Showing papers in "Surface & Coatings Technology in 2019"
TL;DR: In this article, the mechanism of electrodeposition and effect of operational parameters and deposit microstructure, together with the mechanical, electrochemical and tribological characteristics of Ni Co alloys and included particle, composite deposits.
Abstract: Ni Co alloy electrodeposits have been widely employed in industry due to their good corrosion and wear resistance, high mechanical strength, moderate thermal conductivity and outstanding electrocatalytic and magnetic properties. This review aims to provide an insight into the mechanism of electrodeposition and effect of operational parameters and deposit microstructure, together with the mechanical, electrochemical and tribological characteristics of Ni Co alloys and included particle, composite deposits. Potential applications of the coatings have also been considered in applications as diverse as additive manufacturing, micro-tools, micro-sensors, electronic imaging and electrochemical energy conversion.
152 citations
TL;DR: In this paper, the microstructure and mechanical properties of fabricated Inconel625 alloy, and the influence of torch travel speed on the properties of the manufactured specimens were investigated.
Abstract: In the present study Inconel 625 alloy fabricated using Cold Metal Transfer (CMT) Wire Arc Additive Manufacturing (WAAM) has been investigated. The microstructure and mechanical properties of the fabricated Inconel625 alloy, and the influence of torch travel speed on the properties of the manufactured specimens were researched. Microstructural studies revealed variation in microstructure in different layers of the specimen, with the bottom layer consisting of fine primary cellular grains. Mechanical properties that include hardness and tensile properties showed that with the increase in the travel speed, average micro-hardness of the manufactured specimens slightly improved from 248 HV to 253 HV. The ultimate tensile strength (UTS) increased from 647 MPa to 687 MPa, while yield strength (YS) increased from 376 MPa to 400 MPa. Results showed that the mechanical performance of the manufactured components by CMT-WAAM method was better than the mechanical properties of Inconel 625 alloy casting parts except UTS, which demonstrated that the Inconel 625 alloys can be fabricated by cold metal transfer process.
131 citations
TL;DR: In this article, the phase composition of high-entropy alloy (HEA) coatings of AlCoCrFeNiTiTix was investigated using X-Ray diffraction.
Abstract: High-entropy alloy (HEA) coatings of AlCoCrFeNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated on AISI1045 steel by laser cladding. X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The microstructure of coatings was analyzed using a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The potentiodynamic polarization behaviour of coatings and substrate was studied. The composition of passive film on the corroded surface of the coating was identified by X-Ray photoelectron spectroscopy (XPS). The phase composition analysis showed that the coating was mainly composed of disordered body-centered cubic (BCC) solid solution phase (Fe-Cr) and ordered BCC phase (Al-Ni). The microstructure of the coatings was mainly composed of equiaxed polygonal grains, micro-nano particles of TiC and nanoparticles of Al2O3. The spinodal decomposition structure of Fe-Cr enrichment and Al-Ni-Ti enrichment was found in grains. The introduction of Ti led to passivation behavior of the coating during corrosion process. The components of the passive film were Al2O3, TiO2, Ti2O3, Cr2O3 and Cr(OH)3. The AlCoCrFeNiTi HEA coating showed the best corrosion resistance.
125 citations
TL;DR: In this article, microhardness, wear properties and microstructure of Fe-based coatings with various WC contents on H13 hot-working die steel by laser cladding were investigated.
Abstract: Microhardness, wear properties and microstructure of Fe-based coatings with various WC contents on H13 hot-working die steel by laser cladding were investigated. Special attention was paid to the effects of various WC contents on the microstructural characterization and wear properties of different coatings by means of optical microscopy (OM) and scanning electron microscopy (SEM). Results indicated that only a small part of the periphery of the WC in the WC-added coatings was melted, and the un-melted WC particles in the coatings acted as a hard reinforcement. Besides, the microhardness in the cladding layer increased with the increment of the mass fraction of WC particles, and presented a gradient distribution along in-depth direction of the coatings. Furthermore, the Fe-based clad coating with WC particles exhibited a higher wear resistance and a lower friction coefficient compared with the substrate and Fe-based clad coating. In addition, the influence mechanism of WC particles on microstructural evolution and wear resistance was also discussed.
120 citations
TL;DR: In this paper, important research progresses achieved in regards to deposition technologies and properties of thermal sprayed Fe-based amorphous coatings are reviewed, and the dependence of wear and corrosion resistance of the coatings on processing parameters, e.g., kinetic energy, particle size, gas flow rate, and heat treatment temperature are summarized.
Abstract: Thermal sprayed Fe-based amorphous coatings exhibit excellent wear and corrosion resistance, and thus have been widely utilized for enhancing the performance of material surfaces. In this paper, important research progresses achieved in regards to deposition technologies and properties of thermal sprayed Fe-based amorphous coatings are reviewed. In particular, the dependence of wear and corrosion resistance of the coatings on processing parameters, e.g., kinetic energy, particle size, gas flow rate, and heat treatment temperature are summarized. Moreover, the utilization of reinforced phases and alloy elements for enhancing the wear and corrosion resistance of the coatings are presented. It is expected that future endeavors will be dedicated to the formation mechanism of amorphous phase and “processing parameter-microstructure-macroscopic property” relationship of Fe-based amorphous coatings.
109 citations
TL;DR: In this paper, a fully integrated two-degree-of-freedom (2DOF) MEMS piezoelectric vibration energy harvester (p-VEH) was designed and fabricated using ZnO thin films for converting kinetic energy into electrical energy.
Abstract: Zinc oxide (ZnO) is an environmental-friendly semiconducting, piezoelectric and non-ferroelectric material, and plays an essential role for applications in microelectromechanical systems (MEMS). In this work, a fully integrated two-degree-of-freedom (2DOF) MEMS piezoelectric vibration energy harvester (p-VEH) was designed and fabricated using ZnO thin films for converting kinetic energy into electrical energy. The 2DOF energy harvesting system comprises two subsystems: the primary one for energy conversion and the auxiliary one for frequency adjustment. Piezoelectric ZnO thin film was deposited using a radio-frequency magnetron sputtering method onto the primary subsystem for energy conversion from mechanical vibration to electricity. Dynamic performance of the 2DOF resonant system was analyzed and optimized using a lumped parameter model. Two closely located but separated peaks were achieved by precisely adjusting mass ratio and frequency ratio of the resonant systems. The 2DOF MEMS p-VEH chip was fabricated through a combination of laminated surface micromachining process, double-side alignment and bulk micromachining process. When the fabricated prototype was subjected to an excitation acceleration of 0.5 g, two close resonant peaks at 403.8 and 489.9 Hz with comparable voltages of 10 and 15 mV were obtained, respectively.
101 citations
TL;DR: In this article, the impact of post-multi-pass friction stir processing (FSP) on the microstructure, mechanical, wear and fracture behaviors of the fabricated 10 cycle-accumulative roll bonded Al-2%B4C composites was analyzed.
Abstract: This paper aims to understand the impact of post-multi-pass friction stir processing (FSP) on the microstructure, mechanical, wear and fracture behaviors of the fabricated 10 cycle-accumulative roll bonded Al-2%B4C composites. The increase in the number of tool-passes directly improved homogeneity and fragmentation of B4C particles, microhardness, tensile strength (86.84–173.92 MPa) and fracture resilience of the Al-2%B4C composite. The tribological properties of the composite are improved with a rise in the number of tool passes. Wear rate, upper boundaries and mid-fluctuation lines of the friction coefficient decreased from 6.198 × 10−5 to 1.095 × 10−5 mm3/Nm, 0.56 to 0.19, and 0.31 to 0.11 respectively as the number of tool passes was varied between 1 and 8 passes. An increase in the sliding distance caused an overshoot of the complete waveform of friction coefficient to be above the mid-line of fluctuation due to the induced frictional/thermal input emanating from the prolonged surface-surface contact. Homogenous particle dispersion imposes abrasion wear mechanism on the composite. Ductile fracture is the predominant failure mode of the composites. Post-multi-pass friction stir processing of the accumulative roll bonded Al-2%B4C composite is an effective approach of achieving high performance in Al-B4C composite.
100 citations
TL;DR: In this article, the effect of the concentration of 0 to 4.5 ǫg·L−1 ZnO NPs in phosphate-based electrolyte on the microstructure, composition, physical features, corrosion and biodegradation properties of coatings was investigated.
Abstract: MgO/ZnO composite coatings were successfully prepared on AZ91 Mg alloy by plasma electrolytic oxidation (PEO) method using electrolytes containing ZnO nanoparticles (NPs) to extend their biomedical applications. The effect of the concentration of 0 to 4.5 g·L−1 ZnO NPs in phosphate-based electrolyte on the microstructure, composition, physical features, corrosion and biodegradation properties of coatings was investigated. Observing the microstructure through field emission scanning electron microscopy (FESEM) confirmed that ZnO NPs were well up-taken in the coating structure with crater-like morphology and, they were mostly accumulated near the pores. As ZnO NPs concentration increased, more particles were incorporated in the coating; however, porosity, thickness and surface roughness reduced. The evaluation of the electrochemical behavior of specimens using potentiodynamic polarization test revealed that the polarization resistance of the samples increased from 9.26 to 683.2 kΩ·cm2 by adding 4.5 g·L−1 ZnO NPs. The study of corrosion mechanism by identifying the coating features using electrochemical impedance spectroscopy (EIS) indicated that the compacting of the coating and the difficulty of the penetration path of corrosive ions between the coating layers due to the presence of ZnO NPs had a more dominant effect relative to thickness reduction. Conducting the bioactivity test by immersion of coatings in simulated body fluid (SBF) solution for 14 days showed the higher growth of calcium phosphate layer formed on the sample as the concentration of ZnO NPs increases. In addition, the changes in weight loss and volume of hydrogen evolution were much less, and the mechanism of these changes was presented.
98 citations
TL;DR: In this article, a general survey of research on the electrodeposition of Ni P binary alloy coatings is provided, as well as the key process variables influencing the phosphorus content of deposits and the roles of the major electrolytic bath constituents.
Abstract: Ni P coatings are extensively employed in engineering, owing to their mechanical and tribological properties which confer protection against corrosion and wear. Classically, such deposits can have a thickness of P metal deposits can approach or exceed that of hard Cr coatings. This paper provides a general survey of research on the electrodeposition of Ni P binary alloy coatings. Proposed phosphorus incorporation mechanisms, Ni P alloy microstructure before and after thermal treatment. Mechanical, tribological, corrosion, catalytic and magnetic properties are considered, as are the key process variables influencing the phosphorus content of deposits and the roles of the major electrolytic bath constituents. The merits of employing pulse plating and fabrication of newer (layered and functionally graded) structures are concisely explored. Interaction of four aspects: substrate state, electrolyte composition, process conditions and deposit properties is seen to be important during electrodeposition of Ni P alloys; areas deserving further study are identified.
95 citations
TL;DR: In this article, a novel kind of low-cost, abundant reserves and environmental friendly carbon materials derived from carbonaceous mudstone and lignin mixture have been prepared and the electrochemical performances have been investigated.
Abstract: To solve the major issues that most carbon materials used as supercapacitors electrode should be prepared from complex chemical products with high cost and side effects to the environment. In this report, a novel kind of low-cost, abundant reserves and environmental friendly carbon materials derived from carbonaceous mudstone and lignin mixture have been prepared and the electrochemical performances have been investigated. By activation treatment with HNO3, the activated carbonaceous mudstone and lignin-derived carbons (ASLDC) has been successfully synthesized. The physical and electrochemical studies exhibit that the ASLDC electrode possesses porous structures and wonderful electrochemical behaviors, a high specific capacitance of 155.6 F g−1 can be achieved when first served as electrodes for supercapacitors, which is three times than that of the untreated carbon electrode. Meanwhile, the charge/discharge measurement further indicates that the ASLDC electrode possess the excellent supercapacitive characteristics. The results demonstrate that the as-prepared low-cost, renewable and environmental friendly carbon electrode materials can be a promising electrode material for high-performance supercapacitors. Furthermore, such abundant reserves materials would be useful for other energy storage and conversion devices.
88 citations
TL;DR: In this paper, a solution coating process was used to fabricate a graphene modified carbon felt (G/CF) electrode for VRB with high performance and this simple method is believed to be promising in other electrocatalysts applications.
Abstract: Graphene deposited on the surface of a carbon felt (CF) using a solution coating method has been developed as a high-performance positive electrode for an all vanadium redox flow battery (VRB). A key to obtain excellent electrochemical activity towards the VO2+/VO2+ redox couple is to wrap the CF using the graphene with high specific surface area and superb conductivity. It is found that the dipping times of CF into the graphene/Nafion solution significantly affect its electrochemical activity. The cyclic voltammetry (CV) results indicate that with 5 dipping times, the graphene coated CF (G/CF) exhibits the highest peak current and lowest peak potential difference towards the VO2+/VO2+ redox couple. More importantly, the VRB assembled with our novel G/CF cathodic electrode shows a decreased polarization during charge/discharge process compared with the control VRB with the pristine CF. Consequently, both the voltage efficiency and energy efficiency of the VRB with G/CF electrode have increased compared to the one with pristine CF. Our work provides a simple solution coating process to fabricate graphene modified CF electrode for VRB with high performance and this simple method is believed to be promising in other electrocatalysts applications.
TL;DR: In this article, the fatigue performance of AISI 304 subjected to shot peening (SP), ultrasonic nanocrystal surface modification (UNSM) and the combination of SP and UNSM processes was systematically assessed by rotary bending fatigue (RBF) tester at different stress levels.
Abstract: In this study, the fatigue performance of AISI 304 subjected to shot peening (SP), ultrasonic nanocrystal surface modification (UNSM) and the combination of SP + UNSM processes was systematically assessed by rotary bending fatigue (RBF) tester at different stress levels. The purpose of combining SP and UNSM processes is to find out whether SP following UNSM process can further improve the fatigue life of AISI 304 in comparison with the SP and UNSM processes alone. Interestingly, the fatigue strength of AISI 304 was deteriorated by the combination of SP + UNSM processes in comparison with the UNSM process alone, but the combination of SP + UNSM processes demonstrated a higher fatigue strength in comparison with the SP process alone.
TL;DR: In this paper, the effect of PEO layers on the surface characteristics of the top sol-gel coatings and, consequently, on the corrosion resistance of the two alloys were characterized in terms of microstructure, morphological features, composition and corrosion properties.
Abstract: Plasma Electrolytic Oxidation (PEO) is a quite new process which allows the formation of porous ceramic oxide layer on metallic substrates. In this work, hybrid organic-inorganic sol-gel hydrophobic coatings, called M7T3, were deposited on PEO layers, produced on 7020 aluminum alloy and AZ80 magnesium alloy with silicates and phosphates solutions. The hydrophobic coating was a silica film functionalized with methyl groups and it was obtained by dip coating. In detail, was studied the effect of PEO layers on the surface characteristics of the top sol-gel coatings and, consequently, on the corrosion resistance of the two alloys. The samples were characterized in terms of microstructure, morphological features, composition and corrosion properties. The top sol-gel layer resulted uniform on the various samples thank to the presence of the PEO coating. The different substrate (7020AA or AZ80) influenced the morphology of the PEO layer and, consequently, the deposition of the Sol-Gel layer. Moreover, also the durability of the sol-gel resulted increased with the possibility to use samples with the combination of PEO and sol-gel in more severe conditions than the samples with only the sol-gel layer.
TL;DR: In this paper, a micro arc oxidation (MAO) coating was applied to AZ91 magnesium alloy in an aluminate-based reference electrolyte with and without additions of Na3PO4 at concentrations of 5 and 10
Abstract: This study was initiated with the aim of extending the usage of magnesium alloys especially in corrosion and wear related engineering applications by coating their surfaces via micro arc oxidation (MAO). Considering the individual influence of phosphate-based and aluminate-based electrolytes on the corrosion and wear performances of the synthesized MAO coatings, respectively, AZ91 magnesium alloy has been subjected to MAO in aluminate-based reference electrolyte with and without additions of Na3PO4 at concentrations of 5 and 10 g/l. As opposed to dry sliding conditions, MAO coatings synthesized in the aluminate-based reference electrolyte did not provide good protection of AZ91 magnesium alloy against wear in corrosive media (0.9 wt% NaCl solution). This study revealed that, addition of 5 g/l Na3PO4 into this reference electrolyte was sufficient for enhanced resistance of MAO coating against chemical and mechanical degradations (i.e. corrosion-wear) without altering its features in terms of surface roughness and thickness.
TL;DR: In this paper, a poly-L-lactic acid (PLLA)-akermanite (AKT)-doxycycline (DOXY) nanofiber coating was used to enhance the corrosion resistance, antibacterial performance, and cytocompatibility of Mg alloys.
Abstract: Magnesium alloys are attracting increasing attention for orthopedic applications on account of their superior biocompatibility and biodegradability. However, such applications have been limited by their high degradation rate and inadequate antibacterial performance. The present study illustrates the use of a poly-L-lactic acid (PLLA)-akermanite (AKT)-doxycycline (DOXY) nanofiber coating, created using the electrospinning method, to enhance the corrosion resistance, antibacterial performance, and cytocompatibility of Mg alloys. The experimental results show the PLLA-based nanofiber coatings are smooth and uniform with fiber diameters ranging from 300 to 350 nm. PLLA nanofibers containing AKT have a higher bonding strength (11.8 MPa) than PLLA nanofibers, owing to the significant effect of AKT on the PLLA structure. An in vitro drug release profile of PLLA-AKT nanofibers containing DOXY shows that the nanofibers allow rapid release of drug in the initial stage to provide antibacterial effects as well as sustained release over the long term to prevent infection. The implants coated with PLLA-AKT nanofibers containing DOXY have excellent antibacterial performance against Gram-positive (Staphylococcus aureus, ATCC 12600) and Gram-negative (Escherichia coli, ATCC 9637) bacteria; those coated with PLLA and PLLA-AKT without DOXY have poor antibacterial performance. Cytotoxicity tests show that PLLA and PLLA-AKT nanofiber coatings considerably enhance the cytocompatibility of Mg alloys, while incorporation of a high concentration of DOXY (10% wt.) into the PLLA-AKT coating has adverse effects on cytocompatibility. Thus, PLLA-AKT nanofiber coatings containing low concentrations of DOXY can be employed to control the degradation rate and enhance the antibacterial performance and biocompatibility of Mg alloys as applied to bone infection treatments. The results of this study represent essential information to direct the development of future orthopedic applications.
TL;DR: In this paper, the effect of the thickness of the adhesion layers (0.3 and 0.7) and the wear-resistant layer (2.0, 4.0 and 8.0) on the microhardness, adhesion bond strength, and performance properties of the ZrN-(Zr,Al,Si)N coatings was investigated.
Abstract: The study involved the investigation of the effect of the thickness of the adhesion layers (0.3 and 0.7 μm) and the wear-resistant layer (2.0, 4.0, 6.0, and 8.0 μm) on the microhardness, adhesion bond strength, and performance properties of the ZrN-(Zr,Al,Si)N coatings. The scratch-test method was applied to study the adhesion bond strength to the substrate and coating failure patterns. The study revealed an effect of the coefficient kwa, determining the effect of the thicknesses of the wear-resistant and adhesion layers of the coating on the value of the critical load LC2. The study investigated the wear patterns and mechanisms for the specified coatings and the tool life of tools with these coatings in turning. An effect of the coefficient kwa which is the adhesion and wear-resistant layer thickness ratio on the tool life and a difference in the wear pattern dynamics for tools with these coatings with wear-resistant layers of equal thickness and adhesion layers of different thicknesses was revealed. The study also determined the chemical and phase composition of the coatings.
TL;DR: In this article, five super-hydrophobic coatings with different structural features at the microscale were studied, together with the effect of moisture condensation on ice adhesion.
Abstract: Among different types of anti-icing coatings, superhydrophobic coatings have attracted considerable attention due to their water repellency and low heat-transfer rate. However, condensation on superhydrophobic surfaces at low temperatures usually causes an increase in ice adhesion because of the induced wetting of micro- and nanostructures. By tuning the weight ratio of surface-modified nanoparticles to unmodified ones, five superhydrophobic coatings with different structural features at the microscale were developed. Ice-adhesion strength and ice-nucleation temperature were studied, together with the effect of moisture condensation on ice adhesion. It was found that the ice-adhesion strength and icing temperature of these coatings do not necessarily follow the same order among these surfaces because of different mechanisms involved. Surface roughness is inadequate to describe the necessary surface features that critically affect the anti-icing behavior of the coatings. Detailed topology/geometry has to be considered when designing icephobic coatings. Superhydrophobic coatings can be adopted for icephobic applications once the surface topology is carefully designed.
TL;DR: In this article, an Al0.6TiCrFeCoNi high entropy alloy coating was produced by high-velocity-oxygen-fuel spraying and the microstructure and phase composition of the coating were investigated.
Abstract: In this study, an Al0.6TiCrFeCoNi high entropy alloy coating was produced by high-velocity-oxygen-fuel spraying. The microstructure and phase composition of the coating were investigated, moreover the hardness and the fracture toughness of the coating were determined. The wear behavior of the coating at different temperatures was evaluated using a pin-on-disc test. The results show that the coating was very dense and consisted of lamellae. Two BCC phases with similar lattice parameters were detected in the as-sprayed coating. The wear of the coating against an Al2O3 counter body was mainly caused by abrasion at all temperatures. The role of fatigue wear increased with increasing test temperature. In addition, tribo-reaction played an important role at the test temperature of T = 500 °C, which led to the lowest friction coefficient of the coating under the given test conditions.
TL;DR: In this paper, a sustainable super-hydrophobic cellulose membrane (SOCM) is prepared via one-step facile sol-gel strategy for efficient oil/water separation.
Abstract: With the rapid development of petrochemical industry, oily wastewater pose a serious threat to environment and human safety. Recently, superhydrophobic and superoleophilic materials have received considerable interest due to their high selective oil/water separation. Nevertheless, facile fabrication, stability, eco-friendly, sustainable and low cost materials are still a great challenge. Here, a sustainable superhydrophobic cellulose membrane (SOCM) is prepared via one-step facile sol-gel strategy for efficient oil/water separation. The superhydrophobicity is endowed with cellulose membrane (CM) by one-step micro/nano hierarchical structures construction and low-surface-energy chemical modification from tetraethyl orthosilicate (TEOS) and hexadecyltrimethoxysilane (HDTMS) hydrolysis and polycondensation. The SOCM shows high separation efficiencies (above 98%) for various oil/water mixtures. Importantly, the SOCM displays well environmental (acid, alkali and salt-resistance) and mechanical durability (tape peeling and scratch-resistance) and remarkable reusability (at least 10 times). The merits of facile fabrication, stability, eco-friendly, sustainable and low cost make SOCM a promising candidate material for large-scale application in oil/water separation.
TL;DR: In this article, the effects of shot peening process on the electrochemical properties of a low-alloy steel were examined in the present study, where microstructural, morphological and surface properties of samples were analyzed by XRD, SEM and 3D surface profilometer.
Abstract: Shot peening treatment is a well-known and practical method to improve surface properties of materials. In this method, surfaces of materials are peened by small steel shots and thus, surface hardening is provided. Although it is used in a wide range of applications, this process could affect the electrochemical behavior of materials because of changing surface properties. Therefore, the effects of shot peening process on the electrochemical properties of a low-alloy steel were examined in the present study. AISI 4140 low-alloy steel samples were shot peened in different intensities of 16 A, 18 A, 20 A and 24 A. Afterwards, corrosion tests were carried out at room temperature in a 3.5% NaCl solution. Open circuit potential (OCP) electrochemical polarization and electrochemical impedance spectroscopy (EIS) analysis were performed in corrosion tests. The microstructural, morphological and surface properties of samples were analyzed by XRD, SEM and 3D surface profilometer. The structural analyses showed that grain structure of the material was affected by shot peening treatment. A plastically deformed zone, which have extended and refined grain structure, formed after shot peening processes. Electrochemical analyses indicated that the corrosion resistance of the material increased with the increasing shot peening intensity owing to grain refinement and formation of sub-grains. Also, examinations on the corroded surfaces showed that crevice corrosion was the main mechanism for shot peened samples.
TL;DR: In this article, an ultrasonic surface rolling process (USRP) was employed for enhancing the fatigue performance of a Ti-6Al-4V alloy, and the effect of USRP on their surface integrity (including microstructure, surface quality, microhardness, and residual stress) were investigated by means of scanning electron microscopy, transmission electron microscope, confocal laser scanning microscope, micro hardness tester and X-ray diffraction residual stress tester.
Abstract: An ultrasonic surface rolling process (USRP) is a novel mechanical surface treatment technique for enhancing the fatigue performance of metallic materials. In this work, USRP with different repeated processing numbers was employed for enhancing the fatigue performance of a Ti-6Al-4V alloy. The effect of USRP on their surface integrity (including microstructure, surface quality, microhardness, and residual stress) were investigated, which were characterized by means of scanning electron microscope, transmission electron microscope, confocal laser scanning microscope, microhardness tester, and X-ray diffraction residual stress tester. Especially, a refined microstructure (grain size: ~100–400 nm) was formed on the topmost surface of twelve-repeat USRP specimen. Subsequently, the fatigue behavior of the specimens was investigated via rotating-bending fatigue tests, and the results suggested that USRP could effectively enhance the fatigue performance of the Ti-6Al-4V alloy. The USRP-induced enhancement mechanism of the fatigue performance can be ascribed to the synergistic effect of the compressive residual stress, microstructure, work hardening, and improved surface quality. The best synergistic effect and, correspondingly, the greatest improvement in the fatigue performance were realized for the one-repeat USRP specimen.
TL;DR: In this article, the microstructure, mechanical and chemical properties of the CoCrBFeNiSi high-entropy alloy (HEA) coatings were investigated, in which 3D wear trace morphology was adopted to analyze the wear resistance of different coatings.
Abstract: The CoCrBFeNiSi high-entropy alloy (HEA) coatings were fabricated on H13 steel using different laser powers. The microstructure, mechanical and chemical properties of the coating and the internal relations between them were investigated, in which 3D wear trace morphology was adopted to analyze the wear resistance of different coatings. The coatings could be divided into three layers with different microstructure including the bottom dendritic layer, the upper amorphous layer and the transition layer. The amorphous content in the coatings was dependent upon laser power which influenced dilution rate and actual cooling rate through changing heat input. Increased amorphous content led to increased microhardness of the coatings which could approach five times of that of the substrate. When the amorphous content decreased, cladded coatings exhibited deeper furrows, more serious adhesive wear and oxidation wear, which gave birth to wider cross section area of the worn track, higher wear weight loss and thus deteriorated wear resistance of the coatings. Moreover, higher amorphous content in the coatings had led to more excellent corrosion resistance to HCl and NaCl solution.
TL;DR: In this article, the corrosion resistance of ZnAl-LDHs intercalated with different anions was compared by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements.
Abstract: Layered double hydroxides (LDHs) have great potential as protective coatings on magnesium alloys due to their nanolamellar structure and exchangeability of interlayer anions. ZnAl layered double hydroxides films intercalated with nitrate anions (ZnAl-NO3−-LDHs) was synthesized on the AZ31 magnesium alloy by hydrothermal method. In order to obtain better corrosion resistance, ZnAl-X-LDHs (X = Cl−, VO43−, PO43−, or MoO42−) were prepared by using ZnAl-NO3−-LDHs as a precursor, and Cl−, VO43−, PO43−, and MoO42− anions intercalated into the LDHs interlayers to replace NO3− through anion-exchange reaction. X-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to investigate structure, morphology and composition of the ZnAl-LDHs. The corrosion resistance of ZnAl-LDHs intercalated with different anions was compared by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the corrosion resistance of ZnAl-LDHs films is ranged in order as follows: ZnAl-VO43−-LDHs > ZnAl-MoO42−-LDHs > ZnAl-PO43−LDHs > ZnAl-Cl−LDHs > ZnAl-NO3−LDHs. ZnAl-VO43−-LDHs has the largest basal spacing distances d(003) value and strongest ability to release anions and absorb chloride ions, so ZnAl-VO43−-LDHs films has the optimal corrosion resistance and can provide enhanced anticorrosion protection for magnesium alloys substrate.
TL;DR: In this paper, the effects of a positive pulse following a high-power impulse magnetron sputtering (HiPIMS) pulse are studied using energy-resolved mass spectrometry.
Abstract: The effects of a positive pulse following a high-power impulse magnetron sputtering (HiPIMS) pulse are studied using energy-resolved mass spectrometry. This includes exploring the influence of a 200 μs long positive voltage pulse (Urev = 10–150 V) following a typical HiPIMS pulse on the ion-energy distribution function (IEDF) of the various ions. We find that a portion of the Ti+ flux is affected and gains an energy which corresponds to the acceleration over the full potential Urev. The Ar+ IEDF on the other hand illustrates that a large fraction of the accelerated Ar+, gain energies corresponding to only a portion of Urev. The Ti+ IEDFs are consistent with the assumption that practically all the Ti+, that are accelerated during the reverse pulse, originates from a region adjacent to the target, in which the potential is uniformly increased with the applied potential Urev, while much of the Ar+ originates from a region further away from the target over which the potential drops from Urev to a lower potential consistent with the plasma potential achieved without the application of Urev. The deposition rate is only slightly affected and decreases with Urev, reaching ~90% at Urev = 150 V. Both the Ti+ IEDF and the small deposition rate change indicate that the potential increase in the region close to the target is uniform and essentially free of electric fields, with the consequence that the motion of ions inside the region is not much influenced by the application of Urev. In this situation, Ti+ will flow towards the outer boundary of the target-adjacent region, with the momentum gained during the HiPIMS discharge pulse, independently of whether the positive pulse is applied or not. The metal ions that cross the boundary in the direction towards the substrate, and do this during the positive pulse, all gain an energy corresponding to the full positive applied potential Urev.
TL;DR: In this paper, the effects of different parameters of USRP on surface roughness, microstructure, mechanical properties and corrosion resistance were investigated, and the results of the test indicate that the surface coarseness is decreased by 91.8% compared with the untreated specimen.
Abstract: Ultrasonic surface rolling process (USRP) is a novel surface nanocrystallization technique based on high frequency impact of tool head. It can generate severe plastic deformation on the surface layer of the material, and greatly enhance the mechanical properties and corrosion resistance of the material. AZ31B Mg alloy was treated by using HK30C ultrasonic surface rolling process (USRP) machine. The effects of different parameters of USRP on surface roughness, microstructure, mechanical properties and corrosion resistance were investigated. The results of the test indicate that the surface roughness is decreased by 91.8% compared with the untreated specimen. Severe plastic deformation in the surface layer of AZ31B Mg alloy is formed by USRP, and the grains in the surfaces layer are remarkably refined. The obvious grain refinement layer is found in surface region of USRPed specimens whose average grain size is 50 times lower than that of the interior grains. The depth of grain refinement layer reaches about 572.71 ± 13.62 μm after USRP. Meanwhile, the surface microhardness is increased by 83.81% compared with inner part. The residual compressive stress, tensile properties, wear resistance and corrosion resistance increase to different degrees after USRP. As the amount of rolling increases, the depth of grain refining layer increases, and the mechanical properties of samples are better. When the amount of rolling is 0.06 mm, compared with the untreated and other treated specimens, it can obtain minimum surface roughness, superior mechanical properties and corrosion resistance, respectively. The surface roughness reduction, surface grain refinement and severe plastic deformation caused by USRP are the main reasons for improving the mechanical properties and corrosion resistance of AZ31B Mg alloy.
TL;DR: In this article, the performance of tungsten carbide (WC-10Co4Cr) and chromium carbide(Cr3C2-25NiCr) based hardmetal coatings sprayed with gaseous and liquid fuelled highvelocity oxygen-fuel (HVOF) spray processes and a modern high-velocity air-fuel spray process was investigated.
Abstract: Thermally sprayed hardmetal coatings are widely used to protect components and surfaces against wear in various applications. Hard and wear resistant coatings increase the component lifetime and can generate significant savings promoting ecological manufacturing. This study focuses on the performance of tungsten carbide (WC-10Co4Cr) and chromium carbide (Cr3C2-25NiCr) based hardmetal coatings sprayed with gaseous and liquid fuelled high-velocity oxygen-fuel (HVOF) spray processes and a modern high-velocity air-fuel (HVAF) spray process. The coating characterisation revealed reduced carbide dissolution with decreasing process temperature and denser feedstock powder particles. Smaller carbide size in the Cr3C2-25NiCr material significantly reduced the carbide rebounding leading to higher carbide content in the sprayed coating and improved erosion wear resistance. Most significant improvements were observed in cavitation erosion for HVAF sprayed WC-10Co4Cr coatings (0.4 μm/h) compared to the HVOF sprayed coatings (1.5–3.7 μm/h). The cavitation erosion resistance of the HVAF sprayed coatings was almost at the level of the WC-10Co sintered bulk (0.2 μm/h).
TL;DR: In this paper, a multi-field coupled 3D mathematical model for cladding Fe60 powder on an ASTM 1045 substrate was established, where the interactions between the powder flow and the laser energy beam, the influence of the surface tension and the buoyancy on the fluid flow in the melt pool, and the instantaneous change in the shape of the cladding layer were considered.
Abstract: Laser cladding is a dynamic physical metallurgy process. Laser cladding exhibits highly complex heat transfer and thermo-elastic-plastic-flow multi-physics field coupling changes, which are accompanied by such physical phenomena as melting, solidification and phase transitions in the metal powder. The temperature and flow fields in the melt pool affect convection, heat transfer, mass transfer, and solidification, which ultimately affect the quality of the cladding layer. It is notably difficult to dynamically track and identify the mechanisms of the multi-physics field coupling evolution process because the laser cladding pool has the characteristics of small volume, large temperature gradient and instantaneous characteristics. In this paper, a multi-field coupled 3D mathematical model for cladding Fe60 powder on an ASTM 1045 substrate was established. In the model, the interactions between the powder flow and the laser energy beam, the influence of the surface tension and the buoyancy on the fluid flow in the melt pool, and the instantaneous change in the shape of the cladding layer were considered. The physical parameters related to the temperature changes in the substrate and the powder were obtained by the CALPHAD (Calculation of Phase Diagram). Finally, the model was solved, and the distribution states and evolution laws for the temperature and velocity fields in the laser cladding process were obtained. The microstructure of the cladding specimen was analyzed by a Zeiss-ƩIGMA HD field emission scanning electron microscope. The experimental results were in good agreement with the calculated results, and the accuracy of the model was verified.
TL;DR: In this paper, the exfoliated graphene from the graphite electrode was electrodeposited into the composite coating by simultaneously exfoliation and deposition in a ternary deep eutectic solvent.
Abstract: How to solve the agglomeration of graphene in the plating bath is an essential challenge to synthesize graphene reinforced composite coatings by electrodeposition. In this paper, the exfoliated graphene (EG) from the graphite electrode was electrodeposited into the composite coating by simultaneously exfoliation and deposition in a ternary deep eutectic solvent. The preparation method is not only simple, but also effective in, and reducing the agglomeration of graphene. The collected EG was characterized by TEM, SEM, and Raman. The results show that few-layers EG is transparent. XRD, SEM, and EDS were used to examine the nickel-graphene composite coating. The results show that the graphene uniformly disperses in the composite coating. The Ni grains are refined, and the crystal plane orientation does not change. Compared with the pure Ni coating, the hardness and wear resistance of the Ni-graphene coating are significantly improved.
TL;DR: In this paper, a detailed wear mechanism of Al-SiC surface composite modified by the impregnation of Graphene, Graphite & carbon nanotubes through friction stir processing (FSP) is documented.
Abstract: Fabricating high wear resistance Al matrix composite without sacrificing its ductility and thermal properties is a critical issue in the designing of Al-based composites. In present study, a detailed wear mechanism of Al-SiC surface composite modified by the impregnation of Graphene, Graphite & carbon nanotubes through friction stir processing (FSP) is documented. The results revealed that with SiC and graphene nanoplatelets (GNP) reinforcements the friction coefficient and specific wear rate decreased by ~34% and ~50% as compared to as-received Al6061 alloy respectively. On the other hand, combination of SiC and carbon nanotubes (CNT) reinforcements severely deteriorates the wear resistance of the composite. The layered structure, large specific surface area and the wrinkled morphology of the graphene flakes are the primary reasons for the increased wear resistance. The exfoliation of GNP to few layered graphene (FLG) under the effect of plastic flow stresses during FSP also contributes significantly to the improvement of surface properties. The abrasion is identified as the dominant wear mechanism in Al-SiC-Graphite & Al-SiC-GNP hybrid composite. Whereas, delamination due to adhesion with the counter surface is the leading mechanism in Al-SiC-CNT hybrid composite. Various characterization strategies such as microstructural characterization through SEM, interfacial study through TEM and phase analysis through XRD corroborate the results. Finally, GNP is identified as the best reinforcement among the carbon family for improvement in wear resistance of Al6061-SiC surface composite.
TL;DR: In this paper, a composite electrode was synthesized through growing V2O5 nanosheet array on free-standing hard carbon fiber fabric by solvothermal reaction, which showed a specific capacity from 241.5 mAh to 77 mAh.
Abstract: Hard carbon with high special capacity has been widely studied as anode for sodium ion batteries (SIBs). Its storage sodium performance still needs to be further improved. Herein, a composite electrode was synthesized through growing V2O5 nanosheet array on free-standing hard carbon fiber fabric by solvothermal reaction. The electrochemical properties of the composite electrode were significantly enhanced compared with pure hard carbon fiber electrode. The composite showed a specific capacity from 241 mA h g−1 at 50 mA g−1 to 77 mA h g−1 at 1000 mA g−1 and a good cycling ability of 184 mA h g−1 after 100 cycles at 100 mA g−1. Except good storage Na ability for V2O5 nannosheets, the improvement of electrochemical performances also benefited from and the synergistic effect from the ability of fast electron transfer of hard carbon and the toleration for Na+ insertion of V2O5 nanosheet array, as well as the inhibitory effect on solid electrolyte interface (SEI) of nanostructure. Additionally, the free-standing electrodes could also increase the energy and power density. This will push the promising hard carbon material used as SIBs anode in practical applications.