Alloy Surface Research Articles

High entropy component-induced nanoscale shear banding and twinning enhance Ti6Al4V alloy surface properties

High-entropy alloys (HEAs) present unique advantages in surface modification due to their stable mixed-state structures and resistance to intermetallic compound formation. This study investigates the surface modification behavior of equiatomic TiNbHfZnZr HEA components in Ti6Al4V alloy using friction stir processing (FSP). The aim is to enhance the mechanical properties and structural stability of Ti6Al4V by incorporating HEA elements. It was found that the introduction of high-entropy alloys forms shear bands with distinctive micro and nano gradient structures on the surface of the Ti6Al4V alloy. These shear bands not only significantly refine the grains but also promote β phase and β twin formation. The HEA-induced shear bands enhance the strength and stability of the alloy by creating bcc twins and dislocation networks that suppress martensitic transformation and maintain superelasticity. Concurrently, the introduction of HEA components leads to the formation of stable dual-phase (α + bcc) microstructures within the α matrix, significantly improving hardness and modulus.

AAO-ZnO nanocomposite coatings on aluminum alloy surface with high bonding strength and long-lasting antibacterial properties

A robust and durable antibacterial nanocomposite coating consisting of anodic aluminum oxide (AAO) and zinc oxide (ZnO) was synthesized by sol–gel deposition of ZnO onto AAO nanotubes. This unique coating features a dual-layer structure: an intermediate AAO + ZnO layer (∼3.9 μm) and a ZnO layer (∼0.8 μm). Nanosized ZnO particles, ranging from 20 to 40 nm, nucleate and grow along the walls of AAO nanotubes within this structure. AAO nanotubes, functioning as “nanocontainers”, offer appropriate sites for the deposition of ZnO particles. The mechanically interlocked AAO + ZnO interlayer enhances the adhesion between the external layer and the inner substrate. Meanwhile, this interlayer facilitates the sustained release of both Zn2+ ions and reactive oxygen species (ROS), effectively impeding bacterial proliferation. Ultraviolet antibacterial tests reveal that the AAO + ZnO interlayer maintains exceptional antibacterial efficacy, even after removing the outermost ZnO layer. The antibacterial rates of the AAO + ZnO interlayer against the above two typical bacteria (E. coli and S. aureus) after 1 h could still reach 91.4 % and 89.0 %, respectively. Specifically, AAO nanopores serve as an inert container for ZnO nanoparticles with consistently release of Zn2+ ions and reactive oxygen species (ROS), thereby ensuring the long-term antibacterial effectiveness of the AAO-ZnO coating. This research also demonstrates the significant potential of AAO-ZnO nanocomposite coating on aluminum alloys for durable antibacterial applications.

Corrosion resistance of magnesium alloy surfaces substantially upgraded by gradient energy irradiation of femtosecond lasers

The poor corrosion resistance of magnesium (Mg) alloys is known to constitute a major obstacle to their practical applications. In this work, we proposed an approach of femtosecond laser multi-grid-scanning with the gradual decreasing energy fluence, to modulate the surface oxide properties for the anti-corrosion performance enhancement. This kind of laser processing can significantly increase the oxide passivation layer thickness by more than 100 times compared with the bare sample, and improve the oxygen content on the material surface to as high as 55.87 %. Simultaneously, the available size of MgO nanograins is further refined and has more spatially uniform distribution. Moreover, the massive production of micro/nano-structures by the femtosecond laser irradiation tends to promote the surface into the superhydrophobic with a contact angle of CA=162 ± 2 ° and a slide angle of SA=1.5 ± 0.5 °. As a result, the obtained optimal values for the corrosion current density and the annual corrosion rate are reduced to Icorr = 0.5 μA/cm2 and CR = 7×10−3 mm/y, respectively, more than 2 orders of magnitude lower than the bare sample. Such a method provides an efficient strategy to enhance the corrosion resistance of metal surfaces for future applications.

Unraveling the effect and difference of S or Si atoms modified Pd-based catalysts in tuning catalytic performance of C2H2 semi-hydrogenation

Modifying the spatial scale of active site has been proven a good strategy for enhancing catalytic performance. In this study, the Pd-based catalysts with different spatial scale of active site were constructed via the modification of non-metallic S or Si atoms over Pd, Cu alloyed Pd SACs, PdAg surface alloy and PdM (M=Au, Ag) IMCs catalysts, then, C2H2 semi-hydrogenation catalytic performance was identified based on DFT calculations. The findings indicate that the catalytic performance of C2H2 semi-hydrogenation is greatly influenced by the spatial extent of active site and the electronic effect modified by the S or Si atoms. Geometric effect caused by S or Si atoms reduces the spatial scale of active site over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1, thereby preventing green oil generation. Electronic effect caused by S or Si atoms leads to far away from the Fermi level of d-band center over S/Pd-2 × 2, Si/Pd-3 × 3, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 to improve C2H4 production activity and selectivity. Seven catalysts S/Pd-2 × 2, Si/Pd-3 × 3, PdCu-2 × 2, S/Pd6Ag, S/Pd1Au1, S/Pd1Ag1 and Si/Pd1Ag1 are screened out to present high selectivity and activity of C2H4 production, and effectively prevent green oil generation. This study provides valuable structural insights for designing high-performance catalysts by the modification of non-metallic atom in C2H2 semi-hydrogenation.

Microstructure evolution and fatigue crack propagation of AlCoCrFeNi2.1 high entropy alloy after electron beam surface modification

AlCoCrFeNi2.1 eutectic high-entropy alloy has good fatigue properties. However, its application in engineering is hindered by as-cast defects. To solve this problem, vacuum electron-beam surface modification is used to strengthen the surface of as-cast high-entropy alloy. It has been discovered that the remelting zone is still composed of body-centered cubic and face-centered cubic phases and that its phase size is refined. A surface-modified structure consisting of the compact RZ and a heat affect zone is obtained, by applying the same fatigue load to the samples before and after electron-beam, respectively. The fatigue crack growth rate of the electron-beam surface-modified material is slower and its life to fracture is longer. Additionally, the fan-shaped fracture and tear edges are typical fracture characteristics of the specimens before and after modification. The results show that with a significant reduction in phase size, the phase boundary density increases. The enhancement of the high-angle grain boundary content and changes in the stress state are also critical factors for the inhibition of fatigue crack growth rate.

Effect of pulse laser nitriding on the superheated steam corrosion behavior of Zr alloy

Zirconium (Zr) alloy fuel cladding is exposed to harsh environments such as high temperature and high pressure for a long time. Surface modification technology can effectively improve its high-temperature oxidation resistance. In this work, pulse laser nitriding technology was used to perform laser nitriding treatment on Zr alloys at different laser energies. The effect of different energy levels of laser nitriding treatments on the superheated steam corrosion resistance of Zr alloys was studied. First-principles was used to reveal the mechanism of how the diffusion layer improves the performance of Zr alloys in resisting superheated steam corrosion after nitriding treatment. Results indicate that the surface of Zr alloys treated with laser nitriding exhibits a molten feature. When the laser energy is 100 mJ, N mainly exists in the form of a diffusion layer in the Zr alloy substrate. As the laser energy rises to 200 mJ and above, the ZrN phase is generated. After 1000 h of superheated steam corrosion, the corrosion weight gain of the 100 mJ sample was reduced by approximately 50 % compared to the Zr alloy. The corrosion weight gain of the 400 mJ sample increased by approximately 12 %. The presence of the ZrN phase accelerates the oxidation degradation rate of Zr alloy. When N atoms exist as a diffusion layer, the transition from tetragonal zirconia to monoclinic zirconia can be suppressed. First-principles calculations showed that when O and N atoms coexist in the Zr alloy substrate, their binding performance with surface O is significantly decreases, thus further improving the 100 mJ sample's resistance to superheated steam corrosion.

A novel strategy for constructing active anti-corrosive coatings by embedding three-dimensional fiber networks

The corrosion protection effectiveness of micro/nanocontainer-based intelligent coatings significantly depends on their dispersion within the coating matrix. Inspired by the bionic concept of a ‘vascular network’ we designed a polylactic acid (PLA) three-dimensional fiber network incorporating the pH-responsive TiO2-8-hydroxyquinoline (TiO2-8HQ) nanotubes using electrospinning technology. These TiO2-8HQ@PLA networks are crosslinked and evenly dispersed on the Mg alloy surface, responsive to local pH variations. The encapsulated 8HQ inhibitors release rapidly in alkaline conditions, transporting through the network to enable continuous self-healing in multi-defect areas. An epoxy coating applied over the network forms a novel vascular network intelligent coating. Electrochemical and surface analysis tests reveal that 2 %TiO2-8HQ@PLA-EP provides the most enduring corrosion resistance over 50 days in a 3.5 wt% NaCl solution, with a coating resistance of 2.33 × 106 Ω cm2 and charge transfer resistance of 4.81 × 106 Ω cm2. Additionally, the network enhances adhesion strength (38.01 MPa) and surface wettability (104.25° ± 0.15°), significantly improving the coating’s physical barrier performance. The combination of the micro/nanocontainers technology and vascular network innovative design provides a unique insight into active corrosion control on diverse metals.

Enhancing the dipole ring of hexagonal boron nitride nanomesh by surface alloying

Surface templating by electrostatic surface potentials is the least invasive way to design large-scale artificial nanostructures. However, generating sufficiently large potential gradients remains challenging. Here, we lay the groundwork for significantly enhancing local electrostatic fields by chemical modification of the surface. We consider the hexagonal boron nitride (h-BN) nanomesh on Rh(111), which already exhibits small surface potential gradients between its pore and wire regions. Using photoemission spectroscopy, we show that adding Au atoms to the Rh(111) surface layer leads to a local migration of Au atoms below the wire regions of the nanomesh. This significantly increases the local work function difference between the pore and wire regions that can be quantified experimentally by the changes in the h-BN valence band structure. Using density functional theory, we identify an electron transfer from Rh to Au as the microscopic origin for the local enhancement of potential gradients within the h-BN nanomesh.

Study on electrochemical polishing mechanism of TC4 titanium alloy

To achieve a high-quality and precise surface on TC4 titanium alloy for demanding engineering applications, electrochemical polishing (ECP) technology was employed to investigate the polishing process of TC4 titanium alloy in an ethylene glycol-sodium chloride green electrolyte. The macro and micro morphology, surface roughness, material removal rate, surface elements, surface corrosion resistance, and surface hardness of TC4 titanium alloy were measured before and after polishing. Single-factor experiments were conducted to explore the effects of processing gap, electrolyte temperature, polishing voltage, and polishing time on TC4 titanium alloy surface quality. Optimal polishing parameters were determined to be an electrode gap of 12 mm, a voltage of 20 V, a temperature of 40 °C, and a polishing time of 10 min. The experimental results indicated that after electrochemical polishing, the workpiece surface roughness Ra decreased from 256 nm to 25 nm, achieving a roughness reduction rate of 90.23%, the material removal rate was 3.348 μm min−1. The self-corrosion potential of the polished surface increased from −0.416 V to −0.375 V and the self-corrosion current density decreased from 4.447 × 10−7 A·cm−2 to 1.873 × 10−7 A·cm−2, the surface indentation hardness of the workpiece decreased from 5.8669 GPa to 4.6726 GPa. Based on the characterization of polished surface, the mechanism of electrochemical polishing of TC4 titanium alloy was proposed. The results demonstrate that electrochemical polishing of TC4 titanium alloy is highly efficient, involves no mechanical action, and causes no subsurface damage, making it a promising technology to meet medical requirements.

Effect of the alloying element Sc and Zr in 5B70 Al alloy on the microstructure, toughness and tribological properties of MAO ceramic film

The existence form of alloying element Sc and Zr in the micro arc oxidation (MAO) ceramic film on 5B70 Al alloy and their effects on the microstructure, fracture toughness, and tribological properties of the MAO ceramic film was investigated. The findings suggested that the Zr element primarily existed in the form of ZrO2, distributed around the Al2O3 phase. The Sc element remained spherical and dispersed in the form of Al3Sc in the ceramic film. The synergistic effect of ZrO2 and Al3Sc significantly improved the hardness, fracture toughness, and wear resistance of the dense layer in MAO ceramic film on 5B70 Al alloy. This provided theoretical basis and technical support for the development of high-performance MAO composite films on Al alloy surfaces.

Substrate dilution and interface structures of tungsten coating deposited by double-glow plasma surface alloying on stainless steel substrate

W-coating layers with varying thicknesses up to 10 μm were deposited by double-glow plasma surface alloying (DGPSA) on finely polished stainless steel (SS304L) substrates to investigate the influence of the substrate on both the W-coating and interface structures. The examination revealed substrate dilution and the presence of oxide crystallites, predominantly FeWO4 and WO2, at the interface between W and SS304L. These observations correlated with the occurrence of cracking and peeling-off of the W-coating. Both Cr and Ni showed decreased distribution in the interface layer compared to their distribution in the W-coating and SS304L substrate. In comparison, Fe demonstrated a more noticeable compositional gradient, decreasing monotonically from SS304L across the interface to the W-coating. The depth distribution of O indicated that its inclusions were influenced not only by DGPSA deposition but also by post-deposition ion-beam milling. Additionally, the presence of spherical particles directly on the substrate's surface provided evidence for surface alloying reactions, while the columnar grains within the interface oxide layer were associated with the texture features of the W-coating, as confirmed by X-ray diffraction and pole-figure measurements. These findings offer valuable insights into the surface alloying process facilitated by DGPSA and its potential for developing W-coatings tailored for plasma-facing applications.

Effect of hot isostatic pressing on microstructure and properties of cooled hot dip aluminum coating in magnetic field

The effect of hot isostatic pressing (HIP) on the microstructure and properties of hot dip aluminum coating cooled in a magnetic field was investigated in this study. In order to improve the microstructure and properties of magnetic dip aluminum coating, hot isostatic pressing technology was used for post-treatment. Initially, a traditional aluminum-impregnated coating was prepared on the surface of titanium alloy TA15, an alternating electromagnetic field was applied during the forming and solidification process of the coating. Finally, the coating was treated with hot isostatic pressing technology. Analyzed three different coatings of the microstructure and element distribution, and tested the microhardness of the coatings at various positions. The test results revealed that the TA15 titanium alloy hot-dip aluminum coatings obtained through the three different processes exhibited a gradient structure. Compared with the traditional hot-dipped aluminum air-cooled coating, when an appropriate intensity of alternating electromagnetic field was applied during the coating solidification process, the outer coating structure was enhanced, the number of holes was reduced, the microstructure density increased, and the number of cracks significantly decreased. The defects of the 800 °C hot isostatic magnetic cold and hot dip aluminum coating were repaired under high temperature and pressure, resulting in a uniform and fine microstructure. The comprehensive properties of the magnetic cold and hot dip aluminum coating on the surface of the titanium alloy were effectively enhanced through hot isostatic pressing.

Ultra-strong bonding of 30-wt% GF/PET-A2024 aluminium alloy via collaborative promotion of ultrasonic-assisted FeCl3+N2H4 corrosion and the coordination bonds by Zr4+

Enhancing the bonding strength between metals and polymers is advantageous for hybrid structures used in aerospace and power electronics applications. This study, conducted for the first time, involves the preparation of multi-scale “honeycomb-meteorite crater” morphologies on the surface of A2024 aluminium alloy through a multi-step ultrasonic-assisted corrosion treatment. The ultrasonic-assisted FeCl3/N2H4 corrosion process increased the interfacial tensile shear strength of a 30-wt% glass fibre reinforced PET-A2024 aluminium alloy joint (expressed as 30-wt% GF/PET-A2024) to 32.0 MPa. Coating Zr4+ substantially enhances the hydrophilicity of the A2024 surface; however, the coordination bonding effect of Zr4+ can only be activated after prolonged heat treatment (100 °C, 3 h). With the combined effects of multi-scale mechanical interlocking and coordination bonding of Zr4+, the tensile shear strength of the 30-wt% GF/PET-A2024 joint can reach 56.5 MPa, surpassing existing works by a significant margin. Experimental results and Density Functional Theory (DFT) calculations demonstrate that the optimal concentration for Zr4+ treatment is 1.5 wt%. Excessive Zr4+ would lead to ion-dipole interactions, which diminish the interface bonding strength; when the concentration of Zr4+ is 2 wt%, The joint strength dropped sharply to 39.1 MPa. This study provides a comprehensive discussion on ultrasonic-assisted corrosion and the effect of Zr4+, offering valuable insights for future research aimed at enhancing the interfacial bonding strength between polymers and metals.

Hydrogen penetration into the NiTi superelastic alloy investigated in-situ by synchrotron diffraction experiments

Microstructural changes induced by a hydrogen permeation into the NiTi superelastic alloy were investigated in-situ using the X-ray synchrotron diffraction. A new design of an electrochemical cell enabled to uncover time and position dependent processes under a flat alloy surface exposed to the cathodic hydrogen. The diffraction data supported by thermo-elastic FEM calculations helped to quantify an evolution of compressive stresses in the B2 austenitic phase hosting hydrogen atoms. The compressive stress state initiates a formation of martensitic phases starting from the exposed surface layer and advancing into the alloy volume with increasing time of hydrogen charging. We have performed the ab-initio DFT study in order to rationalize volumetric changes associated with variations in the B2 austenite and B19′ martensite lattice parameters. The numerical results also contributed to the identification of a new hydride phase with orthorhombic crystal structure and lattice parameters a = 0.8505 nm, b = 0.7366 nm and c = 0.4722 nm.

Effect of the energy density of pulsed electron beam on the microstructure and properties of Mo-Zr surface alloys

Lasers and electron beams have been widely used to synthesize various surface alloys (SAs) but no data have been reported so far on the molybdenum-zirconium (Mo-Zr) ones. To partially fill this knowledge gap, Mo-Zr SAs were formed by processing molybdenum films on zirconium substrates with low-energy high-current electron beams (LEHCEBs). The effect of the energy density of LEHCEBs on the microstructure, phase composition, nanohardness and corrosion resistance of the Mo-Zr SAs were investigated. Basically, the Mo-Zr SAs consisted of a solid solution of Mo in the β-Zr phase, Mo2Zr second phase particles (SPPs) and a solid solution Zr in Mo. Increasing in the energy density decreased the concentration of the SPPs and enhanced the content of the β-Zr phase. Also, it affected the depth of the highest concentration of the SPPs. In the zones of the highest molybdenum contents, the nanohardness values reached 9.4–12.7 GPa, which was higher by 3.2–4.4 times than that of the zirconium substrates. In a 3.5 % NaCl solution at room temperature, the corrosion current densities and the corrosion potentials were greater than those of the zirconium substrates by six and almost two times, respectively.

High temperature oxidation resistance and thermodynamic properties of (TaNbZr)N and (TaNbZr)C quaternary ceramic coating

A TaNbZr-based quaternary ceramic coating with a metallurgical transition layer on a titanium alloy surface has been produced. The quaternary ceramic coatings exhibit a face-centered cubic structure and distinct structural orientation. The introduction of carbon and nitrogen significantly improved high-temperature oxidation resistance compared to metallic coatings in cyclic oxidation tests. Specifically, the (TaNbZr)N coating provided effective thermal protection during 800 °C cyclic oxidation for 100 hours (10 cycles). The phase stability and evolution of quaternary ceramic coatings were clarified using in-situ XRD. Further, first-principles calculations elucidated the enhanced thermal stability and high-temperature performance of (TaNbZr)N and (TaNbZr)C coatings.

Research on the osteogenic properties of 3D-printed porous titanium alloy scaffolds loaded with Gelma/PAAM-ZOL composite hydrogels

Although titanium alloy is the most widely used endoplant material in orthopedics, the material is bioinert and good bone integration is difficult to achieve. Zoledronic acid (ZOL) has been shown to locally inhibit osteoclast formation and prevent osteoporosis, but excessive concentrations of ZOL exert an inhibitory effect on osteoblasts; therefore, stable and controlled local release of ZOL may reshape bone balance and promote bone regeneration. To promote the adhesion of osteoblasts to many polar groups, researchers have applied gelatine methacryloyl (Gelma) combined with polyacrylamide hydrogel (PAAM), which significantly increased the hydrogen bonding force between the samples and improved the stability of the coating and drug release. A series of experiments demonstrated that the Gelma/PAAM-ZOL bioactive coating on the surface of the titanium alloy was successfully prepared. The coating can induce osteoclast apoptosis, promote osteoblast proliferation and differentiation, achieve dual regulation of bone regeneration, successfully disrupt the balance of bone remodelling and promote bone tissue regeneration. Additionally, the coating improves the metal biological inertness on the surface of titanium alloys and improves the bone integration of the scaffold, offering a new strategy for bone tissue engineering to promote bone technology.

Study on the synergistic effect of second phases and product films to significantly improve the corrosion resistance of Mg-Gd-Y-Nd alloy

A uniform and compact product film with the same microstructure as Mg substrate is formed on the surface of Mg-RE alloy in NaCl solution, which still keeps in good condition after immersion for 5 months. Formation mechanism of the special film was investigated by electrochemical measurements, transmission electron microscopy (TEM), scanning kelvin probe microscopy (SKPM) and finite element modelling (FEM). The results show that fine and evenly distributed second phases provide reasonable galvanic effects, resulting in uniform self-corrosion of substrate, the stable “skeleton structure” of second phases and product film PBR of 1.33 also play key roles in corrosion resistance.

Dual-metal-based (Mo, Ni) MOFs nanoplates for enhanced corrosion resistance and frictional resistance of epoxy resin on magnesium alloy surfaces

Magnesium alloys face severe corrosion issues due to their high electrochemical activity. In recent years, polymer coatings containing metal-organic frameworks (MOFs) have shown great potential in improving the corrosion resistance of metals. In this study, nickel salts and molybdate were used as metal sources, and 4,4′-bipyridine was used as the organic ligand. For the first time, a nickel and molybdenum-based metal-organic framework (Mo-Ni-MOF) was synthesized via hydrothermal method. Mo-Ni-MOFs were then incorporated as nanofillers into epoxy resin and coated on AK61M magnesium alloy to enhance its long-term corrosion resistance. Characterization tests including FT-IR, FE-SEM, EDX, XRD and XPS confirmed the successful reaction between metal ions and organic ligands, indicating successful coordination. TEM analysis revealed that the MOFs consisted of nanosheets with diameters ranging from 20 to 100 nm. BET analysis demonstrated the porous structure of the synthesized nanoparticles, with a high specific surface area ranging from 6 to 44 m2.g−1 and an average pore size ranging from 9 to 32 nm. Salt spray tests demonstrated that MOFs synthesized under different conditions exhibited superior long-term corrosion resistance compared to pure epoxy coatings in artificial scratch coating performance. Electrochemical impedance spectroscopy (EIS) testing revealed a three-order-of-magnitude enhancement in |Z| at 0.01 Hz for the most effective MOF compared to pure epoxy resin. Tafel tests showed a significant decrease in corrosion current, with reductions of 2–3 orders of magnitude. Friction tests revealed a decrease in the coefficient of friction after the addition of MOFs, with reductions ranging from 0.1 to 0.4, indicating improved durability of the coating against friction.

Preparation and characterisation of black conversion coating of Cr(NO3)3–CoCl2–NiCl2 of Zn–Ni alloy electroplated on 2024 aluminium alloy surface

AbstractTo meet the application requirements of electronic connectors, a trivalent chromium process (TCP) conversion coating was prepared on the Zn–Ni alloy plating of 2024 aluminium alloy. The composition of the TCP solution was as follows: 45 g/L Cr(NO3)3, 14 g/L CoCl2, 1.3 g/L NiCl2, 10 g/L citric acid, 10 g/L succinic acid and 1 g/L sodium dodecyl sulphate. The properties of TCP were characterised by a range of techniques, including macroscopic observations, scanning electron microscope, energy‐dispersive X‐ray spectrometer, three‐dimensional (3D) morphometry, electrochemical impedance spectroscopy, polarisation curves and conductivity tests. The TCP prepared in this experiment exhibits a uniform black colour and bright appearance, predominantly composed of Zn, Ni, O, Cr and Co. The TCP enhances the impedance of Zn–Ni alloys, reduces the corrosion current to 1.99 × 10−5 A/cm2 and maintains a flatter surface 3D morphology and less surface roughness following electrochemical testing. It has better corrosion resistance. Following the preparation of the TCP on a suitably sized shell sample, the shell resistance was 1.2 mVDC with good electrical conductivity, which meets the requirements for electrical connector applications.