Papers by Keyword: Boride Layers

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Authors: Ivan Campos-Silva, N. López-Perrusquia, E. Hernández-Sánchez, M. Ortíz-Domínguez, D. Bravo-Bárcenas, José Martínez-Trinidad
Abstract: The growth of iron borides over the surface of different steels is of high anisotropy. It was determined that the anisotropy of borided phases reveals a significant instability of properties in service. One of the techniques to determine the effect of anisotropy on the mechanical properties of boride layers is the induced-fracture by Vickers microindentation. During the present work, the fracture toughness (KC) of the Fe2B hard coatings has been estimated at the surface of AISI 4140 borided steels. The force criterion of fracture toughness was determined from the extent of brittle cracks originating at the tips of an indenter impression. The indentation loads were established between 1.9 to 9.8 N at three different distances from the borided surface. The KC values were expressed as a function of temperature, treatment time and the indentation distances from the surface. Likewise, the adherence of the coated system was evaluated by Rockwell-C indentation, where the borided steel showed sufficient adhesion.
Authors: M. Ortíz-Domínguez, Ivan Campos-Silva, José Martínez-Trinidad, Milton Elías-Espinosa, E. Hernández-Sánchez, D. Bravo-Bárcenas
Abstract: The present work estimated the growth kinetics of Fe2B layers formed at the surface of AISI 4140 steels. The thermochemical treatment was applied in order to produce the Fe2B phase, considering temperatures of 1123, 1173, 1223 and 1273 K with five exposure times (2, 4, 5, 6, and 8 h), using a 4 mm thick layer of boron carbide paste over the material surface. The growth of boride layers was described by the mass balance equation between phases in thermodynamic equilibrium, assuming that the growth of boride layers obeys the parabolic growth equation and the boron concentration at the interfaces remains constant. Also, the boron diffusion coefficient at the Fe2B ( ) was established as a function of boriding temperature. Likewise, the parabolic growth constant (k), the instantaneous velocity (v) of the Fe2B/substrate interface and the weight-gain of borided steels were established as a function of the parameters and , which are related to the boride incubation time ( ) and boron surface concentration ( ), respectively.
Authors: Vasil I. Dybkov
Abstract: Two borides FeB and Fe2B were found to form as separate layers at the interface between a 13% Cr steel and boron at 850-950 oC and reaction times up to 12 h. The chromium distribution within the boride layers is rather irregular. Its average content is 8 at. % in the FeB layer and 9 at. % in the Fe2B layer. Both layers are characterized by a pronounced texture. The strongest reflections are {002} and {020} for the orthorhombic FeB phase and {002} for the tetragonal Fe2B phase. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data.
Authors: Vasil I. Dybkov, L.V. Goncharuk, V.G. Khoruzha, K.A. Meleshevich, A.V. Samelyuk, V.R. Sidorko
Abstract: Two boride layers were found to form at the interface of iiron-chromiium alllloys (10 and 25% Cr) or an industrial 13% Cr steel and boron at 850-950 oC and reaction times in the range 1-12 h. In the case of a Fe-10% Cr alloy and the steel, the layers are based on the FeB and Fe2B compounds. With a Fe-25% Cr alloy, the constituent phases are FeB and CrB for the outer layer and Fe2B and Cr2B for the inner layer. Both layers are characterized by a pronounced texture. Diffusional growth kinetics of boride layers are close to parabolic and can alternatively be described by a system of two non-linear differential equations, producing a good fit to the experimental data. The temperature dependence of the layer growth-rate constants obeys a relation of the Arrhenius type.
Authors: Muhamad Hafizuddin Mohamad Basir, Bulan Abdullah, Mohd Faizul Idham, Muhammad Hussain Ismail
Abstract: This investigation was conducted to study on the effect of shot blasting on the case depth of boride layers produced and microhardness after performing paste boronizing on 316L stainless steel. 250 micron diameter of glass beads had been used in the process of shot blasting with variation in the blasting pressure. Paste boronizing was performed at 850°C with 8 hours of soaking time. The samples involved were tested and analyzed on the microstructure and microhardness. Boride layers of FeB and Fe2B formed due to paste boronizing improve the microhardness of 316L stainless steel and the effect of shot blasting with increasing the blasting pressure increase both of case depth of boride layers and microhardness on the studied metal.
Authors: Ivan Campos-Silva, M. Ortíz-Domínguez, E. Hernández-Sánchez, D. Bravo-Bárcenas, O. Bravo-Bárcenas, Marco Antonio Doñu-Ruíz, J. Martínez-Trinidad, J.A. Jiménez-Bernal, Y. Domínguez-Galicia
Abstract: Fracture indentation was applied to estimate the fracture toughness of AISI 1018 borided steels. The Fe2B hard layers were formed using the powder-pack boriding process for two temperatures with 4 and 8 h of exposure times. The fracture toughness of the iron boride layer of the AISI 1018 borided steels was estimated using a Vickers microindentation induced-fracture testing at distances of 15 and 30 m from the surface, applying four loads (0.49, 0.98, 1.96 and 2.9 N). The microcracks generated at the corners of the Vickers microindentation were considered as experimental parameters, which are introduced in a Palmqvist crack model to determine their corresponding fracture toughness KC. As a result, the experimental parameters, such as exposure time and boriding temperature are compared with the resulting fracture toughness of the borided phase.
Authors: G. Ramírez, Ivan Campos-Silva, Alexander S. Balankin
Abstract: The fracture toughness of the Fe2B phase was evaluated in this study. Formation of the Fe2B boride is carried out though paste boriding process applied on AISI 1045 steel surface. The treatment was carried out at temperatures of 1193, 1223 and 1273 K for 6 h using a 5 mm thick boron paste. A Vickers microhardness tester was used to generate microcracks at a load of 200g. The indentations were made across the thickness of the iron boride layer at four different distances from the substrate. The experimental results show that the critical stress intensity factor KIC for the Fe2B phase shows a potential law dependence on crack length; this contradicts the concepts of Linear Elastic Fracture Mechanics, which establish that the fracture toughness value is a constant of the material.
Authors: Ivan Campos-Silva, M. Ortíz-Domínguez, José Martínez-Trinidad, N. López-Perrusquia, E. Hernández-Sánchez, Giselle Ramírez-Sandoval, Ramon Escobar-Galindo
Abstract: Some physicochemical and mechanical properties of surface hard coatings obtained by the paste-boriding process are summarized in this work. Different grades of borided ferrous alloys were used to develop the formation of surface layers type Fe2B or FeB/Fe2B. Furthermore, in order to characterize the nature of boride layers, some classical techniques are presented and discussed such as Glow Discharge Optical Emission Spectrometry (GDOES), Atomic Force Microscopy (AFM) and estimation of residual stresses by X-Ray Diffraction method. Also, the morphology of borided interfaces was evaluated by concepts of fractal theory.
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