High cooling rates and metastable phases at the interfaces of explosively welded materials

International audienceDuring an explosion, the interfaces of welded materials experience fast heating due to high strain rate severe plastic deformation. This leads to the formation of local zones, where melting and mixing of welded materials is observed. These zones are frequently referred to as vortexes, eddies or swirls, due to the specific rotational movement of materials during mixing. This study is primarily devoted to the discussion of the structures that appear in these zones. Simple approaches to estimate the heating and cooling rates at the interfaces between explosively welded materials were proposed. It was concluded that the heating rate at the interfaces was of the order of 10(9) K/s, while the cooling rate achieved 10(7) K/s. Several combinations of explosively welded alloys (steel/steel, Ti alloy/steel, Zr/Cu, Zr/Ni, Ta/Cu, Al/ magnesium alloy and Cu/brass) were thoroughly analyzed using scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. In most of these combinations, metastable crystalline, quasicrystalline or glassy phases were observed. The formation of different types of metastable phases is discussed with respect to the compositions of the welded alloys. It was concluded that solidification conditions at the interfaces of explosively welded materials are similar to those during rapid solidification. Thus, the results of numerous experiments on rapid solidification of alloys could be applied to analyze the structures that appear in mixing zones. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved

In-situ imaging of tungsten surface modification under ITER-like transient heat loads

Experimental research on behavior of rolled tungsten plates under intense transient heat loads generated by a powerful (a total power of up to 7 MW) long-pulse (0.1–0.3ms) electron beam with full irradiation area of 2 cm2 was carried out. Imaging of the sample by the fast CCD cameras in the NIR range and with illumination by the 532nm continuous-wave laser was applied for in-situ surface diagnostics during exposure. In these experiments tungsten plates were exposed to heat loads 0.5–1MJ/m2 with a heat flux factor (Fhf) close to and above the melting threshold of tungsten at initial room temperature. Crack formation and crack propagation under the surface layer were observed during multiple exposures. Overheated areas with excessive temperature over surrounding surface of about 500K were found on severely damaged samples more than 5ms after beam ending. The application of laser illumination enables to detect areas of intense tungsten melting near crack edges and crack intersections

A novel operando approach to analyze the structural evolution of metallic materials during friction with application of synchrotron radiation

International audienceIn this study, we describe an experimental setup and a new approach for operando investigation of structural evolution of materials during wear and friction. The setup is particularly suited for testing various friction pairs, including those in which both rubbing bodies are made of metals. The developed device allows circumventing the problems related to significant scattering of X-rays produced by metals and makes it possible using “real samples” in synchrotron beamlines operating in reflection mode. To demonstrate the capabilities of the device and the proposed new approach, an iron-based massive sample was subjected to thousands of friction cycles using a cemented carbide pin. The material was probed with synchrotron X-ray radiation within a few milliseconds after leaving the friction zone. The results of the microstructural and structural analysis, as well as results obtained from diverse mathematical models, allowed us to evaluate several features, including gradual accumulation of defects, microstructural refinement, dislocation density changes, surface layer oxidation, as well as several other phenomena caused by the dry sliding friction process. Mainly, it was possible to conclude that the process of wear occurred due to the cooperative action of oxidation and plastic deformation, which began during the first cycle of frictional interaction and was manifested in increasing the dislocation density, whose type was changed gradually during testing. The number of defects quickly reached a threshold value and subsequently fluctuated around it due to periodically repeated processes of defect accumulation and stress relaxation resulting from material wear. It was also observed that friction led to the quick formation of a mechanically mixed layer, consisting of the sample material and a mixture of two types of iron oxide – hematite and magnetite. The delamination of this layer was probably the primary wear mechanism

Microstructure and lattice parameters of suction-cast Ti–Nb alloys in a wide range of Nb concentrations

International audienc

Surgycal treatment of the Pectus Excavatum in children

Nuss repair of funnel chests is used increasingly, but has a high bar dislocation rate. The authors intended to reduce this by technical modifications of the original Nuss technique. Methods: In 350 patients from 6 to 17 years of age (mean, 12.4 ± 3.8) were operated by Nuss procedure at the Filatov Children’s Hospital in Moscow for the last 10 years. 37% of patients had Sindromalny pathology. Operation technique: The bars were placed from left to right with use of specially metal conductor; introduced of the T-shaped titanic plate; fixing of both ends of a plate. Plate was removed in 4 years after surgery. Results. Duration of operation averaged 38±7 minutes. Terms of hospitalization averaged 8,5±2 days. Thoracoscopy was used only at 8 (2,2%) patients. From them 4 patients were previous operated by Paltia plate repair, at 3(0,8%) patients – after sternotomiya for correction of CHA and 1 patient after a pulmonectomiya. Simultanny operations were done in 4 (1,1%) patients: Thoracoscopycal ductus arteriosus repair - 2 patients, Thoracoscopycal resection of a lung - 2 patients. Complications: pheumothorax – 2(0,5%), gemathorax– 2(0,5%), plate shift – 1(0,2%) patient. One patient observed hyper correction of the chest. In 98% we had the excellent cosmetic and functional result. Residual deformation was observed - 7 (2%) patients. All patients were reoperated with excellent results. Conclusion. The modified technique more safely and has reduced the incidence of bar dislocation