Zn Ca Alloy Research Articles

Optimization of ball-burnishing process parameters on surface roughness, micro hardness of Mg–Zn–Ca alloy and investigation of corrosion behavior

In this work, optimization of ball burnishing parameters (depth of press, feed, burnishing force, number of passes) and their effect on surface roughness, microhardness and corrosion behavior of Mg-4%Zn-1%Ca alloy is investigated. The Taguchi optimization technique was used to determine the number of experiments and by considering S/N ratios, right combination of ball burnishing parameters were selected. Results obtained from the experiments were investigated and it is understood that depth of press, feed and number of passes have a significant effect on surface roughness, microhardness and consequently improves corrosion resistance of Mg-4%Zn-1%Ca alloy. From ball burnishing experiments it is deduced that there is large increase in microhardness of 107 Hv and surface roughness of 129 nm, achieved for the depth of press 0.45 mm, burnishing force 250 N, feed 450 mm min−1 and number of passes: 2. Corrosion behavior of the alloys were analyzed using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in Hank’s balanced salt solution. The lowest corrosion rate was observed in DFN 442 sample (1.43 mm y−1) which is 4.7 times better than the homogenized alloy (6.73 mm y−1). It has been found that the ball burnishing plays an important role on surface roughness, microhardness and corrosion behavior of Mg-4%Zn-1%Ca alloy.

In vitro and in vivo biocompatibility of Mg–Zn–Ca alloy operative clip

At present, titanium (Ti) and its alloys are most commonly use in hemostasis clip clinical applications. However, the Ti Clip cannot be absorbed in human body and produce artifacts on computed tomography (CT), and induce clinically relevant hypersensitivity in patients. In order to overcome the drawbacks of the non-degradable Ti clips, an Mg–Zn–Ca alloy operative clip was fabricated by combining hot extrusion and blanking processing. In vitro and in vivo biocompatibility of Mg–Zn–Ca alloy operative clip were evaluated by L-929 Cells and SD rat model respectively. It was found that Mg–Zn–Ca alloy exhibited non-cytotoxic to L929 cells. In vivo implantation showed that the newly designed Mg–Zn–Ca clip can successfully ligated carotid artery and no blood leakage occurred post-surgery. During the period of the clip degradation, a small amount of H2 gas formation and no tissue inflammation around the clips were observed. The degradation rate of the clip near the heart ligated the arteries faster than that of clip far away the heart due do the effect of arterial blood. Histological analysis and various blood biochemical parameters in rat serum samples collected at different times after clip implantation showed no tissue inflammation around the clips.

Corrosion Resistance and Apatite-Forming Ability of Composite Coatings formed on Mg-Al-Zn-Ca Alloys.

The properties of composite coatings formed by plasma electrolytic oxidation (PEO) were affected by the alloy composition. The corrosion resistance and apatite-forming ability of PEO coatings formed on Mg–6Al–1Zn–xCa alloys with a variation of Ca content were investigated. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements showed an order magnitude improvement of corrosion resistance in the AZ61 alloy as a result of the coating. A higher enhancement in polarization resistance was obtained in the Mg–6Al–1Zn–1Ca and Mg–6Al–1Zn–2Ca alloys due to thicker coatings were formed as a result of the incorporation of calcium oxide/hydroxide. However, the underlying substrates were more prone to localized corrosion with increasing Ca content. The microstructure investigation revealed an enlargement in precipitates (Al2Ca, Mg2Ca) sizes with increasing Ca content in the alloys. The growth of larger size precipitates increased the danger to micro galvanic corrosion. Apatite layers were formed on all of the coatings indicating high apatite-forming ability, but the layers formed on the Mg–6Al–1Zn–1Ca and Mg–6Al–1Zn–2Ca alloys contained higher Mg, possibly due to the accumulation of corrosion product, than that on the Mg–6Al–1Zn alloy. The alloying element Ca should be limited to 1 wt.% as the excess tended to degrade the corrosion resistance and apatite-forming ability of the PEO coating.

Predicting the Biodegradation of Magnesium Alloy Implants: Modeling, Parameter Identification, and Validation.

Magnesium (Mg) and its alloys can degrade gradually up to complete dissolution in the physiological environment. This property makes these biomaterials appealing for different biomedical applications, such as bone implants. In order to qualify Mg and its alloys for bone implant applications, there is a need to precisely model their degradation (corrosion) behavior in the physiological environment. Therefore, the primary objective develop a model that can be used to predict the corrosion behavior of Mg-based alloys in vitro, while capturing the effect of pitting corrosion. To this end, a customized FORTRAN user material subroutine (or VUMAT) that is compatible with the finite element (FE) solver Abaqus/Explicit (Dassault Systèmes, Waltham, MA, USA) was developed. Using the developed subroutine, a continuum damage mechanism (CDM) FE model was developed to phenomenologically estimate the corrosion rate of a biocompatible Mg–Zn–Ca alloy. In addition, the mass loss immersion test was conducted to measure mass loss over time by submerging Mg–Zn–Ca coupons in a glass reactor filled with simulated body fluid (SBF) solution at pH 7.4 and 37 °C. Then, response surface methodology (RSM) was applied to calibrate the corrosion FE model parameters (i.e., Gamma (γ), Psi (ψ), Beta (β), and kinetic parameter (Ku)). The optimum values for γ, ψ, β and Ku were found to be 2.74898, 2.60477, 5.1, and 0.1005, respectively. Finally, given the good fit between FE predictions and experimental data, it was concluded that the numerical framework precisely captures the effect of corrosion on the mass loss over time.

Effects of Ag, Nd, and Yb on the Microstructures and Mechanical Properties of Mg‒Zn‒Ca Metallic Glasses

Mg‒Zn‒Ca metallic glasses are regarded as promising biodegradable materials. Previous studies on this alloy system have mostly focused on the composition regions with a large critical size (Dc) for the formation of metallic glasses, while this paper investigates the composition regions with a small Dc, which has been overlooked by researchers for a long time. The effects of the addition of Ag, Nd, and Yb elements on the microstructure and mechanical properties of Mg‒Zn‒Ca metallic glasses were studied. It was found that the Mg‒Zn‒Ca metallic glass exhibits a single and uniform amorphous structure with a compressive strength of 590 MPa. After the addition of a small amount of Ag into the alloy, the amorphous matrix is retained and new precipitate phases that lead to the decrease of the compressive strength are formed. The addition of the rare earth elements Nd and Yb changes the microstructure from a single amorphous matrix to a large number of quasicrystal phases, which results in an increase in compressive strength. The compressive strength of the Mg‒Zn‒Ca‒Yb alloy increases to 606.2 MPa due to the formation of multi-layered swirling solidified structure and a large number of small quasicrystals with high microhardness. Moreover, this study can be considered as a useful supplement to the existing studies on the Mg‒Zn‒Ca alloy system; it also provides new ideas for designing the microstructure and spatial structure of quasicrystal containing alloys with high performances.

Effect of the second-step voltages on the structural and corrosion properties of silicon-calcium-phosphate (Si-CaP) coatings on Mg-Zn-Ca alloy.

The applications of magnesium (Mg) alloys as biodegradable orthopedic implants are mainly restricted due to their rapid degradation rate in the physiological environment. In this study, Si–CaP micro-arc oxidation (MAO) coatings were prepared on a Mg–Zn–Ca alloy by a second-step MAO process at different voltages in order to decrease the degradation rate and increase the bioactivity of the alloy. The microstructure and morphology of the samples were characterized using XRD, FT-IR SEM and EDS. The degradation behaviours of samples were evaluated using electrochemical techniques, and immersion tests in simulated body fluid (SBF). The results indicate that the morphology of the Si–CaP coatings changed significantly with the increase in Ca/P ratio as the second-step voltage increased. The Si–CaP containing coating produced at 450 V could significantly decrease the degradation rate of Mg and caused a slow increase in pH of the SBF solution. The haemolysis test concluded that the coating C3 did not cause a haemolytic reaction. The corrosion resistance of Mg alloy was greatly improved with the Si–CaP coatings, and the Mg alloy with Si–CaP coating prepared at 450 V had the best corrosion resistance, which indicates that the Si–CaP coatings are promising for improving the biodegradation properties of Mg-based orthopedic implants. Haemolysis tests indicated that the Si–CaP coating prepared at 450 V conforms to the given standard (YY/T0127.1-93).

Tomographic investigation of the effects of second phases on the biodegradation and nano-mechanical performance of a Mg–Zn–Ca alloy

A combination of 3D tomography techniques provides direct evidence that links the phase assemblage to the bio-corrosion behaviour of a magnesium–zinc–calcium (Mg–Zn–Ca) alloy. The true shape, connectivity and volume fraction of the components have been determined using focused ion beam (FIB) tomography. The mechanism of the effect of the components with different morphologies on biodegradation was studied with the help of FIB. Micro X-ray CT (MicroCT) was used to investigate the degradation of the magnesium (Mg) alloys after 10 days’ immersion in simulated body fluid (SBF). Furthermore, the second phases affect the mechanical performance of the alloys. Nanoindentation was used to evaluate the nanohardness and elastic modulus of the (α-Mg + Ca2Mg6Zn3) eutectic products. The amount of second phase, however, is the key controlling factor in the bio-corrosion behaviour: any effect of configuration is undetectable.

Degradation Rates of Pure Zinc, Magnesium, and Magnesium Alloys Measured by Volume Loss, Mass Loss, and Hydrogen Evolution

Degradation rate is an important property to evaluate bioabsorbable metallic material; however, values vary depending on the method of measurement. In this study, three different methods of measuring corrosion rate are compared. The degradable samples to analyze corrosion rates include pure magnesium (Mg), lab produced Mg–Zn–Ca alloy (47-7-2), Mg–Zn–Zr–RE (rare earth) alloys (60-13, 60-14), Mg–Zn–Ca–RE alloy (59B), and pure zinc (Zn). A eudiometer was used to measure hydrogen evolution from the reaction of degradable alloys in Hank’s Balanced Salt Solution (HBSS). Corrosion rates based on volume loss of tested alloys in 30 days were calculated using Micro-computed tomography (micro-CT). Final mass change due to corrosion and corrosion removal was measured with a scale. We observed that the corrosion rates indicated by hydrogen evolution were high initially, and slowed down sharply in the following measurements. The corrosion rates of tested alloys calculated by volume loss and mass loss from high to low are: 60–13 ≈ 60–14 ≈ 47–7–2 > 59B > Mg > Zn (p < 0.05). The results provide instruction to experimental methodology to measure corrosion rates of degradable alloys.

Effects of Zn content on the microstructure and the mechanical and corrosion properties of as-cast low-alloyed Mg–Zn–Ca alloys

The effects of Zn content on the microstructure and the mechanical and corrosion properties of as-cast low-alloyed Mg–xZn–0.2Ca alloys (x = 0.6wt%, 2.0wt%, 2.5wt%, hereafter denoted as 0.6Zn, 2.0Zn, and 2.5Zn alloys, respectively) are investigated. The results show that the Zn content not only influences grain refinement but also induces different phase precipitation behaviors. The as-cast microstructure of the 0.6Zn alloy is composed of α-Mg, Mg2Ca, and Ca2Mg6Zn3 phases, whereas 2.0Zn and 2.5Zn alloys only contain α-Mg and Ca2Mg6Zn3 phases, as revealed by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Moreover, with increasing Zn content, both the ultimate tensile strength (UTS) and the elongation to fracture first increase and then decrease. Among the three investigated alloys, the largest UTS (178 MPa) and the highest elongation to fracture (6.5%) are obtained for the 2.0Zn alloy. In addition, the corrosion rate increases with increasing Zn content. This paper provides an updated investigation of the alloy composition–microstructure–property relationships of different Zn-containing Mg–Zn–Ca alloys.

Deformation-Induced Dynamic Precipitation and Resulting Microstructure in a Mg–Zn–Ca Alloy

The microstructure of an Mg–Zn–Ca extrusion was investigated by transmission electron microscopy, and the interaction between dynamic precipitation and dynamic recrystallization was analyzed. The results showed that dynamic precipitation significantly affected the microstructure of the as-extruded Mg–Zn–Ca alloy. The pinning effects of precipitates on dislocations effectively prohibited dynamic recrystallization processes, while the grain boundary precipitate Ca2Mg6Zn3, inhibited the growth of dynamically recrystallized grains. Consequently, a bimodal microstructure with fine dynamically recrystallized (DRXed) grains and elongated deformed regions was obtained for the Mg–Zn–Ca extrusion. High-resolution transmission electron microscopy indicated that the intragranular precipitate MgZn2 had a crystal orientation relationship with α-Mg in the form of (0002)Mg//(10–13)MgZn2 and [1–100]Mg//[1–210]MgZn2, which was beneficial for strength improvement.

Study on corrosion behavior of nano-structured coatings developed on biodegradable as cast Mg–Zn–Ca alloy by plasma electrolyte oxidation

Despite some potentially desired properties of magnesium alloys for biomedical application, their utilizations are usually extremely restricted due to their low corrosion resistance. Therefore, the objective of this study was to apply a modified coating on a cast Mg-Zn-Ca alloy through plasma electrolytic oxidation process. This process was conducted under constant pulsed DC current conditions in a phosphate-based electrolyte and their corrosion properties were compared with the substrate. Surface characterizations and corrosion behavior by electrochemical impedance spectroscopy and potentiodynamic polarization tests in PBS solution was investigated and the results were compared with the substrate. The Kramers-Kronig relations were used to evaluate the quality of the EIS data. The nano-structured coating showed a pancake shape structure with an average pores size of ~0.7 μm which uniformly covered the ~8% of the coating area. The coating microstructure was consisted of 3-layers with complex impedance spectrum involved three times constant. Corrosion resistance of PEO coated sample was increased by about two orders of magnitude. Corrosion rate measurements demonstrated the occurrence of steeply fast corrosion reaction on Mg alloy. An increase of corrosion rate with immersion time was also observed for coated sample but with lesser extent.

Microstructure modification and resultant mechanical properties of Mg–6Zn–1.5Ca (wt%) alloy through hot extrusion

Abstract

Effects of Ca concentration on degradation behavior of Zn-x Ca alloys in Hank’s solution

The microstructure, mechanical properties and in vitro degradation behavior of Zn-x Ca (x = 0.5, 1, 2, 3 wt%) alloys were investigated with pure Zn as control. The results indicated Zn-Ca alloys exhibited much stronger hardness and faster corrosion rate than those of pure Zn. And Zn-2Ca alloy presented the superior comprehensive performance with 90.94 ± 1.71 HV, 0.074 ± 0.010 mm·y−1 (weight loss) and 0.084 ± 0.021 mm·y−1 (polarization curve). And the element analysis indicated the corrosion products preferentially formed in the two-phase boundary and the main composition was calcium orthophosphate, which was the main constituent in human bone and teeth. Those results suggested Zn-Ca alloys, especial for Zn-2Ca alloy, would be promising as biodegradable implant material.

Impact of Zn and Ca on dissolution rate, mechanical properties and GFA of resorbable Mg–Zn–Ca metallic glasses

This article presents investigations utility of Mg-based metallic glasses for resorbable orthopedic implants. Exploration of biocompatible Mg–Zn–Ca alloys in order to determine Zn and Ca optimum concentration were conducted, based on three criteria: sufficiently high GFA (glass forming ability), sufficiently high tensile strength, microhardness and the suitable dissolution rate (corrosion rate) in Ringer's solution. Fulfillment of these criteria should ensure bone union before implant dissolution. The optimatization of Ca and Zn concentration in the range of 4–6at.% Ca and 28–32at.% Zn was executed. The samples in form of ribbons (0.02–0.05mm thickness) and rods (about diameter up to 4mm) with amorphous structure were produced. These investigations allowed to determine the GFA. The optimal results for Mg66Zn30Ca4 and Mg64Zn32Ca4 alloys: tensile strength: 191–166MPa, microhardness: 291–263 HV and volume of released hydrogen 0.04–0.12ml/cm2/h. The corrosion studies - immersion and potentiodynamic methods were conducted (including measurement specific corrosion current density for Mg alloys). Finally, a comparative analysis was performed, which indicated the impact of Ca and Zn concentration on: GFA, mechanical properties and dissolution rate of studied metallic glasses.

On the texture evolution of Mg–Zn–Ca alloy with different hot rolling paths

Abstract In the present study, the texture evolution and mechanical anisotropy in a typical Mg–Zn–Ca alloy through hot cross rolling (CR) and unidirectional rolling (UR) were systematically studied. The results show that the rolling path greatly affects the annealed texture. The UR develops a texture with basal poles mainly distributing along the transverse direction (TD). By contrast, an ellipse-like (0002) texture with basal pole inclining largely away from the normal direction (ND) is developed after hot cross rolling and annealing. Therefore, the CR is an effective method to tailor the texture of the experimental alloy. Unfortunately, this ellipse-like texture could not reserve during the subsequent unidirectional hot rolling and annealing. Both UR and CR plates exhibit a strong planar mechanical anisotropy compared with the traditional unidirectional rolled plate.

Characterization and corrosion property of nano-rod-like HA on fluoride coating supported on Mg-Zn-Ca alloy

The poor corrosion resistance of biodegradable magnesium alloys is the dominant factor that limits their clinical application. In this study, to deal with this challenge, fluoride coating was prepared on Mg–Zn–Ca alloy as the inner coating and then hydroxyapatite (HA) coating as the outer coating was deposited on fluoride coating by pulse reverse current electrodeposition (PRC-HA/MgF2). As a comparative study, the microstructure and corrosion properties of the composite coating with the outer coating fabricated by traditional constant current electrodeposition (TED-HA/MgF2) were also investigated. Scanning electron microscopy (SEM) images of the coatings show that the morphology of PRC-HA/MgF2 coating is dense and uniform, and presents nano-rod-like structure. Compared with that of TED-HA/MgF2, the corrosion current density of Mg alloy coated with PRC-HA/MgF2 coatings decreases from 5.72 × 10−5 A/cm2 to 4.32 × 10−7 A/cm2, and the corrosion resistance increases by almost two orders of magnitude. In immersion tests, samples coated with PRC-HA/MgF2 coating always show the lowest hydrogen evolution amount, and could induce deposition of the hexagonal structure-apatite on the surface rapidly. The results show that the corrosion resistance and the bioactivity of the coatings have been improved by adopting double-pulse current mode in the process of preparing HA on fluoride coating, and the PRC-HA/MgF2 coating is worth of further investigation.

Threshold creep behaviour of an aged Mg–Zn–Ca alloy

The creep characteristics of an aged Mg–4Zn–0.5Ca (wt%) were investigated using impression creep tests in the temperature range of 423–523K and under punch stresses in the range of 225–750MPa for dwell times up to 3600s. The creep behaviour of the alloy was found to be associated with a threshold stress and well-described by the Garofalo hyperbolic sine equation modified for the threshold stress concept. The stress exponent of 5 and the activation energy for creep close to that of pipe diffusion in Mg, i.e. 97kJmol−1, implies that dislocation climb controlled by diffusion through dislocation cores is the dominant rate-controlling mechanism. However, fitting the Garofalo equation to the experimental data showed that power-law breakdown (PLB) occurred in the material at high stress levels, especially at low temperatures. The threshold stress, appeared at low stress levels and low temperatures, was attributed to the nano-precipitates formed in the microstructure during aging treatment. The threshold stress was temperature-dependent, decreasing with increasing testing temperature and disappearing at about 575K.

The microstructure and corrosion resistance of biological Mg–Zn–Ca alloy processed by high-pressure torsion and subsequently annealing

Abstract

Microstructure and corrosion study of porous Mg–Zn–Ca alloy in simulated body fluid

Magnesium alloys had been considered as promising biomedical devices due to their biocompatibility and biodegradability. In this present work, microstructure and corrosion properties of Mg–Zn–Ca–CaCO3 porous magnesium alloy were examined. Porous metals were fabricated through powder metallurgy process with CaCO3 addition as a foaming agent. CaCO3 content was varied (1, 5, and 10%wt) followed by sintering process in 650 °C in Argon atmosphere for 10 and 15 h. The microstructure of the resulted alloys was analyzed by scanning electron microscopy (SEM) equipped with energy dispersive spectrometry data (EDS). Further, to examine corrosion properties, electrochemical test were conducted using G750 Gamry Instrument in accordance with ASTM standard G5-94 in simulated body fluid (Hank’s solution). As it was predicted, increasing content of foaming agent was in line with the increasing of pore formation. The electrochemical testing indicated corrosion rate would increase along with the increasing of foaming agent. The porous Mg–Zn–Ca alloy which has more porosity and connecting area will corrode much faster because it can transport the solution containing chloride ion which accelerated the chemical reaction. Highest corrosion resistance was given by Mg–Zn–Ca–1CaCO3-10 h sintering with potential corrosion of −1.59 VSCE and corrosion rate of 1.01 mmpy. From the microstructure after electrochemical testing, it was revealed that volcano shaped structure and crack would occur after exposure to Hank’s solution

Effect of Solution Pretreatment on Homogeneity and Corrosion Resistance of Biomedical Mg–Zn–Ca Alloy Processed by High Pressure Torsion

Orthopedic Mg–Zn–Ca alloy is prepared by solution pretreatment and then processed by high pressure torsion (HPT). The results show that the second phases in solution treated (ST) alloy processed by HPT disperse uniformly. While the second phases in HPT‐treated cast alloy without solution pretreatment are not completely fragmented and distributed non‐uniformly. After five revolutions, the grain refinement is completed. The microhardness of the alloys is significantly improved after HPT, and the microhardness distribution is homogeneous in HPT‐treated ST alloy. The corrosion resistance of HPT‐treated ST alloy is more excellent than that of HPT‐treated cast alloy in physiological environment.