New results about the growth kinetics of nickel boride layers on an Inconel 718 superalloy were obtained. The nickel boride layers were developed by means of the powder-pack boriding process at ...1173–1223 K with different exposure times for each temperature. According to optical and scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and nanoindentation techniques, the microstructure of the boride layer consisted in three zones: a high content of Ni4B3 on the outer-zone of the borided surface, while Ni2B and Ni3B were revealed at the inner zone of the layer and diffusion zone, respectively. Moreover, the boriding growth kinetics of nickel boride layers was estimated using the Heat Balance Integral Method (HBIM) based on a numerical resolution of a system formed by differential algebraic equations, and considering that the evolution of the layers is governed by the parabolic growth law. For the range of boriding temperatures, the boron activation energies in the Ni4B3, Ni2B and Ni3B resulted in 233, 206 and 218 kJ mol−1, respectively.
•New results of growth kinetics of boride layer on Inconel 718 alloy were obtained.•The HBIM was used to evaluate the growth kinetics of Ni4B3, Ni2B and Ni3B phases.•Boron diffusion in Ni borides was obtained by a particular solution of DAE system.•The Q values were 233, 206 and 218 kJ mol −1 for Ni4B3, Ni2B and Ni3B phases.
This study evaluated the influence of the TiO2 nanoparticles (NPs) on the mechanical and chemical performance of Sn and Sn–Ag alloys. The XRD (X-ray diffraction) and HR-TEM (high ...resolution-transmission electron microscopy) methods were used to characterize the NPs synthesized by the sol-gel microwave process. The chemical composition of the alloys was Sn, Sn+3TiO2 NPs, Sn–5Ag+1.5TiO2 NPs, Sn–10Ag, and Sn–10Ag+3TiO2 NPs, obtained from an experimental factorial design (EFD). A statistical model was used to determine the mechanical and chemical properties, showing the Vickers hardness response surface, tensile strength, wear, and corrosion resistance. The wear and corrosion tests for the various alloy compositions were performed using human artificial saliva solution. The results indicated that the Sn–10Ag+3TiO2 NPs exhibited the highest mechanical performance due to their increased hardness (380 HV), tensile strength (370 N), and wear resistance (0.34 × 10−3 mm3 Nm−1); in all the cases, the inclusion of TiO2 NPs enhanced the corrosion resistance of the alloys. According to the American Dental Association (ADA), Sn–10Ag+3TiO2 NPs alloy could be classified as a possible type IV restorative material.
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•The sol-gel microwave method was successfully used for the synthesis of TiO2 NPs.•The addition of TiO2 NPs modified the microstructure Sn–Ag alloys.•The addition of TiO2 NPs enhanced hardness and wear performance of the Sn–Ag alloy.•The TiO2 NPs remarkably increased the corrosion resistance of Sn–Ag alloy.•According to the results, Sn–Ag + NPs might be reclassified as ADA type IV material.
This study analyzes the influence of cryogenic treatments, before the pre-tempering treatment on the microstructure, and the mechanical properties of the H13 tool steel. The H13 tool steel was ...subjected to the shallow cryogenic treatment SCT (at –80 °C for 24 h) and deep cryogenic treatment DCT (at –185 °C for 24 h) between hardening and pre-tempering processes (at 650 °C for 15 min). Alternatively, the tool steel was exposed only to the hardening and pre-tempering processes. The characterization of the microstructures and phase transformations of the specimens was established via scanning electron microscopy and X-ray diffraction, respectively. The mechanical behavior of the treated H13 tool steel was estimated using the Rockwell hardness and abrasive wear tests. Upon completion of the quenching treatment, the H13 tool steel presented the formation of fine, thin crystals of lath-shaped martensite, while the subsequent pre-tempering treatment formed a microstructure with wider martensite laths than the as-quenched state. The sub-zero treatments on the H13 tool steel promoted several phenomena, such as the martensitic transformation, the refinement of martensite laths, and the formation of large and fine carbides dispersed in the whole microstructure. The specimens exposed to SCT and DCT achieved an improvement in hardness values due to structural changes, which also contributed to a better wear resistance (17 and 25%, subsequently) in comparison with the tool steel exposed exclusively to the pre-tempering treatment. Meanwhile, the failure mechanisms on worn surfaces of the treated H13 tool steel were micro-cutting and pitting, which were developed during the interactions among the specimen surfaces-abrasive particles-rubber wheel.
The corrosion susceptibility of borided CoCrMo alloy exposed to a diffusion annealing process (DAP) and immersed during 7 days in a Hank's solution was evaluated, being compared with the results ...obtained in the borided CoCrMo alloy and the CoCrMo alloy. Firstly, the CoCrMo alloy was exposed to the powder-pack boriding process during 5 h at 1273 K, to obtain a biphasic layer (CoB-Co2B) with a total thickness around 33 μm. Then, the DAP was performed on the borided CoCrMo alloy during 2 h at 1273 K in an inert argon atmosphere to obtain a 29 μm of monophasic Co2B layer. The corrosion tests were performed by the potentiodynamic polarization technique to estimate the corrosion resistance (Rp) and the corrosion current density (jcorr) by means of the linear polarization and the Tafel extrapolation techniques, respectively. The results showed, in the 7th day of immersion in the Hank's solution, that the borided CoCrMo alloy exposed to the DAP exhibited a corrosion value ~22 times higher (~357 kΩ cm2) than that obtained in the borided CoCrMo alloy (~15 kΩ cm2), reaching a value close to the CoCrMo alloy (~385 kΩ cm2). The corrosion performance of the borided CoCrMo alloy exposed to the diffusion annealing process was attributed to i) the presence of the monophasic Co2B layer and high contents of Cr and Mo on the outer-zone of the borided surface, and ii) the depletion of the B2S3 and CrPO4 species at the surface of the borided CoCrMo alloy. Finally, the borided CoCrMo alloy exposed to the DAP exhibited a corrosion susceptibility around 7%, meanwhile the borided CoCrMo alloy obtained a value of 96%, approximately.
•The corrosion resistance of the cobalt boride layer was improved by the DAP.•The DAP increased the Cr and Mo contents on the outermost zone of the Co2B layer.•Depletion of B2S3 and CrPO4 was observed in the boride layer exposed to the DAP.•The boride layer exposed to the DAP showed a corrosion susceptibility of ~7%.
The corrosion behavior of borided X12CrNiMoV12-3 steel immersed during 5 days in a 0.1 M NaCl + 0.04 M Na
2
SO
4
aqueous solution was obtained. The boride layer (FeB/Fe
2
B) formed on the surface of ...the material was developed using the powder-pack boriding process at 1223 K during 6 hours of exposure. Some corrosion electrochemical parameters such as the polarization resistance, the current density, the anodic and cathodic Tafel slopes were determined by means of the potentiodynamic polarization technique, in which the corrosion resistance values of the borided stainless steel were compared with those estimated for the non-borided X12CrNiMoV12-3 steel (reference material).The corrosion behavior of the borided X12CrNiMoV12-3 steel was associated with the development of B
2
S
3
and Fe
2
O
3
on the surface of the boride layer as well as for the presence of texture fibers such as {020}//ND and {021}//ND (estimated from crystallographic texture analysis), which drastically reduced the corrosion resistance values of the boride layer exposed to the aqueous solution. Finally, the electrochemical reactions produced during the immersion of the borided X12CrNiMoV12-3 steel in the neutral chloride-sulfate aqueous solution were proposed.
In pursuit of innovating the conventional powder-pack boriding (CPB) process by introducing an electrical driving force, novel findings regarding the kinetics growth of boride layers produced on an ...AISI 8620 steel through the pulsed-DC powder-pack boriding process (PDCPB) were obtained. The PDCPB accelerates B diffusion on the surface of the specimen, resulting in an augmentation of the growth kinetics around 12 % and 15 % for FeB and Fe2B, respectively, compared to those observed in the CPB process. Additionally, the effect of polarity inversion half-cycles on the growth of the FeB-Fe2B layer during the PDCPB was studied. The experiments were conducted at temperatures of 850 °C, 900 °C, and 950 °C, with different exposure times, and polarity inversion half-cycles of 30 s and 50 s, maintaining a constant current density of around 177 mA cm−2. An estimation of the electric charge (q) using a transfer function considering minimal and maximum temperatures was achieved. It was confirmed that, with a symmetrical inversion, q was similar for both 30 s and 50 s polarity inversion half-cycles, indicating no influence on the growth kinetics of the boride layers.
•Each component of boriding media influenced its electrical behavior during PDCPB.•A holistic explanation of the boriding media electrical behavior was developed.•Transfer function was used for the estimation of electric charge during PDCPB.•Similar electric charge was obtained for half-cycles >7 ms.•Electric charge did not influence the boride layer growth kinetics.
Novel results about the growth kinetics of Fe2B layers produced by pulsed-DC powder-pack boriding (PDCPB) on AISI 1018 and 4140 steels were obtained. In the process, a DC-field is applied to ionize ...the B atoms and implements a programmable electronic control device (PECD) to maintain a constant B flux on both surfaces of the material. During PDCPB, the electrical resistivity (ER) was reduced due to the percolation of KBF4 in the boriding media. Nevertheless, the increase of ER was caused by the depletion of KBF4 after 1000s of the current induction. The PDCPB enhanced the growth kinetics of the Fe2B layer around of 9% for both borided steels compared to those estimated in the conventional powder-pack process.
•A low potential boriding media allows the formation of Fe2B layer.•The pulsed-DC field enhances growth kinetics of the Fe2B layer.•The electromigration energy contribution decreases boron activation energy in Fe2B.•Boron activation energy in Fe2B is 9% lower than traditional powder-pack boriding.•DC field modifies the electrical behavior of boriding media due to Joule effect.
It is shown for the first time that the deep eutectic solvent, DES, formed by acetylcholine chloride and urea can be successfully used for Ag recovery from the cathode powder of spent silver oxide ...batteries. This DES performs two important functions namely, as selective leaching liquor to extract Ag(I) ions from the remaining Ag2O, leaving intact the metallic Ag in the solid phase, and as electrolytic bath for silver electrodeposition onto a glassy carbon electrode or graphite. Using potentiodynamic and potentiostatic electrochemical measurements, it was possible to quantify both: the Ag(I) leaching rate and the concentration of Ag(I) ions leached after 24 h. From this value, it was possible to estimate that about 7% of the original mass of the cathode powder corresponds to Ag2O and the rest to metallic Ag. Moreover, from potentiostatic current density transients, recorded during Ag electrodeposition, it was shown, for the first time in this DES, that this process occurs via multiple 3D nucleation with diffusion-controlled growth and valuable practical information i.e. the diffusion coefficient of Ag(I) ions in this media was quantified. From scanning electron microscopy images and energy-dispersive X-ray spectroscopy, the morphology and composition of the resulting deposits were characterized.
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