Inhibition Performance of Enhanced-Mo Inhibitor for Carbon Steel in 55% LiBr Solution

The inhibition performance of enhanced-Mo inhibitor for carbon steel in 55% LiBr solution was measured by means of chemical immersion,electrochemical measurements,and physical detection technologies.Results indicated that enhanced-Mo inhibitor showed excellent inhibition performance of carbon steel in 55% LiBr solution,especially at high temperature.With increasing the temperature of solution from 160 ℃ to 240 ℃,the corrosion rates of carbon steel increased from 17.67 μm/a to 33.07 μm/a.Enhanced-Mo inhibitor might improve the anodic polarization performance of carbon steel and widen the passive potential region of carbon steel in 55% LiBr solution.Enhanced-Mo inhibitor belongs to anodic inhibitor.In 55% LiBr solution,the relationship between corrosion current density icorr and corrosion potential Ecorr of carbon steel accorded with the equation lgicorr=-2.66-3.54Ecorr,and the value of cathodic Tafel constant βc for the H2 reaction was 282 mVSCE.When 55% LiBr solution contained enhanced-Mo inhibitor,a passive film comprising Fe3O4 and MoO2 was formed on the carbon steel surface by electrochemical reactions.The corrosion of carbon steel might be retarded by this protective film,and the anticorrosion performance of carbon steel in 55% LiBr solution might be improved by enhanced-Mo inhibitor.     

Inhibition Performance of EnhancedMo Inhibitor for Carbon Steel in 55% LiBr Solution

The inhibition performance of enhancedMo inhibitor for carbon steel in 55% LiBr solution was measured by means of chemical immersion, electrochemical measurements, and physical detection technologies. Results indicated that enhancedMo inhibitor showed excellent inhibition performance of carbon steel in 55% LiBr solution, especially at high temperature. With increasing the temperature of solution from 160 ℃ to 240 ℃, the corrosion rates of carbon steel increased from 1767 μm/a to 3307 μm/a. EnhancedMo inhibitor might improve the anodic polarization performance of carbon steel and widen the passive potential region of carbon steel in 55% LiBr solution. EnhancedMo inhibitor belongs to anodic inhibitor. In 55% LiBr solution, the relationship between corrosion current density icorr and corrosion potential Ecorr of carbon steel accorded with the equation lgicorr=-266-354Ecorr, and the value of cathodic Tafel constant βc for the H2 reaction was 282 mVSCE. When 55% LiBr solution contained enhancedMo inhibitor, a passive film comprising Fe3O4 and MoO2 was formed on the carbon steel surface by electrochemical reactions. The corrosion of carbon steel might be retarded by this protective film, and the anticorrosion performance of carbon steel in 55% LiBr solution might be improved by enhancedMo inhibitor.     

Effect of Nb Solute and NbC Precipitates on Dynamic or Static Recrystallization in Nb Steels

 Nb is often considered to be a powerful alloying element for controlling the recrystallization process in microalloyed high strength steels. However, Nb can be presented either as solute in solution, where it is thought to exhibit a strong solute drag effect, or as NbC precipitates, which are thought to be effective at pinning grain boundaries. Therefore, it is very important to quantitatively measure Nb in solution or in NbC precipitates. A quantitative analysis method of Nb in solution and in precipitates was proposed. The test procedure involved chemical dissolution, filtration and inductively coupled plasma atomic emission spectroscopic (ICP-AES) analysis. The amount of Nb in solution in Nb-microallyed steels under different treatment conditions was evaluated. The results show that the niobium and carbon contents in steels have a great effect on niobium dissolution kinetics. The solute Nb is more effective to retard dynamic recrystallization, while the NbC precipitates are more effective to inhibit static recrystallization. The results may help to comprehend effect of Nb in steels, and provide some guides in the design of new high strength Nb-bearing steels.     

Interstitial Solution Carbon Concentration and Defects of Ti+Nb ULC-BH Steel by Internal Friction and Positron Annihilation Methods

The interstitial solution carbon concentration and defects in continuously annealed Ti+Nb bearing ULCBH(ultra-low carbon bake hardening)steel samples are investigated by multi-functional internal friction apparatus, positron annihilation lifetime spectroscopy(PALS)and coincidence Doppler broadening spectroscopy(CDBS).The relationship of internal friction peaks,interstitial solution carbon concentrations and movable dislocations in the samples under different conditions is analyzed.A correlation of lifetime componentτ1 values with interstitial solution carbon concentrations in the samples for different continuous annealing processes is established,while a correlation of lifetime componentτ2 values with multi-vacancies,vacancy clusters,microvoids and other types of defects for various continuous annealing processes is also demonstrated.Furthermore,the average lifetime results illustrate the overall defect densities for various continuous annealing processes.The CDBS analysis reflects the chemical surroundings of the defects at the annihilation sites and reveals that the peak heights of the ratio curves relate to the total number of defects such as interstitial carbon atoms,dislocations,vacancies and other types of defects.The results show that internal friction,PALS and CDBS are effective techniques to identify and characterize the interstitial solution carbon concentration,multi-vacancies,vacancy clusters,microvoids and other types of microscopic defects in annealed Ti+ Nb bearing ULC-BH steel.     

Morphological Changes During Annealing of Electrodeposited Ni-Cr Coating on Steel and Their Effect on Corrosion in 3% of NaCl Solution

 Steel containing carbon of 02% was coated with Ni and Cr through electrodeposition, and subsequently annealed at 400 and 600 ℃ for 5 min, 30 min, 1 h and 2 h. During annealing at 400 ℃, the formation and growth of oxides occurred in the form of petals along with voids, cracks and porosities. However, at 600 ℃, the nucleation and growth of chromium oxide whiskers produced a surface almost free from crack, porosity and void for 1 h and 2 h of holding. In accordance with the surface morphology, the bare steel, as-deposited steel, all specimens deposited and annealed at 400 ℃, and specimens deposited and annealed at 600 ℃ for 5 and 30 min exhibited continuous corrosion in 3% of NaCl solution. However, the specimens deposited and annealed at 600 ℃ for 1 and 2 h exhibited an improved corrosion resistance in 3% of NaCl solution with high pitting potential due to presence of a dense passive oxide film almost free from voids at the surface.     

Wetting of molten cerium on typical carbon materials(graphite,CVD-diamond and NWCNT) and molten Cu-Ce alloys on graphite at 950℃

A series of experiments were conducted to investigate the wettability of graphite plate,graphite paper,NWCNTs Buckypaper,CVD-diamond by molten Ce and graphite plate by Cu-Ce binary alloy using a modified sessile drop method at 950℃.The remarkable apparent equilibrium contact angles(graphite plate(0°) graphite paper(18°) CVD-diamond(24°) NWCNT(62°)) were obtained in the Ce/carbon system.When Ce concentration in Cu-Ce/graphite is above 20 at%,the wettability of graphite plate can be improved significantly.As a result,the dissolution of graphite into Ce makes infiltrated process proceeded easily due to the decrease of surface tension of liquid,which is different from Ce/graphite paper.In Ce/CVD diamond system,the dissolution of diamond layer and the decomposition reaction of WC lead to the good wettability.A relatively higher contact angle is caused by high stability of carbon wall in Ce/NWCNT system.The reaction product at interface and the decrease of surface tension due to surface tension-active character of Ce together induce the improved wettability.     

Extraction of scandium from red mud by acid leaching with CaF_2 and solvent extraction with P507

The extraction of Sc by acid leaching with CaF_2 and solvent extraction with P507 from red mud was proposed.The influence of acid leaching and solvent extraction on recovery of Sc was investigated.The CaF_2 can obviously improve the leaching efficiency of Sc and reduce the acid consumption.The leaching efficiency of Sc increases from 74% to 92% and the dosage of acid reduces under suitable conditions by adding 5% CaF_2.The minerals in red mud can easily be decomposed and leached into the acid solution with CaF_2 through analysis of XRD pattern.The particles of red mud become smaller and multihole.The Sc can be selectively extracted with 10% P507 at the pH value of 0.1 from the acid leaching solution.More than 98% of Sc and less than 10% of Al and Fe are extracted.The SC_2O_3 with purity of 99% is obtained after the process of reverse extraction with NaOH,H_2SO_4 dissolution,precipitation by oxalic acid and roasting at 750℃.     

Effect of Solute Drag and Precipitate Pinning on Austenite Grain Growth in Ti-Nb Microalloyed Steels

A metallurgical model concerning the co-effect of the Nb solute drag and the complex carbonitride precipitates pinning is proposed to predict the recrystallization austenite grain growth of low carbon Nb-containing microalloyed steels.The analysis,both predicted and experimental,reveals the precipitate pinning plays a dominate role in suppressing the austenite grain growth with less Nb solute drag effect in high temperature region whereas the Nb solute drag predominates in relatively low temperature region.A factor p is suggested to assess the effectiveness of drag and pinning.The pinning and the drag are more effective in restraining grain growth as p>0 and p<0,respectively.A low carbon Nb microalloyed steel and a kind of Ti-modified low carbon Nb steel by Ti substituting for part of Nb are employed to validate the modeling results.The theoretical calculations show a good agreement with experimental results.     

Analysis of Valence Electron Structure of RE in Solid Solution in Medium and Low Carbon Steel

According to EET theory, the valence electron structures of RE in the solid solution of austenite, pearlite and martensite were calculated. The influence of RE in solid solution on phase transformation of pearlite and recrystallization of martensite was explained by the valence electron structure data of phases. Calculating results indicate that C element is favorite to enhance the number of RE in the solid solution. RE in the solute solution shortens the incubation period of proeutectoid ferrite, increases its quantity and carbon content, decreases the quantity of pearlite and thickness of its lamellas and lamellar spacing, then the strength and hardness of pearlite are improved and granular pearlite can be obtained. RE dissolved in martensite intensifies martensite, enhances tempering stability of martensite, increases its recrystallization temperature and prolongs the holding time needed during tempering.     

Effects of Cu on Corrosion Resistance of Low Alloyed Steels in Acid Chloride Media

The corrosion resistance of two kinds of low alloyed steels was studied according to the test procedures for qualification of corrosion resistant steel for cargo oil tanks issued by International Maritime Organization.The results indicated that the addition of Cu improved the corrosion resistance of the NS-D36 steel to more than three times that of the conventional D36 steel in the strong acid solution containing chloride(10% NaCl,pH=0.85).The anodic polarization behavior of the copper-bearing steel was studied by polarization curves and electrochemical impedance spectroscopy(EIS),and alloying element Cu showed beneficial effects including an active potential range,low current density and high transfer resistance of electric charge.The rust layer was analyzed by scanning electron microscopy(SEM)and Auger electron spectroscopy(AES),and the results pointed out that the mechanism of copper′s beneficial effects was based on the suppression of anodic dissolution by metallic copper re-deposition on the steel surface immersed in the strong acid chloride media.     

Effect of Compositional Variation on the Microstructural Evolution and the Castability of Al–Mg–Si Ternary Alloys

This study examined the microstructural evolution and castability of Al–Mg–Si ternary alloys with varying Si contents. Al–6Mg–xSi alloys (where x = 0, 1, 3, 5, and 7; all compositions in mass pct) were examined, with Al–6 mass pct Mg as a base alloy. The results showed that in the ternary alloys with Si ≤ 3 pct, the solidification process ended with the formation of eutectic α-Al–Mg₂Si phases generated by a univariant reaction. However, in the case of ternary alloys with Si > 3 pct, solidification was completed with the formation of α-Al–Mg₂Si–Si ternary eutectic phases generated by a three-phase invariant reaction. In addition to the eutectic Mg₂Si phases, the primary Mg₂Si phases formed in each of the ternary alloys, and the size of both sets of phases increased with increasing Si content. The two-phase eutectic α-Al–Mg₂Si nucleated from the primary Mg₂Si phases. The inoculated Al–6Mg–1Si alloy had the smallest grain size. Moreover, the grain-refining efficacy of the Al–5Ti–B master alloy in the ternary alloys decreased with increasing Si content in the alloys. Despite the poisoning effect of Si on the potency of TiB₂ compounds in the inoculated Al–6Mg–1Si alloy, the grain size of the alloy was slightly smaller than that of the Al–6Mg binary alloy. This resulted from the increasing growth restriction factor (induced by Si addition) of the Al–6Mg–1Si alloy. In terms of the castability, the examined alloys showed different levels of susceptibility to hot tearing. Among the alloys, the ternary Al–6Mg–5Si alloy exhibited the highest susceptibility to hot tearing, whereas the Al–6Mg–7Si exhibited the lowest. The severity of hot tearing initiated by the unraveling of the bifilm was determined by the freezing range, grain size, and the amount of eutectic phases at the end of the solidification process.

     

Kinetics of Reverse Transformation from Pearlite to Austenite in an Fe-0.6 Mass pct C Alloy and the Effects of Alloying Elements

Substitutional alloying effects on reversion kinetics from pearlite structure at 1073 K (800 °C) in an Fe-0.6 mass pct C binary alloy and Fe-0.6C-1 or 2 mass pct M (M = Mn, Si, Cr) ternary alloys were studied. Reverse transformation in the Fe-0.6C binary alloy at 1073 K (800 °C) was finished after holding for approximately 5.5 seconds. The reversion kinetics was accelerated slightly by the addition of Mn but retarded by the addition of Si or Cr. The difference of acceleration effects by the addition of the 1 and 2 mass pct Mn is small, whereas the retardation effect becomes more significant by increasing the amount of addition of Si or Cr. It is clarified from the thermodynamic viewpoint of carbon diffusion that austenite can grow without partitioning of Mn or Si in the Mn- or Si-added alloys. On the one hand, austenite growth is controlled by the carbon diffusion, whereas the addition of them affects carbon activity gradient, resulting in changes in reversion kinetics. On the other hand, thermodynamic calculation implies that the long-range diffusion of Cr is necessary for austenite growth in the Cr-added alloys. It is proposed that austenite growth from pearlite in the Cr-added alloys is controlled by the diffusion of Cr along austenite/pearlite interface.     

Interactions between SiC fibers and a titanium alloy during infrared liquid infiltration

The rapid interaction between SiC fibers (SCS-0) and a liquid titanium alloy has been investigated using an infrared processing technique. Experimental results revealed that disso-lution of the fibers in the alloy occurred within seconds without forming a continuous layer of reaction products at the interface. Thermodynamic analysis indicated that SiC is unstable in the presence of liquid titanium and dissociates into Si and C in the metal. With increasing carbon concentration, TiC will form when the carbon solubility limit in Ti is exceeded. The Ti-rich corner of the Ti-Si-C phase diagram with supercooled liquid Ti at 1300 °C was used to illustrate the tendency of TiC formation in this system. The fiber-matrix interface comprised two distinct morphologies: uniform dissolution fronts and scalloped dissolution fronts. The uniformly dis-solved domains are believed to be caused by an isothermal dissolution mechanism controlled by a zeroth-order chemical reaction, whereas the scalloped interfaces are believed to be caused by an accelerated dissolution mechanism resulting from localized heating. A model employing heat balance and reaction kinetics indicates that the conditions for accelerated dissolution are satisfied by the observed dissolution rates in the scalloped domains.     

Microstructural characterization of the dispersed phases in Al-Ce-Fe system

Analytical electron microscopy studies were conducted on a rapidly solidified Al-8.8Fe-3.7Ce alloy and arc melted buttons of aluminum rich Al-Fe-Ce alloys to determine the characteristics of the metastable and equilibrium phases. The rapidly solidified alloy consisted of binary and ternary metastable phases in the as-extruded condition. The binary metastable phase was identified to be Al₆Fe, while the ternary metastable phases were identified to be Al₁₀Fe₂Ce and Al₂₀Fe₅Ce. The Al₂₀Fe₅Ce was a decagonal quasicrystal while the Al₁₀Fe₂Ce phase was determined to have an orthorhombic crystal structure belonging to space group Cmmm, Cmm2, or C222. Microscopy studies of RS alloy and cast buttons annealed at 700 K established the equilibrium phases to be Al₁₃Fe₄, Al₄Ce, and an Al₁₃Fe₃Ce ternary phase which was first identified in the present study. The crystal structure of the equilibrium ternary phase was determined to be orthorhombic with a Cmcm or Cmc2 space group. The details of X-ray microanalysis and convergent beam electron diffraction analysis are described.     

Interface characterization of ceramic fiber-reinforced ti alloy composites manufactured by infrared processing

Interfacial reactions between several ceramic fibers (SCS-0, SCS-6, and carbon fibers) and a liquid titanium-nickel-copper alloy were investigated using electron microscopic analysis. Composite spec-imens were produced using a rapid infrared manufacturing (RIM) process. In SCS-O/Ti alloy com-posites, SiC dissolved in the alloy. The main reaction product was discontinuous agglomerates of titanium carbide which formed from the reaction between dissolved carbon and titanium. Polygonal precipitates of Ti₅Si₃, which are believed to have formed during cooling, were also noticed. Two distinct interface morphologies were observed in these composites: uniform fronts caused by iso-thermal dissolution and scalloped fronts formed as a result of an accelerated dissolution mechanism caused by localized heating. The presence of the accelerated dissolution mechanism suggests that SiC fibers cannot be infiltrated with liquid titanium alloys without applying a coating. In the C/Ti system, carbon fibers reacted with the liquid alloy to form a continuous layer of Ti_xC_1-x. Further growth of this layer occurred by the diffusion of carbon atoms across the reaction product. In SCS-6/Ti alloy composites, free carbon present in the coating formed a discontinuous layer of Ti^C,^, whereas SiC particles dissolved in the alloy. Due to channeled dissolution in the coating, the accel-erated dissolution mechanism was not observed in these composites. As a result, the presence of the carbon-rich coating prevented degradation of the fibers. Although the coating present on SCS-6 fibers moderately retarded reactions in the SiC/Ti alloy composite system during infrared liquid infiltration, it is recommended that the fibers be coated with pure carbon to effectively limit the attack of the fiber by molten titanium. Formaly Postdoctoral Fellow, Department of Materials Science and Engineering, University of Cincinnati     

Mechanism of Crack Propagation during Hot-Rolling Process of a Medium-Carbon 40Cr Alloy Steel

In this work, the mechanism of crack propagation during hot-rolling process of a typical medium-carbon 40Cr alloy steel is investigated by cracks characterization, thermodynamic calculation, and confocal laser scanning microscopy (CLSM). The depth of cracks is about 2.5 mm and its length along with rolling direction can even reach 2000–3000 mm. Thermodynamic calculations show that the oxide phases including MnSiO₃ and MnCr₂O₄ can generate when the oxygen content is 0.3–1.0 wt%, suggesting that low oxygen is beneficial to the selective oxidation of Si, Mn, and Cr elements from the medium-carbon low alloy. Furthermore, in situ experiment by CLSM indicates that the submicron Cr–Mn–Si–O particles can refine austenite grains. In addition, the contents of chain proeutectoid ferrite in the steel containing Cr–Mn–Si oxides increase by 6.3% and 12.0% at the lower cooling rates of 5 and 10 °C min⁻¹, respectively, comparing with that of no-oxide particles steel. The submicron Cr–Mn–Si–O particles can refine austenite grains, which induces the precipitation of chain proeutectoid ferrite. Thus, the serious surface cracks propagate along the chain proeutectoid ferrite with the submicron Cr–Mn–Si–O particles during the hot-rolling process.     

Characterization of dispersed intermetallic phases in rapidly quenched Al-Ti-Ce alloys

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly solidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure(a _o =1.44 ±0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence suggests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C. Formerly Research Fellow, Department of Materials Engineering, Monash University.     

Wetting behaviour in the Al-Si/SiC system: interface reactions and solubility effects

The sessile drop technique was used to study the wetting behaviour of Al-Si alloys on SiC sintered ceramic substrates under vacuum in the 700–1100°C temperature interval. Al-Si alloys with Si concentrations up to 50% were tested. An expected non-wetting/wetting transition was observed at 900–1000°C due to the presence of an alumina film surrounding the molten alloy. At higher temperatures wetting was observed and the Si concentration of the alloy has a marked effect on the measured contact angles, θ. At 1100°C θ decreases from 55° to 25° when instead of pure al and A112.3%Si or an A116.6%Si alloy is used. The suppression of the formation of a continuous Al₄C₃ layer at the interface and a process of dissolution and reconstruction of the SiC surface, due to the increased Si concentration of the Al-Si alloys, are the key factors to explain the observed behaviour.     

High temperature properties of Cu–Cr–Zr alloys processed by conventional inverse extrusion of atomised powders and comparison with Conform consolidated powders

Abstract

Water atomised Cu–Cr–Zr alloy powders were consolidated by inverse warm extrusion and by the commercial continuous rotary extrusion method, Conform. Those alloys consolidated by inverse warm extrusion exhibited enhanced mechanical properties compared with their respective Conform extruded counterparts, when tested at both room and elevated temperatures. The processing parameters adopted in the inverse extrusion experiments resulted in products which retained enough amounts of solutes in solid solution, which in turn, led to improved mechanical properties after aging. Conversely, the excessive adiabatic heat generated in the Conform machine eliminated the saturation effect produced by rapid solidification, negating any possible further improvement on the mechanical properties by aging. The mechanical properties of an inverse extruded Cu–2.8Cr–0.39Zr (at.-%) alloy at temperatures above 450°C were higher than those strengths reported for Cu–Be alloys and comparable to that of Cu–Ta and Cu–Nb composites. Therefore, rapidly solidified Cu–Cr–Zr alloys can be possible candidates for replacing such alloy systems for high temperature applications.     

Characterization of dispersed intermetallic

The microstructures of Al-3Ti-lCe (wt pct) and Al-5Ti-5Ce alloys melt-spun under controlled He atmosphere have been characterized using analytical electron microscopy. The rapidly so- lidified microstructures comprise uniform, fine-scale dispersions of intermetallic phase in an aluminum matrix, and particular attention has been given to identification of the dispersed phases. In the Al-3Ti-lCe alloy, the dispersed particles are polycrystalline with a complex twinned substructure and a diamond cubic crystal structure (α _o = 1.44 ± 0.01 nm) and composition consistent with the ternary compound Al₂₀Ti₂Ce (Al₁₈Cr₂Mg₃ structure type, space group Fd3m). In the Al-5Ti-5Ce alloy, there is, in addition to the dispersed ternary phase, a separate uniform array of fine-scale particles of the binary compound Al₁₁Ce₃. The majority of such particles have the body-centered orthorhombic structure of the low-temperature polymorph, α-Al₁₁Ce₃, but there is evidence to suggest that at least some particles developvia initial formation of the high-temperature body-centered tetragonal phase, β-Al₁₁Ce₃. The accumulated evidence sug- gests that both binary and ternary particles formed as primary phases directly from the melt during rapid solidification, leaving only small concentrations of solute in aluminum matrix solid solution. Both phases are observed to be resistant to coarsening for up to 240 hours at 400 °C. Formerly Research Fellow, Department of Materials Engineering,