Adsorption of Oil onto API-X100 Pipeline Steel in CO2-Saturated Solutions

This research explores the validity of Langmuir adsorption theorem in analyzing the natural corrosion inhibition by an aromatic C₁₀H₁₂ compound, in a hydrocarbon fuel, in 1-bar CO₂-saturated solutions. The adsorption isotherms were constructed from the efficiencies of inhibition, by 10, 20, and 30 vol pct of the fuel, of the corrosion rates calculated from potentiodynamic polarization measurements, in 2 NaCl g/L solutions at 293 K, 323 K, and 353 K (20 °C, 50 °C, and 80 °C). The corrosion rates increased with temperature, and the hydrocarbon fuel, seemingly showing cathodic-inhibition characteristics, acted less efficiently accordingly; two main results the potentiodynamic polarization, electrochemical impedance spectroscopy and open-circuit measurements, demonstrated agreement on with each other.     

Effects of Alloying Elements on the Thermal Stability and Corrosion Resistance of an Fe-based Metallic Glass with Low Glass Transition Temperature

The effects of alloying elements on the thermal stability, glass-forming ability (GFA), corrosion resistance, and magnetic and mechanical properties of a soft magnetic Fe₇₅P₁₀C₁₀B₅ metallic glass with a low glass transition temperature (T _g) of 723 K (450°C) were investigated. The addition of Mo, Ni, and Co significantly increased the stabilization of supercooled liquid, GFA, and corrosion resistance in the H₂SO₄ solution. The maximum critical diameter (d _c) of 4 mm for glass formation was obtained for the Fe₅₅Co₁₀Ni₅Mo₅P₁₀C₁₀B₅ alloy, which shows the largest supercooled liquid region (ΔT _x ) of 89 K (89 °C). The substitution of Cr for Mo further enhanced the corrosion resistance of the Fe₅₅Co₁₀Ni₅Mo₅P₁₀C₁₀B₅, while the ΔT _x and d _c decreased. The (Fe, Ni, Co)₇₀(Mo, Cr)₅P₁₀C₁₀B₅ bulk metallic glasses showed low T _g of 711 K to 735 K (438 °C to 462 °C), wide ΔT _x of 67 K to 89 K, high saturation magnetization of 0.79 to 0.93 T, low coercive force of 2.36 to 6.61 A m^?1, high compressive yield strength of 3271 to 3370 MPa, and plastic strain of 0.8 to 2.3 pct. In addition, the mechanism for enhancing stability of supercooled liquid was discussed in terms of the precipitated phases during crystallization.     

Hot Corrosion Behaviour of Detonation-Gun Sprayed Cr3C2–NiCr Coating on Inconel-718 in Molten Salt Environment at 900 °C

Detonation gun sprayed Cr₃C₂–NiCr coating was deposited on nickel-based superalloy Inconel-718. Hot corrosion studies were conducted on uncoated as well as Cr₃C₂–NiCr coated superalloy in 75 wt% Na₂SO₄ + 25 wt% NaCl salt environment at 900 °C for 50 cycles. The thermo-gravimetric technique was used to establish kinetics of corrosion. X-ray diffraction and scanning electron microscopy/energy-dispersive X-ray analysis techniques were used to analyze the corrosion products. The uncoated superalloy suffered intense spalling, while the Cr₃C₂–NiCr coating provided good protection against hot corrosion in the given salt environment.     

Solubility of Chromium(III) Oxide in the Molten Cryolite System

The solubility of Cr(III) species originating from dissolution of Cr₂O₃ in cryolite-based melts was studied in the temperature range 1173 K to 1293 K (900 °C to 1020 °C). The molar ratio n(NaF)/n(AlF₃) was in the range of 1.4 to 2.6. It was found that the solubility depends markedly on the molar ratio n(NaF)/n(AlF₃), high ratios resulting in higher solubility. A semi-empirical model describing the solubility of Cr₂O₃ was developed. The standard deviation between calculated and experimental data is 10 pm (ca 2.4 pct).     

Corrosion Behavior of Alloy 625 in PbSO4-Pb3O4-PbCl2-ZnO-10?Wt?Pct CdO Molten Salt Medium

Corrosion behavior and degradation mechanisms of alloy 625 under a 47.288 PbSO₄-12.776 Pb₃O₄-6.844PbCl₂-23.108ZnO-10CdO (wt pct) molten salt mixture under air atmosphere were studied at 873?K, 973?K, and 1073?K (600?°C, 700?°C, and 800?°C). Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurements, and potentiodynamic polarization techniques were used to evaluate the degradation mechanisms and characterize the corrosion behavior of the alloy. Morphology, chemical composition, and phase structure of the corrosion products and surface layers of the corroded specimens were studied by scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) and X-ray map analyses. Results confirmed that during the exposure of alloy 625 to the molten salt, chromium was mainly dissolved through an active oxidation process as CrO₃, Cr₂O₃, and CrNbO₄, while nickel dissolved only as NiO in the system. Formation of a porous and nonprotective oxide layer with low resistance is responsible for the weak protective properties of the barrier layer at high temperatures of 973?K and 1073?K (700?°C and 800?°C). There were two kinds of attack for INCONEL 625, including general surface corrosion and pitting. Pitting corrosion occurred due to the breakdown of the initial oxide layer by molten salt dissolution of the oxide or oxide cracking.     

Effects of Phosphorus and Carbon Contents on Amorphous Forming Ability in Fe-based Amorphous Alloys Used for Thermal Spray Coatings

Cost-effective Fe-based amorphous alloys used for thermal spray coatings were developed by varying contents of P and C, and their microstructure, hardness, and corrosion resistance were analyzed. In order to achieve chemical compositions having high amorphous forming ability, thermodynamically calculated phase diagrams of Fe-Al-P-C-B five-component system were used, from which compositions of super-cooled liquid having the lowest driving force of formation of crystalline phases were obtained. The thermodynamic calculation results showed that only phases of Fe₃P and Fe₃C were formed in the Fe₇₈Al₂P_(18.3?x)C _x B_1.7 alloy system. Considering driving force curves of Fe₃P and Fe₃C, the carbon contents were selected to be 6.90 and 7.47 at. pct, when the thermodynamic calculation temperatures were 697 K (414 °C) and 715 K (442 °C), respectively. According to the microstructural analysis of suction-cast alloys, the Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed a fully amorphous microstructure, whereas the Fe₇₈Al₂P_11.40C_6.9B_1.7 and Fe₇₈Al₂P_10.3C_8.0B_1.7 alloys contained Fe₃P and Fe₃C phases. This Fe₇₈Al₂P_10.83C_7.47B_1.7 alloy showed the better hardness and corrosion resistance than those of conventional thermal spray coating alloys, and its production cost could be lowered using cheaper alloying elements, thereby leading to the practical application to amorphous thermal spray coatings.     

Processing and Consolidation of Nanocrystalline Cu-Zn-Ti-Fe-Cr High-Entropy Alloys via Mechanical Alloying

In the current investigation, nanocrystalline multicomponent high-entropy alloys (HEAs) have been synthesized in the Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ system (x/y = 1/0, 3/1, 1; and x + y = 40) by mechanical alloying and subsequently consolidated using spark plasma sintering (SPS) in argon atmosphere at a pressure of 50 MPa. A detailed X-ray diffraction and transmission electron microscopy study reveals the presence of both FCC copper solid-solution, (Cu)_ss and BCC chromium solid-solution, (Cr)_ss phases in both the mechanically alloyed powders as well as the sintered compacts. The phase formation and stability of the sintered multicomponent Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ with x/y = 3/1 and x + y = 40 pellet have been studied at different sintering temperatures, i.e., 873 K, 973 K, 1073 K, and 1173 K (600 °C, 700 °C, 800 °C, and 900 °C). The important findings include that high Vickers bulk hardness of around 6 GPa and relative density of around 95 pct reported in the Cu _x Zn _y Ti₂₀Fe₂₀Cr₂₀ with x/y = 3/1 and x + y = 40 HEAs, SPSed at 1173 K (900 °C). The formation, consolidation, and microstructural details are analyzed critically and discussed.     

A Novel Bonding Method of Pure Aluminum and SUS304 Stainless Steel Using Barrel Nitriding

A great deal of research is being carried out on welding or bonding methods between iron and aluminum. However, it is not so easy to make Fe-Al bonding materials with both high strength and light weight. Recently, a new nitriding process has been proposed to produce aluminum nitride on an aluminum surface using a barrel. This study proposes a new concept in the production of a multilayer which has an AlN and Fe-Al intermetallic compound layer between the aluminum and steel using a barrel nitriding process. The bonding process was carried out from 893 K to 913 K (620 °C to 640 °C) for 18, 25.2, and 36 ks with Al₂O₃ powder and Al-Mg alloy powder. After the process, an aluminum nitride (AlN) layer and a Fe-Al intermetallic compound (Fe₂Al_5.4) layer were formed at the interface between the pure aluminum and SUS304 austenitic stainless steel. The thicknesses of the AlN layer and the intermetallic compound layer increased with increasing treatment temperature and time. The maximum hardnesses of the AlN layer and Fe₂Al_5.4 layers were found to be 377HV and 910HV, respectively, after barrel nitriding at 893 K (620 °C) for 18 ks.     

Oxidation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Scale-Forming MAX Phases in Turbine Environments

High temperature oxidation of alumina-forming MAX phases, Ti₂AlC and Cr₂AlC, were examined under turbine engine environments and coating configurations. Thermogravimetric furnace tests of Ti₂AlC showed a rapid initial transient due to non-protective TiO₂ growth. Subsequent well-behaved cubic kinetics for alumina scale growth were shown from 1273 K to 1673 K (1000 °C to 1400 °C). These possessed an activation energy of 335 kJ/mol, consistent with estimates of grain boundary diffusivity of oxygen (~375 kJ/mol). The durability of Ti₂AlC under combustion conditions was demonstrated by high pressure burner rig testing at 1373 K to 1573 K (1100 °C to 1300 °C). Here good stability and cubic kinetics also applied, but produced lower weight gains due to volatile TiO(OH)₂ formation in water vapor combustion gas. Excellent thermal stability was also shown for yttria-stabilized zirconia thermal barrier coatings deposited on Ti₂AlC substrates in 2500-hour furnace tests at 1373 K to 1573 K (1100 °C to 1300 °C). These sustained a record 35 µm of scale as compared to 7 μm observed at failure for typical superalloy systems. In contrast, scale and TBC spallation became prevalent on Cr₂AlC substrates above 1423 K (1150 °C). Cr₂AlC diffusion couples with superalloys exhibited good long-term mechanical/oxidative stability at 1073 K (800 °C), as would be needed for corrosion-resistant coatings. However, diffusion zones containing a NiAl-Cr₇C₃ matrix with MC and M₃B₂ particulates were commonly formed and became extensive at 1423 K (1150 °C).     

Effect of Thermal Aging on Ductile-Brittle Transition Temperature of Modified 9Cr-1Mo Steel Evaluated with Reference Temperature Approach Under Dynamic Loading Condition

The effect of thermal aging on the ductile-brittle transition behavior has been assessed for a modified 9Cr-1Mo steel (P91) using the reference temperature approach under dynamic loading condition (T ₀ ^dy ). The steel in normalized and tempered (NT) condition and in different levels of subsequent cold work (CW) was subjected to thermal aging at temperatures of 873 K and 923 K (600 °C and 650 °C) for 5000 and 10,000 hours. For the NT and all the cold work conditions of the starting material, a drastic increase in T ₀ ^dy has been noticed after aging at 923 K (650 °C) for 10,000 h. A moderate increase was observed for the NT steel aged at 873 K (600 °C) for 5000 hours and for the 10 pct CW steel aged at 873 K (600 °C) for 10,000 h. A detailed transmission electron microscope (TEM) study of the embrittled materials aged at 923 K (650 °C)/10,000 hours and 873 K (600 °C)/10,000 hours has indicated presence of hexagonal Laves phase of Fe₂(Mo,Nb) type with different size and spatial distributions. The increase in the T ₀ ^dy is attributed to the embrittling effect of a network of Laves phase precipitates along the grain boundaries.     

Surface Hardening of Powder Injection Molded 316L Stainless Steels Through Low-Temperature Carburization

The surface hardness of powder injection molded (PIM) 316L is generally low due to the inherited austenitic structure and large grains induced during high-temperature sintering. To increase the surface hardness and the wear resistance, low-temperature carburization (LTC) was applied to PIM 316L. With carburization at 773 K (500 °C) for 24 hours, the resulting hardness at the surface increases from 160 to 810 HV due to the “colossal” supersaturation of interstitial carbon and M₅C₂ carbide, and the corrosion resistance is not deteriorated. The carburized depth is about 40 μm, and the carbon content in this layer is about 3.25 wt pct or 13.5 at. pct, which causes lattice expansion of the austenite. When the carburization temperature increases to 823 K (550 °C), or the carburization time increases to 72 hours, chromium carbides are observed and the corrosion resistance is impaired. One distinct advantage of applying LTC to PIM 316L is that no acid cleaning process is required, unlike for wrought counterparts, because of the clean surface of the sintered materials.     

Thermodynamic modeling of chemical reactions in the heating of stainless steel H18N15 with Cr2C3, MoS2, and carbon additions in a hydrogen atmosphere

A thermodynamic modeling of the chemical reactions occurring during the heating of H18N35 stainless steel with Cr₃C₂, MoS₂ and C additions in a hydrogen atmosphere at the 1000–1800 K temperature interval has been conducted. The formation of CrS, MoS₂, Cr₇C₂, and the (Cr_0.66Fe_0.34)_2.52C double carbide with the emission of H₂S, CH₄, C₂H₂, and the components of the steel into the gaseous phase at 1600 K (or above) has been detected. The results of the thermodynamic modeling are confirmed by the experimental data. Translated from Poroshkovaya Metallurgiya, Nos. 1–2(411), pp. 67–71, January–February, 2000.     

Role of Silicon Carbide in Phase-Evolution and Oxidation Behaviors of Pulse Electrodeposited Nickel-Tungsten Coating

Silicon carbide (SiC) was reinforced in the pulse electrodeposited nickel-tungsten (Ni-W) coatings deposited on the steel substrate, and isothermal oxidation test was performed at 1273 K (1000 °C) for 24 hours. Addition of just 2 vol pct of SiC showed 26 pct increase in the relative oxidation resistance of Ni-W coating. The increased oxidation resistance was attributed to the phase evolution (SiO₂, Cr₂O₃, CrSi₂, Ni₂SiO₄, Cr₇C₃, Cr₃C₂, and Cr₃Si), which suppressed the spallation of the oxide scale in Ni-W-2 vol pct SiC. The presence of Fe₂O₃ phase in the oxidized Ni-W coating was mainly responsible for the major multiple spallations at the interface and in the bulk, which resulted in the degradation of oxidation resistance.

     

Optimization of Mold Flux for the Continuous Casting of Cr-Contained Steels

To compensate the negative effect caused by the absorption of chromium oxide inclusions during the casting process of Cr-contained steels, a new mold flux system has been designed and investigated. The melting temperature range of the newly designed mold flux system is from [1124 K to 1395 K (851 °C to 1122 °C)]. The viscosity at 1573 K (1300 °C) and the break temperature increase with the addition of MnO and Cr₂O₃ but decrease with the addition of B₂O₃. The crystalline fraction of mold flux decreases from 81 to 42.1 pct with the addition of MnO and Cr₂O₃, and then further decreases to 25.3 pct with the addition of B₂O₃; however, it improves from 54.4 to 81.5 pct when the basicity increases. Besides, the heat-transfer ability of mold flux is inverse to the crystallization ratio of the slag. The comprehensive study of the properties for the four designed mold fluxes suggests that the mold flux with 1.15 basicity-3.01 pct B₂O₃-1.10 pct MnO-2.10 pct Cr₂O₃ shows the best properties for the continuous casting of Cr-contained steels.     

Host Atom Diffusion in Ternary Fe-Cr-Al Alloys

In the Fe-rich corner of the Fe-Cr-Al ternary phase diagram, both interdiffusion experiments [1048 K to 1573 K (775 °C to 1300 °C)] and ⁵⁸Fe tracer diffusion experiments [873 K to 1123 K (600 °C to 850 °C)] were performed along the Fe₅₀Cr₅₀-Fe₅₀Al₅₀ section. For the evaluation of the interdiffusion data, a theoretical model was used which directly yields the individual self-diffusion coefficients of the three constituents and the shift of the original interface of the diffusion couple through inverse modeling. The driving chemical potential gradients were derived using a phenomenological Gibbs energy function which was based on thoroughly assessed thermodynamic data. From the comparison of the individual self-diffusivities of Fe as obtained from interdiffusion profiles and independent ⁵⁸Fe tracer diffusivities, the influence of the B2-A2 order–disorder transition becomes obvious, resulting in a slightly higher activation enthalpy for the bcc-B2 phase and a significantly lower activation entropy for this phase.     

Influence of Gas Atmosphere Dew Point on the Selective Oxidation and the Reactive Wetting During Hot Dip Galvanizing of CMnSi TRIP Steel

The selective oxidation and reactive wetting of intercritically annealed Si-bearing CMnSi transformation-induced plasticity steels were investigated by high-resolution transmission electron microscopy. In a N₂ + 10 pct H₂ gas atmosphere with a dew point (DP) ranging from 213 K to 278 K (?60 °C to 5 °C), a continuous layer of selective oxides was formed on the surface. Annealing in a higher DP gas atmosphere resulted in a thinner layer of external oxidation and a greater depth of internal oxidation. The hot dipping was carried out in a Zn bath containing 0.22 mass pct Al, and the bath temperature was 733 K (460 °C). Coarse and discontinuous Fe₂Al_5?x Zn _x grains and Fe-Zn intermetallics (?? and ??) were observed at the steel/coating interface after the hot dip galvanizing (HDG) of panels were annealed in a low DP atmosphere 213 K (?60 °C). The Fe-Zn intermetallics were formed both in areas where the Fe₂Al_5?x Zn _x inhibition layer had not been formed and on top of non-stoichiometric Fe-Al-Zn crystals. Poor wetting was observed on panels annealed in a low DP atmosphere because of the formation of thick film-type oxides on the surface. After annealing in higher DP gas atmospheres, i.e., 263 K and 278 K (?10 °C and 5 °C), a continuous and fine-grained Fe₂Al_5?x Zn _x layer was formed. No Fe-Zn intermetallics were formed. The small grain size of the inhibition layer was attributed to the nucleation of the Fe₂Al_5?x Zn _x grains on small ferrite sub-surface grains and the presence of granular surface oxides. A high DP atmosphere can therefore significantly contribute to the decrease of Zn-coating defects on CMnSi TRIP steels processed in HDG lines.     

Precipitation Kinetics in a Nb-stabilized Ferritic Stainless Steel

The precipitation occurring in a Nb-stabilized ferritic stainless steel, containing initially Nb(C, N) carbonitrides and Fe₃Nb₃X precipitates, was investigated during aging treatments performed between 923 K and 1163 K (650 °C and 890 °C) by combining different techniques, (thermoelectric power (TEP), scanning/transmission electron microscopy (SEM/TEM), and atom probe tomography (APT)), in order to determine the precipitation kinetics, the nature and morphology of the newly formed precipitates as well as the chemistry of the initial Fe₃Nb₃X precipitates, where X stands for C or N. The following composition was proposed for these precipitates: (Fe_0.81 Cr_0.19)₃ (Nb_0.85 Si_0.08 Mo_0.07)₃ (N_0.8 C_0.2), highlighting the simultaneous presence of N and C in the precipitates. With regard to the precipitation in the investigated temperature range, two main phenomena, associated with a hardness decrease, were clearly identified: (i) the precipitation of Fe₂Nb precipitates from the niobium initially present in solution or coming from the progressive dissolution of the Fe₃Nb₃X precipitates and (ii) the precipitation of the χ-phase at grain boundaries for longer aging times. From the TEP kinetics, a time–temperature–precipitation diagram has been proposed.     

Effects of the Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Content on the Viscosity of CaO-SiO<Subscript>2</Subscript>-10 Pct Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> Quaternary Slag

The present study experimentally investigates the effect of Cr₂O₃ on the viscosity of molten slags. The viscosities of CaO-SiO₂-10 pct Al₂O₃-Cr₂O₃ quaternary slags with two different binary basicities (R, basic slag with R = 1.2 and acidic slag with R = 0.8) were measured by the rotating cylindrical method from 1813 K to 1953 K (1540 °C to 1680 °C). The results showed that the viscosity of both types of slag decreased as the Cr₂O₃ content increased, but the viscosity of acidic slags exhibited a greater decrease. The slags showed good Newtonian behavior at such high temperatures. Cr₂O₃ could act as a network modifier to simplify the Si-O-Si tetrahedral structure, as verified by the Raman spectral analysis, which was consistent with the decreasing trend of viscosity. The activation energy of viscous flow decreased slightly with increasing Cr₂O₃, but increasing the basicity seemed to be more effective in decreasing the viscosity than adding Cr₂O₃.     

Microstructure and Properties of Fe–Cr–B–Al Alloy After Heat Treatment

By means of optical microscope, scanning electron microscope, X-ray diffraction, energy dispersive spectrometer, Rockwell and Vickers hardness tester, and wear tester, the microstructure and properties of Fe–10Cr–1B–4Al alloy quenched in different temperature has been studied. The results show that the microstructure of as-cast Fe–10Cr–1B–4Al are composed of pearlite, ferrite and the eutectic borocarbide which shows a network distribution along grain boundaries. The eutectic borocarbides are composed of M₇(C, B)₃, M₂(B, C) and M₂₃(C, B)₆. As the quenching temperature increases, the network structure of eutectic borocarbide breaks, but the type of eutectic borocarbide has no obvious change, and the matrix structure changes gradually from ferrite to pearlite. As the quenching temperature increases, the macro-hardness and the matrix micro-hardness of Fe–10Cr–1B–4Al alloy increases gradually. The macro-hardness and matrix micro-hardness of alloy reach the highest value of 45.7 HRC and 388.1 HV, respectively when the quenching temperature is 1150 °C. The hardness of alloy decreases slightly when the quenching temperature is too high. While quenching at 1150 °C, the alloy has the highest wear resistance and good comprehensive properties.     

Dry Sliding Wear Behavior of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si Alloy

Dry sliding wear tests were performed for Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy against AISI 52100 steel under the loads of 50 to 250 N at 298 K to 873 K (25 °C to 600 °C). The wear behavior of the alloy varied with the change of test conditions. More or less tribo-oxides TiO₂ and Fe₂O₃ formed on worn surfaces under various conditions. At lower temperature [298 K to 473 K (25 °C to 200 °C)], less and scattered tribo-oxide layers did not show wear-reduced effect. As more number of and continuous tribo-oxide layers appeared at higher temperatures [773 K to 873 K (500 °C to 600 °C)], the wear rate would be substantially reduced. It can be suggested that Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy possessed excellent wear resistance at 773 K to 873 K (500 °C to 600 °C). The wear-reduced effect of tribo-oxides seemed to depend on the appearance of Fe₂O₃ and the amount of tribo-oxides.