Results 1 - 10 of 2889
Results 1 - 10 of 2889. Search took: 0.023 seconds
|Sort by: date | relevance|
[en] Nano-polycrystalline boron nitride (BN) is expected to replace diamond as a superhard and superstiff material. Although its hardening was reported, its elasticity remains unclear and the as-measured hardness could be significantly different from the true value due to the elastic recovery. In this study, we measured the longitudinal-wave elastic constant of nano-polycrystalline BNs using picosecond ultrasound spectroscopy and confirmed the elastic softening for small-grain BNs. We also measured Vickers and Knoop hardness for the same specimens and clarified the relationship between hardness and stiffness. The Vickers hardness significantly increased as the grain size decreased, while the Knoop hardness remained nearly unchanged. We attribute the apparent increase in Vickers hardness to the elastic recovery and propose a model to support this insight.
[en] Highlights: • New application of LIBS in industry. • Hardness of metallic alloys estimation using LIBS calibration curves. • Linear correlation between the plasma temperature and the hardness of metallic alloys. • The shock wave is fast when the material is hard. - Abstract: Surface hardness is a very important characteristic of metals. Its monitoring plays a key role in industry. In the present paper, using laser induced breakdown spectroscopy (LIBS), Fe–V18%–C1% alloys with different heat treatments have been used for making the correlation between surface hardness and laser-induced plasma temperatures. All investigated samples were characterized by the same ferrite phase with different Vickers surface hardnesses. The differences in hardness values were attributed to the crystallite size changes. A linear relationship has been obtained between the Vickers surface hardness and the laser induced plasma temperature. For comparison the relation between surface hardness and the ratio of the vanadium ionic to atomic spectral lines intensities (VII/VI) provided good linear results too. However, adopting the proposed approach of using the plasma temperature, instead, is more reliable in view of the difficulties that could be encountered in choosing the proper ionic and atomic spectral lines. To validate this approach we have investigated the shock wave speed induced by laser interaction with the used samples. It was found that harder is the material faster is the shock wave. The determination of the surface hardness via measuring Te shows the feasibility of using LIBS as an easy and reliable method for in situ industrial application for production control
[en] Ion implantation causes changes in mechanical properties such as hardness and fracture toughness on the ion-implanted surface. The purpose of this study is to experimentally investigate the effects of substrate temperature during ion implantation on the hardness and fracture toughness of an ion-implanted silicon wafer. A silicon (1 0 0) wafer was implanted by 3 MeV ions of Au and Si at different substrate temperature of 100, 200 and 300 K, respectively. After ion implantation, Vickers indentation experiments were carried out on the ion-implanted surface of the silicon wafer at room temperature. The results of the Vickers indentation tests show a significant decrease of hardness and an increase of fracture toughness of the ion-implanted silicon with decreasing the substrate temperature during ion implantation. It was found that the lower the substrate temperature during implantation, the greater the effectiveness of ion implantation on the changes in mechanical properties of the ion-implanted silicon
[en] Scheme of irradiation energy transformation is presented in the chapter. The scheme includes generation and interaction of radiation, thermal and mechanical fields having different spatial-time scales and defining stable structure formation in materials. Microhardness was chosen as generalized characteristic (optimization parameter) defined by radiation action. It is noted, that some methods (Brinell, Rockwell, Vickers) are broadly used for hardness definition. In the work the Vickers method was chosen for microhardness measuring. There are following subdivisions in the chapter - 3.1. General scheme of modification process. Choice of optimization parameter; - 3.2. Microhardness as optimization parameter; - 3.3. Methodic of microhardness definition; - 3.4. Energy transformation under high-intensive electron and ion irradiation; - 3.5. Action of shock wave on metals. 1 tab., 3 figs
[en] The objective of the this study was to analyze the under-surface hardness of light-cured nanofilled composite resins of different shades. The specimens were resin composites of each light (B1), medium (A3), and dark (C3) shades packed in a cylinder mold and subsequently polymerized. The hardness was tested using a Knoop system. The hardness test results for the bright (B1), medium (A3), and dark (C3) shades were 82.4+1.1, 75.9+1.2 and 65.9+1.9, respectively, and indicated significant differences between the under-surface hardness of each shade. It was concluded that resin composites of darker to brigher shades demonstrated lower to higher under-surface hardness. (paper)
[en] Ion implantation can improve the resistance of surfaces of materials to wear, corrosion and fatigue. In the current work plane bending constant maximum stress cantilever fatigue samples of thermomechanically treated (TMT) eutectoid steel were subjected to boron ion implantation. Improvement in fatigue life was experienced under certain conditions but the detailed reasons were unknown. The present work will compare results between samples immediately after ion implantation and after diffusion annealing and will compare results for samples ion-bombarded both before and after TMT. Knoop hardness was also measured. (author)
[en] Investigations on the evolution of the ablated depth over a large number of incident femtosecond laser pulses and the occurrence of structure and hardness changes in the immediate vicinity of the laser induced craters (for two sorts of steel and a hard metal substrate) are reported in this work. Experiments were performed in air with a Ti:sapphire laser (800 nm, 100 fs) at mean fluences of 2, 5 and 10 J/cm2. After the laser irradiation, cuts were made through the processed samples and pore cross-sections were obtained. Through their metallographical analysis it was possible to evidence crystalline structure changes in the immediate vicinity of the laser induced microholes; the extent of modified material zones increased for higher laser fluences. In such zones, a chemical composition quasi similar to that of the raw material was found and the performed nanohardness tests revealed hardness increases
[en] Highlights: • We proposed a new REBCO coil structure for Maglev in post study. • In actual use, the magnets receive electromagnetic agitation and mechanical force. • We conducted the repeated bending tests of these REBCO pancake coils. • The coils have no deterioration even if the repeated bending deformation was applied. • We confirmed the durability of the coils manufactured by the method that we proposed. - Abstract: In the past study, two manufacturing methods were developed that can manufacture pancake coils by using REBCO coated conductors. It was confirmed that the conductors have no electric degradation that caused by the manufacturing method. The durability evaluation tests of the pancake coils were conducted as the final evaluation of the coil manufacturing method in this study. The repeated bending deformation was applied to manufactured pancake coils in the tests. As the results of these tests, it was confirmed that the pancake coils that were manufactured by two methods had the durability for the repeated bending deformation and the coils maintained the appropriate mechanical performance and electric performance. We adopted the fusion bonding method as the coil manufacturing method of the HTS magnet Furthermore, using the prototype pancake coil that was manufactured by the fusion bonding method as a test sample, the repeated bending test under the exited condition was conducted. Thus it was confirmed that the coil manufactured by the fusion bonding method has no degradation of the electricity performance and the mechanical properties even if the repeated bending deformation was applied under the exited condition.
[en] To measure the hardness and elastic modulus of a composite system in the nano-scale range, precise determination of the cross-section area of the indenter tip at different heights is a key. A method of using scanning probing microscopy to image the tip and then using its analysis software, Histogram program, and Bearing curve, combined with the information of the area of each pixel, to determine the cross-section area at different heights are introduced in this paper. Compared with other techniques, it is simple, straightforward, and readily provides a precise relationship between the cross-sectional area and the height