Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent.The corrosion behavior of pure zinc exposed to r-SBF up to 336 h was investigated by electrochemical measurements a...Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent.The corrosion behavior of pure zinc exposed to r-SBF up to 336 h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02-0.07 mmy;during the immersion, which suggests the suitability of pure Zn for biomedical applications.展开更多
Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid.The configuration,structure and bioactivity of the coating were investigated with sca...Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid.The configuration,structure and bioactivity of the coating were investigated with scanning electron microscopy(SEM),X-ray diffraction analyzer(XRD)and Fourier transform infrared spectros-copy(FTIR)techniques.The results demonstrated that pure and homogeneous hydroxyapatite coating can be obtained without any post-treatment.The prepared coating showed good bioactivity in simulated body fluid(SBF).The time required for a fully covered dense hydroxyapatite coatings was 4 days immersion in SBF.展开更多
Magnesium alloys were considered to be used as biodegradable implants due to their biocompatibility,biodegradability and nontoxicity.However,under the simultaneous action of corrosive environment and mechanical loadin...Magnesium alloys were considered to be used as biodegradable implants due to their biocompatibility,biodegradability and nontoxicity.However,under the simultaneous action of corrosive environment and mechanical loading in human body,magnesium alloys are easy to be affected by corrosion fatigue and stress corrosion cracking.In this work,the fatigue behavior of the extruded Mg-Zn-Y-Nd alloy used for vascular stents was studied both in air and in simulated body fluid(SBF).It was revealed that the fatigue limit of as-extruded Mg-Zn-Y-Nd alloy in air is about 65 MPa at 10^7 cycles,while there is no limit in SBF and shows a linear relationship between the fatigue life and stress amplitudes.The fatigue crack source in air was formed by the inclusions and defects.However,the stress corrosion and hydrogen embrittlement are the main reasons for the formation of the fatigue initial crack source in SBF.展开更多
In this study,a KrF excimer laser was used to modify the biodegradable Mg-1Ca alloy and the time-evolution degradation behavior of the alloy before and after laser treatment was investigated in simulated body fluid(SB...In this study,a KrF excimer laser was used to modify the biodegradable Mg-1Ca alloy and the time-evolution degradation behavior of the alloy before and after laser treatment was investigated in simulated body fluid(SBF)solution using immersion tests and electrochemical impedance spectroscopy(EIS).A 5μm melted layer with a homogeneous microstructure and an MgO film on the surface were achieved by laser radiation.Corrosion observations(hydrogen evolution,morphology and corrosion products)and EIS results revealed an improvement of corrosion resistance after laser treatment for 48 h.It was found a two-layer structure developed after 2 h immersion on both the untreated and laser-treated alloys,but the sequence of forming the two layers was opposite and greatly influenced by the laser-treated layer.The time-evolution corrosion processes on the untreated and laser-treated alloys were discussed,providing a better understanding of corrosion behavior of biodegradable Mg alloys modified by excimer laser.展开更多
Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass （BMG） have been studied under three-point-bending test in a simulated body fluid （SBF） at 37 ℃ and compared w...Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass （BMG） have been studied under three-point-bending test in a simulated body fluid （SBF） at 37 ℃ and compared with those in air at room temperature （RT）. The BMG shows a high fatigue limit of approximately 366 MPa in SBF, which was slightly lower than that in air （400 MPa）. The fatigue cracks tended to initiate from the defects such as cast-pores, inclusions and corners of the samples and propagate in a similar path in SBF and in air. Three distinct regions, i.e. a crack-initiation region, a stable crack-growth region and an unstable fast-fracture region were clearly observed on the fatigue-fractured surface. Although pitting occurred at the defects where crack initiated, it does not affect significantly the fatigue life of the BMG, because the lifetime in the present BMG is mainly determined by crack propagation. The high corrosion-fatigue limit of the studied BMG results from its excellent corrosion resistance in SBF and intrinsically good toughness.展开更多
Porous and dense TiNi alloys were successfully fabricated by powder metallurgy(P/M) method, and to further improve their surface biocompatibility, surface modification techniques including grind using silicon-carbide(...Porous and dense TiNi alloys were successfully fabricated by powder metallurgy(P/M) method, and to further improve their surface biocompatibility, surface modification techniques including grind using silicon-carbide(SiC) paper, acid etching and alkali treatment were employed to produce either irregularly rough surface or micro-porous surface roughness. X-ray diffractometry(XRD), scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDX) attached to SEM were used to characterize surface structure and the Ca-P coatings. Effects of the above surface treatments on the surface morphology, apatite forming ability were systematically investigated. Results indicate that all the above surface treatments increase the apatite forming ability of TiNi alloys in varying degrees when soaked in simulated body fluid(SBF). More apatite coatings formed on TiNi samples sintered at 1050℃ and 1100℃ due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation. Furthermore, more uniform apatite was fabricated on the sample sintered from the mixture of Ni and Ti powders.展开更多
Fatigue and tensile behaviors of homogenized WE 54 magnesium alloy before and after immersion in simulated body fluid(SBF)were investigated.According to the tensile test,the alloy without immersion in SBF solution has...Fatigue and tensile behaviors of homogenized WE 54 magnesium alloy before and after immersion in simulated body fluid(SBF)were investigated.According to the tensile test,the alloy without immersion in SBF solution has the highest tensile strength of 278 MPa,which decreased to 190 MPa after 336 h of immersion..The fatigue life of the homogenized WE 54 magnesium alloy before immersion in the SBF solution under a constant stress of 15 MPa is 3598 cycles.However,the fatigue life of the alloy decreased to 453 cycles after 336 h of immersion in the SBF solution under the same stress.Examination of the fracture surface of the samples by SEM reveals that the origin of the fatigue crack before immersion is micro-pores and defects.While corrosion pits and cracks are the main reasons for forming the initial fatigue crack after immersion.Moreover,the results obtained from practical work were evaluated and compared to theoretical calculations.The area of the hysteresis loops of the samples after the fatigue test,determined using Triangles and Monte Carlo methods,decreased from 4954.5 MPa and 4842.9 MPa before immersion to 192.0 MPa and 175.8 MPa after 336 h of immersion,respectively.展开更多
For deposit body medium, the internal structural properties may be the controlling factors for the strength of the material and the mechanical response. Based on the results of soil-rock meso-statistics using digital ...For deposit body medium, the internal structural properties may be the controlling factors for the strength of the material and the mechanical response. Based on the results of soil-rock meso-statistics using digital imaging, a simulated annealing algorithm is adopted to expand the meso-structural features of deposit bodies in 3D. The construction of the 3D meso-structure of a deposit body is achieved, and then the particle flow analysis program PFC3 D is used to simulate the mechanical properties of the deposit body. It is shown that with a combination of the simulated annealing algorithm and the statistical feature functions, the randomness and heterogeneity of the rock distribution in the 3D inner structure of deposit body medium can be realized, and the reconstructed structural features of the deposit medium can match the features of the digital images well. The spatial utilizations and the compacting effects of the body-centered cubic, hexagonal close and face-centered packing models are high, so these structures can be applied in the simulations of the deposit structures. However, the shear features of the deposit medium vary depending on the different model constructive modes. Rocks, which are the backbone of the deposit, are the factors that determine the shear strength and deformation modulus of the deposit body. The modeling method proposed is useful for the construction of 3D meso-scope models from 2D meso-scope statistics and can be used for studying the mechanical properties of mixed media, such as deposit bodies.展开更多
Dense natural wollastonite bioceramics (CaSiO3) were prepared by a sintering method, varying the pressing load and sintering temperature, in order to obtain different phases of wollastonite, and different physical pro...Dense natural wollastonite bioceramics (CaSiO3) were prepared by a sintering method, varying the pressing load and sintering temperature, in order to obtain different phases of wollastonite, and different physical properties in the materials. The products were characterized by TGA-DTA, XRD, FT-IR, SEM-EDS, TEM and XPS techniques. The results indicate the presence of two polymorphic phases of wollastonite, the β-wollastonite and α-wollastonite with a transition temperature of the β phase to α phase at approximately 1250℃. These materials were soaked in a simulated body fluid (SBF) during 1, 2 and 3 weeks, to study their solubility and bioactivity. The effect of different wollastonite phases on the solubility of Ca and Si, as well as the capacity of producing layers of “newly formed apatite” on the surfaces of these materials in SBF solution were analyzed.展开更多
The results and main findings of studies reported in the literature in relation to the deposition of calcium phosphate on Ti in simulated body fluids are summarized. The effects of the surface hydroxyl groups and the ...The results and main findings of studies reported in the literature in relation to the deposition of calcium phosphate on Ti in simulated body fluids are summarized. The effects of the surface hydroxyl groups and the sign of surface charge on the nucleation of calcium phosphate are reviewed. One major controversy among the conclusions of different studies is the order of adsorption of the calcium ions and the phosphate ions in the initial stage of immersion. A simple model based on the amphoteric nature of the hydroxyl groups on Ti is proposed in an attempt to delineate the nucleation process for calcium phosphate on Ti in simulated body fluids. HPO4^2- ions interact with the hydroxyl groups via ion exchange and/or electrostatic attraction, and Ca^2＋ ions, via electrostatic attraction only. There is no preferential order of adsorption. Seemingly inconsistent results in different studies possibly arise from different prior treatments of the samples, which affect the adsorption properties.展开更多
It is confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body.It is proposed that a hydrated silica formed on the...It is confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body.It is proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer,which has not been proved yet.It is shown experimentally that a pure hydrated silica gel can induce the apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.展开更多
Modern high speed printing machines are able to print up to 700 m/min. At this rate, little excita-tions lead to vibrations, which may lead to loss of contact between the rollers (bouncing). This bouncing results in w...Modern high speed printing machines are able to print up to 700 m/min. At this rate, little excita-tions lead to vibrations, which may lead to loss of contact between the rollers (bouncing). This bouncing results in white stripes, being visible on the printed image. To enable the simulation of the whole printing process, including effects like bouncing, a discrete multibody model is developed. The rollers are modeled by several rigid bodies. These bodies are connected to each other by rotational springs, which allow simulation of the first bending eigenmodes of each roller. The contact area between the rollers is modeled by several nonlinear translational springs and damping elements. These elements change their stiffness and damping values depending on the distance between the rollers. If a defined distance is exceeded, the values become zero, which represents the loss of contact (bouncing). The unknown spring and damping elements of this model are parametrized with help of an experimental modal analysis. This paper presents the development of a flexible multibody model to simulate nonlinear effects in printing process.展开更多
The coupled motion of two flexible bodies with different lengths immersed in moving fluid is studied numerically. The flapping frequency, flapping amplitude and average drag coefficient of each body are calculated and...The coupled motion of two flexible bodies with different lengths immersed in moving fluid is studied numerically. The flapping frequency, flapping amplitude and average drag coefficient of each body are calculated and the influences of the arranging manner and separation distance are analyzed. In our simulation, when placed in the flow individually, the flexible body with a longer length will flap in period and the shorter one will maintain still straightly in the flow direction. The numerical results show that, two different flexible structures near placed in moving flow would strongly interact. When they are placed side by side, the existence of the stable shorter flexible body will restrain the flapping of the longer one while the existence of the longer flexible body may also induce the shorter one to flap synchronously. When placed in tandem with the shorter flexible body in upstream, the flapping of the longer one in downstream will be obviously enhanced. In the situation for the longer flexible body placed in upstream of the shorter one, the coupled flapping amplitude and average drag coefficients increase and decrease periodically with increasing the arranging space, and peak values appear as a result of the mediate of the tail wakes.展开更多
Though magnesium(Mg)alloys are highly attractive for their use as biodegradable/temporary implants,they can be critically compromised in such applications due to their susceptibility to corrosion and stress corrosion ...Though magnesium(Mg)alloys are highly attractive for their use as biodegradable/temporary implants,they can be critically compromised in such applications due to their susceptibility to corrosion and stress corrosion cracking(SCC)in human body fluid(such as Hanks’solution).This study investigated the role of additions of bovine serum albumin(BSA)and glucose to Hanks’solution in SCC of a Mg alloy,ZK60.The study reproducibly demonstrated the novel and unique characteristic of the acutely elliptical shape of the overall fracture surface of alloy subjected to SCC tests,exclusively when BSA was added to the Hanks’solution,whereas tests in the Hanks’solution without BSA produced the fracture surface of usual circular shape.Also,the BSA addition to the Hanks’solution produced contrasting influences on SCC and electrochemical corrosion.The study provides a comprehensive mechanistic explanation for the two phenomena.展开更多
A chemical method was used to deposit dicalcium phosphate dehydrate coatings on AZ91 magnesium alloy. The aim was to improve the biodegradation behavior of magnesium alloy in a simulated body fluid. The microstructure...A chemical method was used to deposit dicalcium phosphate dehydrate coatings on AZ91 magnesium alloy. The aim was to improve the biodegradation behavior of magnesium alloy in a simulated body fluid. The microstructures of the coating before and after immersion in the simulated body fluid were characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD） The results indicated that the dicalcium phosphate dehydrate coatings exhibited two morphologies during the pre-calcification process. The titration speed of the pre-calcification process had great influence on the morphologies of the pre-calcification coatings. As the soaking time increased, the diffraction peaks of dicalcium phosphate dehydrate disappeared and hydroxyapatite precipitated on the coated substrate surfaces. This indicates the dissolution of dicalcium phosphate dehydrate during the immersion process. The structures of the dicalcium phosphate dehydrate coatings and the formation mechanisms of the hydroxyapatite coatings were investigated in detail.展开更多
Magnesium and its alloys are ideal candidates for bioabsorbable implants.However,they can dissolve too rapidly in the human body for most applications.In this research,high purified magnesium(HP-Mg)was coated with ste...Magnesium and its alloys are ideal candidates for bioabsorbable implants.However,they can dissolve too rapidly in the human body for most applications.In this research,high purified magnesium(HP-Mg)was coated with stearic acid(SA)to slow the corrosion rate of magnesium in simulated body fluid at 37±1°C.HP-Mg was anodized(AC and DC voltages)to form an oxide/hydroxide layer,and then it was immersed in a SA solution.The SA coated layer surface,anodized layer,and the thickness of the oxide/hydroxide layer were investigated with Scanning Electron Microscopy(SEM).Electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization(PDP)were used to estimate the corrosion rate of HP-Mg specimens.The results confirm that the hydrophobic coating can decrease the corrosion rate of HP-Mg by more than 1000x.The protectiveness of coated layer for anodized specimens with AC voltage continue for 2 and 3 weeks.For the HP-Mg coated anodized with DC voltage,the coated layer could improve the corrosion resistance for only a few days.展开更多
Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy we...Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy were used for characterization.X-ray diffractometer（XRD） was used for analyzing the elemental composition and phase constituents.The hardness,wear and corrosion properties were achieved.The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution（simulated body fluid,SBF）.The microstructures of Nb coatings reveal the presence of orthorhombic,dendritic α″ and metastable β-Nb phases which produce uneven hardness with an average of HV 364.For Ti-13 Nb coatings,martensitic α′ and metastable β-Nb phases with an average hardness of HV 423 were observed.The resistance of wear on dry sliding of Ti-13 Nb coating is attributed to the increase in hardness.Experimental results indicate that deposition of Nb and Ti-13 Nb on Ti6Al4 V grossly reduces the mass fractions of Al and V in all coatings.In SBF,Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate.Hence,this coating will perform best for orthopaedic implant material enhancement.展开更多
This work presents a simple method to functionalise the surface of AZ31 magnesium alloy by applying a duplex MgF_(2)/chitosan coating,which improves its corrosion resistance and provides it with some antibacterial per...This work presents a simple method to functionalise the surface of AZ31 magnesium alloy by applying a duplex MgF_(2)/chitosan coating,which improves its corrosion resistance and provides it with some antibacterial performance.First,the effect of three chitosan solutions with different concentrations on the growth of the bacteria Klebsiella pneumoniae in nutritive medium(TSB)was evaluated by absorbance kinetics experiments,where the chitosan solution at 2%(m/V)was selected for the coating preparation.Before coating application,the AZ31 substrate was pretreated with hydrofluoric acid for 48 hours in order to form a MgF_(2)conversion layer.Subsequently,the coating was applied to the pretreated substrate through the dry-casting method.Samples of the alloy in each surface condition(bare,pretreated,and pretreated+coated with chitosan)were exposed to simulated body fluid(SBF)for 21 days at 37°C,with the solution renewed every 24 hours and the wastes stored.The surfaces were characterised by SEM-EDS,and XPS after the immersion tests,whereas the stored solutions were employed to measure the change in the Mg-ions concentration.Electrochemical impedance spectroscopy and potentiodynamic polarisation were performed in each surface condition to compare their corrosion resistance in SBF.The antibacterial activity of the functionalised surfaces was evaluated by the plate counting method and compared with bare samples.All results were correlated and demonstrate that the modified surface of AZ31 achieved a higher corrosion resistance when it was exposed to SBF,as well as a reduction of the bacterial growth during in vitro tests.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51503014 and No.51501008)the State Key Laboratory for Advanced Metals and Materials(No.2016Z-03)
文摘Zinc was recently suggested to be a potential candidate material for degradable coronary artery stent.The corrosion behavior of pure zinc exposed to r-SBF up to 336 h was investigated by electrochemical measurements and immersion tests. The morphology and chemical composites of the corrosion products were investigated by scanning electron microscope, grazing-incidence X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectrometer. The results demonstrate that the initial corrosion products on the pure zinc mainly consist of zinc oxide/hydroxide and zinc/calcium phosphate compounds. The pure Zn encounters uniform corrosion with an estimated corrosion rate of 0.02-0.07 mmy;during the immersion, which suggests the suitability of pure Zn for biomedical applications.
基金Supported by the Young Scholars Fund of Beijing University of Chemical Technology(QN0713)
文摘Hydroxyapatite coatings were directly prepared on anodized titanium by electro-deposition method in a modified simulated body fluid.The configuration,structure and bioactivity of the coating were investigated with scanning electron microscopy(SEM),X-ray diffraction analyzer(XRD)and Fourier transform infrared spectros-copy(FTIR)techniques.The results demonstrated that pure and homogeneous hydroxyapatite coating can be obtained without any post-treatment.The prepared coating showed good bioactivity in simulated body fluid(SBF).The time required for a fully covered dense hydroxyapatite coatings was 4 days immersion in SBF.
基金The authors are grateful for the financial support of Key Projects of the Joint Fund of the National Natural Science Foundation of China(No.U1804251)the National Key Research and Development Program of China(No.2018YFC1106703,2017YFB0702504 and 2016YFC1102403).
文摘Magnesium alloys were considered to be used as biodegradable implants due to their biocompatibility,biodegradability and nontoxicity.However,under the simultaneous action of corrosive environment and mechanical loading in human body,magnesium alloys are easy to be affected by corrosion fatigue and stress corrosion cracking.In this work,the fatigue behavior of the extruded Mg-Zn-Y-Nd alloy used for vascular stents was studied both in air and in simulated body fluid(SBF).It was revealed that the fatigue limit of as-extruded Mg-Zn-Y-Nd alloy in air is about 65 MPa at 10^7 cycles,while there is no limit in SBF and shows a linear relationship between the fatigue life and stress amplitudes.The fatigue crack source in air was formed by the inclusions and defects.However,the stress corrosion and hydrogen embrittlement are the main reasons for the formation of the fatigue initial crack source in SBF.
文摘In this study,a KrF excimer laser was used to modify the biodegradable Mg-1Ca alloy and the time-evolution degradation behavior of the alloy before and after laser treatment was investigated in simulated body fluid(SBF)solution using immersion tests and electrochemical impedance spectroscopy(EIS).A 5μm melted layer with a homogeneous microstructure and an MgO film on the surface were achieved by laser radiation.Corrosion observations(hydrogen evolution,morphology and corrosion products)and EIS results revealed an improvement of corrosion resistance after laser treatment for 48 h.It was found a two-layer structure developed after 2 h immersion on both the untreated and laser-treated alloys,but the sequence of forming the two layers was opposite and greatly influenced by the laser-treated layer.The time-evolution corrosion processes on the untreated and laser-treated alloys were discussed,providing a better understanding of corrosion behavior of biodegradable Mg alloys modified by excimer laser.
基金financially supported by the National Nature Science Foundation of China (Grant Nos. 51071072 and 51271081)
文摘Fatigue behaviors of a biocompatible Ni-free Zr60.14Cu22.31Fe4.85Al9.7Ag3 Zr-based bulk metallic glass （BMG） have been studied under three-point-bending test in a simulated body fluid （SBF） at 37 ℃ and compared with those in air at room temperature （RT）. The BMG shows a high fatigue limit of approximately 366 MPa in SBF, which was slightly lower than that in air （400 MPa）. The fatigue cracks tended to initiate from the defects such as cast-pores, inclusions and corners of the samples and propagate in a similar path in SBF and in air. Three distinct regions, i.e. a crack-initiation region, a stable crack-growth region and an unstable fast-fracture region were clearly observed on the fatigue-fractured surface. Although pitting occurred at the defects where crack initiated, it does not affect significantly the fatigue life of the BMG, because the lifetime in the present BMG is mainly determined by crack propagation. The high corrosion-fatigue limit of the studied BMG results from its excellent corrosion resistance in SBF and intrinsically good toughness.
基金Project(51274247) supported by the National Natural Science Foundation of ChinaProject(2014zzts177) support by the Fundamental Research Funds for the Central Universities,China
文摘Porous and dense TiNi alloys were successfully fabricated by powder metallurgy(P/M) method, and to further improve their surface biocompatibility, surface modification techniques including grind using silicon-carbide(SiC) paper, acid etching and alkali treatment were employed to produce either irregularly rough surface or micro-porous surface roughness. X-ray diffractometry(XRD), scanning electron microscopy(SEM) and energy dispersive X-ray spectroscopy(EDX) attached to SEM were used to characterize surface structure and the Ca-P coatings. Effects of the above surface treatments on the surface morphology, apatite forming ability were systematically investigated. Results indicate that all the above surface treatments increase the apatite forming ability of TiNi alloys in varying degrees when soaked in simulated body fluid(SBF). More apatite coatings formed on TiNi samples sintered at 1050℃ and 1100℃ due to their high porosity and pure TiNi phase that is beneficial to heterogeneous nucleation. Furthermore, more uniform apatite was fabricated on the sample sintered from the mixture of Ni and Ti powders.
文摘Fatigue and tensile behaviors of homogenized WE 54 magnesium alloy before and after immersion in simulated body fluid(SBF)were investigated.According to the tensile test,the alloy without immersion in SBF solution has the highest tensile strength of 278 MPa,which decreased to 190 MPa after 336 h of immersion..The fatigue life of the homogenized WE 54 magnesium alloy before immersion in the SBF solution under a constant stress of 15 MPa is 3598 cycles.However,the fatigue life of the alloy decreased to 453 cycles after 336 h of immersion in the SBF solution under the same stress.Examination of the fracture surface of the samples by SEM reveals that the origin of the fatigue crack before immersion is micro-pores and defects.While corrosion pits and cracks are the main reasons for forming the initial fatigue crack after immersion.Moreover,the results obtained from practical work were evaluated and compared to theoretical calculations.The area of the hysteresis loops of the samples after the fatigue test,determined using Triangles and Monte Carlo methods,decreased from 4954.5 MPa and 4842.9 MPa before immersion to 192.0 MPa and 175.8 MPa after 336 h of immersion,respectively.
基金Projects(51309089,11202063)supported by the National Natural Science Foundation of ChinaProject(2013BAB06B01)supported by the National High Technology Research and Development Program of China+1 种基金Project(2015CB057903)supported by the National Basic Research Program of ChinaProject(BK20130846)supported by Natural Science Foundation of Jiangsu Province,China
文摘For deposit body medium, the internal structural properties may be the controlling factors for the strength of the material and the mechanical response. Based on the results of soil-rock meso-statistics using digital imaging, a simulated annealing algorithm is adopted to expand the meso-structural features of deposit bodies in 3D. The construction of the 3D meso-structure of a deposit body is achieved, and then the particle flow analysis program PFC3 D is used to simulate the mechanical properties of the deposit body. It is shown that with a combination of the simulated annealing algorithm and the statistical feature functions, the randomness and heterogeneity of the rock distribution in the 3D inner structure of deposit body medium can be realized, and the reconstructed structural features of the deposit medium can match the features of the digital images well. The spatial utilizations and the compacting effects of the body-centered cubic, hexagonal close and face-centered packing models are high, so these structures can be applied in the simulations of the deposit structures. However, the shear features of the deposit medium vary depending on the different model constructive modes. Rocks, which are the backbone of the deposit, are the factors that determine the shear strength and deformation modulus of the deposit body. The modeling method proposed is useful for the construction of 3D meso-scope models from 2D meso-scope statistics and can be used for studying the mechanical properties of mixed media, such as deposit bodies.
文摘Dense natural wollastonite bioceramics (CaSiO3) were prepared by a sintering method, varying the pressing load and sintering temperature, in order to obtain different phases of wollastonite, and different physical properties in the materials. The products were characterized by TGA-DTA, XRD, FT-IR, SEM-EDS, TEM and XPS techniques. The results indicate the presence of two polymorphic phases of wollastonite, the β-wollastonite and α-wollastonite with a transition temperature of the β phase to α phase at approximately 1250℃. These materials were soaked in a simulated body fluid (SBF) during 1, 2 and 3 weeks, to study their solubility and bioactivity. The effect of different wollastonite phases on the solubility of Ca and Si, as well as the capacity of producing layers of “newly formed apatite” on the surfaces of these materials in SBF solution were analyzed.
文摘The results and main findings of studies reported in the literature in relation to the deposition of calcium phosphate on Ti in simulated body fluids are summarized. The effects of the surface hydroxyl groups and the sign of surface charge on the nucleation of calcium phosphate are reviewed. One major controversy among the conclusions of different studies is the order of adsorption of the calcium ions and the phosphate ions in the initial stage of immersion. A simple model based on the amphoteric nature of the hydroxyl groups on Ti is proposed in an attempt to delineate the nucleation process for calcium phosphate on Ti in simulated body fluids. HPO4^2- ions interact with the hydroxyl groups via ion exchange and/or electrostatic attraction, and Ca^2＋ ions, via electrostatic attraction only. There is no preferential order of adsorption. Seemingly inconsistent results in different studies possibly arise from different prior treatments of the samples, which affect the adsorption properties.
文摘It is confirmed that the essential condition for glasses and glass-ceramics to bond to living bone is the formation of an apatite layer on their surfaces in the body.It is proposed that a hydrated silica formed on the surfaces of these materials in the body plays an important role in forming the surface apatite layer,which has not been proved yet.It is shown experimentally that a pure hydrated silica gel can induce the apatite formation on its surface in a simulated body fluid when its starting pH is increased from 7.2 to 7.4.
文摘Modern high speed printing machines are able to print up to 700 m/min. At this rate, little excita-tions lead to vibrations, which may lead to loss of contact between the rollers (bouncing). This bouncing results in white stripes, being visible on the printed image. To enable the simulation of the whole printing process, including effects like bouncing, a discrete multibody model is developed. The rollers are modeled by several rigid bodies. These bodies are connected to each other by rotational springs, which allow simulation of the first bending eigenmodes of each roller. The contact area between the rollers is modeled by several nonlinear translational springs and damping elements. These elements change their stiffness and damping values depending on the distance between the rollers. If a defined distance is exceeded, the values become zero, which represents the loss of contact (bouncing). The unknown spring and damping elements of this model are parametrized with help of an experimental modal analysis. This paper presents the development of a flexible multibody model to simulate nonlinear effects in printing process.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51479007,51309017,and 11102027the Natural Science Foundation of Hubei Province under Grant No 2015CFA026the Fundamental Research Fund for State Public-Benefic Scientific Institutes of CRSRI under Grant No CKSF2015026/SL
文摘The coupled motion of two flexible bodies with different lengths immersed in moving fluid is studied numerically. The flapping frequency, flapping amplitude and average drag coefficient of each body are calculated and the influences of the arranging manner and separation distance are analyzed. In our simulation, when placed in the flow individually, the flexible body with a longer length will flap in period and the shorter one will maintain still straightly in the flow direction. The numerical results show that, two different flexible structures near placed in moving flow would strongly interact. When they are placed side by side, the existence of the stable shorter flexible body will restrain the flapping of the longer one while the existence of the longer flexible body may also induce the shorter one to flap synchronously. When placed in tandem with the shorter flexible body in upstream, the flapping of the longer one in downstream will be obviously enhanced. In the situation for the longer flexible body placed in upstream of the shorter one, the coupled flapping amplitude and average drag coefficients increase and decrease periodically with increasing the arranging space, and peak values appear as a result of the mediate of the tail wakes.
基金funded by Monash University,AustraliaDepartment of Biotechnology,India through IITB-Monash Research Academy.
文摘Though magnesium(Mg)alloys are highly attractive for their use as biodegradable/temporary implants,they can be critically compromised in such applications due to their susceptibility to corrosion and stress corrosion cracking(SCC)in human body fluid(such as Hanks’solution).This study investigated the role of additions of bovine serum albumin(BSA)and glucose to Hanks’solution in SCC of a Mg alloy,ZK60.The study reproducibly demonstrated the novel and unique characteristic of the acutely elliptical shape of the overall fracture surface of alloy subjected to SCC tests,exclusively when BSA was added to the Hanks’solution,whereas tests in the Hanks’solution without BSA produced the fracture surface of usual circular shape.Also,the BSA addition to the Hanks’solution produced contrasting influences on SCC and electrochemical corrosion.The study provides a comprehensive mechanistic explanation for the two phenomena.
基金Project(51272055) supported by the National Natural Science Foundation of China
文摘A chemical method was used to deposit dicalcium phosphate dehydrate coatings on AZ91 magnesium alloy. The aim was to improve the biodegradation behavior of magnesium alloy in a simulated body fluid. The microstructures of the coating before and after immersion in the simulated body fluid were characterized by scanning electron microscopy （SEM） and X-ray diffraction （XRD） The results indicated that the dicalcium phosphate dehydrate coatings exhibited two morphologies during the pre-calcification process. The titration speed of the pre-calcification process had great influence on the morphologies of the pre-calcification coatings. As the soaking time increased, the diffraction peaks of dicalcium phosphate dehydrate disappeared and hydroxyapatite precipitated on the coated substrate surfaces. This indicates the dissolution of dicalcium phosphate dehydrate during the immersion process. The structures of the dicalcium phosphate dehydrate coatings and the formation mechanisms of the hydroxyapatite coatings were investigated in detail.
文摘Magnesium and its alloys are ideal candidates for bioabsorbable implants.However,they can dissolve too rapidly in the human body for most applications.In this research,high purified magnesium(HP-Mg)was coated with stearic acid(SA)to slow the corrosion rate of magnesium in simulated body fluid at 37±1°C.HP-Mg was anodized(AC and DC voltages)to form an oxide/hydroxide layer,and then it was immersed in a SA solution.The SA coated layer surface,anodized layer,and the thickness of the oxide/hydroxide layer were investigated with Scanning Electron Microscopy(SEM).Electrochemical impedance spectroscopy(EIS)and potentiodynamic polarization(PDP)were used to estimate the corrosion rate of HP-Mg specimens.The results confirm that the hydrophobic coating can decrease the corrosion rate of HP-Mg by more than 1000x.The protectiveness of coated layer for anodized specimens with AC voltage continue for 2 and 3 weeks.For the HP-Mg coated anodized with DC voltage,the coated layer could improve the corrosion resistance for only a few days.
基金financially supported by the National Research Foundation of South AfricaThe National Laser Centre,CSIR,Pretoria,South Africa,is appreciated for laser facilitythe support from Tshwane University of Technology,South Africa
文摘Nb and Ti-13 Nb powders were used for improving the surface of Ti6Al4 V alloy.The deposition of the powders was carried out at various laser powers.The scanning electron microscopy（SEM）-EDS and optical microscopy were used for characterization.X-ray diffractometer（XRD） was used for analyzing the elemental composition and phase constituents.The hardness,wear and corrosion properties were achieved.The corrosion and the wear behaviours of the deposited layers were studied in a Hanks solution（simulated body fluid,SBF）.The microstructures of Nb coatings reveal the presence of orthorhombic,dendritic α″ and metastable β-Nb phases which produce uneven hardness with an average of HV 364.For Ti-13 Nb coatings,martensitic α′ and metastable β-Nb phases with an average hardness of HV 423 were observed.The resistance of wear on dry sliding of Ti-13 Nb coating is attributed to the increase in hardness.Experimental results indicate that deposition of Nb and Ti-13 Nb on Ti6Al4 V grossly reduces the mass fractions of Al and V in all coatings.In SBF,Nb reinforcement produces the best coating that reveals the best wear and corrosion resistances as compared with the substrate.Hence,this coating will perform best for orthopaedic implant material enhancement.
基金CONACYT for his scholarship as a Ph.D.student at CINVESTAV-IPN
文摘This work presents a simple method to functionalise the surface of AZ31 magnesium alloy by applying a duplex MgF_(2)/chitosan coating,which improves its corrosion resistance and provides it with some antibacterial performance.First,the effect of three chitosan solutions with different concentrations on the growth of the bacteria Klebsiella pneumoniae in nutritive medium(TSB)was evaluated by absorbance kinetics experiments,where the chitosan solution at 2%(m/V)was selected for the coating preparation.Before coating application,the AZ31 substrate was pretreated with hydrofluoric acid for 48 hours in order to form a MgF_(2)conversion layer.Subsequently,the coating was applied to the pretreated substrate through the dry-casting method.Samples of the alloy in each surface condition(bare,pretreated,and pretreated+coated with chitosan)were exposed to simulated body fluid(SBF)for 21 days at 37°C,with the solution renewed every 24 hours and the wastes stored.The surfaces were characterised by SEM-EDS,and XPS after the immersion tests,whereas the stored solutions were employed to measure the change in the Mg-ions concentration.Electrochemical impedance spectroscopy and potentiodynamic polarisation were performed in each surface condition to compare their corrosion resistance in SBF.The antibacterial activity of the functionalised surfaces was evaluated by the plate counting method and compared with bare samples.All results were correlated and demonstrate that the modified surface of AZ31 achieved a higher corrosion resistance when it was exposed to SBF,as well as a reduction of the bacterial growth during in vitro tests.
