AZ31 Alloy Substrate Research Articles

Effect of SiC content on the microstructure and wear behavior of cold-sprayed Al-SiC coatings deposited on AZ31 alloy substrate

As a promising and recently developed deposition technique, cold spray deposition method is among the most recently implemented approaches to enhance the poor hardness and wear resistance of AZ31B magnesium alloy. This study investigated the effect of SiC content on the microstructural characteristics, microhardness, and wear behavior of cold-sprayed Al-(16, 28, and 38 wt%) SiC composite coatings. The incorporation of SiC particles into the Al-matrix coating led to the development of a mechanical interlocking mechanism and improved coating-substrate interfacial bonding. The microhardness of the Al-38 wt% SiC coating was approximately 80 % higher than that of the bare substrate due to reduced porosity and a uniform distribution of SiC particles. For coatings with higher SiC content, the dominant wear mechanism transitioned from adhesive to abrasive wear, as evidenced by the friction coefficient (COF) values and wear track micromorphology. The Al-16 wt% SiC coating exhibited the lowest COF and wear rate values, indicating superior wear resistance among the specimens.

In vitro corrosion behavior of PTFE coating on AZ31 by RF magnetron sputtering for biomedical application

Surface coatings are widely used for improving the biocompatibility or corrosion resistance of Mg alloy implant materials. Polytetrafluoroethylene (PTFE) coating with about 100 nm thickness was prepared on AZ31 alloy substrate by radio frequency magnetron sputtering. The coating was characterized via X-ray photoelectron spectroscopy, fourier transform infrared spectrometer, X-ray diffractometer, scanning electron microscope, contact angle goniometer, atomic force microscope and white light interferometer. The corrosion behavior of PTFE coating were analyzed by electrochemical and immersion measurements in SBF. The results showed that PTFE coating with dense and flat surface can be formed on AZ31 alloy substrate by sputtering a PTFE target directly at room temperature. The corrosion current density declined from 1.92 × 10−4 A/cm2 (bare AZ31 alloy) to 1.07 × 10−8 A/cm2 (sample with PTFE coating), and the 7 days immersion tests revealed a complete surface morphology and very slight variation in pH value of the SBF, suggesting a significant increase in corrosion resistance. High viability rate of endothelial cells of the PTFE coated AZ31 proved the good biocompatibility. These results manifest that the PTFE is a protective coating on magnesium alloys for implants application.

Ce-doped MgO films on AZ31 alloy substrate for biomedical applications: preparation, characterization and testing

Magnesium ions, MgO nanoparticles and thin films, magnesium alloys and cerium compounds are materials intensively studied due to their corrosion protection, antibacterial and pharmacological properties. In this work, we have designed, prepared and investigated, novel thin films of MgO doped with cerium, deposited on Mg alloy (AZ31) for temporary implants, in order to enhance their life time. More precisely, we report on microstructure and corrosion behavior of MgO pure and doped with 0.1 at % Ce films, fabricated by sol–gel route coupled with spin-coating technique, on AZ31 alloy substrate. A modified sol–gel method that start from magnesium acetylacetonate, cerium nitrate and 2–methoxyethanol (as a stabilizer for the sol) was been used successfully for cerium doped MgO sol precursor preparation. The structure and morphology of the surface of the coatings, before and after immersion for 7–30 d in Hank’s solution at 37 °C, were characterized by x-ray diffraction (XRD), scanning electron microscopy, high-resolution transmission electron microscope, x-ray photoelectron spectroscopy and Fourier infrared transmittance spectrum (FT–IR). A comparison between the corrosion protection of undoped MgO and MgO doped with 0.1 at % Ce coatings on the AZ31 alloy substrate is performed by electrochemical tests and immersion tests using open circuit potential and electrochemical impedance spectroscopy in Hank’s solution, at 37 °C. The electrochemical results showed that the protection of the AZ31 alloy substrate against corrosion was better with the doped with 0.1 at % Ce MgO film deposited than with pure MgO coting. The investigations of the films after immersion in Hank’s solution, at 37 °C, for 7, 21 and 30 d indicated that the grown layer on the film is bone like apatite that suggests a good bioactivity of 0.1 at % Ce–doped MgO coating. Our work demonstrates that the performance corrosion protection of the biodegradable magnesium alloys used for orthopedic applications, in simulated physiological environments (Hank and Ringer) can be enhanced through coating with Ce3+ doped MgO sol–gel thin film.

Effect of cold spray processing parameters on the microstructure, wear, and corrosion behavior of Cu and Cu–Al2O3 coatings deposited on AZ31 alloy substrate

Cold spray coatings represent a newly emerging and recently implemented approach to enhance the poor wear and corrosion resistance of AZ31 magnesium alloy. In this study, the authors applied pure Cu and Cu-50 wt% Al2O3 composite coatings on an AZ31B substrate using the cold spray deposition method and investigated the effects of gas pressure (1, 2, and 3 MPa) and stand-off distance (1, 2, and 3 cm) on their microstructure characteristics. An increase in gas pressure from 1 MPa to 3 MPa resulted in a decrease in porosity, ranging from 33 % to 38 %, across varying stand-off distances. Increasing the stand-off distance from 1 to 3 cm resulted in a nearly four-fold rise in porosity for 2 and 3 MPa pressures and about 1.5 times for 1 MPa. The porosity increased with higher pressure due to the fragmentation of Al2O3 particles but decreased with greater spraying distance due to reduced Al2O3 retention. Additionally, the incorporation of Al2O3 particles into Cu coatings led to a significant improvement in sliding wear resistance, by up to 50 %, compared to the bare substrate. Abrasive wear and delamination were identified as the dominant wear mechanisms for the composite coatings based on friction coefficient values and micromorphology of wear tracks. Electrochemical results indicated a significant increase in the corrosion resistance of the Cu coating compared to both the bare Mg substrate and Cu–Al2O3 coating, attributed to improved resistance to galvanic corrosion.

The effects of chemical conversion parameters on morphology and corrosion performance of calcium phosphate coating on AZ31 alloy

To improve the corrosion resistance of magnesium alloy, Ca–Ph coatings were prepared on AZ31 alloy substrates by chemical conversion. The treatment time and temperature have been adjusted to prepare the coatings with various morphologies, compositions, and properties. The surface morphologies and chemical compositions were investigated using a scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS), and the phase structure was investigated using X-ray diffraction (XRD). The corrosion performance of the coatings was investigated by an electrochemical test and immersion test. All the coatings showed significant corrosion protection to the substrate in the simulated body fluid (SBF) solution. The coating prepared at 5 h duration was thicker than other coatings but with the lowest corrosion current density in the electrochemical test and weight loss studies after being immersed in the SBF solution for 7 days had the slightest loss. The results showed that higher temperatures favored the presence of hydroxyapatite and that the coating thickness had an enhanced influence on the corrosion performance.

Anticorrosion and Cytocompatibility Assessment of Graphene-Doped Hybrid Silica and Plasma Electrolytic Oxidation Coatings for Biomedical Applications.

Magnesium AZ31 alloy substrates were coated with different coatings, including sol–gel silica-reinforced with graphene nanoplatelets, sol–gel silica, plasma electrolytic oxidation (PEO), and combinations of them, to improve cytocompatibility and control the corrosion rate. Electrochemical corrosion tests, as well as hydrogen evolution tests, were carried out using Hanks’ solution as the electrolyte to assess the anticorrosion behavior of the different coating systems in a simulated body fluid. Preliminary cytocompatibility assessment of the different coating systems was carried out by measuring the metabolic activity, deoxyribonucleic acid quantification, and the cell growth of premyoblastic C2C12-GFP cell cultures on the surface of the different coating systems. Anticorrosion behavior and cytocompatibility were improved with the application of the different coating systems. The use of combined PEO + SG and PEO + SG/GNP coatings significantly decreased the degradation of the specimens. The monolayer sol–gel coatings, with and without GNPs, presented the best cytocompatibility improvement.

Microstructure and Selected Properties of Cr3C2-NiCr Coatings Obtained by HVOF on Magnesium Alloy Substrates.

In present work the Cr3C2–NiCr coating was deposited on magnesium alloy substrate with high velocity oxygen fuel (HVOF) spraying. The microstructure of the samples has been characterized by means of electron microscopy, SEM and phase composition analysis carried out. The porosity of coatings has been also estimated. Finally, tests of selected mechanical properties, such as instrumented indentation, abrasive erosion have been performed. The results of the investigations confirmed that dense, homogeneous and well-adhered Cr3C2–NiCr cermet coating is possible to obtain onto the magnesium AZ31 alloy substrate. Moreover, the coatings exhibit high resistance to erosion.

A novel self-lubricating Ni-P-AlN-WS2 nanocomposite coating

In this study, a novel Ni-P-AlN-WS2 nanocomposite coating has been successfully prepared on AZ31 alloy substrate by electroless co-deposition process. The effect of nanoWS2 concentration in the plating bath on the surface morphology, microhardness, friction coefficient and wear behavior of the composite coatings have been investigated. The results showed that the Ni-P-AlN-WS2 nanocomposite coatings had a fine nodular structure and AlN and WS2 nanoparticles were uniformly dispersed in the composite coatings. The Ni-P-AlN nanocomposite exhibited the highest hardness of 810 HV200, which is 291 higher than that of conventional Ni-P coating. The incorporation of WS2 nanoparticles in the Ni-P-AlN nanocomposite coatings reduced the hardness of Ni-P-AlN-WS2 nanocomposite coatings, which is 702 HV200 at 1.5 g l−1 nanoWS2 concentrations in the bath and the hardness decreased with the increase of nanoWS2 concentration in the bath. However, the incorporation of WS2 nanoparticles in the Ni-P-AlN nanocomposite coatings significantly decreased the friction coefficient and improved wear resistance of Ni-P-AlN-WS2 nanocomposite coatings. It indicated that Ni-P-AlN-WS2 nanocomposite coatings exhibited both lower friction coefficient and higher wear resistance at the same time.

Electrochemical Corrosion and In vitro Biocompatibility Performance of AZ31Mg/Al2O3 Nanocomposite in Simulated Body Fluid

In this present investigation, AZ31 alloy nanocomposite was prepared with the inclusion of Al2O3 nanoparticles using innovative disintegrated melt deposition (DMD) process followed by hot extrusion to improve the corrosion resistance and in vitro biocompatibility in simulated body fluid (SBF). This investigation systematically inspected the degradation performances of AZ31 alloy with Al2O3 nanoparticles through hydrogen evolution, weight loss and electrochemical methods in SBF. Further, the surface microstructure with the in vitro mineralization of the alloys in SBF was characterized by XRD, XPS, and SEM/EDS analysis. It was seen that the addition of Al2O3 nanoparticles significantly decreased the weight loss of AZ31 alloy substrates after 336 h of exposure in SBF. The corrosion resistance of the monolithic and nanocomposite samples was evaluated using potentiodynamic polarization tests, electrochemical impedance spectroscopy measurements in short- and long-term periods. Accordingly, the electrochemical analysis in SBF showed that the corrosion resistance performance of the AZ31 alloy enhanced considerably due to the incorporation of Al2O3 nanoparticles as reinforcement. Moreover, the rapid formation of bone-like apatite layer on the surface of the nanocomposite substrate demonstrated a good bioactivity of the nanocomposite samples in SBF.

Corrosion Resistance of the Superhydrophobic Mg(OH)2/Mg-Al Layered Double Hydroxide Coatings on Magnesium Alloys

Coatings of the Mg(OH)2/Mg-Al layered double hydroxide (LDH) composite were formed by a combined co-precipitation method and hydrothermal process on the AZ31 alloy substrate in alkaline condition. Subsequently, a superhydrophobic surface was successfully constructed to modify the composite coatings on the AZ31 alloy substrate using stearic acid. The characteristics of the composite coatings were investigated by means of X-ray diffractometer (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electronic microscope (SEM) and contact angle (CA). The corrosion resistance of the coatings was assessed by potentiodynamic polarization, the electrochemical impedance spectrum (EIS), the test of hydrogen evolution and the immersion test. The results showed that the superhydrophobic coatings considerably improved the corrosion resistant performance of the LDH coatings on the AZ31 alloy substrate.

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)5/AZ31. Then, the (PAH/PSS)5/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)5/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)5/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca3(PO4)2 and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.

The effects of pulse electrodeposition parameters on morphology and formation of dual-layer Si-doped calcium phosphate coating on AZ31 alloy

Controlling the corrosion rate of magnesium alloys in vivo to match the bone repair is crucially important for application as biodegradable orthopedic implants. To solve this challenge, a Si-doped Ca–P coating with a novel dual-layer structure was deposited on AZ31 alloy substrate by pulse electrodeposition. The morphology, composition and formation of dual-layer coating were believed to be determined by pulse electrodeposition parameters, thus the deposition time, temperature, duty cycle, pH value of the electrolyte and the standing duration of mixed electrolyte were regulated to seek possible influences and mechanism on the coating formation. Weight gain and pH monitoring tests were also used to evaluate the performance of coating under the varied parameters. The results indicated that deposition temperature and time remarkably influenced the morphology, homogeneity and crystallinity of Ca–P coating. A uniform and compact coating with better degradation performance was obtained at 60°C with deposition time of 40min. The shorter standing duration of the electrolyte lead to an incomplete coating and uneven distribution of Si contents. The two coupled deposition models contributed to this dual-layer structure of Si-doped Ca–P coating and possible formation mechanism was proposed.

Corrosion resistance of Mg–Al-LDH coating on magnesium alloy AZ31

Mg–Al-layered double hydroxide (LDH) coatings were fabricated by a combined co-precipitation method and hydrothermal process on an AZ31 alloy substrate. The characteristics of the coatings were investigated using SEM, XRD, FT-IR and EDS. The corrosion resistance of the LDH coatings was studied using potentiodynamic polarization and electrochemical impedance spectrum. The results demonstrated that the LDH coatings, characterized by nanoplates stacked vertically to the substrate surface and ion-exchange ability, possess excellent corrosion resistance.

Preliminary research on a novel bioactive silicon doped calcium phosphate coating on AZ31 magnesium alloy via electrodeposition

A silicon doped calcium phosphate coating was obtained successfully on AZ31 alloy substrate via pulse electrodeposition. A novel dual-layer structure was observed with a porous lamellar-like and outer block-like apatite layer. In vitro immersion tests were adopted in simulated body fluid within 28days of immersion. Slow degradation rate obtained from weight loss was observed for the Si-doped Ca–P coating, which was also consistent with the results of electrochemical experiments showing an enhanced corrosion resistance for the coating. Further formation of an apatite-like layer on the surface after immersion proved better integrity and biomineralization performance of the coating. Biological characterization was carried out for viability, proliferation and differentiation of MG63 osteoblast-like cells. The coating showed a good cell growth and an enhanced cell proliferation. Moreover, an increased activity of osteogenic marker ALP was found. All the results demonstrated that the Si-doped calcium phosphate was perspective to be used as a coating for magnesium alloy implants to control the degradation rate and enhance the bioactivity, which would facilitate the rapidity of bone tissue repair.

In vitro degradation of AZ31 magnesium alloy coated with nano TiO 2 film by sol–gel method

A nano TiO 2 film was coated on AZ31 alloy substrate by sol–gel method. The TiO 2 film was characterized by X-ray diffractometry (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TG), field emission scanning electron microscopy (FE-SEM) and energy dispersion spectroscopy (EDS). The degradation of the nano-TiO 2 coated alloy was evaluated by immersion test and electrochemical measurement. An attempt was made to relate corrosion of coated alloys with the annealing treatment and resultant structural evolution.

Characterization and degradation behavior of AZ31 alloy surface modified by bone-like hydroxyapatite for implant applications

Hydroxyapatite (HA) coating on AZ31 alloy substrate was prepared by a cathodic electrodeposition method. The as-deposited specimen was then post-treated with hot alkali solution to improve the corrosion resistance and bioactivity for implant applications. The microstructure and composition of HA coating, as well as its degradation behavior in simulated body fluid (SBF) were investigated. It reveals that the as-deposited coating consists of dicalcium phosphate dehydrate (DCPD, CaHPO 4·2H 2O) and HA. While 10 μm-thick nanowhisker HA coatings doped with Na +, Mg +, HPO 4 2−and CO 3 2− can be found after NaOH alkali treatment, which exhibits a very similar composition of natural bone. The post-treated coating was composed of needle-like particles with 1000 nm in length and 35 nm in diameter, having a slenderness ratio of about 28.6. Electrochemical tests shows that the E corr of Mg substrate significantly increased from −1.6 to −1.42 V after surface modified by HA coatings. There was obvious mass gain on post-treated specimen immersed in SBF during the first 30 days due to the Ca–P–Mg deposition. The HA-coated AZ31 alloy could slow down the degradation rate and effectively induce the deposition of Ca–P–Mg apatite in SBF, showing a good bioactivity.