Mean grain size determination in marbles by ultrasonic first backwall echo height measurements

In ultrasonic grain size determination several techniques are in use. In this paper, the Ultrasonic Relative Attenuation (URA) method has been used to estimate the mean grain size of marble samples. Also, mean grain size versus first backwall echo height graphs have been plotted to see the direct relation between these two parameters. The results show less than 10% difference compared with values obtained in an optic microscope. In a comparison, mean grain size values of marbles determined by ultrasonic velocity methods are given.     

超声电火花复合加工在模具制造中的应用

电火花加工技术能对高硬度、高强度金属材料加工,但存在加工效率低和加工表面质量不好的缺陷。通过对超声电火花复合加工研究,探讨了放电参数对加工速度影响的规律,指出超声电火花复合加工工艺可弥补电火花加工在加工效率及质量方面的不足,将会对模具型腔、型芯的制造产生重要影响。     

Simulation of high velocity compaction of powder in a two dimension mould using lattice Boltzmann method

This work presents a numerical study on the dynamic high velocity compaction of the metal powder. The analysis of the process is based on a mesoscopic approach using multi-speed lattice Boltzmann method. The boundary condition and the relaxation time are tailored to the situation. The dynamic compaction process is vividly presented and the shock wave can be easily found in the simulation. The density is analyzed in order to explore the mechanism of the high velocity compaction.     

The formation of a tungsten containing surface layer in a carbon steel by compression plasma flow

Morphology, phase and elemental composition of a carbon steel surface layer after treatment by compression plasma flows containing a dispersed tungsten powder have been investigated in this work. The action of relatively short (∼ 120 μs) and intense (15-20 J/cm² per pulse) plasma pulses resulted in the formation of tungsten containing thin film consisting of clusters with the size of 100-200 nm. Besides, the film formation treatment with a few pulses allowed to alloy a surface steel layer with tungsten. This treatment also led to the formation of Fe₃W₃C and WC carbides in the surface layer.     

An insight into the role of the grain boundary in plastic deformation by means of a bicrystalline pillar compression test and atomistic simulation

A combination of experimental and molecular dynamics (MD) simulations is used to investigate the interaction of dislocations with a selected grain boundary (GB) in bicrystalline pillars (BCPs) with component crystals oriented for single slip and multiple slip. As a reference, single-crystalline pillars with the same orientations are also tested and compared with the BCPs. Orientations identical to the experiments are used to generate models in MD simulations. Further, electron backscatter diffraction (EBSD) measurements on the cross-section of the pillars are performed to investigate the crystal lattice rotation in correlation with the excess dislocation density. A clear change in mechanical behavior of the BCP was observed when the size of the component crystals reduced below 1 μm. The EBSD analyses of these small BCPs showed an increase in the misorientation in the vicinity of the GB. MD simulation provided atomistic insights into the dislocation nucleation process and the BCPs’ interaction with the GB. On the basis of these observations, it is concluded that in BCPs smaller than 1 μm the dislocation–GB interaction plays a more crucial role than the dislocation–dislocation interaction.