Diffusion of Hard Coatings on Ductile Cast Iron
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Diffusion of Hard Coatings on Ductile Cast Iron N. López Perrusquia1*, M. Antonio Doñu Ruiz1, E. Y. Vargas Oliva2, V. Cortez Suarez3 1
Instituto Politécnico Nacional, SEPI-ESIME, U. P. Adolfo López Mateos, Zacatenco, 07738, México. 2 Universidad Politécnica del Valle de México, Grupo Ciencia e Ingeniería de Materiales, 54910, Tultitlán, Estado de México 3 Universidad Autónoma Metropolitana Unidad Azcapotzalco, México. * E-mail: [email protected] ABSTRACT This work estimate the growth kinetics of Fe2B coatings created on surface nodular cast iron ASTM A-536 class 80-56-06. The Fe2B coatings were formed by power packaging boriding process, considering three temperatures and exposure times different treatment. The hard coatings were evaluated through X-ray diffraction (XRD) and scanning electron microscopy (SEM). The model of diffusion employs the mass balance equation at the (Fe2B/substrate) interface to evaluate the boron diffusion coefficient in the Fe2B coating DFe2B, an expression of the parabolic growth constant, the instantaneous velocity of the Fe2B/substrate interface, and the weight gain in the boriding sample were establish as a function of the parameter H (T ) and K (T ) , dependents of boriding process in function of the temperature related and the time of boriding t (T ) , respectively in the Fe2B coating. Model validation was extended considering the treatment of 1273 and 1123 K for 10 h respectively, obtaining a good correlation with experimental data. 0
Keywords: diffusion, kinetics, x-ray diffraction, scanning electron microscopy (SEM), packaging. INTRODUCTION Boronizing is technically well developed and widely used in industry to produce extremely hard and wear resistant surface layer on metallic substrate. This treatment is similar to other surface hardening treatments like carburization and nitriding in respect of physical and chemical characteristics [1-2]. It is successfully applied to all ferrous materials, nickel alloys, titanium alloys, and sintered carbides. This thermochemical treatment, carried out at temperatures in the range 800–1100 C for periods varying between 1 and 12 h, using gases or powders as boronizing media, gives rise to hard coatings constituted by an inner layer of Fe2B (Boron rich 8.83 wt. % B) and an outer layer of FeB (Boron rich 16.23 wt. % B) and thickness in the range of 40–270 μm [3]. Ductile cast iron is the one in which the graphite is present as tiny spheres. The relatively high strength and toughness of ductile iron give it some advantages over other cast iron and steel types in many structural applications and industrial applications requiring wear and corrosion resistance; components include drive shafts, camshafts, pulleys, machine slide-ways, tanks, weapons and part for agricultural machinery.
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To control the boronizing processes, knowledge of kinetic parameters is essential. The recent work respecting the modeling growth kinetic of Fe2B coating has been developed for the establishment of the variables that affect the boronizing process.
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