Metallic contact formation and growth by dislocation glide

The theoretical objections to glide dislocation nucleation during metallic contact formation (sintering) are discussed, and their limitations at small particle sizes and under certain geometrical conditions are pointed out. A mechanism for contact formation by the direct conversion of surface free energy to glide dislocation strain energy is presented and evaluated with respect to the activation energy for nucleation and the limiting extent of the process for sphere-flat plate contacts. Finally, some diverse experimental observations from the literature are interpreted in terms of the proposed mechanism.     

Role of plastic deformation in the structure formation of ceramic materials

Translated from Poroshkovaya Metallurgiya, No. 3, pp. 80–88, March, 1992.     

Roles of microalloying elements on the cluster formation in the initial stage of phase decomposition of Al-based alloys

In age-hardenable aluminum alloys, nanoscale clusters composed of solute atoms and vacancies are formed and play very important roles in microstructure control and alloy properties. The microalloying elements in the aluminum alloys affect the cluster formation and resultantly precipitate microstructures. The fundamental effects of microalloying elements on Al-Cu, Al-Zn, Al-Li-Cu, and Al-Mg-Si alloys are demonstrated through changes in the electrical resistivity, hardness, differential scanning calorimetry (DSC), and microstructural evolution. In order to understand the complicated effects of microalloying elements, a Monte Carlo simulation model was developed and performed. In the simulation, it was found that some microalloying elements preferentially trap quenched-in excess vacancies to retard cluster formation in the initial stage of aging. The complex clusters of solute/microalloying element/vacancy were found to be formed in the subsequent stage and act as effective nucleation sites for clusters and Guinier-Preston (GP) zones. The roles of microalloying elements are well understood in terms of the ordering parameters and are well predicted based on the ordering parameter maps (OP maps) proposed in this work.     

Certain features in the initial stages of structure formation for titanium carbonitride-based hard alloys

Translated from Poroshkovaya Metallurgiya, No. 12 (348), pp. 29–35, December, 1991.     

Growth characteristics in the initial stage of micrometastasis formation by bacterial LacZ gene-tagged rat prostatic adenocarcinoma cells

In a previous study we observed that protein tyrosine phosphorylation was significantly diminished in the focal adhesions of human fibroblasts attached on a hydrophobic surface in comparison with hydrophilic glass. This result raises the possibility that the tyrosine phosphorylation pathway may be involved in the regulation of cell-biomaterial interaction. To learn more about the interaction of anchorage-dependent cells with biomaterials, four different materials with wettability ranging from hydrophilic (water contact angle 25 degrees) to hydrophobic (water contact angle 111 degrees) were investigated, i.e. clean glass (glass), aminopropylsilane (APS), octadecylsilane (ODS) and silicone (SI). Immunofluorescence microscopy revealed increased stress formation and fibronectin (FN) receptor-rich focal adhesions for fibroblasts attached on more hydrophilic surfaces (glass and APS) in comparison to the relatively hydrophobic materials (ODS and SI). Phosphorylation of tyrosine residues, also studied by immunofluorescence microscopy, was considerably higher on glass and APS, lower for ODS, negligible for SI, and was found to colocalize with FN receptor-rich focal adhesions. Preadsorption of FN tended to restore cell adhesion and spreading on the hydrophobic ODS and SI. Quantitative data on cell proliferation and tyrosine phosphorylation showed moderate wettable material maximum values for APS, followed by glass. ODS and SI, demonstrating a non-linearity of these parameters with the wettability of materials. Interestingly, the preadsorption of FN increased both parameters, particularly for the hydrophobic materials ODS and SI. Phosphorylation of tyrosine on FN-coated substrata was corroborated by the accessibility of binding sites estimated by ELISA using polyclonal and monoclonal FN antibodies. Our results suggest that measurement of the phosphotyrosine activity of cells may be a sensitive parameter for the ability of biomaterials to support the attachment and proliferation of cells.     

Densification of powders in the initial stage of pressing

Conclusions It has been established that the compressibility of a powder at the initial instant of shaping is not significantly affected by the yield stress of the material of its particles. The compressibility of a powder in the initial stage of densification is determined mainly by its relative apparent density.Translated from Poroshkovaya Metallurgiya, No. 3(219), pp. 25–31, March, 1981.     

MIM热脱脂初始阶段行为研究

采用PW-EVA-HDPE-SA粘结剂,研究了MIM不锈钢热脱脂初始阶段的脱脂行为。生坯与脱脂样的SEM照片对比研究,发现:随着脱脂的进行,试样中的小颗粒金属球随着粘结剂的流动向试样外表面流动,造成脱脂样表面小球聚集;只要脱除4％左右的粘结剂,试样中就会形成初始孔隙。在热脱脂初始阶段,由于粘结剂在不同的曲率半径处蒸气压不同,生坯表面小球之间粘结剂能较快地脱出,而大球之间的粘结剂脱除较慢。     

Effect of an electric potential on the formation of a dislocation structure during creep of aluminum

The effect of an electric potential on the formation of a dislocation substructure at the stage of steady-state creep in commercial-purity aluminum is analyzed using the theoretical concepts of steady-state creep and the equations describing a dislocation ensemble with allowance for an applied electric potential. The effect of an electric potential on the creep rate and acceleration is considered through the mechanism of the effect of the potential on the surface energy of aluminum.     

Hot stage TEM investigations of dislocation climb in NiAl

Hot stage was used to investigate dislocation loop formation and growth at climb sources in Al rich alloys of β-NiAl. The loops grew by absorbing vacancies retained during cooling of the samples. The growth rate was dependent on the speed of cooling and anomalously high growth of loops occurred near the foil surfaces. The loop shapes were nearly square as a result of loop growth by a jog mechanism. Estimates of the vacancy concentration contained in the loops after growth demonstrated that nearly all thermal vacancies can be retained in NiAl.     

Hot stage TEM investigations of dislocation climb in NiAl

Hot stage was used to investigate dislocation loop formation and growth at climb sources in Al rich alloys of β-NiAl. The loops grew by absorbing vacancies retained during cooling of the samples. The growth rate was dependent on the speed of cooling and anomalously high growth of loops occurred near the foil surfaces. The loop shapes were nearly square as a result of loop growth by a jog mechanism. Estimates of the vacancy concentration contained in the loops after growth demonstrated that nearly all thermal vacancies can be retained in NiAl.