Typical Lamellar Structure Research Articles

The Preparation of g-C3N4/ZnIn2S4 Nano-Heterojunctions and Their Enhanced Efficient Photocatalytic Hydrogen Production.

Hydrogen production technology has triggered a research boom in order to alleviate the problems of environmental pollution and the pressure on non-renewable energy sources. The key factor of this technology is the use of an efficient photocatalyst. g-C3N4 is a typical semiconductor photocatalytic material that is non-toxic and environmentally friendly and does not cause any serious harm to human beings. Therefore, it can be applied to drug degradation and the photocatalytic production of H2. Combined with ZnIn2S4, this semiconductor photocatalytic material, with a typical lamellar structure, has become one of the most promising catalysts for research due to its suitable bandgap structure and excellent photoelectric properties. In this study, 10% g-C3N4/ZnIn2S4 nano-heterojunction composite photocatalytic materials were successfully prepared by compounding ZnIn2S4 and g-C3N4 semiconductor materials with good visible-light-trapping ability. Under visible light irradiation, the photocatalytic activity of the composites was significantly better than that of pure g-C3N4 and ZnIn2S4. This is attributed to the formation of a heterojunction structure, which effectively inhibited the recombination of photogenerated carriers through the interfacial contact between the two semiconducting materials, and then improved the separation efficiency of the photogenerated electron-hole pairs, thus enhancing the catalytic activity. In this study, pure g-C3N4 and ZnIn2S4 were prepared using calcination and hydrothermal methods, and then, the composites were synthesized using ultrasonic and hydrothermal means. The differences in the structure, morphology, and hydrogen production performance of the materials before and after recombination were analyzed in detail using XRD, SEM, and FTIR characterization, which further verified that the 10% g-C3N4/ZnIn2S4 nano-heterojunction composites possessed excellent photocatalytic activity and stability, providing new possibilities for the optimization and application of photocatalytic hydrogen production technology.

Layered double hydroxide for slowing selenium fertilizer release and improving selenium utilization efficiency in vegetables

Selenium (Se) is a beneficial plant micronutrient, and the application of Se fertilizers can promote plant growth and enhance the Se content in crops. However, traditional soluble Se fertilizers have low utilization efficiency of Se due to adsorption or leaching. Here, selenite (SeO32−) -intercalated Mg/Al layered double hydroxide (Se-Mg/Al) for SeO32− slow-release was synthesized by co-precipitation and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Se-Mg/Al possessed a typical lamellar structure, combining with selenite by electrostatic interaction in interlayer and chemisorption on the surface. The release mechanism of selenite in distilled water from Mg/Al layered double hydroxide (Mg/Al LDH) was Fickian diffusion with gradually released 97.86% after 20 h (Over 90% within 2 h for sodium selenite). At pH range 4.0–8.0, Se-Mg/Al had a stable slow-release ability. And, the sulfate and phosphate anions could effectively trigger the release of selenite through anions exchange. The pot experiments showed that Se-Mg/Al increased Se content of vegetables, more than twice that of directly using sodium selenite. Compared with control treatment, the average stem height and fresh weight per 10 plants with Se-Mg/Al treatment improved approximately 1.48 times and 2.34 times, respectively. This work provides a feasible way for achieving crops selenium supplementation and improving selenium utilization efficiency.

Enhanced wear resistance of AlCoCrFeMo high entropy coatings (HECs) through various thermal spray techniques

The remarkable mechanical and wear properties of high entropy alloys (HEAs) have opened up exciting possibilities for their use in aerospace applications. This study explores the potential of AlCoCrFeMo high entropy coatings (HECs) fabricated using three thermal spray techniques, namely low-pressure cold spray (LPCS), flame spray (FS), and high-velocity oxy fuel spray (HVOF) as wear resistant surfaces. The coatings were investigated in terms of their microstructures, phases, mechanical properties, and sliding wear characteristics from room temperature up to 350 °C. Ex-situ characterization was performed using XRD for phase analysis and SEM-EDS for cross-sectional microscopy and phase compositions of the coatings. All three coatings exhibited a typical lamellar structure with the formation of BCC solid solution phase and variations in porosity and oxide content. The HVOF sprayed coatings showed higher hardness values compared to the FS and LPCS coatings, which can be attributed to their fine splats microstructure, lower porosity, and oxide inclusions compared to the other two coatings. In terms of tribological performance, the LPCS coatings exhibited overall lower frictional coefficient than the FS and HVOF coatings at both tested temperatures. However, the HVOF coatings exhibited relatively lower wear rates, correlating well with observations from ex-situ analysis, highlighting lower material transfer and decreased formation of debris particles compared to LPCS and FS coatings. These findings suggest that the HEA materials have great potential as next-generation tribological interfaces under high-temperature wear conditions, emphasizing the importance of designing materials with improved microstructural features.

Elevated-temperature wear behavior and mechanisms of APS-sprayed Al0.6TiCrFeCoNi high entropy alloy coating

Thermal sprayed high entropy alloy coatings have garnered substantial attention for their remarkable mechanical properties and wear resistance. In this study, we explored the wear behavior and mechanisms of Al0.6TiCrFeCoNi coatings produced through atmospheric plasma spray (APS) at both room temperature and 500 °C. The microstructural and mechnical characterization of the APS-sprayed coating was performed using XRD, OM, SEM, CSLM and hardness testing techniques. The dry sliding wear test of the coating against Al2O3 ball were conducted on a pin-on-disc tribometer at room temperature and 500 °C. The coating exhibited a single body-centered cubic (BCC) phase, with a typical lamellar structure marked by oxides and pores. Wear tests showed that the APS-sprayed coating exhibits superior wear resistance at elevated temperatures compared to room temperature due to the formation of compact oxide layer on the wear track. Detailed investigations on wear track reveal that abrasive wear, oxidation wear and fatigue wear are the prominent wear mechanisms on both conditions, while tribo-oxidation is dominated at 500 °C. Furthermore, We demonstrated that the looser, more porous microstructure of the APS-sprayed coating contributes to its enhanced wear resistance, preventing crack propagation and increasing strain tolerance. This provides a promising strategy for outstanding wear resistant coatings by designing looser lamellar coating structure.

Formation process, microstructure, and mechanical properties of an ultrafine dual-phase alloy formed through phase transition of 18R-type long-period stacking ordered in Mg85Zn6Y9 under high pressure

The 18R-type long-period stacking ordered (LPSO) structure in Mg85Zn6Y9 exhibits phase transition into D03 and α-Mg (D03/α-Mg) before it transforms into a liquid phase with the increase in temperature at 7.8 GPa. First-principles calculations suggest that the energy barrier between 18R-type LPSO and D03/α-Mg decreases with pressure. A further increase in the temperature decreases the energy difference between LPSO and D03/α-Mg. Therefore, the free energy variations due to the effects of both pressure and temperature cause phase transition. The D03/α-Mg phases formed at high pressure can be recovered at 0.1 MPa and room temperature. The phase transition from 18R-type LPSO structure to D03/α-Mg causes inner-grain diffusion and generates a lamellar structure. The thickness of the lamellar structure decreases with the increasing pressure until it reaches 65 nm at 15 GPa. Moreover, the alloy solidified above 5 GPa also comprises D03/α-Mg phases. The alloy solidified at 5 GPa exhibits a typical eutectic lamellar structure. However, spherulite-like polycrystalline microstructures containing ultrafine grains are obtained when the alloys are solidified at 10 and 15 GPa. The microstructure variations are caused by an increase in the degree of supercooling due to atomic diffusion suppression with the increasing pressure. The alloys containing D03/α-Mg exhibit both low modulus and ultrahigh strength. The Young’s modulus is related to the presence of the D03 and α-Mg phases in the alloy structure. In contrast, the increase in σy can be attributed to the grain refinement strengthening.

Synthesis of highly thermal conductive carbon nanotubes on cellulose nanofiber film-loaded polyethylene glycol phase change material with flame retardancy by layered double hydroxide

The nitrogen-doped carbon nanotubes (CNTs) were obtained by using methyl orange as a soft template and high temperature treatment, on which the layered double hydroxide (LDH) was grown in situ by hydrothermal method, and finally mixed with the phase change materials (PCM) by vacuum filtration to obtain a series of novel composite films with great flame retardancy and thermal conductivity. The use of cellulose nanofiber (CNF), polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) as PCM increased the film-forming properties, and the CNTs could improve the thermal conductivity of composites, while reducing the agglomeration of LDH nanolayers and improving the flame retardancy of the composite films. The results showed that the LDH grown on the nanotubes had a typical hexagonal lamellar structure, and its uniform distribution was the fundamental reason for the flame retardancy of the films which was verified by defined combustion experiments, the shortest self-extinguishing time and the least unburned area were achieved at a mass ratio of 7.14 % of LDH material. The melt and crystallization enthalpies of the thermally conductive flame-retardant films were 74.65 J/g−1 and 74.82 J/g−1, and the thermal conductivity of the material was increased to 0.04129 W/(m·K) after the use of 2.5 % thermally conductive filler. It can reduce the temperature of LED by up to 5.9 °C during the LED opening process and up to 5.2 °C during the LED closing process.

Influence of vacuum heat treatment on wear behavior of HVAF sprayed WC-Cr3C2–Ni coatings

WC-Cr3C2–Ni coating was deposited on SK5 steel substrate by high velocity air fuel (HVAF) spraying. The effect of vacuum heat treatment temperature on the phase composition, microstructure, microhardness and wear resistance of the coating was investigated. Inspections by scanning electron microscope (SEM) and X-ray diffraction (XRD) indicated that new phases FeW3C and Fe7W6 produced by heat treatment above 550 °C due to metallurgical reaction. When the heat treatment temperature exceeded 700 °C, typical lamellar structure disappeared, and overall uniformity of the coating was improved. The microhardness of the coatings was investigated by Vickers hardness tester and disclosed that the highest value of 1486 HV was detected in coating heat treated at 700 °C, with an increase of 15% compared to as-sprayed condition. The results from ball-on-disk wear test showed that coefficient of friction and wear rate were decreased to varying degrees after heat treatment. The coating heat treated at 700 °C had optimal wear resistance, which wear rate was 1.79 × 10−10 cm3/Nm, approximately 30% lower than as-sprayed coating. Wear equation W=6×10−7×μ/H is obtained to describe the relation between wear rate, coefficient of friction and hardness of the WC-Cr3C2–Ni coating heat treated at 550–1000 °C.

The interfaces of Ag-rich and Cu-rich AgCu phases boost oxygen reduction activity

In this study, we demonstrated that the interface between Ag-rich and Cu-rich AgCu phases enhances the oxygen reduction activity of the model alloys. Ag-rich and Cu-rich AgCu alloys (86.8 and 4.5 at. % of Ag, respectively) displayed the homogeneous microstructure representing solid solutions while the AgCu with eutectic composition (59.7 at. % of Ag) showed a typical lamellar structure of Ag-rich and Cu-rich AgCu phases. The eutectic AgCu alloy exhibited better oxygen reaction activity than Ag-rich AgCu alloy despite less phase fraction of Ag-rich AgCu phase. After the activation process, the presence of a CuO layer at the interface of the Ag-rich and Cu-rich AgCu phases was discovered by atom probe tomography analysis. Density functional theory calculations further revealed that the preferential adsorption of OH near the interface between CuO and Ag-rich AgCu lowers the binding strength of OH in the Ag-rich AgCu phase. As a result, the oxygen reduction activity was enhanced by facilitating the most sluggish OH desorption step. These findings provide new insights into the role of phase boundaries in catalytic activity and guidelines for the design of novel electrocatalysts.

Directly Using Ti3C2Tx MXene for a Solid-Contact Potentiometric pH Sensor toward Wearable Sweat pH Monitoring.

The level of hydrogen ions in sweat is one of the most important physiological indexes for the health state of the human body. As a type of two-dimensional (2D) material, MXene has the advantages of superior electrical conductivity, a large surface area, and rich functional groups on the surface. Herein, we report a type of Ti3C2Tx-based potentiometric pH sensor for wearable sweat pH analysis. The Ti3C2Tx was prepared by two etching methods, including a mild LiF/HCl mixture and HF solution, which was directly used as the pH-sensitive materials. Both etched Ti3C2Tx showed a typical lamellar structure and exhibited enhanced potentiometric pH responses compared with a pristine precursor of Ti3AlC2. The HF-Ti3C2Tx disclosed the sensitivities of -43.51 ± 0.53 mV pH-1 (pH 1-11) and -42.73 ± 0.61 mV pH-1 (pH 11-1). A series of electrochemical tests demonstrated that HF-Ti3C2Tx exhibited better analytical performances, including sensitivity, selectivity, and reversibility, owing to deep etching. The HF-Ti3C2Tx was thus further fabricated as a flexible potentiometric pH sensor by virtue of its 2D characteristic. Upon integrating with a solid-contact Ag/AgCl reference electrode, the flexible sensor realized real-time monitoring of pH level in human sweat. The result disclosed a relatively stable pH value of ~6.5 after perspiration, which was consistent with the ex situ sweat pH test. This work offers a type of MXene-based potentiometric pH sensor for wearable sweat pH monitoring.

Janus nanographene oxide with aerophilic/hydrophilic characteristics for enhancing foam stability in high-temperature reservoirs

Foam technology is currently recognized as one of the most promising technical means to further enhance oil recovery. However, the poor stability of foam in harsh reservoirs with high temperatures limits the further application of foam fluids in oil fields. Based on the Pickering emulsion template method, this paper proposed a synthesis strategy for Janus nanographene oxide with aerophilic/hydrophilic characteristics as a novel foam stabilizer. A high-stability foam reinforced by Janus nanographene oxide was constructed. In addition, this paper clarified the relationship between foam stability and the interfacial characteristics of foam and revealed the probable mechanism by which Janus nanographene oxide enhances foam stability. The results showed that the synthesized Janus nanographene oxide has a typical two-dimensional lamellar structure with an obvious asymmetric characteristic. The negatively charged Janus nanographene oxide showed a small particle size, high ζ potential, high thermal stability, satisfactory amphiphilicity, and high interfacial adsorption, which was beneficial for enhancing foam stability at high temperatures. The foam stability was positively correlated with the interfacial viscoelastic modulus of the foam. Janus nanographene oxide was irreversibly adsorbed onto the gas–liquid interface, which increased the interfacial viscoelastic modulus, especially the interfacial elastic modulus increased from 2.94 mN·m−1 to 16.21 mN·m−1. As a result, the ability of the foam to resist deformation due to external forces was enhanced, which can be reflected in the enhancement of the foam stability. The half-life of foam at high temperature increased from 26 min to 49 min. An appropriate amount of Janus nanographene oxide can form a solid-like film with high mechanical strength on the gas–liquid interface and gradually fill the Plateau boundary of the foam. It can not only effectively reduce the drainage rate of the liquid film but also hinder gas diffusion between adjacent bubbles, which delays the further thinning of the film and coarsening behavior of the foam. Therefore, the constructed reinforced foam can be considered as a promising candidate for further enhancing oil recovery in high-temperature reservoirs, especially for steam channeling control. In addition, this work contributes to a better understanding of the mechanism by which Janus nanomaterials can enhance foam stability and provides theoretical guidance for the further application of foam technology.

Preparation and Properties of a Plasma-Sprayed Fe-Cr-B-C Coating

Fe-Cr-B-C wear-resistant coating was prepared by atmosphere plasma spraying. The effects of the spraying current, main gas flow, secondary gas flow, and spraying distance on the microstructure, hardness, and bonding strength of the coating were studied. The results show that the cross-section of the coating is a typical lamellar structure. There are unmelted particles with high hardness in the Fe-Cr-B-C coating, and the hard phase particles are spherical and dispersed. As a result, the microhardness of the Fe-Cr-B-C coating is relatively uniform, within the range of 820~860 HV0.1. Spraying process parameters significantly affect the bonding strength of the coating, but have little effect on the microhardness. The matrix of the coating is an α-Fe phase and the hard phase is mainly a (Fe, Cr)2(B, C) phase and a (Fe, Cr)3(B, C) phase. Due to the spheroidized coating structure, the wear rate of the FeCrBC coating is only 0.62 × 10−5 mm3/Nm, which is 51% of the 304 stainless steel. The wear mechanism of the Fe-Cr-B-C coating is mainly abrasive wear and fatigue wear.

Relationship between Manufacturing and Properties of Vacuum Sintered Ti and Ti-6Al-7Nb

Titanium alloys are ideal for a great range of engineering applications; however, their high manufacturing costs hinder their widespread use. This study investigates the relationship between the processing and properties of representative Ti-based materials manufactured via powder metallurgy in order to reduce the manufacturing costs. This is possible as powder metallurgy techniques are near-net shape processes with high yield of material. It is found that the relative density increases with the sintering temperature, and it is slightly higher for longer processing times, reaching values in the 94–97% range. Moreover, homogeneous microstructures are obtained for all the conditions investigated, achieving an equiaxed microstructure for Ti and the typical lamellar structure for the Ti-6Al-7Nb alloy. However, the increment of the temperature also leads to a higher amount of interstitial pick-up, with a maximum increment of 0.21 wt.% and 0.028 wt.% for oxygen and nitrogen, respectively. The highest properties achieved for Ti and Ti-6Al-7Nb are 272 HV (hardness), 17.9 W/m·K (thermal conductivity), and 62.7 μohm·cm (electrical resistivity) and 336 HV, 6.9 W/m·K, and 180 μohm·cm, respectively.

Synthesis of In Situ ZrB2-SiC-ZrC Coating on ZrC-SiC Substrate by Reactive Plasma Spraying.

In situ synthesis feasibility of ZrB2-SiC-ZrC composite coatings on ZrC ceramics by reactive plasma spraying (RPS) was investigated. To help to understand the phase evolution during plasma spraying process, reaction behavior in the ZrH2-Si-B4C system was explored carefully by differential scanning calorimetry. The results indicated that the phase transformation sequence in the ZrH2-Si-B4C system could be described as ZrH1.66, Zr3O, ZrC, ZrB2, Zr2Si, ZrSi, and SiC. The prior formation of ZrC was due to high diffusion rate of C atoms from B4C. ZrB2 was produced above 1100 °C. As the temperature increased, SiC were finally formed by the reaction of ZrC with ZrSi and B4C. The RPS composite coatings mainly consisted of ZrB2, SiC, and ZrC phases, except for a small fraction of ZrO2 phase. The microstructural characterization exhibited more dense melted splats, which appears to increase gradually with the increase in spraying currents and distances. The coatings had typical lamellar structure and adhered to the substrate well. The microhardness values were higher than 1000 HV1, but there were few variations with varying spraying currents and distances.

Mg/Al-LDH as a nano-adjuvant for pertussis vaccine: a evaluation compared with aluminum hydroxide adjuvant

Background. Layered double hydroxide (LDH) has been demonstrated as a highly efficient antigen platform to induce effective and durable immune response. However, whether LDH nanoparticles could act as an adjuvant for pertussis vaccines is still unknown. Here we evaluated the potential of Mg/Al-LDH as a nano-adjuvant to improve immune response against pertussis and compared it with commercial aluminum hydroxide (AH) adjuvant. Method. The Mg/Al-LDH nanoparticles were synthesized by a hydrothermal reaction. The morphology, structure and size of Mg/Al-LDH were characterized by transmission electron microscope, x-ray diffraction and MALVERN particle analysis. The ovalbumin and Pertussis toxin (PTd) was adsorbed to Mg/Al-LDH. The immune response of antigen-LDH complex was evaluated in mice, compared with commercial adjuvant alum. Hematoxylin-eosin staining was used to evaluate the inflammatory response at injection site. Results. The synthetic Mg/Al-LDH nanoparticles showed a typical hexagonal lamellar structure. The average size of synthetic nanoparticles was 102.9 nm with PDI of 0.13 and zeta potential was 44.4 mV. Mg/Al-LDH nanoparticles effectively adsorbed protein antigen and mediated antigen uptake by DC cells. Animal experiments showed that Mg/Al-LDH gave enhancement in anti-pertussis toxin (PTd) humoral immune response, which was considerable to commercial AH adjuvant. Finally, Mg/Al-LDH produced a slighter inflammatory response than AH at injection site and this injury was quickly recovered. Conclusion. Our study demonstrated the potential of Mg/Al-LDH as an effective adjuvant for pertussis vaccine, which induced comparable antibody response and had a better safety compared with commercial AH adjuvant.

Influence of Al content and post-annealing on synthesis and mechanical properties of plasma sprayed Cr–Al–C composite coatings

Due to ultra-high temperature and short reaction time, it was very challenging to produce high purity MAX phase by plasma spraying. In this study, Cr–Al-graphite agglomerated powders with different Al additions (x = 0.2–1.5) was used to prepare Cr–Al–C composite coatings by atmospheric plasma spraying followed with annealing. Results showed that the as-sprayed coatings displayed typical lamellar structure, mainly composed of Cr–C binary carbides (Cr7C3 and Cr23C6) and residual Al. After annealing at 700 °C, the newly formed Cr2AlC phase increased significantly in the coatings. The higher addition of Al, the more Cr2AlC phase formed after annealing. The enhanced atomic diffusion, sufficient Al source and existence of (Cr, Al)Cx contributed to the formation of Cr2AlC under annealing. Annealing treatment improved the hardness of the coating, but with the increase of Cr2AlC phase content, the hardness decreased slightly. The Al content and post-annealing had a synergistic effect on the formation of Cr2AlC phase in the sprayed coatings. This provided an effective route to control the Cr2AlC content in sprayed Cr–Al–C composite coatings.

Na0.78CoO2 as a novel microwave absorbing material

A novel microwave absorbing material, sodium cobaltates (Na0.78CoO2) was synthesized by solid-state reaction, which shows a good electromagnetic attenuate property. Because of preferential growth along the C axis, the Na0.78CoO2 powder reveals a typical lamellar structure. Theoretical calculations suggest that there is a minimum reflection loss (RL) around −51.7 dB at a frequency of 8.2 GHz in the composite with 50 wt% Na0.78CoO2 and 50 wt% paraffin when the thickness of the composite is about 2.41 mm. Moreover, its effective absorbing bandwidths (RL < −10 dB) are in a range from 12.5 to 15.6 GHz in the case of the sample thickness of around 1.5 mm. The electromagnetic attenuation mechanisms of the composite are relevant to conductive loss, multiple reflection loss, and dipole or interfacial polarization loss.

High performance GO/MXene/PPS composite filtration membrane for dye wastewater treatment under harsh environmental conditions

As the world continues to develop, it faces increasingly serious environmental problems. For wastewater, membrane separation is widely used as an efficient technology. However, less research has been done for applications in harsh environments. Therefore, we proposed a two-dimensional (2D) composite GO/MXene-PPS (GMS) membrane formed by a simple vacuum self-assembly method. The obtained GMS membrane has a typical lamellar structure, and the composite membrane showed great surface wettability to water and organic solvents, as well as high resistance to harsh environments. The composite membranes allow ultra-fast transport of water molecules to reach a high pure water flux of 45.78 Lm-2h-1bar-1, meanwhile ensuring a high rejection rate of 99.99% for many organic dyes such as MB. In addition, the prepared composite membranes exhibited excellent performance in harsh environments such as strong acids/bases and organic solvents, indicating its potential application in dye wastewater purification treatment.

Tripolycyanamide-2,4,6-triformyl pyrogallol covalent organic frameworks with many coordination sites for detection and removal of heavy metal ions

Here, tripolycyanamide (TPA) and 2,4,6-triformyl pyrogallol (TDBA) are used to prepare a highly crystalline covalent-organic frameworks based on imine linkages (COFTDBA-TPA) for heavy metal ions (HMIs) detection and removal. Each unit of COFTDBA-TPA had 6 adsorption sites for HMIs (–CO, –NH2, –CN), which could selectively capture HMIs. The typical lamellar structure made COFTDBA-TPA have a larger specific surface area, and the mesoporous structure provided numerous channels for the adsorption of HMIs. Therefore, the COFTDBA-TPA-based electrochemical sensor could realize the detection of Cd2+, Cu2+, Pb2+, Hg2+ and Zn2+ in drinking water, simultaneously. The limits of detection for five HMIs were as low as 0.922 nM, 0.450 nM, 0.309 nM, 0.208 nM and 0.526 nM, respectively. The adsorption capacity of COFTDBA-TPA for each HMI was as high as 711.6 mg/g, 716.9 mg/g, 603.7 mg/g and 618.3 mg/g, respectively. Compared with other adsorbents, it had higher capacity and faster adsorption kinetics. After being recycled five times, the adsorption performance was maintained. This not only provides a reliable platform for the removal of HMIs in wastewater, but also provides new ideas for the use of COFs in the electrochemical field.

Enhanced slurry and cavitation erosion resistance of deep cryogenically treated thermal spray coatings for hydroturbine applications

The deterioration of fluid machines due to slurry and cavitation erosion significantly impairs their serviceability. In the present work, we investigated the influence of deep cryogenic treatment (DCT) on the slurry and cavitation erosion resistance of WC-10Co-4Cr coatings developed using the detonation spraying technique. For comparison, hydroturbine steels and other conventional (Alumina and Stellite 6) coatings were also investigated. All thermal spray coatings showed typical lamellar structure along with the presence of pores and splat boundaries. Among all the coatings, the WC-10Co-4Cr showed the highest slurry (up to 15 times) and cavitation (2 times) erosion resistance owing to high hardness and fracture toughness. Post DCT, the WC-10Co-4Cr coating showed further improvement due to reduced porosity and improved hardness without decrement in fracture toughness. As a result, the DCT coating showed 1.5 to 4.2 times improved slurry erosion resistance than the as-sprayed counterpart, along with 1.6 times higher cavitation erosion resistance. The improved tribological performance of the coating after DCT is associated with enhanced hardness due to the presence of nano precipitates and densification as analyzed using electrochemical techniques. The topological analysis of the eroded surfaces indicated micro-cutting, micro-cracking, and delamination as the primary mechanism controlling the erosion behavior of the coatings.

Enhanced structural refinement on eutectic medium-entropy alloy CrCoNiNb0.48 by laser remelting

A novel efficient method to design eutectic medium-entropy alloys with typical lamellar structure is successfully proposed. The CrCoNiNb0.48 alloy is prepared with microstructure comprised of FCC and Laves phases. After laser remelting, the nano-scale eutectic lamellar is formed and the eutectic lamellar spacing is refined to approximately 30 nm from 300 nm (as-cast). Thus, the hardness of CrCoNiNb0.48 with laser remelting is approximately 50% increase over as-cast. Moreover, through calculation, the strain hardening exponent of the laser-treated alloy is almost twice of that in the as-cast alloy.