Pure Titanium Substrate Research Articles

Titanium surface functionalization via directed energy deposition of CuNiTi ternary alloy

Pure titanium is a soft material that tends to degrade quickly during service due to wear and microbiologically influenced corrosion. Therefore, current research aims at the deposition, microstructural characterization, and surface functionalization of the TiCuNi coatings on pure titanium substrate to improve its surface properties. Cu–Ni premixed elemental powders are deposited on the pure Ti by laser-directed energy deposition (LDED) using a novel method of extracting Ti from the substrate through melt pool convection. The single-track deposit geometry and integrity characterization using dilution percentage, heat-affected zone width (HAZ), and microhardness values show the sound metallurgical bonding with the substrate. The X-ray diffraction (XRD) pattern and microstructure image reveal the presence of NiTi binary (B2) and Ti2CuNi ternary (B19) hard phases and equiaxed dendritic morphology, respectively, demonstrating ternary alloy coating formation. The microhardness value of the coatings is thrice that of the substrate due to the presence of hard NiTi (B2) binary and Ti2CuNi (B19) ternary phases. The coating’s wear resistance is significantly (80%) higher than the substrate, owing to hard phases and Cu as a solid lubricant. The wear track consists of small grooves, adhered debris, and a smooth profile, mainly due to a significant reduction in adhesion and abrasion compared to the substrate. Moreover, the polarisation corrosion potential and current density are increased and decreased by 53% and 97%, respectively, displaying symbolic improvement in the corrosion resistance. Hence, this work has presented the LDED ability to enhance the pure Ti anti-wear and corrosion resistance properties by depositing CuNiTi ternary alloy coating for potential aerospace, marine, and biomedical applications.

Cytotoxicity and antibacterial susceptibility assessment of a newly developed pectin–chitosan polyelectrolyte composite for dental implants

Biopolymers such as chitosan and pectin are currently attracting significant attention because of their unique properties, which are valuable in the food industry and pharmaceutical applications. These properties include non-toxicity, compatibility with biological systems, natural decomposition ability, and structural adaptability. The objective of this study was to assess the performance of two different ratios of pectin–chitosan polyelectrolyte composite (PCPC) after applying them as a coating to commercially pure titanium (CpTi) substrates using electrospraying. The PCPC was studied in ratios of 1:2 and 1:3, while the control group consisted of CpTi substrates without any coating. The pull-off adhesion strength, cytotoxicity, and antibacterial susceptibility tests were utilized to evaluate the PCPC coatings. In order to determine whether the composite coating was the result of physical blending or chemical bonding, the topographic surface parameters were studied using Fourier transform infrared spectroscopy (FTIR) and atomic force microscopy (AFM). PCPC (1:3) had the highest average cell viability of 93.42, 89.88, and 86.85% after 24, 48, and 72 h, respectively, as determined by the cytotoxicity assay, when compared to the other groups. According to the Kirby–Bauer disk diffusion method for testing antibacterial susceptibility, PCPC (1:3) showed the highest average diameter of the zone of inhibition, measuring 14.88, 14.43, and 11.03 mm after 24, 48, and 72 h of incubation, respectively. This difference was highly significant compared to Group 3 at all three time periods. PCPC (1:3) exhibited a significantly higher mean pull-off adhesion strength (521.6 psi) compared to PCPC (1:2), which revealed 419.5 psi. PCPC (1:3) coated substrates exhibited better surface roughness parameters compared to other groups based on the findings of the AFM. The FTIR measurement indicated that both PCPC groups exhibited a purely physical blending in the composite coating. Based on the extent of these successful in vitro experiments, PCPC (1:3) demonstrates its potential as an effective coating layer. Therefore, the findings of this study pave the way for using newly developed PCPC after electrospraying coating on CpTi for dental implants.

Electrophoretic Deposition and Characterization of Curcumin/Chitosan Coatings

The purpose of the study was to investigate the electrophoretic deposition (EPD) route, microstructure and surface properties of composite curcumin/chitosan coatings on commercially pure titanium substrates for biomedical applications. Multiple routes of preparation of the dispersed systems for the EPD process and their electrokinetic properties have been investigated to obtain homogeneous coatings. The zeta potential of solutions with various curcumin content in ethanol or isopropanol proved their relatively low electrophoretic mobility. Thus, curcumin was co-deposited with chitosan molecules on the cathode. The surface morphology of the coatings consisted of submicrometric curcumin particles embedded in the chitosan matrix. The increase in the curcumin content in the ethanol caused large agglomerates and undissolved curcumin particles to appear on the coating surface. The coatings were characterized by high adhesion to the substrate and a water contact angle in the range of 85° to 95°. The coatings changed the zeta potential of the titanium surface from significantly negative (−46.7 ± 2.3 mV) to less negative values (−20.6 ± 2.6 mV). The developed coatings are promising for mitigating biofilm formation on the surface of titanium bone implants.

Characterization of Electrochemical and Biocompatibility of Zinc Oxide Coating Electrodeposited on Commercial Pure Titanium Alloy

This study examines how the duration of electrodeposition affects the morphology and electrochemical characteristics of zinc oxide coatings applied to a pure titanium substrate. The morphology of the coating and the phases present within it are analyzed using a scanning electron microscope and the X‐ray diffraction technique. The coating's resistance to corrosion in a phosphate‐buffered saline solution is evaluated using two electrochemical methods: impedance spectroscopy and potentiodynamic polarization tests. The surface roughness of the coated samples is assessed using interferometry. The results demonstrate that an increase in electrodeposition time, ranging from 150 to 1200 s, leads to an enhanced texture intensity in the (0002) and (010) planes of the ZnO coating. Furthermore, the thickness of the ZnO crystals and surface roughness increases by factors of 3.25 and 2.79, respectively, as the deposition time is extended. This extended duration results in the formation of larger needle‐shaped and flower‐like ZnO crystals, leading to a significantly nonuniform structure. Correspondingly, the corrosion rate also increases as the electrodeposition time is extended from 150 to 1200 s, rising from 0.001951 to 9.117 μm year−1. The lowest corrosion rate (1.654 μm year−1) is achieved in coatings deposited for 300 s using a potential of 3 V.

Improvement of biomedical properties of PEO-treated titanium with flurbiprofen and exosome conjugation

Exosome (EXO)-based drug delivery systems have attained a desirable position among scientific researchers and in biomedical applications. In this study, an exosomal coating comprising the anti-inflammatory drug flurbiprofen (FLB) was applied on a commercially pure titanium (cp-Ti) substrate that had undergone surface treatment using plasma electrolytic oxidation (PEO) process. The samples were characterized through field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and water contact angle (WCA) measurement. The results indicated that FLB was loaded onto the EXO and the formation of FLB.EXO was confirmed by FTIR, XRD, AFM and FESEM. Furthermore, FLB.EXO system was treated on PEO-treated substrates and FLB.EXO@PEO system demonstrated a considerable degree of roughness (Ra= 51.16 nm) and exceptional WCA (37.2 ± 0.7 ̊) in comparison to the other samples. The cellular inquiries were assessed through examination of the morphology of bone marrow mesenchymal stem cells (BMMSc) and the MTT assay. The cytotoxicity assessment showed that the FLB.EXO@PEO improved BMMSCs attachment without toxicity. The antibacterial efficacy was determined by means of bacterial adhesion testing against both gram-positive Staphylococcus aureus (S. aureus) and gram-negative Escherichia coli (E. coli) bacterial strains. FLB.EXO@PEO sample also revealed an excellent antibacterial rate of ∼ 86 % against S. aureus and ∼ 55 % against E. coli. Additionally, in vitro drug release evaluations indicated that sustained drug release was occurred and FLB released from FLB.EXO@PEO during 191 h that was lower than release time in FLB.EXO (120 h). Moreover, the prolonged release was confirmed by constant release rate in both of systems of FLB.EXO and FLB.EXO@PEO after 191 h and 167 h, respectively. The release kinetic of FLB.EXO and FLB.EXO@PEO followed the zero order and first-order model, respectively. Overall, the results indicate that the designed sustained release system have a high potential for development of advanced biomedical implants.

A novel synthetic strategy of mesoporous Ti4O7-coated electrode for highly efficient wastewater treatment

Suboxidized titanium, as a promising anode for electrocatalytic oxidation reactions in wastewater treatment, presents a viable pathway to solve the challenging water pollution. However, current suboxidized titanium anodes are primarily fabricated hot pressing of by suboxidized titanium powders, further hampering their application in wastewater treatment due to high costs and complex shaping processes. To overcome these limitations, this work employs the plasma electrolytic oxidation (PEO) technology to in-situ fabricate porous TiO2 coating precursors on commercial pure titanium substrates, followed by an annealing process to carefully reduce the TiO2 coatings with hydrogen gas, and finally achieving the cost-effective production of high-purity Magnéli phase Ti4O7-coated electrode. The obtained Ti4O7-coated electrodes exhibit a highly ordered granular structure, good crystallinity, wide electrochemical window, and low interfacial charge transfer resistance. Importantly, the Ti4O7-coated electrodes also offer a simple fabrication process, lower energy consumption, and reduced costs compared to advanced boron-doped diamond (BDD) and bulk Ti4O7 electrode. The electrochemical oxidation tests also demonstrate that Ti4O7-coated electrodes can achieve the complete degradation of 100 mg/L phenol within 240 minutes, exhibiting excellent catalytic activity and potential applications in wastewater treatment.

Influence of Thickness on the Structure and Biological Response of Cu-O Coatings Deposited on cpTi

This work presents results on the influence of thickness on the structure and biological response of Cu-O coatings deposited on commercially pure titanium (cpTi) substrates using direct current (DC) magnetron sputtering. The deposition times were 5, 10, and 15 min to obtain coatings with different thicknesses. The results show that the films deposited for 5, 10, and 15 min correspond to thicknesses of 41, 74, and 125 nm, respectively. The phase composition of the coatings is in the form of a double-phase structure of CuO and Cu2O in all considered cases. The roughness is on the nanometric scale and no obvious trend as a function of the thickness can be observed for the deposited films. Also, it was found that, with an increase in the thickness of the films, the distribution of the heights becomes closer to symmetrical. The antimicrobial efficacy of different Cu-O-coated cpTi substrates was examined using a direct contact experiment. A possible bactericidal effect was investigated by inoculating a 200 μL bacterial suspension on CuO-coated cpTi and cpTi (control) for 24 h at 37 °C. The results showed that Cu-O-coated cpTi substrates have a 50%–60% higher antimicrobial activity than the substrate. At the same time, human osteosarcoma (MG-63) cells growing on Cu-O-coated cpTi substrates showed 80% viability following 24 h incubation. Depending on magnetron sputtering process parameters, a different coating thickness, various crystallite phase compositions, and diverse biocompatibility were obtained.

C.P titanium/Ti–6Al–4V joint by spark plasma welding: Microstructure and mechanical properties

The welding ability of Ti–6Al–4V alloy is weak due to their two-phase microstructure. On the other hand, friction welding methods lead to significant microstructural changes. In this research, for the first time, pure titanium was successfully joined to the Ti–6Al–4V alloy, without any change in the microstructure and mechanical properties of both alloys, by applying the SPW method. Further, the effects of temperature, pressure, and time of the SPW process on the microstructure and mechanical properties of commercial pure (C.P) titanium joined to the Ti–6Al–4V alloy were investigated. The results indicated that the effect of temperature and pressure on the SPW process was greater than that of time. Further, mechanical properties investigations showed that the yield strength of the joint interface was larger than that of the substrate metal, following which necking and fracture occurred in the pure titanium substrate metal. The alloy (Ti–Ti64) bonded at 800 °C, with a time of 10 min and pressure of 20 MPa, exhibited the superior bonding of 7–9 μm interface thickness, and excellent tensile strength (534 ± 13 MPa) and Vickers micro-hardness (190 ± 5 HV0.1). Investigation of the effect of pressure (normal stress) also showed that with an increase in pressure, because of the reduction of the chemical potential of diffusing species, the joint temperature would drop, and the joint could be created at a temperature below 800 °C.

Penning ion source based surface modification of titanium by nitrogen ion implantation

The nitrogen ions of the Penning ion source are bombarded on commercially available pure titanium substrates in pulses of about 5.6 μs duration. A thin film (∼500 nm) of multiphase titanium nitride is produced without additional heating of the substrate. The surface modification is studied for various energies of implanted ions at a low flux density. The 2.4 × 109 ions of specific energy are bombarded on the sample in each single pulse of the ion. Each sample is exposed to one thousand such pulses at a repetition rate of 0.1 Hz. The corresponding energy flux was transferred to the sample, promoting the growth of a thin nitride layer. X-ray diffraction (XRD) analysis demonstrates the formation of a monocrystalline multiphase titanium nitride thin film. The XRD spectra show the multiphase reflections of Ti4N2 (111), Ti9N3.87 (009), and Ti12N7 (0012) that depend on the energy of the ion beam. Ti4N2 is observed to be the dominant phase in this ion implantation process. The morphological and compositional changes of ion implanted samples are investigated using field emission scanning electron microscopy (SEM) along with energy dispersive x-ray spectroscopy (EDX). Raman scattering analysis of treated samples verified the XRD results. The penetration depth of nitrogen ions inside the titanium is calculated using the SRIM code. Vickers hardness has improved three times compared to the original sample.

Exploring the potential of a newly developed pectin-chitosan polyelectrolyte composite on the surface of commercially pure titanium for dental implants

Pectin and chitosan are natural polysaccharides obtained from fruit peels and exoskeletons of crustaceans and insects. They are safe for usage in food products and are renewable and biocompatible. They have further applications as wound dressings, body fat reduction, tissue engineering, and auxiliary agents in drug delivery systems. The healing process is usually long and painful. Adding a new material such as a pectin-chitosan composite to the implant surface or body would create unique biological responses to accelerate healing and delivery of target-specific medication at the implant site. The present study utilized the electrospraying process to create pectin-chitosan polyelectrolyte composite (PCPC) coatings with various ratios of 1:1, 2:1, 1:2, 1:3, and 3:1 on commercially pure titanium substrates. By means of FESEM, AFM, wettability, cross-cut adhesion, and microhardness were assessed the PCPC coatings’ physical and mechanical properties. Subsequently, the antibacterial properties of the coating composite were assessed. AFM analysis revealed higher surface roughness for group 5 and homogenous coating for group 1. Group 3 showed the lowest water contact angle of 66.7° and all PCPC coatings had significantly higher Vickers hardness values compared to the control uncoated CpTi samples. Groups 3 and 4 showed the best adhesion of the PCPC to the titanium substrates. Groups 3, 4, and 5 showed antibacterial properties with a high zone of inhibitions compared to the control. The PCPC coating's characteristics can be significantly impacted by using certain pectin-chitosan ratios. Groups 3 (1:2) and 4 (1:3) showed remarkable morphological and mechanical properties with better surface roughness, greater surface strength, improved hydrophilicity, improved adhesion to the substrate surface, and additionally demonstrated significant antibacterial properties. According to the accomplished in vitro study outcomes, these particular PCPC ratios can be considered as an efficient coating for titanium dental implants.

Effects of Electrical Parameters on Micro-Arc Oxidation Coatings on Pure Titanium.

The micro-arc oxidation process was used to apply a ceramic oxide coating on a pure titanium substrate using calcium acetate and sodium dihydrogen phosphate as an electrolyte. The influence of the current frequency and duty ratio on the surface morphology, phase composition, wear behavior, and corrosion resistance were analyzed by employing a scanning electron microscope, X-ray diffractometer, ball-on-disk apparatus, and potentiodynamic polarization, respectively. Analyses of the surface and cross-sectional morphologies revealed that the MAO films prepared via a low current frequency (100 Hz) and a high duty ratio (60%) had a lower porosity and were more compact. The medium (500 Hz) and high (1000 Hz) frequencies at the higher duty ratios presented with better wear resistance. The highest film thickness (11.25 µm) was achieved at 100 Hz and a 20% duty ratio. A negligible current density was observed when the frequency was fixed at 500 Hz and 1000 Hz and the duty cycle was 20%.

Nano selenium-doped TiO2 nanotube arrays on orthopedic implants for suppressing osteosarcoma growth.

Osteosarcoma, the most common primary malignant bone tumor, is characterized by malignant cells producing osteoid or immature bone tissue. Most osteosarcoma patients require reconstructive surgery to restore the functional and structural integrity of the injured bone. Metal orthopedic implants are commonly used to restore the limb integrity in postoperative patients. However, conventional metal implants with a bioinert surface cannot inhibit the growth of any remaining cancer cells, resulting in a higher risk of cancer recurrence. Herein, we fabricate a selenium-doped TiO2 nanotube array (Se-doped TNA) film to modify the surface of medical pure titanium substrate, and evaluate the anti-tumor effect and biocompatibility of Se-doped TNA film. Moreover, we further explore the anti-tumor potential mechanism of Se-doped TNA film by studying the behaviors of human osteosarcoma cells in vitro. We provide a new pathway for achieving the anti-tumor function of orthopedic implants while keeping the biocompatibility, aiming to suppress the recurrence of osteosarcoma.

Improving corrosion resistance of pure titanium by simple and controlled oxidation for biomedical applications

AbstractIn this study, the TiO2 passive layer was formed on a pure titanium substrate by simple oxidation in an aqueous solution of H2O2 35 wt.%. In order to determine the appropriate time for the oxidation of the pure titanium substrate, the corrosion rate of the metal in the solution of H2O2 was investigated. The electrochemical behaviour of the TiO2 passive layer on the Ti substrate was investigated in Hank's solution at 37.5°C. The results show that Tafel‐plot extrapolations from the potentiodynamic curves revealed a substantial improvement in the corrosion potentials for the TiO2 coatings. According to the theory calculation, to obtain the optimal surface roughness values, around 100 nm to 300 nm, the oxidation time in H2O2 35 wt.% solution is controlled in the range of 2‐5 hours. The results were explained by considering the effects of crystal morphology and roughness. The results indicated that the controlled oxidation‐prepared TiO2 coatings have attractive prospects for use in biomedical applications since better corrosion protection of pure Ti can be expected.

Role of TiO2 Nanoparticles in Wet Friction and Wear Properties of PEO Coatings Developed on Pure Titanium

The present study aims to explain how the incorporation of anatase TiO2 nanoparticles at three different concentrations, i.e., 1, 3, and 5 g/L, into the ceramic-like oxide plasma electrolytic oxidation (PEO) coatings on pure titanium substrate can affect the friction and wear behavior of the coatings in simulated body fluid (SBF) aqueous solution. For this purpose, a ball-on-disk friction and wear tester was utilized to characterize the wear performance of the PEO coatings. The morphology and dimensions (width and depth) of wear tracks were analyzed by scanning electron microscopy (SEM) and 2D depth profilometry, respectively. The results indicated that abrasive wear was identified in all PEO coatings; however, the coefficient of friction (COF), wear volume loss, and wear rate were strongly affected by the concentration of TiO2 nanoparticles. The coatings containing TiO2 nanoparticles presented a lower COF, less wear volume loss, reduced wear rate, and improved wear resistance due to having smoother surfaces and the presence of hard TiO2 nanoparticles on their surfaces and inside the pores. The coating with 3 g/L of TiO2 nanoparticles demonstrated the lowest wear rate value of 1.33 × 10−6 mm3/Nm (about a 32% reduction compared with that of coating without TiO2 nanoparticles) and the best wear protection properties among all coatings under investigation. The findings suggest TiO2 nanoparticles incorporated PEO coatings as a promising choice of surface treatment wherein the load-bearing capacity of titanium implants is critical.

High-entropy carbides designed to resist cavitation erosion-corrosion in an acidic environment: Surface engineering guided by first-principles calculations and experiments

In this study, the influence of chemical composition on phase stability, mechanical and electronic properties of (TixZr0.2Nb0.2Ta0.2Mo0.4-x)C (x = 0.3, 0.2, 0.1) high entropy carbide ceramics (HECCs) were first explored by first-principles calculations. The results showed that the composition (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C has higher values of electron work function (EWF) value and theoretical hardness than that of the other HECCs with lower Ti concentrations. Following this investigation, a (Ti0.3Zr0.2Nb0.2Ta0.2Mo0.1)C HECC coating was deposited onto a commercially pure titanium substrate by a reactive-sputtering method. The as-prepared HECC coating had a uniform thickness of ∼17 μm and consisted of equiaxed nanocrystals with a mean diameter of ∼7 nm. The cavitation erosion-corrosion behavior of the HECC coating was studied by combining electrochemical impedance spectroscopy (EIS) and electrochemical noise (EN) measurements in a 0.05 M H2SO4 solution. The EIS results revealed that with increasing time of cavitation exposure, the resistance value of the HECC coating was an order of magnitude larger than that for uncoated CP-Ti for a given cavitation time. EN analysis indicated that under cavitation conditions, uncoated CP-Ti was more vulnerable to localized corrosive attack than the HECC coating in an acidic environment.

Preparation of Bio-Composite Coatings on Titanium Substrate by Electrostatic Spray Deposition

In this research, the most modern deposition technique used will be utilized for biomedical applications is Electrostatic Spray Deposition (ESD), which focused on enhancing the corrosion resistance as well as biocompatibility of commercially pure titanium substrate by constructing bio composite coating, various percentages (2, 6, and 10) wt.% of Hydroxyapatite (HAP) powder were combined with (98, 94, and 90) wt.% of polymethyl methacrylate (PMMA) powder, and the same percentages (2, 6, and 10) wt.% of Nickel Oxide (NiO) powder also combined with (98, 94, and 90) wt.% of PMMA. The effects of HAP and NiO percentages in the PMMA matrix on the surface characteristics of titanium were analyzed. The FESEM, XRD, contact angle, and anti-bacterial test demonstrated that the coating layer was successfully made consistent throughout and devoid of cracks. the samples exhibited favorable wetting qualities and inhibited bacterial growth.

Effects of Micro-Arc Oxidation Discharge Parameters on Formation and Biomedical Properties of Hydroxyapatite-Containing Flower-like Structure Coatings.

The micro-arc oxidation (MAO) process was used to prepare hydroxyapatite-containing flower-like structure coatings on commercially pure titanium substrates with various values of the applied voltage (330, 390, 450 V), applied current (0.4, 0.5, 0.6 A), and duration time (1, 3, 5 min). It was found that the surface morphology of the coatings was determined primarily by the applied voltage. A voltage of 330 V yielded a flower-like/plate-like structure, while voltages of 390 V and 450 V produced a flower-like structure and a porous morphology, respectively. The applied current and duration time mainly affected the coating formation speed and petal size of the flower-like structures, respectively. The coatings prepared using voltages of 330 V and 390 V (0.6 A, 5 min) both contained Ti, TiO2-A (anatase), TiO2-R (rutile), DCPD (CaHPO4·2H2O, calcium hydrogen phosphate), and hydroxyapatite (HA). However, the latter coating contained less DCPD and had a higher HA/DCPD ratio and a Ca/P ratio closer to the ideal value of HA. The coating prepared with a voltage of 450 V consisted mainly of Ti, TiO2-A, TiO2-R, and CaTiO3. For the coatings prepared with a voltage of 390 V, the flower-like structures consisted mainly of HA-containing compounds. DCPD plate-like structures were observed either between the HA-containing flower-like structures (330 V samples) or within the flower-like structures themselves (390 V samples). The coating surfaces with flower-like/plate-like or flower-like structures had a greater roughness, which increased their hydrophilicity and resulted in superior bioactivity (SBF immersion) and biocompatibility (MG-63 cell culture). The optimal biomedical performance was found in the 390 V coating due to its flower-like structure and high HA/DCPD ratio.

Enhancement of tensile plastic stability of Ti-based metallic glass composite with substrate of titanium alloy

The tensile plastic stability of Ti-based metallic glass composites (MGCs) with substrates of titanium alloys was investigated. The findings have shown that the tensile plastic stability of MGC bimetals was significantly dependent on both the yield strength and geometrical dimension of the substrate. The substrate of high-strength Ti6Al4V (T64) alloy can enhance the ductility of the MGC greatly, while the MGC bimetal combined with low-strength pure titanium (PT) displayed worsen plastic stability. Further results showed that the plastic stability of the MGC was enhanced remarkably by increasing the thickness ration of the PT substrate. The enhancement of plasticity stability in the bimetals were explained and discussed from the perspective of normalized strain-hardening rate. These findings indicates that the plastic stability of MGCs can be enhanced by suitable reinforcer with optimized geometrical dimension. • The plastic deformation of Ti-based metallic glasses strongly depends on the mechanical properties of the substrates. • Homogeneous plastic deformation under tension can be realized in the MGC bimetals with substrate of titanium alloy. • The plastic stability of MGC bimetals can be explained by the concept of normalized strain-hardening rate.

Electrochemical Behavior and Surface Conductivity of C/TiC Nanocomposite Coating on Titanium for PEMFC Bipolar Plate

In this study, a C/TiC nanocomposite coating has been prepared by magnetron sputtering technology and vacuum heat treatment technology on a titanium surface, which is used for bipolar plates (BPs) in a proton exchange membrane fuel cell (PEMFC). This prepared C/TiC nanocomposite coating was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, electrochemical testing and interfacial contact resistance (ICR). The results show that a C/TiC nanocomposite coating consists of a single C surface layer (~28.88 nm) and TiC interface layer (~19.5 nm). In addition, compared with commercially pure titanium substrate (icorr = 345.10 μA cm−2), the corrosion resistance of a C/TiC nanocomposite coating (icorr = 0.74 μA cm−2) was greatly improved in 0.5 M H2SO4 + 5 ppm HF solution at 80 °C. The corrosion current density (icorr) decreased 3 orders of magnitude in a simulated cathodic environment. Moreover, the interfacial contact resistance of a C/TiC nanocomposite coating is 2.34 mΩ cm2 under 1.4 MPa compaction force, which is much lower than that of raw CP Ti (38.66 mΩ cm2).

Nanocrystalline TaCN coated titanium bipolar plate dedicated to proton exchange membrane fuel cell

To promote the corrosion resistance and surface conductivity of metal bipolar plates (BP) in proton exchange membrane fuel cells (PEMFC), a TaCN nanoceramic coating with TaN and TaC dual phase structures was engineered onto a commercially pure titanium substrate employing the double cathode glow discharge plasma (DCGDP) technique. The as-prepared TaCN coating was well-adhered to the substrate with a thickness of ∼16.5 μm. The coating exhibited a microstructure comprising equiaxed grains with an average size of ∼10.3 nm. The electrochemical behavior of the TaCN coating was evaluated in a simulated PEMFC environment containing various HF concentrations. Open circuit potential (OCP), potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), potentiostatic polarization, and Mott-Schottky tests showed that the addition of HF enhanced the corrosion rate of both the Ti substrate and the TaCN coating. Nevertheless, the TaCN coating exhibited improved corrosion potential, lower corrosion current density and larger resistance than that of Ti for all HF concentrations. The Hilbert-Huang and corrosion morphology analysis indicated that the TaCN coating maintained a passive state with increasing HF concentration. First-principle calculations investigated the adsorption capacity of the F− ions on the passive film on the TaCN coating. Furthermore, the TaCN coating possesses desirable interfacial contact resistance (ICR) (about 10 mΩ cm2 under a compressive force of 140 N cm−2) and outstanding hydrophobicity (92.9° ± 2°). Overall, the TaCN coating, which can deliver appreciable enhancement relative to the performance of titanium, represents an extremely competitive candidate as a protective coating for bipolar plates.