Papers by Keyword: Microhardness

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Authors: Hong Tao Zhang, Hong Yu Gao, Wen Jie Jiang, Shi Sheng Zhong
Abstract: Bead-on-plate welds was made by underwater wet welding with flux-cored wire in a tailor-made pentrough. The effect of welding parameters such as welding speeds, welding currents and welding voltages on welds surface appearances and microstructure were studied. Orthogonal experiment method was used to optimize combination of different welding parameters. The results showed that the hardness (HV) of welds fusion zone ranged between 515 and 670 while the hardness (HV) of base metal was only 350. The fusion zone of the welds was mainly composed of columnar grain structure.
Authors: D.V. Gadeev, Sergey Demakov, F.V. Vodolazskiy
Abstract: The diagrams of continuous cooling transformation (CCT) of β-phase decomposition for hot-rolled VT8M titanium alloy were obtained using the differential thermal analysis, scanning electron microscopy, and X-Ray diffraction (XRD) analysis for heating temperatures from 880 to 960 °C. The decomposition process was found to occur with several distinguishable stages. The transformation begins from high-temperature stage of the growing of primary alpha precipitates. At lower temperatures, it is followed by the medium-temperature stage accompanied by precipitation of grain-boundary alpha and the formation of coarse secondary alpha-lamellae. The low-temperature stage has been established to be characterized by the formation of dispersed alpha-platelets within beta-grains.
Authors: R. Rahouadj, O. El Kedim, Ph. Lesage, M. Abdellaoui, Eric Gaffet
Authors: Shu Xiao, Xi Yun Cheng, De Gui Ma
Abstract: Carbon nanotubes (CNTs) was introduced into Ni60/Al2O3 coating by flame spraying. The effect of adding CNTs on the tribological properties of the coating was studied by varying the CNTs content as 0.0, 1.5, 3.0 and 4.5 wt% in the Ni60/Al2O3 powders. The microhardness tester was used to measure the microhardness of the coating. Wear tests were performed on a pin-on-disk tribometer, to evaluate the tribological properties of the Ni60/Al2O3/CNTs coatings. Microstructural characterization was performed using scanning and transmission electron microscopy. Ni60/Al2O3/CNTs coatings revealed a lower wear rate and friction coefficient compared with the original coating, and their wear rates and friction coefficients showed a decreasing trend with increasing mass fraction of CNTs within the range from 0 to 3.0 wt% due to the effects of the reinforcement and reduced friction of CNTs. The results showed that the CNTs played dual roles in improving the tribological performance of the coating, indirectly by influencing the microstructure and mechanical properties of the coating and directly by acting as a lubricating medium.
Authors: Liu Qing Tu, Wen Bing Xu, Wei Chen
Abstract: The effects of carbonation age, fly ash content in the binder and the water to binder ratios on the carbonation depth of fly ash concrete is investigated and the micromechanical properties of the hardened paste and the inter facial transition zone is analyzed with the micro-hardness method. The experimental results show that replacing Portland cement in concrete with fly ash increases the carbonation rate at early ages, while the late age carbonation rate is lowered. Micromechanical analysis shows that the carbonation reaction increases the micro-hardness of the paste and the compactness of the ITZ. For the relative low replacement levels, the width of the ITZ is reduced if the concrete is carbonated.
Authors: Wei Chen, Xiao Xing Chen, Shi Zhe Zhang
Abstract: A new method for establishing the carbonation profile of cement paste and concrete with the micro-hardness analysis is proposed in this study. This method is able to probe the changes in the microstrucure during the carbonation process. The results are validated with the conventional phenolphthalein indicator method.
Authors: Wioletta Gorczyńska-Zawiślan, Ewa Benko, Piotr Klimczyk
Abstract: In this work cBN-TiN composites were studied. The composites were prepared by the HPHT technique (p=8 GPa, T=1750 0C). A TiN binding phase was used in two forms: as micro and nanomaterials. Thermodynamic calculations showed that formation of new phases in the cBNTiN composites was not possible in the experimental conditions which was confirmed by XRD investigations carried out. The surface morphology of nanocomposites was studied by scanning electron microscopy. The structure of these composites was compact; a TiN phase was uniformly distributed between cBN grains. Hardness was measured by the Vickers method using an indentation load of 9.81 N. The hardness of the investigated samples was dependent on the volume and grain size of the binding phase. Young's modulus of elasticity was determined, but its value was found to be dependent on the grain size of the TiN phase.
Authors: Janette Brezinová, Anna Guzanová, Peter Balog, Ján Viňáš
Abstract: This contribution deals with the analysis of the renovation layer quality of continuous casting steel rollers, developed through the submerged arc surfacing method (SAW). The continuous casting roller was analysed through the degradation phenomena which act during the operation. Four kinds of filler materials were used for the renovation of the worn roller. Surfacing was carried out as a three-layer in order to eliminate the need for intermediate layer formation. The quality of weld deposits was evaluated in terms of the structure and microhardness after thermal cyclic loading. The best properties showed newly developed filler material W8-WLDC8 from point of view of the microhardness.
Authors: J. Maszybrocka, Jerzy Cybo, J.E. Frąckowiak, K. Krzemień
Abstract: The influence of a tribological process in the polymer/metal system on changes in microhardness (H) and Young’s modulus (E) of the surface under friction and UHMWPE volume has been studied. Twelve samples of polyethylene characterized by a different degree of initial plastic deformation and different electron irradiation dose were analyzed. For four of the samples a decrease by 5÷10 times in polyethylene degradation has been found. This result is promising in that a prolonged durability can be expected in case of application for endoprostheses acetabular cups. It has been found also that a polyethylene material irradiated after initial prestraining only once shows enhanced micromechanical properties after friction. It has been found that this result was due to reorientation of lamellas on the friction surface taking place during deformation which accompanies the tribological process. It has been proved that the increase of H and E values in the layers situated at a depth of 1.5 mm÷7.5 mm is due to a decrease of the free volume centers in the UHMWPE polyethylene and to an increase of the degree of spatial arrangement of the structure (absorption in crystallinity band of FTIR spectrum).
Authors: Mazhyn Skakov, Bauyrzhan Rakhadilov, Erlan Batyrbekov, Michael Scheffler
Abstract: In the article changes in the structure and mechanical properties of R6M5 steel surface layer after electrolytic-plasma nitriding are shown. The optimal mode of electrolytic-plasma nitriding of R6M5 high-speed steel in electrolyte based on carbamide, which allows saturation of the surface with nitrogen from low-temperature plasma and get the modified layer of high hardness and wear-resistance. It is established, that after electrolytic-plasma nitriding reduced R6M5 steel wear rate and increases its resistance to abrasive wear. Perspectivity of use an electrolytic-plasma nitriding method to improve performance cutting tools made from R6M5 steel is shown.
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