5 research outputs found

    Degradation failure features of chromium-plated gun barrels with a laser-discrete-quenched substrate

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    The effect of substrate laser-discrete quenching on the degradation failure of chromium-plated gun barrels was metallurgically investigated. The results show that substrate laser-discrete quenching changes the failure patterns of chromium coatings during firing, and some periodic through-thickness cracks in the fired chromium coatings are justly located at original substrate zones between two adjacent laser-quenched tracks. Moreover, chromium coatings and the laser-quenched zones on the substrate are simultaneously degraded in microstructure and property during firing. Furthermore, the periodic structure of the laser-discrete-quenched steel (LDQS) substrate near the breech remains after firing, and the hardness of the fired laser-quenched zones is still higher than that of original substrates. The specific failure features were utilized to illustrate the mechanism of the extended service life of chromium-plated gun barrels with the LDQS substrate. (c) 2007 Elsevier B.V All rights reserved

    Characteristics of the interface of a laser-quenched steel substrate and chromium electroplate

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    The interface of a laser-discrete-quenched steel substrate and as-deposited chromium electroplate was investigated by ion beam etching, dissolving-substrate-away and using a Vickers microhardness tester, in an attempt to reveal the mechanism that the service life of the chromium-coated parts is increased by the duplex technique of laser pre-quenching plus chromium post-depositing. The laser quenching of the steel substrate can reduce the steep hardness gradient at the substrate/chromium interface and improve the load-bearing capacity of chromium electroplate. Moreover, the laser quenching prior to plating has an extremely great effect on the morphologies and microstructure of the substrate/chromium interface: there is a transient interlayer at the original substrate/chromium interface while there is not at the laser-quenchedzone/chromium interface; the near-substrate surface microstructure and morphologies of the free-standing chromium electrodeposits, whose substrate was dissolved away with nital 30% in volume, inherit the periodically gradient characteristics of the laser-discrete-quenched substrate surface. (c) 2006 Elsevier B.V. All rights reserved

    Turbulent phase screens generated by covariance approach and their application in numerical simulation of atmospheric propagation of laser beam - art. no. 634628

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    Multiple phase screen (PS) method is typically used in numerical simulations of light propagation through a turbulent atmosphere and an adaptive optics (AO) system for phase compensation. One of key problems in it is generation of turbulent PS for describing the turbulent atmosphere. The covariance approach is a relatively new approach for generating PS. In this paper, the covariance approach is used to generate turbulent PS and a preliminary numerical simulation investigation on this approach and its generated PS is carried out. We propose to use three methods to evaluate the generated PS in a combining way. It is found that a comparison of the phase structure function of generated PS with the theoretical one is not enough and often inefficient. By contrast, a comparison of open loop and close loop laser propagation results by using generated PS can give a deeper insight. Open loop and close loop results by using PS generated by covariance approach are obtained and compared with those by using PS generated by spectral approach for the first time. It is shown that PS generated by covariance approach includes more abundant frequency components and these components have obvious influences on light propagation through a turbulent media

    Preliminary numerical simulation investigation of the cone effect in an adaptive optics system using a laser guide star

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    So-called cone effect or focus anisoplanatism is produced by the limited distance of a laser guide star (LGS) which is created within the Earth atmosphere and consequently located at a finite distance from the observer. We believe this is the first time to investigate the cone effect of the LGS by means of a pure numerical simulation. In this paper, the cone effect of the LGS for different vertical profiles of the refractive index structure constant C-n(2) is numerically investigated by using a revised computer program of atmospheric propagation of optical wave and an adaptive optics (AO) system including dynamic control process. It is surprisingly found that the effect of altitudes of the LGS on the AO phase compensation effectiveness by using the commonly-available vertical profiles of C-n(2) and the lateral wind speed in the atmosphere is relatively weak, and the cone effect for some C-n(2) profiles is even negligible. It is found that the cone effect seems not have obvious relationship with the turbulence strength, however, it depends on the vertical distribution profile of C-n(2) apparently. On the other hand, the cone effect depends on the vertical distribution of the lateral wind speed as well. The cone effect becomes more obvious as the zenith angle increases. In comparison to a near infrared wavelength, the cone effect becomes larger in the case of the visible wavelength. In all cases concerned in this paper, an AO system by using a sodium guide star has almost same phase compensation effectiveness as that by using the astronomical target itself as a beacon

    Characterization of a Laser-Discrete Quenched Steel Substrate/Chromium System by Dissolving Coatings

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    A laser-discrete quenched steel (LDQS) substrate/as-deposited chromium (top high-contraction (HC) and underlying low-contraction (LC) chromium) system was investigated by dissolving coatings in order to reveal the mechanism that the service life of the coated parts is largely improved using the hybrid technique of laser pre-quenching plus chromium post-depositing. It was found that the surface characteristics of the substrate, LC and HC chromium layer can be simultaneously revealed owing to the dissolution edge effect of chromium coatings. Moreover, the periodical gradient morphologies of the LDQS substrate are clearly shown: the surfaces of laser transformation-hardened regions are rather smooth; a lot of fine micro-holes exist in the transition zones; there are many micro-dimples in the original substrate. Furthermore, the novel method of dissolving coatings with sharp interfaces may be used to reveal the structural features of a substrate/coating system, explore the effect of the substrate on the initial microstructure and morphologies of coatings, and check the quality of the coated-parts
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