Fe2B Phase Research Articles

Rapidly quenched heavy rare earth-based ternary Lu-Fe-B alloys: Phase evolution and hard magnetic properties

Aiming to clarify the fundamental properties of Lu-Fe-B alloys and facilitate the application of the Lu in rare earth (RE)-iron-boron permanent magnets, the phase constitutions, phase precipitation behavior, and hard magnetic properties of Lu12+xFe82−xB6 alloys (x = 0–4) prepared by melt spinning were systematically studied. The intrinsic coercivity Hcj= 313 kA/m, remanence Jr = 0.72 T, and maximum energy product (BH)max= 68.5 kJ/m3 were obtained in optimally quenched Lu12Fe82B6 alloy. Different from many other RE-Fe-B alloys, increasing Lu content leads to the formation of the soft magnetic amorphous phase and Lu6Fe23 phase, which eventually increases the exchange coupling effect and decreases Hcj and (BH)max of the Lu-rich alloys (x = 1–4). For the amorphous Lu12+xFe82−xB6 alloys, after annealing treatment, Lu2Fe14B and Fe2B phases precipitate in the alloys with x = 0 and 1, but the crystalline phases change into Lu6Fe23, Lu2Fe14B, and Fe2B phases in the alloys with x = 2–4. For the Lu-rich alloys, all crystalline phases tend to precipitate simultaneously from the amorphous matrix, which is beneficial to obtaining optimized microstructure under various processes. The alloy with x = 2 annealed at 750 °C for 10 min exhibits a good combination of magnetic properties with Jr = 0.69 T, Hcj= 234 kA/m, and (BH)max= 51.9 kJ/m3. The present results can serve as a useful reference for promoting the utilization of Lu in RE permanent magnets.

Laser Boronizing of Additively Manufactured 18Ni-300 Maraging Steel Part Surface.

The problem of insufficient wear resistance of maraging steels (MSt) has so far been solved mainly by the use of the thermochemical nitriding process, which has a number of limitations and disadvantages. In the present work, for MSt parts manufactured by laser powder bed fusion (LPBF), a more flexible laser alloying process was suggested as an alternative surface hardening process. The purpose of the present work is to give a better understanding on the possible hardening effect obtainable when amorphous boron is used as an alloying additive in relation with microstructural evolution and specific process parameters and to promote further development of this technology. For the alloying, a one kilowatt CO2 laser was applied at 0.5–4.0 mm laser spot and 250–1500 mm/min laser operating speed, providing 50,955–796 W∙cm−2 power density and 24.0–4.0 J∙mm−1 heat input. Before laser processing, surfaces were covered with amorphous boron. The appropriate melt pool geometry was obtained at 0.5 mm laser spot, for which XPS analysis revealed an increase in boron concentration from ~3.1 to ~5.7 wt.% with a laser speed increase from 500 to 1500 mm/min. XRD analysis revealed domination of Fe3B type borides along with the presence of FeB, Fe2B, Ni4B3 borides, austenitic and martensitic phases. The microstructure of modified layers exhibited evolution from hypoeutectic microstructure, having ~630–780 HK0.5 hardness, to superfine lamellar nanoeutectic (~1000–1030 HK0.2) and further to submicron-sized dendritic boride structure (~1770 HK0.2). Aging of laser-boronized layers resulted in the change of phase composition and microstructure, which is mainly expressed in a plenty precipitation of Mo2B5 borides and leads to a reduction in hardness—more significant (by ~200–300 HK0.2) for hypoeutectic and hypereutectic layers and insignificant (by ~50 HK0.2) for near-eutectic. With the application of the laser boronizing technique, the hardness of MSt parts surface was increased up to ~three times before aging and up to ~2.3 times after aging, as compared with the hardness of aged MST part.

Effect of Cu and Co addition on non-isothermal crystallization kinetics of rapidly quenched Fe-Sn-B based alloys

Crystallization kinetics of rapidly quenched Fe-Sn-B alloys under non-isothermal conditions were studied using differential scanning calorimetry. Formation of crystalline phases was analyzed by X-ray diffraction. Nominal chemical compositions were Fe81Sn7B12, (Fe3Co1)81Sn7B12 and (Fe81Sn7B12)99Cu1. Alloys were prepared by planar flow casting in the form of ribbons approximately 20 µm thick and 6 mm wide. Mechanism of crystallization was studied under framework of the Johnson-Mehl-Avrami-Kolmogorov model. Alloys exhibit two stages of crystallization. Results show decrease in activation energy of the first stage of crystallization with addition of Cu and increase with addition of Co. Crystallization mechanism of the first stage of crystallization for Fe81Sn7B12 and (Fe81Sn7B12)99Cu1 alloy starts as growth with increasing nucleation rate and continues as growth with decreasing nucleation rate. Addition of Co changes mechanism of crystallization. Which in case of (Fe3Co1)81Sn7B12 alloy starts as a growth with increasing nucleation rate. Then changes to growth with decreasing nucleation rate. After which nucleation rate decreases to zero. Rest of crystallization stage is governed by growth of pre-existing nuclei. In the first stage of crystallization α-Fe phase with bcc structure crystallizes from amorphous matrix. In the second stage of crystallization the remaining amorphous matrix crystalizes into tetragonal Fe2B phase and hexagonal FeSn phase. After the first stage of crystallization, 50 % to 55 % volume of studied alloys were crystalized. Addition of Cu decreases crystalline size of α-Fe crystallites by 60 % and decreases concentration of Sn in α-Fe phase by 0.8 at. %. Addition of Co doesn't affect the size of α-Fe crystallites and decreases the concentration of Sn in α-Fe phase by 1.7 at. %.

Single Fe2B Phase Particle Production by Calciothermic Reduction in Molten Salt

In this study, calciothermic single phase iron boride(Fe2B) production was investigated in a scalable molten salt system, starting from inexpensive, easily accessible oxide materials. First, the formation of Fe2B was examined in detail in the light of thermodynamic data and literature. After, effects of CaO amount (0-10 wt.%) and time (30-60 min) on particle synthesis were investigated under at constant 3.0 V cell voltage and 1273 K temperature. It was determined that the average current increased continuously with the increase in the amount of CaO, and the current efficiency increased up to 7% by weight of CaO. After the CaO ratio was determined, the effect of the electrolysis duration was examined. In durations experiments, it has been observed that, in 30 minutes’ duration, the particles are composed of Fe, Fe2B and FeB, and by increasing the experiment time to 60 min, single-phase Fe2B particles are obtained. The magnetic properties of the single-phase Fe2B particles obtained at the end of the experiment period of 60 minutes were investigated by VSM. The saturation magnetization, permanent magnetization and coercivity values of the Fe2B particles were determined as 90.718 emu/g, 33.311 Oe, 1.684 emu/g, respectively.

Влияние борирования и алитирования на структуру и микротвердость низкоуглеродистых сталей

Introduction. Boriding and aluminizing are among the effective methods for improving the performance properties (corrosion resistance, heat resistance and wear resistance) of machine parts and tools. Solid-phase methods of carrying out techniques of thermochemical treatment (TCT) require long-term exposure at elevated temperatures, which negatively affects the structure and properties of the base material. From these positions, the selection of reasonable temperature-time parameters of solid-phase boriding and aluminizing processes is an urgent task. The purpose of this work is to assess the effect of low-temperature boriding and aluminizing processes on the structure and microhardness of diffusion layers on the surface of low-carbon steels. The paper considers two grades of steels with a carbon content of up to 0.4%: low-carbon steel St3 and alloy steel 3Cr2W8V. The use of the second steel is due to the need to identify the effect of alloying elements in steel on the thickness of diffusion layers and its composition. Powder mixtures based on boron carbide and aluminum carbide are selected as sources of boron and aluminum. Results and discussions. It is found at a process temperature of 900 °C and holding for 2 hours after boriding, iron borides are formed on the surface of both steels. At the same time, two borides FeB and Fe2B are detected on St3 steel by X-ray phase analysis (XRD), and only the Fe2B phase is detected on 3Cr2W8V steel. After aluminizing, aluminum-containing phases such as Al5Fe2, Na3AlF6 and Al2O3 are formed in both steels. The thickness of the resulting diffusion layer on St3 after boriding is 35 μm, after aluminizing – 65 μm. The thickness of the diffusion layer on 3Cr2W8V steel is equal to 15 μm after boriding and 50 μm after aluminizing, which is significantly less than on carbon steel and is obviously due to the effect of alloying elements. It is established that TCT leads to a significant increase in the microhardness of the samples surface. Thus, the maximum microhardness of St3 steel increased to 2,000 HV, and the maximum microhardness of 3Cr2W8V steel increased to 1,700 HV after boriding. The microhardness after aluminizing is comparable for both steels and is equal to 1,000-1,100 HV. Elemental analysis of the upper sections of the diffusion layers shows that the content of boron (7-9%) and aluminum (50-53%) corresponds to the detected XRD iron borides and aluminides. In all cases, there is a gradual decrease in the diffusing elements in the direction from the surface to the base.

Peculiarities of conventional HDDR process in (Nd,Pr)-Fe-B alloy powders under low hydrogen pressure

The relationship between the temperature of the start, peak and finish of conventional disproportionation and recombination, in hydrogen, reactions and the low starting hydrogen pressure of 10, 20, 30, 40, 50, 60, 70 and 80 kPa and maximum processing temperature of 950–1015 °C was studied by DTA and X-ray diffraction measurements for 10 g of (Nd,Pr)-Fe-B ferromagnetic powder batches. It was shown that the starting temperature of the disproportionation reaction increases when hydrogen pressure decreases. A similar dependence took place for finishing temperature of the disproportionation when pressure was in the range of 40–80 kPa. At a hydrogen pressure of 10–30 kPa, finishing temperature of the disproportionation decreased with decreasing of pressure. The temperature of the recombination reaction in hydrogen increased with increasing of the hydrogen pressure. The non-equilibrium pressure–composition–temperature schema with four zones for the (Nd,Pr)-Fe-B alloy–hydrogen system was built. The remnants of the (Nd,Pr)2Fe14B phase and disproportionation products – (Nd,Pr)H2±x, α-Fe and Fe2B were in zone I – zone of the disproportionation reaction and in zone II – interstitial zone. The recombined (Nd,Pr)2Fe14B phase, (Nd,Pr)H0–2±x, α-Fe and Fe2B phases were in the zone III – zone of the recombination reaction. And the (Nd,Pr)2Fe14B phase, recombined in hydrogen, existed in the zone IV – zone of the existence of (Nd,Pr)2Fe14B phase.

Duplex surface treatment on ASTM A-36 steel by slide burnishing and powder pack boriding

In this work, a novel duplex surface treatment (DST) was done on ASTM (American Society for Testing and Materials) A-36 steel bar by combining burnishing and boriding processes. Initially, the slide burnishing method on ASTM A-36 steel was carried out using a burnishing force of 200 N and a travel speed of 127 mm/min. Then, powder pack boriding process was conducted on burnished steel at 950 °C for 5 h. The X-ray diffraction analysis shows the formation of the Fe2B phase. The hardness increases from 216 HV0.05 to 2290.3 HV0.05 for the burnished-boride sample. According to electrochemical impedance spectroscopy (EIS) and Tafel (potentiodynamic polarization) results, burnished-boride steel showed a higher corrosion resistance than that of boride steel.

Microstructure and properties of B + C + N ternary hardening layers on Q235 low-carbon steel prepared by plasma electrolysis

Ternary surface hardening layers were prepared on the Q235 low-carbon steel by plasma electrolytic borocarbonitriding(PEB/C/N) under constant voltage of 260–300 V for 30 min. The microstructure, phase components and hardness depth profiles of the B + C + N ternary hardening layers were examined. The ternary hardening layers were composed of a boride layer with single Fe2B phase and a transition layer. The thickness of modified boride layers on the PEB/C/N samples was about 10 μm, 15 μm and 22 μm at 260 V, 280 V and 300 V, respectively. The maximum hardness of boride layer was 2400 HV for the 300 V PEB/C/N sample. The surface free energy of bare Q235 steel and PEB/C/N samples at 260, 280 and 300 V were 41.084, 32.039, 26.906 and 25.726 mJ/m2, which were calculated on the basis of their contact angles for water and n-hexadecane. Furthermore, the hardening layers exhibited excellent corrosion behavior due to the improved hydrophobicity for the dense boride layer. The lowest wear rate of PEB/C/N sample at 300 V is about 2.0375 × 10−6 mm3/ N·m, which is only 1/15 of the bare Q235 steel, the ternary hardening treatment shows a better wear resistance than the bare Q235 steel.

MORPHOLOGICAL BEHAVIOR OF FEB AND FE2B IN BORIDE LAYER OF 304 STAINLESS STEEL UNDER DIFFERENT MEDIUM

This study investigates the morphological behavior of FeB and Fe2B phase in boronized 304 stainless steel under two different mediums which is powder and paste. Surface attrition was implemented in order to initiate better boron diffusivity. The comparison of microstructure in term of grain size and boride layer thickness were also analyzed. Scanning electron microscopy, X-Ray diffraction analysis and energy dispersive X-Ray Analysis were conducted to prove the existence of FeB and Fe2B phases. The relationship between the phase and Vickers microhardness was also investigated. The results show formation of flat-toothed boride layer in both sample with different FeB and Fe2B layer uniformity. Paste boronized sample with120 µm boride layer thickness had outperformed the powder boronized sample that with 43 µm boride layer thickness, thus providing significant improvement in microhardness values from 1500 Hv to 1800 Hv. In conclusion, paste medium provide outstanding boride layer thickness with 300% enhancement and excellent microhardness with 20% improvement. The results of this findings could offer a new insight in pack boronizing of stainless steel that can be complicated to boronized due to its high alloying element content.

Theoretical critical metastability temperature to interpret phase formation in a lamellar-like-structured high entropy alloy

Control over a lamellar-like-structured high entropy alloy (HEA) system is found to be possible by replacement of aluminium with boron into the FeCoNi(Bx Al1-x)0.1Si0.1 composition in the range of x = 0 to 1.0. The BCC/B2 microstructure of FeCoNi(Al0.1Si0.1) HEA is changed into a multiple phase system comprising of BCC/B2, FCC and Fe2B-type intermetallic phases. The microstructures of as-cast alloys were seen to be a lamellar-like structure comprised of nanostructured lamellae with alternating FCC and Fe2B phases. The concept of critical metastability temperature from nucleation theory is employed phenomenologically, and found to correlate with the presence of Fe2B in this alloy at different boron additions. With the substitution of boron, the stability of the disordered BCC solid solution is reduced, promoting the formation of secondary phases. We show a link between the interfacial energy of the phases present, the interlamellar spacing, and alloy metastability as a function of boron addition, the key relationship being that Fe2B phase formation correlates with a drastic reduction in the interfacial energy. These correlations bear further investigation and may be useful in the design of lamellar-like-structured multi-component systems.

Effect of boronising on the cavitation erosion resistance of stainless steel used for hydromachinery applications

Erosive wear due to cavitation severely affects hydromachinery and consequently various sectors of industry, including hydroelectric plants. ASTM A743 CA6NM steel, which is typically used in hydromachinery, was boronised using the packing method at 950 °C for durations of 2, 6, and 8 h Fe2B and FeB phases were identified and characterised using optical microscopy, X-ray diffraction, scanning electron microscopy, and microhardness tests. Under all of the boronising conditions, a surface FeB phase was obtained. Its hardness was 5.22 times that of the base material. The resistance to erosion due to cavitation was evaluated according to the ASTM G32 standard by exposure for 15 h to vibrations that induced cavitation. The boronising time influenced the resistance to cavitation. After boronising for 2, 6, and 8 h, the erosion rates were reduced by 72%, 57%, and 55%, respectively, compared to the erosion rate of untreated ASTM A743 CA6NM steel. According to scanning electron microscopy, the worn surfaces differed for non-boronised steel (ductile behaviour) and boronised steels (brittle behaviour) exhibiting micro-cracks, micro-pores, and detachment of the boride layers.

The Effect of Hf Addition on the Boronizing and Siliciding Behavior of CoCrFeNi High Entropy Alloys.

The effect of a boronizing and siliciding process on CoCrFeNiHf0.1–0.42 high entropy alloys was examined in this study. When increasing the amount of added Hf in CoCrFeNiHfx, the structure of the alloys gradually transformed from single-phase FCC to firstly Ni7Hf2 + FCC, and finally to C15 Laves and FCC phases. The boronizing/siliciding process resulted in the formation of a silicon-rich layer and a boride layer (BL). Increasing the amount of Hf in the alloys resulted in a decrease in the combined layer thickness, which was measured for CoCrFeNi, CoCrFeNiHf0.1, CoCrFeNiHf0.2, and CoCrFeNiHf0.42 to be 70 µm, 63 µm, 20 µm, and 15 µm, respectively. In contrast, the thickness of the transition zone/diffusion zone increased with more Hf in the alloys. While silicon atoms were gathered close to the BL, they were not transferred into the CoCrFeNi substrate. In contrast to the observation for CoCrFeNi, Si atoms penetrated through the Ni-rich phase (Ni7Hf2) in the CoCrFeNiHfx alloys. Furthermore, the Cr-B rich area (Cr5B3) in the coating limited the transport of Si into the CoCrFeNiHfx substrates. XRD analysis showed that the BL contained Ni2Si, FeB, Fe2B, Co2B, and Cr5B3 phases.

Features of formation of diffusion zone obtained on steel 20 by boriding in induction furnace

The article presents data on studies of iron borides synthesis during induction heating to 1000 °C for 5 min of steel 20 samples with a coating from a charge containing Fe – H3BO3. Content of boric acid in the charge varied from 25 to 75 % wt. Charge in the experiments could be diluted with a solution of liquid glass in water with addition of small amount of ammonium hydroxide and coal. Study of the surface layer microhardness showed that during saturation of the surface layer of carbon steel 20 with boron, a macroscopically extensive diffusion zone 900 – 1000 μm in size is formed, in which the boride content gradually decreases when moving deeper into the matrix. Such a size of the diffusion zone indicates an anomalously high mass transfer during boriding of steel 20. Indeed, the calculated diffusion coefficient during boriding under induction conditions (about 1.35·10–9 m2/s) is two orders of magnitude higher than the diffusion coefficient in the classical boriding. X-ray studies showed that, under the considered conditions, Fe2B and FeB borides are synthesized, and a solid solution of boron in α­iron is also formed. An analysis of phase composition of the diffusion zone structural components indicates that, from the surface to the matrix, formation of boride phases occurs in the following sequence: FeB → Fe2B → (α­phase + B) → base metal. Microstructure of the diffusion zone consists of more or less pronounced layers consisting of FeB and Fe2B boride phases. On the whole, especially deep-ying regions of the diffusion zone are a composite material consisting of plastic α-phase and iron boride crystals. Crystals in FeB and Fe2B in the layer are oriented mainly perpendicular to the diffusion front. Perhaps, this is due to the rapid predominant growth of the boride phase under conditions of high diffusion mobility of boron atoms in one direction and hindered in others.

In-situ STEM study on thermally induced phase transformation of magnetic (Nd0.75Ce0.25)2Fe14B ribbons

Studying the phase transformation and microstructure evolution of magnetic Nd-Ce-Fe-B nanocrystalline melt-spun ribbon is of paramount significance in developing this important class of magnetic materials. In this work, the thermal-induced phase transformation of (Nd0.75Ce0.25)2Fe14B nanocrystalline sample was revealed via in-situ heating scanning transmission electron microscopy (STEM) experiment (RT-750 ℃). Starting from a single-phase (Nd0.75Ce0.25)2Fe14B nanocrystalline matrix at room temperature (RT), grain boundary (GB) diffusion behavior was investigated at an atomic scale. Our result shows that the rare earth elements accumulate at GB area from 200 °C and form a uniform thin amorphous layer between grains. The decomposition of the primary phase was observed at about 350 ℃ and crystalized as BCC-Fe, Fe2B, and (Nd0.75Ce0.25)2O3 phases driven by thermal activation at a higher temperature. This work provides the essential information of phase transformation and microstructure evolution of NdCeFeB-based magnets at high temperatures and new insights into thermal treatment designing and thermal stability considerations.

Microstructure, hardness and high temperature wear characteristics of boronized Monel 400

Boronizing processes were carried out at 900 °C, 950 °C and 1000 °C for 2, 4 and 6 h to improve the wear performance of Monel 400 alloy. According to microstructure analyses and nanoindentation tests, Ni2B, FeNiB and FeB phases were detected as dominant phases in the boronized layer. Apart from this, it was observed that the amount of Cu deposits in the boronized layers increased depending on the increasing boronizing temperature. After the boronizing process, the boride layer thickness and hardness values were found to be in the range of 32–272 μm and 12.76–17.83 GPa, respectively. From the results of dry sliding wear test, the wear volume loss values of the boronized Monel 400 alloy decreased by approximately 25 times compared to the untreated samples. The lowest volume loss value among all test samples was observed in the boronized sample at 950 °C for 4 h. In addition to the hardness value, it was determined that the morphology and mechanical properties of the boronized layer were also effective on the wear results. Plastic deformation, delamination and oxidation type wear mechanisms were observed as the dominant wear mechanisms in the room and high temperature tests of boronized samples.

Phase selection and characterization of Fe-based multi-component amorphous composite

Phase selection and amorphous transition play a significant role for controlling of the microstructure and properties of multi-component alloys. In the present work, the solidified microstructure evolution of Fe52-xCo20NixB19Si5Nb4 (x = 7,12, labeled as 7 Ni, 12 Ni) alloys were studied in a wide range of cooling rate, and the effect of phase constitutions on the magnetic and micromechanical properties were systematically investigated. The results show that the microstructures of the two master alloys are composed of α-Fe, γ-Fe, Fe2B and Nb6Co16Si7 phases. As the solid solubility increases, the content of the intermetallic Nb6Co16Si7 phase decreases or even disappears, while the metastable Fe3B phase and Fe23B6 phase grow competitively. With the rise of the cooling rate, there is a transition from eutectic microstructure to internal amorphous structure plus peripheral crystalline/amorphous composite, and then to complete amorphous state in the two alloys. For the 7 Ni alloy, when the droplet diameter reduces, the coercivity of the alloy decreases continuously. As the content of the main magnetic α-Fe phase decreases, the saturation magnetization of the alloy diminishes firstly, and then slightly heightens when it is completely amorphous. From the perspective of solid solubility, the difference in hardness of the α-Fe and Fe2B phases with the undercooling is clarified. The hardness of the amorphous phase is slightly lower than that of the Fe2B phase. Finally, the nanoindentation technique was used to explore the indentation size effect and creep behavior of amorphous composite under different peak loads and different loading rates. As the peak load decreases or the loading rate increases, the hardness and elastic modulus of the alloy enhance, while the maximum creep displacement, stress factor and activation volume all increase with the rise of the peak load.

Boride Coatings on Steel Protecting it Against Corrosion by a Liquid Lead-Free Solder Alloy

The goal of this research is to study the applicability of the diffusion boriding process as a high-temperature thermochemical heat treatment to enhance the lifetime of steel selective soldering tools. The main purpose of the work is to discuss the behavior of double-phase (FeB/Fe2B) iron-boride coating on the surface of different steels (DC04, C45, CK60, and C105U) against the stationary SAC309 lead-free solder liquid alloy. The boride coating was formed on the surface of the steel samples through the powder pack boriding technique. The microstructure of the formed layer was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The borided samples were first cut in half and then immersed into a stationary SAC309 lead-free solder liquid alloy (Sn–3Ag–0.9Cu) for 40 days. Microstructure examinations were performed by SEM with energy-dispersive spectroscopy and an elemental distribution map after the dissolution test. Excessive dissolution/corrosion of the original steel surface was observed at the steel/SAC interfaces, leading also to the formation of Fe–Sn intermetallic phases. This was found to be the major reason for the failure of selective soldering tools made of steel. On the contrary, no dissolution and no intermetallic compounds were observed at the FeB/SAC and at the Fe2B/SAC interfaces; as a result, the thicknesses of the FeB and Fe2B phases remained the same during the 40-day dissolution tests. Thus, it was concluded that both FeB and Fe2B phases show excellent resistance against the aggressive liquid solder alloy. The results of the dissolution tests show a good agreement with the thermodynamic calculations.

Study of wear characteristics under conditions of dry sliding friction of 08Kh18N10T steel after electrolysis-free boriding

Effect of liquid electrolysis-free boriding on tribotechnical characteristics of 08Kh18N10Т steel is studied. It is established that after boriding at temperature 900 °С and 5 h soaking it is formed a boride two-phase layer with thickness of 30...35 microns and transition zone with thickness of 10 microns. The microhardness in FeB and Fe2B phases is 2000...2100 and 1800...1900 HV 0.1 respectively. The wear tests under dry friction conditions showed that coefficient of friction for specimens made of 08Kh18N10Т steel without treatment and with boriding in pair with counterbody made of ShKh15 steel is 0.83 and 0.85 respectively. At the same time, the wear intensity of samples with boration is an order of magnitude less than that of samples without treatment, and on average is 7.7 · 10–6 mm3 /(H · m) instead of 8.5 · 10–5 mm3 /(H · m). The average depth of the wear track of the sample with boriding is 5 times less than that of the sample without treatment.

Prediction models for the kinetics of iron boride layers on AISI 316L steel

Abstract The boronizing kinetics of AISI 316L steel has been analyzed by employing five prediction models. The boron diffusion coefficients as well as the growth rate constants in the FeB and Fe2B phases were firstly evaluated in the range of 1123-1223 K. Afterwards, the values of boron activation energies in FeB and Fe2B were secondly deduced by adopting the Arrhenius relationships.In addition, the prediction models have been validated experimentally for two boronizing conditions (1170 K for 1.6 h and 1210 K for 1.1 h). The predicted results were deemed very concordant with the experiments. Furthermore, advantages and limitations about the applicability of these models were also discussed.

Effects of Sodium Octaborate on AISI 4140 Steel Machined by Die-sinking EDM

Researchers are constantly developing processes aiming to improve the properties of metal surfaces, especially related to the wear resistance of components, as in the case of the nitrided layer obtained by die-sinking electrical discharge machining (EDM). Following this line of research, this work investigated the effects of sodium octaborate (Na2B8O13.4H2O), mixed into deionized water as a dielectric fluid on AISI 4140 steel surfaces machined by die-sinking EDM. An adapted EDM machine was employed in the process using electrolytic copper as tool. The effects on AISI 4140 steel-machined surfaces were evaluated by optical microscopy, Vickers microhardness, X-ray diffraction, and energy dispersion X-ray spectroscopy (EDS) analyses. The results showed a hardness gain of approximately 146.8% in the modified layer when compared to the AISI 4140 steel (base material). This suggests the formation of a borided layer, such as the Fe2B phases identified on sample surfaces, which can be explained by the boron element decomposed from the dielectric solution.