Showing papers in "Acta Metallurgica Sinica (english Letters) in 2017"

A Review on Grain Refinement of Aluminum Alloys: Progresses, Challenges and Prospects

Abstract: Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging, building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry. Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows: grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.

Effects of Process Parameters of Semisolid Stirring on Microstructure of Mg–3Sn–1Mn–3SiC (wt%) Strip Processed by Rheo-rolling

Abstract: A novel semisolid stirring and rheo-rolling process for preparing Mg–3Sn–1Mn–3SiC (wt%) composite strips was proposed, and the effects of process parameters of semisolid stirring on microstructures of Mg–3Sn–1Mn–3SiC (wt%) composite strips were investigated The average grain size and roundness decrease, and the distribution of SiC becomes more homogeneous with the decrease in stirring temperature and the increase in the stirring speed When the stirring time is increased, the distribution of SiC particles tends to be homogeneous, and the average grain diameter and roundness of α-Mg grain decrease Under the following process parameters: the stirring temperature at 640 °C, the stirring speed at 1100 rpm, the stirring time at 30 min and the roll speed at 02 m/s, Mg–3Sn–1Mn–3SiC (wt%) strip with a cross-sectional size of 4 mm × 160 mm was prepared The ultimate tensile strength and elongation of Mg–3Sn–1Mn–3SiC (wt%) composite strip reached 226 ± 6 MPa and (74 ± 02)%, which are obviously improved in comparison with Mg–3Sn–1Mn (wt%)

Microstructure and Thermal Conductivity of Al-Graphene Composites Fabricated by Powder Metallurgy and Hot Rolling Techniques

Abstract: The objective of this research is to improve the thermal conductivity and mechanical properties of Al/GNPs (graphene nanoplatelets) nanocomposites produced by classical powder metallurgy and hot rolling techniques. The microstructural evaluation confirmed the uniform dispersion of GNPs at low content and agglomeration at higher contents of GNPs. The structure of graphene was studied before and after the mixing and the Raman spectrum proofs that the wet mixing has a great potential to be used as a dispersion method. There was no significant peak corresponding to the Al4C3 formation in both the differential scanning calorimetry curves and X-ray diffraction patterns. The microstructural observation in both fabrication techniques showed grain refinement as a function of the GNPs content. Moreover, the introduction of the GNPs not only improved the Vickers hardness of the composites but also decreased their density. The thermal conductivity investigations showed that in both the press-sintered and hot-rolled samples, although the thermal conductivity of composites was improved at low GNPs contents, it was negatively affected at high GNPs contents.

Localized Corrosion Characteristics of Nickel Alloys: A Review

Abstract: There are a great variety of commercial nickel alloys mainly because nickel is able to dissolve a large amount of alloying elements while maintaining a single ductile austenitic phase. Nickel alloys are generally designed for and used in highly aggressive environments, for example, those where stainless steels may experience pitting corrosion or environmentally assisted cracking. While nickel alloys are generally resistant to pitting corrosion in chloride-containing environments, they may be prone to crevice corrosion attack. Addition of chromium, molybdenum and tungsten increases the localized corrosion resistance of nickel alloys. This review on the resistance to localized corrosion of nickel alloys includes specific environments such as those present in oil and gas upstream operations, in the chemical process industry and in seawater service.

Solidification of Immiscible Alloys: A Review

Abstract: Immiscible alloys gained a considerable interest in last decades due to their valuable properties and potential applications. Many experimental and theoretical researches were carried out worldwide to investigate the solidification of immiscible alloys under the normal gravity and microgravity condition. The objective of this article is to review the research work in this field during the last few decades.

Microstructure, Mechanical Properties and Fracture Behavior of As-Extruded Zn–Mg Binary Alloys

Abstract: In the present work, Zn–(0–1)Mg (wt%) alloys were prepared by casting and indirect extrusion at 200 and 300 °C, respectively. With Mg addition, both the size and amount of second phase Mg2Zn11 increased, and the equiaxed grains were significantly refined. The extrusion temperature had little influence on Mg2Zn11, but the grains were refined at low extrusion temperature. For the alloys extruded at 200 °C, as Mg content increased, the tensile yield strength (TYS) increased from 64 MPa for pure Zn to 262 MPa for Zn–1Mg; the elongation increased from 14.3% for pure Zn to 25% for Zn–0.02Mg and then decreased to 5% for Zn–1Mg. For the alloys extruded at 300 °C, as Mg content increased, the TYS increased from 67 MPa for pure Zn to 252 MPa for Zn–1Mg, while the elongation decreased from 11.7% to 2%. The alloy extruded at 200 °C exhibited higher TYS and elongation than the corresponding alloy extruded at 300 °C. The combination of grain refinement and second phase Mg2Zn11 contributed to the improvement in the TYS, and the grain refinement played a major role in strengthening alloy. Zn–0.02Mg and Zn–0.05Mg alloys extruded at 200 °C show a mixture of cleavage and ductile fracture corresponding to higher elongation, while the other alloys show cleavage fracture.

Characterization of Prealloyed Ti–6Al–4V Powders from EIGA and PREP Process and Mechanical Properties of HIPed Powder Compacts

Abstract: Prealloyed Ti–6Al–4V powders were prepared by electrode induction melting gas atomization (EIGA) and plasma rotating electrode process (PREP) in this work. A comparative study of EIGA and PREP powders for hot isostatic pressing (HIPing) compaction was conducted. Characterization of important technological parameters such as particle size distribution, powder surface morphology and flowability was carried out. Microstructure and mechanical properties of Ti–6Al–4V powder compacts HIPed from EIGA and PREP powders were also investigated. The results showed that the EIGA powder has a finer average particle size and higher tap density, while the PREP powder has better flowability and less pores. Micropores can be observed in heat-treated EIGA powder compacts by X-ray tomography and the porosity was found to be about 0.02%. There are no micropores (≥4 μm) to be detected in heat-treated PREP powder compacts. Transgranular fracture mode as well as micropores contributes to the scatter in fatigue property of heat-treated PREP powder compacts. The respective advantages and disadvantages of both EIGA and PREP powders for producing Ti-based complex parts through HIPing were also discussed.

Influence of Pre-deformation on Aging Precipitation Behavior of Three Al–Cu–Li Alloys

Abstract: The influence of pre-deformation on aging precipitates of three near peak-aged Al–Cu–Li alloys, 1460 alloy with a low Cu/Li ratio (1.46), 2050 alloy with a high Cu/Li ratio (4.51) and 2A96 alloy with a medium Cu/Li ratio (2.97), was investigated. The strength of the aged alloys is enhanced by the pre-deformation. The effectiveness of pre-deformation on precipitates is dependent on the alloy’s composition. With increasing the pre-deformation, the population density of T1 (Al2CuLi) precipitates increases in all three Al–Cu–Li alloys and their diameter decreases in 2050 and 2A96 alloys, and the greatest effectiveness is observed in 2A96 alloy. The pre-deformation also increases the population density of θ′ (Al2Cu) precipitates and decreases their diameter in 2050 and 2A96 Al–Li alloys, but the effectiveness is smaller compared to that on T1 precipitates. In 1460 alloy subjected to two-step aging at 130 °C for 20 h followed by 160 °C for 12 h, the main precipitates are δ′ (Al3Li). At 2%–6% pre-deformation, GP-I zones form and pre-deformation displays little influence. Eight percentage pre-deformation promotes θ″/θ′ precipitation and increases their population density.

Thermal Characteristics, Mechanical Properties, In Vitro Degradation and Cytotoxicity of Novel Biodegradable Zn-Al-Mg and Zn-Al-Mg-xBi Alloys

Abstract: Ternary Zn–0.5Al–0.5Mg and quaternary Zn–0.5Al–0.5Mg–xBi (x = 0.1, 0.3 and 0.5) alloys were studied to evaluate the thermal and structural characteristics, mechanical properties, cytotoxicity and in vitro degradation behavior. Thermal analysis and microstructural observations showed that Zn–0.5Al–0.5Mg is composed of FCC-Al + HCP-Zn + Mg2(Zn,Al)11 while a new phase α-Mg3Bi2 appeared after the addition of Bi to the Zn–0.5Al–0.5Mg ternary alloy. The results revealed that the quaternary Zn–Al–Mg–Bi alloys have higher tensile strength, elongation and hardness but slightly lower corrosion resistance than those of the ternary Zn–Al–Mg alloy. Based on the MTT assay, the Zn–Al–Mg and Zn–Al–Mg–Bi alloys were found to be biocompatible, and thus, they can be considered for further investigation in an in vivo environment.

Tribological Characterization of Hybrid Metal Matrix Composites Processed by Powder Metallurgy

Abstract: Aluminum (Al)-based aluminum oxide (Al2O3) and silicon carbide (SiC) particles hybrid metal matrix composites were processed by powder metallurgy technique, followed by sintering at 500 °C and then hot extrusion. The tribological properties of these composites with different weight fractions of Al2O3 and SiC were investigated; extrusion process significantly reduces the extent of porosity after cold compaction and sintering processes. Hybridization of the two reinforcements improved hardness and wear resistance of the composites. With an increase in SiC content, hardness was increased and consequently the wear resistance was enhanced also. Scanning electron microscopy observations show a better interfacial bond between matrix and reinforcements and a better distribution of the reinforcements.

Effects of Ca Addition on the Mechanical Properties and Corrosion Behavior of ZM21 Wrought Alloys

Abstract: The microstructures, mechanical properties, and corrosion resistance of ZM21 magnesium alloys with a wide range of calcium (Ca) addition (0.1–1.6 wt%) were investigated. Results showed that the mechanical properties and corrosion resistance were improved with Ca addition because of grain refinement and formation of Ca2Mg6Zn3. However, these properties were deteriorated when Ca contents reached 1.6 wt%. The optimal Ca content of alloys was 0.7 wt%; alloy with this Ca content showed good mechanical performance and corrosion resistance, having a strength of 260 MPa, an elongation of 21.5%, and an average weight loss of 0.77 mg/(cm2 days).

Effect of Small Content of Chromium on Wet–Dry Acid Corrosion Behavior of Low Alloy Steel

Abstract: Effect of small content of chromium (Cr) on wet–dry acid corrosion behavior of low alloy steels has been investigated. The results show that the corrosion resistance of the steels increased with increasing Cr content from 0.10 to 0.50 wt%. Higher content of Cr promotes initial corrosion and accelerates the formation of dense and protective rust in long-term corrosion. The enhanced protectiveness of the rust is closely related to its composition. High content of Cr increases the content of amorphous phases and decreases the content of γ-FeOOH in the rust, resulting in the high compactness of the rust and low electrochemical activity in acid condition. Cr dopes in rust and depresses the transformation from amorphous phases to α-FeOOH, as well as the growth process of FeOOH particles, which is responsible for the enhanced compactness of rust in long-term corrosion.

Correlations of Ni Contents, Formation of Reversed Austenite and Toughness for Ni-Containing Cryogenic Steels

Abstract: It has been widely demonstrated that addition of Ni in low-carbon steels can effectively improve the cryogenic toughness, but the mechanism behind it has yet to be clarified. In the present work, the evolutions of microstructure and mechanical properties after quenching and tempering for Ni-containing cryogenic steels with different Ni contents (3.5–9 wt%) were investigated. The results showed that after quenching and tempering, the Ni-containing cryogenic steels were composed of tempered martensite and reversed austenite. The volume fraction of reversed austenite has increased from 0 up to 6.3% when the Ni content increases from 3.5% to 9%. The Charpy impact tests indicated that the low-temperature toughness was markedly improved with the increase in Ni content, which can be correlated with the increase in reversed austenite amount. The main contribution of reversed austenite to the toughness lies in: (1) the elimination of cementite precipitates improved the plastic deformation capacity of matrix, and (2) the crack propagation is hindered through plastic deformation.

Facile Synthesis, Characterization of Flower-Like Vanadium Pentoxide Powders and Their Photocatalytic Behavior

Abstract: In this paper, V2O5 sol was firstly prepared using vanadyl sulfate as a vanadium source by modified sol–gel method at room temperature. Then flower-like V2O5 powders were prepared by coagulating as-prepared sol with anhydrous ethanol and subsequent annealing crystallization. The X-ray diffraction analysis indicated that V2O5 powders exhibited orthorhombic crystal structure after annealing at 450 °C. The experimental data obtained from both field emission scanning electron microscopy and high-resolution transmission electron microscopy identified that V2O5 powders were approximately flower-like in shape and about 5 μm in size. Besides, the Brunauer–Emmett–Teller specific surface area of flower-like V2O5 powders was 24.25 m2/g. According to Uv–Vis spectroscopy, the degradation rate of toluidine blue O (TBO) on as-prepared flower-like V2O5 powders during 10 h of visible light irradiation with an intensity of 15.4 mW/m2 was 88%, which was faster than those over P25 (46%) as a comparison. In addition, the mineralization process of TBO was investigated, which primarily consisted of demethylation and ring-opening oxidation processes, and confirmed by liquid chromatograph-mass spectrometry. The precipitation–oxidation–peptization, coagulation, and crystallization processes were proposed as the formation mechanism for the preparation of flower-like V2O5.

Green Synthesis of Silver Nanoparticles and Their Reduced Graphene Oxide Nanocomposites as Antibacterial Agents: A Bio-inspired Approach

Abstract: In this paper, silver nanoparticles (AgNPs) and AgNPs/reduced graphene oxide (RGO) nanocomposites were prepared using lemon juice under microwave irradiation (MWI) and UV light irradiation. AgNPs with face-centered cubic structure RGO peaks were observed by X-ray diffraction. The UV–Vis spectrum showed modifications in the absorption peaks of the AgNPs with the concentration of the precursor solution and irradiation time, and the optimized condition was obtained for 20 min MWI and 60 s of UV light. Raman analysis confirmed the presence of RGO as D and G bands in the spectrum. Transmission electron microscopy analyses confirmed that the AgNPs of size ranging from 3 to 8 nm were anchored onto the RGO sheets. The antibacterial properties of the AgNPs/RGO nanocomposites were investigated using gram-negative bacteria. The results revealed that AgNPs/RGO nanocomposites consisting of approximately 5 wt% AgNPs can achieve antibacterial performance similar to that of neat AgNPS. This method can be useful for the applications of AgNPs-based nanocomposites, where minute amount of silver will be utilized.

Effect of Replacing Vanadium by Niobium and Iron on the Tribological Behavior of HIPed Titanium Alloys

Abstract: This study aims to examine the effect of replacing vanadium by niobium and iron on the tribological behavior of hot-isostatic-pressed titanium alloy (Ti–6Al–4V) biomaterial, using a ball-on-disk-type oscillating tribometer, under wet conditions using physiological solution in accordance with the ISO7148 standards. The tests were carried out under a normal load of 6 N, with an AISI 52100 grade steel ball as a counter face. The morphological changes and structural evolution of the nanoparticle powders using different milling times (2, 6, 12 and 18 h) were studied. The morphological characterization indicated that the particle and crystallite size continuously decrease with increasing milling time to reach the lowest value of 4 nm at 18-h milling. The friction coefficient and wear rate were lower in the samples milled at 18 h (0.226, 0.297 and 0.423; and 0.66 × 10−2, 0.87 × 10−2 and 1.51 × 10−2 µm3 N−1 µm−1) for Ti–6Al–4Fe, Ti–6Al–7Nb and Ti–6Al–4V, respectively. This improvement in friction and wear resistance is attributed to the grain refinement at 18-h milling. The Ti–6Al–4Fe samples showed good tribological performance for all milling times.

Molecular Dynamics Simulations and Experimental Investigations of Atomic Diffusion Behavior at Bonding Interface in an Explosively Welded Al/Mg Alloy Composite Plate

Abstract: In this study, 6061 aluminum alloy and AZ31B magnesium alloy composite plate was fabricated through explosive welding. Molecular dynamics (MD) simulations were conducted to investigate atomic diffusion behavior at bonding interface in the Al/Mg composite plate. Corresponding experiments were conducted to validate the simulation results. The results show that diffusion coefficient of Mg atom is larger than that of Al atom and the difference between these two coefficients becomes smaller with increasing collision velocity. The diffusion coefficient was found to depend on collision velocity and angle. It increases linearly with collision velocity when the collision angle is maintained constant at 10° and decreases linearly with collision angle when the collision velocity is maintained constantly at 440 m/s. Based on our MD simulation results and Fick’s second law, a mathematical formula to calculate the thickness of diffusion layer was proposed and its validity was verified by relevant experiments. Transmission electron microscopy and energy-dispersive system were also used to investigate the atomic diffusion behavior at the bonding interface in the explosively welded 6061/AZ31B composite plate. The results show that there were obvious Al and Mg atom diffusion at the bonding interface, and the diffusion of magnesium atoms from magnesium alloy plate to aluminum alloy plate occurs much faster than the diffusion of aluminum atoms to the magnesium alloy plate. These findings from the current study can help to optimize the explosive welding process.

Metallurgical Behaviour and Carbon Diffusion in Buttering Deposits Prepared With and Without Buffer Layers

Abstract: Use of a buttering deposit on ferritic steel in dissimilar metal weld (DMW) joint is a common practice in nuclear plants to connect pressure vessel components (ferritic steel) to pipelines (austenitic stainless steel). Carbon migration and metallurgical changes near fusion interface (ferritic steel–austenitic stainless steel) lead to a steeper gradient in material properties, and minimizing this gradient is the major challenge in the manufacturing of DMW joints. Inconel 82 is often deposited on ferritic steel material as buttering to reducing the gradient of physical and attaining material compatibility. Inconel 82/182 fillers are used to minimize the carbon migration, but the results are not truly adequate. In this paper, Ni–Fe alloy (chromium-free) has been used as the intermediate buffer layer in the weld buttering deposit to address the issue of carbon migration and subsequent metallurgical deterioration. The weld pads with and without buffer layers of Ni–Fe alloy have been investigated and compared in detail for metallurgical properties and carbon diffusivities. Ni–Fe buffer layer can significantly control the carbon migration which resists the metallurgical deterioration. It showed the better results in post-weld heat treatment and thermally aged conditions. The buttering deposit with Ni–Fe buffer layer could be the better choice for DMW joints requirements.

Corrosion and Cavitation Erosion Behaviors of Two Marine Propeller Materials in Clean and Sulfide-Polluted 3.5% NaCl Solutions

Abstract: The corrosion and cavitation erosion behaviors of two main materials for ship propellers, i.e., nickel–aluminum bronze (NAB) and manganese–nickel–aluminum bronze (MAB) were investigated in a clean and sulfide-polluted 3.5% NaCl solutions. The presence of sulfide increased the corrosion damage of both NAB and MAB by rendering the corrosion product film thicker, more porous and less protective. For MAB, the formation of Fe oxides/sulfides within the corrosion product film may reduce the film compactness and responsible for the lower corrosion resistance, compared with NAB. The presence of sulfide caused the occurrence of more severe corrosion on the surface and therefore further enhanced the cavitation erosion damage. Compared with the result in the clean solution, the cavitation–erosion mass loss rate was raised by a factor of about 11.88% for MAB, and 58.6% for NAB. For NAB, the mechanical erosion dominated the damage in the clean solution, while the cavitation erosion synergy made a significant contribution to the overall damage in the sulfide-polluted solution. For MAB, it was the mechanical damage that contributed mainly to the cavitation erosion damage in both solutions. The exfoliation of large-sized κ phase and the cleavage rupture of β phases resulted in lower cavitation erosion resistance of MAB, compared with NAB.

Effect of Surface Polishing Treatment on the Fatigue Performance of Shot-Peened Ti–6Al–4V Alloy

Abstract: In this study, shot peening is applied to the titanium alloy Ti–6Al–4V, and the surface treatment effect on fatigue life of shot-peened specimens under high cycle loading is investigated. The induced residual stress is measured by using the orbital hole-drilling method. Surface profilometer and optical microscopy are employed to characterize the surface roughness and morphology. The deformed microstructure layers of the shot-peened specimens are investigated by using scanning electron microscopy. Experiments reveal that the fatigue life of Ti–6Al–4V is improved by the shot peening process, and the surface pre-peening polishing. The combination of pre- and post-peening polishing treatments further improves fatigue life of Ti–6Al–4V specimens. The present work provides useful guidelines for developing more efficient shot peening strategies.

Performance of Corrosion-Resistant Alloys in Concentrated Acids

Abstract: Nickel alloys containing optimum amounts of chromium (Cr), molybdenum (Mo) and tungsten (W) are widely used in the chemical processing industries due to their tolerance to both oxidizing and reducing conditions. Unlike stainless steel (SS), Ni–Cr–Mo (W) alloys exhibit remarkably high uniform corrosion resistance in major concentrated acids, like hydrochloric acid (HCl) and sulfuric acid (H2SO4). A higher uniform corrosion resistance of Ni–Cr–Mo (W) alloys, compared to other alloys, in concentrated acids can be attributed to the formation of protective oxide film of Mo and W in reducing acids, and Cr oxide film in oxidizing solutions. The localized corrosion resistance of Ni–Cr–Mo (W) alloys, containing high amount Cr as well as Mo (or Mo + W), is also significantly higher than that of other commercially available alloys. The present study investigates the role of alloying elements, in nickel alloys, to uniform corrosion resistance in concentrated acids (HCl, HCl + oxidizing impurities and H2SO4) and localized corrosion performance in chloride-rich environments using ASTM G-48 test methodology. The corrosion tests were conducted on various alloys, and the results were analyzed using weight loss technique and electrochemical techniques, in conjunction with surface characterization tools.

Corrosion Behavior and Hardness of Al– M ( M : Mo, Si, Ti, Cr) Alloys

Abstract: The corrosion behavior of Al–5 at.% Cr, Al–5 at.% Si, Al–5 at.% Mo and Al–5 at.% Ti produced via casting and Al–5 at.% Cr produced by high-energy ball milling and subsequent consolidation by cold pressing was studied using potentiodynamic polarization and surface analysis following constant immersion tests. Alloys were characterized using a scanning electron microscope coupled with the energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. Hardness, a representative of the strength, was also measured. The alloys produced by casting contained coarse intermetallics and therefore exhibited poor corrosion resistance. Al–5 at.% Cr alloy produced by high-energy ball milling exhibited a significantly improved corrosion resistance and hardness, which was attributed to the grain refinement to nanoscale and extended solid solubility of Cr in Al. The study indicated that the high-energy ball milling was capable of producing Al alloys with improved corrosion behavior and hardness.

Dynamic Recrystallization Behavior and Processing Map Development of 25CrMo4 Mirror Plate Steel During Hot Deformation

Abstract: The dynamic recrystallization behavior of 25CrMo4 steel was systematically investigated by compression deformation at different temperatures and strain rates on a Gleeble 1500 thermal mechanical simulation tester. The flow curves under different deformation conditions were obtained, and the effects of deformation temperature and strain rate on the appearance of the flow curves were discussed. Based on the experimental flow curves, the activation energy determined by regression analysis was Q = 337 kJ/mol, and the constitutive model was constructed. All the characteristic points of the flow curves were identified from the work hardening rate curves ( $$\theta = {\text{d}}\sigma /{\text{d}}\varepsilon \;{\text{vs}} \;\sigma$$ ), which were derived from the flow curves. Then, the kinetics model of dynamic recrystallization was determined by combining the Avrami equation with the stress loss resulted from the dynamic recrystallization. With the aid of the kinetics model, the effect of strain on the efficiency of power dissipation was discussed. Furthermore, the optimum parameters for the forging process were determined based on the processing maps.

Spheroidizing Behavior and Spheroidizing Kinetics of W-phase During Solid-Solution Treatment in Mg–Zn–Y–Mn–(B) Alloys

Abstract: The spheroidizing mechanism of W-phase in the Mg–Zn–Y–Mn–(B) alloys during solid-solution treatment was investigated by using kinetic methodologies. The microstructure and mechanical properties of heat-treated Mg94Zn2.5Y2.5Mn1 alloy containing 0.003 wt% B were compared with heat-treated Mg94Zn2.5Y2.5Mn1 alloy. The heat-treated Mg94Zn2.5Y2.5Mn1 alloy with 0.003 wt% B contained fine and uniform W-phase particles, which exhibited optimal mechanical performance. The ultimate tensile strength, yield strength and elongation were 287.7, 125.5 MPa and 21.1%, respectively.

Microstructural Characterization and Phase Separation Sequences During Solidification of Ni 3 Al-Based Superalloy

Abstract: As-cast microstructure of a designed polycrystalline Ni3Al-based superalloy is characterized using optical microscope, scanning electron microscope, transmission electron microscope equipped with selected area diffraction system, and the intermetallic phase transformations involved during solidification process are determined based on thermal analysis measurements. The as-cast microstructure is mainly composed of 80.63 vol% dendritic and 19.37 vol% interdendritic phases, and the dendrite is identified as quasi-cuboidal $$\gamma_{\text{I}}^{\prime }$$ phase connected by γ-channels where ultrafine $$\gamma_{\text{II}}^{\prime }$$ particles are distributed, and the interdendritic phases are determined as γ′–γ eutectic structure consisting of γ E phase with dotted quasi-spherical $$\gamma_{\text{E}}^{\prime }$$ particles. During solidification, the dendrite firstly nucleates from liquid melt near 1348 °C; subsequently, the residual liquidoid is transformed into interdendritic phases around 1326 °C. Afterward, γ′ phase will precipitate from dendritic γ-matrix with two-stage characteristics, resulting in the distinct precipitation of $$\gamma_{\text{I}}^{\prime }$$ and $$\gamma_{\text{II}}^{\prime }$$ phases when approaching to 1190 and 1043 °C, respectively. The corresponding transformations involved during the solidification process can be translated as:

Influence of Al Content on the Microstructure and Properties of the CrAlN Coatings Deposited by Arc Ion Plating

Abstract: Four CrAlN coatings with various Al content were prepared by arc ion plating technology under different target currents The effect of the Al content on the microstructure, chemical compositions, element chemical bonding states and mechanical properties of the CrAlN coatings was analyzed X-ray diffraction results show that the primary phase of the CrAlN coating is fcc-(Al, Cr)N when the Al content is about 4402 at% However, when the Al content increases to about 5334 at%, hcp-AlN phase emerges in the coating And the hcp-AlN phase becomes the main phase in the CrAlN coating with Al content of about 6955 at% Cross-sectional images show that all the four coatings possess dense structures and the deposition rate of Al atom is higher than that of Cr atom The hardness of the CrAlN coating with Al content about 4402 at% is the largest (314972 HV) due to the solid solution hardening effect of the Al element When the hcp-AlN phase is generated in the CrAlN coating, the hardness declines The tribological experiment shows that the wear resistance of the CrAlN coating decreases gradually with increasing Al content when sliding against 100Cr6 steel ball

A Synergistic Acceleration of Corrosion of Q235 Carbon Steel Between Magnetization and Extracellular Polymeric Substances

Abstract: In this work, surface characterization and electrochemical measurement were employed to investigate the effects of magnetic field (MF) on the corrosion of Q235 carbon steel in a NaCl solution containing sulphate-reducing bacteria (SRB) or extracellular polymeric substances (EPS). Results demonstrated that a 150 mT MF enhanced steel corrosion in a SRB-containing NaCl solution by 202% calculated from weight loss with pitting corrosion as the main corrosion type. Either EPS or MF rendered steel corrosion, but a synergistic interaction between MF and EPS boosted up steel corrosion. This synergistic enhancement could be referred to the alteration in orientation of EPS induced by MF. The presence of higher percentage of chloride ions on the carbon steel surface manifested that MF initiated the erosion of chloride ions on the carbon steel coupon.

Synthesis and Characterization of Electroless Ni-P/Ni-Mo-P Duplex Coating with Different Thickness Combinations

Abstract: In this work, a novel duplex Ni–P/Ni–Mo–P coating upon the aluminum (Al) substrate was synthesized via an electroless plating, i.e., the binary Ni–P coating as a transition layer and the ternary Ni–Mo–P coating on the top. It was found that the duplex coating was of a high hardness, large elastic modulus, low porosity and excellent corrosion resistance. In addition, experimental results revealed that for a total 20 μm coating thickness, the duplex coating with a 7 μm of the Ni–Mo–P coating exhibited the best corrosion resistance in 0.5 mol/L sulfuric acid solution, which was attributed to its compact structure and low porosity. This duplex Ni–P/Ni–Mo-P coating with a thin ternary Ni–Mo–P layer is expected to solve the problem of low deposition rate of ternary alloy coating and thereby may expand applications of Al and its alloys in the fields of machine manufacture and corrosion environment.

Dielectric Properties of Eu-Doped CaCu 3 Ti 4 O 12 with Different Compensation Mechanisms

Abstract: To get a better understanding of the influence of rare-earth element doping, CaCu3Ti4O12 (CCTO) samples with a partial substitution of Ca with Eu with different compensation mechanisms were designed and prepared by solid-state reaction. All the ceramics were single phase, while the dielectric constants and thermally activated energy values for dielectric relaxation in Eu-doped ceramics were both lower than those of CCTO. Ca0.875Eu0.1Cu3Ti4O12 (CECT1) exhibited a slight decrease in both the permittivity and electric resistance of grain boundaries compared with CCTO, while Ca0.85Eu0.1Cu3Ti4O12 (CECT2) underwent a sharp decrease in permittivity associated with an abnormally large resistance. The different dielectric behavior indicates that the dielectric properties of CCTO are sensitive to the valence states of cations and defects. The variation of permittivity is related to the localization of carriers, which, according to the XPS results, should be caused by the presence of oxygen vacancies. The formation of defect complexes between cations and oxygen vacancies leads to the increase in resistance and prevents the hopping between Cu+ and Cu2+, which is an important source of the polarization in grain boundaries.

Effects of substrate pulse bias duty cycle on the microstructure and mechanical properties of Ti-Cu-N films deposited by magnetic field-enhanced arc ion plating

Abstract: Ti–Cu–N films were deposited on 316L stainless steel substrates by magnetic field-enhanced arc ion plating. The effect of substrate pulse bias duty cycle on the chemical composition, microstructure, surface morphology, mechanical and tribological properties of the films was systemically investigated. The results showed that, with increasing the duty cycle, Cu content decreases from 3.3 to 0.58 at.%. XRD results showed that only TiN phase is observed for all the deposited films and the preferred orientation transformed from TiN(200) to TiN(111) plane with the increase in duty cycle. The surface roughness and deposition rate showed monotonous decrease with increasing the duty cycle. The residual stress and hardness firstly increase and then decrease afterwards with the increase in duty cycle, while the variation of critical load shows reverse trend. Except for the film with duty cycle of 10%, others perform the better wear resistance.