Kinetics of the Diffusion Chromium Plating of Steels with Nickel-Cobalt-Phosphorus Coating
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KINETICS OF THE DIFFUSION CHROMIUM PLATING OF STEELS WITH NICKEL-COBALT-PHOSPHORUS COATING О. V. Man’ko1, 2 and A. E. Stets’ko1
UDC 669.295
We study the kinetics of formation of a diffusion layer after chromium plating with a nickel–cobalt– phosphorus coating. It is shown that the presence of phosphorus in the chemical coating affects the formation of an outer composite zone formed by columnar chromium carbides and the matrix of solid solution of chromium in α-iron. At the same time, in the early stages, atomic chromium displaces nickel and cobalt into the bulk of the material but does not affect the distribution of phosphorus. We also explain the appearance of directed zones with higher degrees of damage in the process of diffusion. Atomic chromium is intensely transported through these zones, which leads to the formation of a regular structure of the outer composite zone. Keywords: diffusion layer, chemical coating, columnar chromium carbides, liquid metal phase, X-ray spectral analysis.
Introduction For the purposes of saving material and energy resources, which now turns into an urgent problem due the permanent growth of the cost of energy carriers and materials, it becomes necessary to develop new and improve the existing resource- and energy-saving technologies in machine building. As one of measures of this kind, we can mention the development of technologies aimed at increasing the service life of articles operating under severe loading conditions. In machine-building, these articles are, as a rule, hardened either by quenching or by using classical procedures of thermochemical treatment, namely, carburization, nitriding, boronizing, etc. The last decades are marked by the intense development of the technologies of gas-thermal spraying [1], laser treatment [2], and formation of fine- and nanocrystalline structures of the surfaces accompanied by changes in their chemical compositions [3–5]. The application of these technologies guarantees high physicomechanical [3, 4] and corrosion [6] properties of machine parts. At the same time, the procedures of thermochemical treatment are also improved. For the several last decades, the researchers investigate the possibilities of complex treatment, which, in most cases, is reduced to the simultaneous or successive application of certain combinations of the well-known procedures of hardening. As one of these technologies, we can mention the diffusion saturation of steels after preliminary application of a nickel-cobalt-phosphorus (Ni–Co–Р) chemical coating. Procedure of Investigations We studied high-quality 45 carbon steel (GOST 1050-88) and U10 and U12 high-carbon steels (GOST 1435-99) by using cubic specimens 10 × 10 × 10 mm in size. The chemical deposition of the Ni–Co–Р coating 1 2
Ukrainian Academy of Printing, Lviv, Ukraine.
Corresponding author; e-mail: [email protected].
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 55, No. 6, pp. 84–90, November–December, 2019. Original article submitted July 25, 2017. 870
1068-820X/20/5506–0870
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