EBSD analysis. It was found that certain growth selection process appeared during diamond deposition which, however, did not lead to a strong film texture. It is indicated that strong fluctuation of growth ratio V<100>/V<111> and frequent growth twinning during film deposition resulted in randomization effect of grain orientations, which can be transformed by adjusting the parameters of film preparation.

Preparation and Corrosion Resistance of Graded Glass Coating on PbTe

Lead telluride (PbTe) is a promising material for the thermoelectric power generation system using combustion heat from municipal solid waste Because the combustion gas from solid waste incinerator generally contains corrosive substances such as HCl and H 2 SO 4 , the corrosion resistance of PbTe becomes important for its thermoelectric application In the present study, SiO 2 -B 2 O 3 -Na 2 O-ZnO system glasses were coated on PbTe in order to improve the corrosion resistance. Addition of PbO and TeO 2 to this system glass significantly improved the adhesion of the glass as well as the oxidation resistance of glass-coated PbTe. However, the addition of PbO and TeO 2 degraded the corrosion resistance of the glass coating because the PbO and TeO 2 reacted with HC at high temperature to form volatile chlorides.In order to incorporate the corrosion resistance and adhesion of glass coating, a two-layer glass was coated on PbTe, in which the inner layer contains 60 mass%PbO.TeO 2 while the outer layer contains no PbO.TeO 2 . Corrosion experiments showed that the glass coating with the graded PbO.TeO 2 content exhibited excellent adhesion and corrosion resistance at an O 2 -HCl-Ar atmosphere.

Thermophysical Properties of Al2O3-TiCx (x = 0~1) Composites Prepared by Self-Propagating High-Temperature Synthesis (SHS)

Al 2 O 3 -TiC ceramic is an important industrial material which is widely used as wear-resistant parts such as cutting tools. Self-propagating high-temperature synthesis (SHS) provides an attractive practical alternative to the conventional methods of producing this kind of materials because SHS offers advantages with respect to process economics and process simplicity. On the other hand, the properties of Al 2 O 3 -TiC ceramic depends on the stoichiometry factor x of TiC x . Out previous work has shown that the properties of Al 2 O 3 -TiC ceramic can be improved by FGMs (Functionally Graded Materials) concept. In the present work, dense Al 2 O 3 -TiC x ceramics with x value in the range of 0∼1 were manufactured by SHS combustion reaction: 3TiO 2 + 3xC + 4Al → 3TiC x + 2Al 2 O 3 . Only cost effective raw materials were used. Thermophysical properties of SHS produced Al 2 O 3 -TiC x ceramics (x=0∼1), such as thermal diffusivity, thennal conductivity and specific heat were investigated as functions of the stoichiometry factor x of TiC x .

Effect of Trench Aspect Ratio on Microstructure and Texture in Damascene Cu Interconnects

The effect of trench aspect ratio and line spacing on microstructure and texture in annealed damascene Cu interconnects has been investigated. The X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) analyses of Cu lines, showed a preferred {111} orientation and the trenches reduce the proportion of high-angle grain boundaries and increase the fraction of coincidence site lattice (CSL) grain boundaries, comparing with the Cu blanket film. In addition, both trench aspect ratio and line spacing can largely affect the microstructure and texture in annealed damascene Cu interconnects.

Texture Analysis of CVD Free-Standing Diamond Films

The crystallographic textures of the free-standing diamond films which were synthesized by the chemical vapor deposition (CVD) using a CH4/H2/Ar gas mixtures have been investigated. Texture components of the diamond films are analyzed with pole figures and orientation distribution function (ODF). The surface morphology of the diamond films grown at different substrate temperatures as well as different gas concentrations is observed with scanning electron microscopy (SEM). The experimental results indicate that the intensity of {110} fibre texture becomes much higher with the increase of the substrate temperature. It is considered that the higher multiplicity of <110> crystallographic direction in diamond octahedron leads to the higher appearance possibility of {110} fibre texture and the final texture components of the diamond films depend upon the CVD deposition parameters.

Reaction Stresses among the Grains during Tensile Deformation of Polycrystalline Metals

A new model describing the reaction stresses during plastic deformation of metals is proposed in which the reaction stresses among the grains and their accumulation are calculated. The model could overcome the shortages of the Sachs and Taylor deformation model. According to the model, the plastic strain tensor induced by activation of slip systems will produce certain elastic reaction stress in the surrounding matrix, which influences the choice of further activation of slip systems as well as the orientation evolution. The model gives more attention to both of the stress and strain compatibility among the grains. The simulation on the tensile deformation of pure copper indicates that the model could exhibit the main characteristics of the real deformation process.

Simulation and Determination of the Goss Texture in Grain-Oriented Silicon Steel

A new approach to simulating the orientation distribution function (ODF) using one diffraction frame collected by X-ray two-dimensional detector is proposed. Based on the concept that the texture component presents a normal distribution form, the volume fraction and the orientation spread of texture component are obtained using curve fitting method from diffraction profile and, the pole figures as well as ODF can be calculated. Thus the texture of grain-oriented silicon steel is determined rapidly and conveniently. A comparison of the simulation ODF with that reconstructed from experimental pole figures by series expansion is presented and the results show that the new approach works correctly.