Boriding of mild steel using the spark plasma sintering (SPS) technique
22 Aug 2002-Surface & Coatings Technology (Elsevier)-Vol. 157, Iss: 2, pp 226-230
TL;DR: In this article, a spark plasma sintering (SPS) technique was employed to perform boriding of mild steel, which was performed in the temperature range 700-1000 °C for 30 min.
Abstract: The spark plasma sintering (SPS) technique was employed to perform boriding of mild steel. A pack boriding method that contained a silicon carbide-boron carbide powder pack mixture was utilized in this study. The process was performed in the temperature range 700-1000 °C for 30 min. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) revealed the microstructure and phase composition of the iron boride layers (FeB and Fe 2 B). Plotting lnD vs. 1/T expresses concisely the boride layer's growth rate constant (D) vs. temperature (T) relation. A linear relationship between lnD and 1/T is confirmed. The kinetics of SPS boronization are discussed, and the effect of SPS on boronization is studied. The results confirmed that SPS required significantly lower activation energy for accomplishing the boriding operation.
TL;DR: In this paper, the authors provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones.
Abstract: This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.
TL;DR: In this article, the diffusion coefficient of boron in FeB and Fe 2 B phases is obtained through fitting the experimental results into the model, and the simulation results are found to be in good agreement with experimental results.
Abstract: The iron boride layer growth kinetics in mild steel through the spark plasma sintering (SPS) pack-boriding technique is investigated at 850 °C with different boriding durations (maximum 240 min). Results show that both FeB and Fe 2 B layers form and grow on the mild steel surface with the FeB layer on the top of Fe 2 B sublayer in the samples with boriding duration less than 90 min. However, at longer boriding duration, the top FeB layer eventually ceases growing, starts to diminish, and, finally disappears completely by transforming into the Fe 2 B phase. Numerical simulation is implemented to explain this phenomenon. Subsequently, the diffusion coefficient of boron in FeB and Fe 2 B phase is obtained through fitting the experimental results into the model. The simulation results are found to be in good agreement with the experimental results, and the estimated diffusion coefficients of boron in FeB and Fe 2 B phases as 2.33 × 10 −9 and 4.67 × 10 −9 cm 2 /s, respectively. Both the simulation and experimental results reveal that the Fe 2 B mono-phase layer can be obtained through the transformation of FeB to Fe 2 B phase due to the depletion of boron concentration in the boriding medium, and is indifferent to the formation of FeB phase at the very onset of the boriding process. This provides a new approach to overcome the side effect of FeB formation in borided components.
TL;DR: In this paper, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 milli-amps/cm2 in a borax-based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5-120 min.
Abstract: In this study, the growth kinetics of the boride layers forming on low carbon steel substrates was investigated during electrochemical boriding which was performed at a constant current density of 200 mA/cm2 in a borax based electrolyte at temperatures ranging from 1123 K to 1273 K for periods of 5–120 min. After boriding, the presence of both FeB and Fe2B phases were confirmed by the X-ray diffraction method. Cross-sectional microscopy revealed a very dense and thick morphology for both boride phases. Micro hardness testing of the borided steel samples showed a significant increase in the hardness of the borided surfaces (i.e., up to (1700 ± 200) HV), while the hardness of un-borided steel samples was approximately (200 ± 20) HV. Systematic studies over a wide range of boriding time and temperature confirmed that the rate of the boride layer formation is strongly dependent on boriding duration and has a parabolic character. The activation energy of boride layer growth for electrochemical boriding was determined as (172.75 ± 8.6) kJ/mol.
TL;DR: In this paper, boride layers on the surface of AISI 8620, 52100 and 440C steels were plasma paste boronized (PPB) by using 100% borax paste.
Abstract: In the present study, AISI 8620, 52100 and 440C steels were plasma paste boronized (PPB) by using 100% borax paste. PPB process was carried out in a dc plasma system at temperature of 700 and 800 °C for 3 and 5 h in a gas mixture of 70%H2–30%Ar under a constant pressure of 4 mbar. The properties of boride layer were evaluated by optical microscopy, X-ray diffraction and Vickers micro-hardness tester. X-ray diffraction analysis of boride layers on the surface of the steels revealed FeB and Fe2B phases for 52100 and 8620 steels and FeB, Fe2B, CrB and Cr2B borides for 440C steel. PPB process showed that since the plasma activated the chemical reaction more, a thicker boride layer was formed than conventional boronizing methods at similar temperatures. It was possible to establish boride layer with the same thickness at lower temperatures in plasma environment by using borax paste.
Cites background from "Boriding of mild steel using the sp..."
...Boronizing process can be applied in solid, liquid and gaseous environment [1–7]....
TL;DR: In this article, boride layers are formed on the surface of W samples using a pack boriding method with the assistant of the spark plasma sintering technique, which is performed in the temperature range 1000-1400 °C with a holding time of 30 min.
Abstract: Metal borides are attractive candidates for high-temperature, wear resistance, and corrosion resistance applications. Tungsten borides (WB and W2B5) are known to have high hardness values, chemical inertness, and electronic conductivity, and have potential industrial applications as abrasive, corrosion-resistant and electrode materials, which are exposed to exacting environments. In this work, boride layers are formed on the surface of W samples using a pack boriding method with the assistant of the spark plasma sintering technique. The process was performed in the temperature range 1000–1400 °C with a holding time of 30 min. The microstructure, microhardness, and fracture toughness of the tungsten boride layer are investigated by optical microscopy, X-ray diffraction and microhardness indentations. Results showed that the boride layer, composed of WB, have thickness in the range ∼35–112 μm. The WB layers are found to have a preferred orientation in the (200) direction, which is reflected by a distinct columnar growth observed in the optical micrographs of polished cross-sections of SPS samples.
TL;DR: In this article, a boron-compound layer was developed consisting of a surface-adjacent "FeB" sublayer on top of an "Fe2B", and the extent of penetration of the two sublayers as a function of boriding time and temperature in the range 1025-1275 K.
Abstract: Specimens of pure Fe and of Fe-0.8 mass % C, Fe-0.5 mass % Cr, Fe-4.0 mass % Cr, Fe-4.0 mass% Ni, and Fe-10.0 mass% Ni alloys were borided in boriding powder. A boron-compound layer developed consisting of a surface-adjacent “FeB” sublayer on top of an “Fe2B” sublayer. Layer-growth kinetics were analyzed by measuring the extent of penetration of the “FeB” and “Fe2B” sublayers as a function of boriding time and temperature in the range 1025–1275 K. Layer growth is dominated by B diffusion through “FeB/Fe2B”. This diffusion process is of strongly anisotropic nature. Consequently, ragged interfaces occur between the substrate and the boride layers. The depths of the tips of the most deeply penetrated “FeB” and “Fe2B” needles have been taken as measures for diffusion in the easy  diffusion directions. Assuming unidirectional B diffusion and parabolic growth, a simple model of layer growth has been given. It accounts for the specific volume difference between “FeB” and “Fe2B”. In contrast with earlier work, the model provides values for the kinetic parameters for growth of each of the phases in the boron-compound layer.
TL;DR: In this paper, the state-of-the-art and recent progress in plasma diffusion treatment is reported, highlighting the recent accomplishments in plasma carburizing and plasma boriding.
Abstract: Although plasma diffusion treatment (PDT) is one of the most promising and economical processes to improve both surface and near-surface properties such as wear and corrosion resistance and fatigue strength, the basic mechanisms are still poorly understood. Despite this fact, significant improvements have been made in equipment and processes. In the present paper, the state-of-the-art and the recent progress in plasma diffusion treatment will be reported. This paper will especially highlight the recent accomplishments in plasma carburizing and plasma boriding. The new trends of applications in plasma diffusion treatment will be described to show the future perspectives of this technology.
TL;DR: In this article, small cylindrical tubes were sintered in a microwave-induced oxygen plasma, initiated and sustained inside a tunable, single-mode cavity, using an optical-fiber thermometer black-body sensor and a dilatometer, respectively.
Abstract: Small cylindrical tubes were sintered in a microwave- induced oxygen plasma, initiated and sustained inside a tunable, single-mode cavity. Temperature and shrinkage measurements of the specimens were achieved using an optical-fiber thermometer black-body sensor and a dilatometer, respectively. Sintering experiments at constant heating rate were accomplished to obtain the activation energy for sintering of alumina in the plasma and in a conventional rapid-heating furnace. Diffusion of aluminum interstitials along grain boundaries was believed to be the dominant sintering mechanism, with an estimated activation energy of 488 ± 20 kj/mol for conventional sintering and an average activation energy of 468 ± 20 kj/mol for plasma sintering. A comparison of specimens sintered in the plasma to those sintered in a conventional furnace under the same temperature-time excursions and oxygen pressures showed an athermal effect due to the plasma. To further explore this athermal effect, sintering experiments in plasmas of different oxygen pressure were conducted. The athermal effect was ascribed to an increase of aluminum interstitial concentration during plasma sintering. Sintering data were interpreted using the combined-stage sintering model.
TL;DR: A multi-component diffusion study of boron, chromium, aluminum and silicon on an AISI 1045 steel substrate has been carried out by pack cementation as mentioned in this paper.
Abstract: A multi-component diffusion study of boron, chromium, aluminum and silicon on an AISI 1045 steel substrate has been carried out by pack cementation A commercial boriding powder (Ekabor-3) and an Fe–Cr alloy powder plus NH 4 Cl activator make up 30 wt% of the pack, and 70 wt% of Al 2 O 3 serves as an inert diluent and supply source of aluminum atoms The structure and constituent changes of the coated layers and their thickness and hardness, as influenced by different pack compositions, have been investigated at 1000°C The kinetics of the reaction, K = K 0 exp(− Q / RT ), have also been determined in this work by varying the NH 4 Cl additions The results show that Q and K 0 decrease with increasing amount of NH 4 Cl addition at temperatures between 900°C and 1000°C
TL;DR: Spark plasma sintering was conducted on nanocrystalline ZrO2(Y2O3) and 20 mol% Al 2O3 powder at a heat rate of 600°C/min with a short holding time.
Abstract: Spark plasma sintering (SPS) was conducted on nanocrystalline ZrO2(Y2O3)–20 mol% Al2O3 powder at a heat rate of 600°C/min with a short holding time. Full density was obtained at sintering temperatures >1300°C. Considerable grain growth occurred relative to the initial powder particles, but smaller grain size and higher density can be obtained as compared to hot-pressing. High flexural strength and fracture toughness were also achieved for the SPS-resulted composite.