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The elevated temperatures influence on the cobalt base cladding layer

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Many structural components contemporary used in engines, gas turbine or industrial applications like for example: moulds for glass and ceramics, automotive valves, chemical and petrol-chemical valves, lamination cylinders, plastics extrusion screws and dies [1] are subjected thermal, mechanical and chemical loads at the same time. It needs materials which presented a good combination of strength and hardness properties, corrosion and thermal fatigue resistance and excellent fabrication. In modern technology hardfacing by producing surface coating is often used. Such surface coating can protect the parts from wear and, depending on coating material selection, from chemical or high temperature corrosion. Various processes such as spray and fusion, gas tungsten arc welding and submerged arc welding process are used to the clad the wear resistant layer. Among these different deposition techniques, plasma-transferred arc (PTA) is one of the most interesting processes because of its high deposition rate and low heat input and especially for its wide range of material which can be used [2÷8] also the deposits can be obtained with completely automated unmanned machines. During recent decades, the high-temperature oxidation on structural materials, such as Fe-, Co-, and Ni-base alloys, for which high-temperature oxidation resistance is an important parameter, has been investigated intensively. In general, these alloys developed good oxidation resistance by possessing proper amounts of Al, Cr, and Si and are called as alumina, chromia, and silica formers. For chromia formers, maximum protection against oxidation is obtained only if a continuous and coherent Cr2O3 scale layer is formed and maintained. That alloys must have a sufficient chromium content to initially form a chromium oxide and supply of chromium by diffusion within the underlying alloy in order to continuous growth of the protective scale. [9]. In spite of the long history [...]

Wpływ czasu i temperatury utleniania na napawane warstwy ze stopu kobaltu

  Ochrona przed Korozją, vol. 54, nr 6 307 ność węglików typu M12C (Cr6W6C) i M23C6 (Cr23C6). Po procesach utleniania obserwuje się wyraźne zmiany w przypowierzchniowych obszarach napoiny. Obejmują one tym głębsze warstwy im czas ekspozycji jest dłuższy - po 50 godzinach warstwa zdegradowana do chodzi do 50 μm. Nawet po najkrótszym czasie - 15 minut obserwuje się niszczenie materiału postępujące po granicach dendrytów (rys. 3). Dla porównania utleniano ten sam materiał przez 200 godzin w temperaturze 750° i nie zaobserwowano postępującej w głąb degradacji materia[...]

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