Investigation of the effects of misch metal in RS Al-Fe-V-Si-Mm nanocrystalline alloys by PAT

The positron lifetime spectra of several Al93.3-xFe4.3V0.7Si1.7Mmx (x = 0.5%, 1.0%, 3.0%, atom fraction) alloys with different content of rnisch metal prepared by rapid solidification were measured, and the variations on the interracial defects with the content of misch metal were revealed by an analysis of the lifetime results. The interface characteristics derived from the lifetime results could be used to give a satisfactory interpretation of the dependence of mechanical properties on the content of misch metal.     

Solid-state reaction in nanocrystalline Fe/SiC composites prepared by mechanical alloying

Different solid-state reactions, i.e. Fe + SiC → Fe₃C + Fe(Si), and Fe + SiC → Fe₃Si + Fe₂Si + C, were found in mechanically alloyed nanocrystalline Fe/SiC composites induced by prolonged milling or heat treatment, respectively. The solid-state reaction between nanocrystalline iron and SiC upon heating is greatly enhanced when compared with that between bulk iron and SiC. It is believed that the prolonged milling-induced reaction is related to the changed thermodynamics and kinetics while the heat-treatment-induced reaction, completed during a short time, is attributable to the changed reaction kinetics. This revised version was published online in November 2006 with corrections to the Cover Date.     

永磁场对焊缝显微组织及焊接接头力学性能的影响

研究了外加永磁场对低碳钢焊缝的显微组织及焊接接头力学性能的影响，得到了在交流电焊机手工电弧焊条件下，细化焊缝显微组织，提高焊接接头力学性能的最佳磁场参数。     

Dependence of thermal residual stress on temperature in a SiC particle-reinforced 6061Al alloy

The thermal stresses (TS) in the matrix of a SiC _p /6061Al composite during thermal cycling were measured by X-ray diffraction. Also, the TS during thermal cycling and residual stress distribution (RSD) at room temperature in the two phases of composite were calculated by finite element modeling (FEM). The measured and calculated results indicated that the closed stress-temperature loop was formed during thermal cycling. The stress state in the matrix changed from tension to compression during heating and from compression to tension during cooling. Plastic deformation took place in the matrix of the composite during thermal cycling. The general change trend of TS with temperature during thermal cycling was in agreement between the experiment and calculation.     

The synthesis of ultrafine SiC powder by the microwave heating technique

Ultrafine powders of silicon carbide synthesized by microwave and conventional heating are described. Silicon carbide powders with diameters in the nanometer range were formed by reducing SiO₂ with various forms of carbon in a nitrogen atmosphere. Ultrafine SiO₂ powder, phenolformaldehyde resin and ultrafine carbon black were used as starting materials. The properties of the powders were determined by means of X-ray diffraction, TEM, etc. The results showed that the technique and conditions for preparing samples, as well as the temperature and type of heating, had obvious effects on the powders characteristics. This revised version was published online in November 2006 with corrections to the Cover Date.     

基于成形工具姿态调整的适应性积层制造技术研究

当前的积层制造技术主要采用2.5D切片。成形中台阶效应不可避免，本文提出了一种新的基于3D切片的适应性成形方法。通过增加成形工具的运动自由度，使之能根据实体的几何外形自动调整姿态，从而有效地克服了台阶效应对成形精度的影响。在保持同等成形精度的前提下。采用适应性斜切成形技术可以使用更厚的层片。提高成形效率，实现了成形精度和速度的兼得。     

The internal oxidation of two-phase binary alloys beneath an external scale of the less-stable oxide

The internal oxidation of two phase binary A-B alloys by a single oxidant at high temperatures, under partial pressures sufficient to also form external scales of the less-stable oxide, is examined by means of quantitative models and compared with the corresponding behavior of single-phase alloys. It is shown that, depending on various factors, particularly on the solubility and diffusivity of the most-reactive component B in the most-noble component A, this process may or may not involve a diffusion process of the alloy components, leading to different scale morphologies. It is also concluded that even when the solubility and diffusivity of B in A are sufficiently high, so that the internal oxidation of the common type occurs, the restriction to the diffusion of B in the alloy due to its limited solubility affects the kinetics of internal oxidation, producing an increase of the rate of internal oxidation and of the critical concentration of B in the alloy required for the transition to the external oxidation of B with respect to single-phase alloys under the same values of all the relevant parameters. The lower the solubility of B in A, the larger these effects.     

反应烧结法合成ALON粉体的研究

采用微米级Al粉和纳米级Al2O3粉为原料，在N2气氛保护下球磨，并在流动N2中煅烧，尝试了纯相ALON粉体的合成。通过改变合成温度和保温时间等工艺参数，使原料反应充分，并通过适当改变原料中Al的含量，以控制合成试样中过量AlN的产生。同时对合成的粉体用XRD进行物相的定性分析，研究了温度、保温时间和原料配比等参数对合成纯相粉体物相的影响，并用TEM对粉体微观形貌进行观察。结果表明，将原料中Al粉的质量比调整为10％后，在1800℃煅烧3h的条件下，可以得到纯相的ALON粉体。     

A relation between multiple-scattering theory and micromechanical models of effective thermoelastic properties

A relation between multiple-scattering theory and micromechanical models of effective elastic material properties of heterogeneous materials has been established within a unified theoretical framework, and exemplified on three important approximations, the average t-matrix (or Mori-Tanaka), symmetric self-consistency (coherent potential), and asymmetric self-consistency approximations.