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Mg-Zn-RE alloys reinforced with quasicrystals have been investigated extensively because they show excellent balance in mechanical properties. Here, we perform deformation and annealing for Mg-1.50Zn-0.25Gd (at.%) alloy at various temperatures, aimed to gain nanoscale precipitates. We find that after the room-temperature compression, the non-basal dislocation, stacking fault and twining are identified in the as-deformed samples, offering clear evidence that these deformation mechanisms can accommodate room-temperature deformation. We also perform systematic transmission electron microscopy observations of the precipitates in both the as-deformed and as-annealed samples. The results identify the formation of a large amount of secondary-phase precipitates, I-phase and MgZn2, when annealed at 200 °C, and precipitation of a small amount of W-phase when annealed at 400 °C. Keywords: Mg alloys, Quasicrystal, Deformation, Annealing, Precipitation

Zn and Zn-based alloys as biodegradable material have drawn more and more attention in recent years due to their good mechanical properties, lower degradation rate than Mg and acceptable biocompatibility. However, too low degradation rate is a challenge for future application of Zn-based alloys. In this study, Zn-3Cu-xFe (x = 0, 0.5 and 1 wt%) alloys were proposed as candidate biodegradable materials. The microstructure, mechanical and in vitro biodegradable properties were investigated systematically. The Zn-3Cu alloy was composed of Zn matrix and CuZn5 phase, while the FeZn13 phase was newly formed with the addition of Fe. Due to the micro-galvanic effect produced by FeZn13 as a cathodic phase to the Zn matrix, in vitro degradation rate in simulated body fluid solution (SBF) was greatly increased by about 52.1%, from 45.3 ± 8.22 for Zn-3Cu alloy to 68.9 ± 7.34 μm/year for Zn-3Cu-1Fe alloy. Although the mechanical properties were decreased slightly due to the introduction of hard and brittle FeZn13 secondary phase to the Zn matrix, Zn-3Cu-0.5Fe alloy still exhibits good combined mechanical properties and the YS, UTS and elongation are 232 MPa, 284 MPa and 33%, respectively. Taken together, the mechanical properties and in vitro degradation behavior of the Zn-3Cu-xFe alloys are more suitable than Zn-3Cu alloy as candidate biodegradable materials.

Biodegradable magnesium (Mg) alloy emerges as revolutionary biomaterial by meeting both engineering and medical requirements for implants. In this study, we report a Mg alloy Mg-2.5Nd-0.21Zn-0.44Zr (wt. %, denoted as JDBM) potential for vascular stent application due to its outstanding performance in corrosion behaviors and biocompatibility. The investigation of corrosion properties evaluated by immersion test and electrochemical measurement shows less susceptibility to pitting corrosion and lower corrosion rate of JDBM as compared with AZ31 alloy. The corrosion products of JDBM do not cause significant adverse effect on the cell viability and growth during in vitro cytotoxicity test of the Mg extract via human vascular endothelial cells (HUVECs). We also investigated macrophage response to the Mg extract and observed compromised foreign body reaction (FBR) determined by human peripheral blood derived macrophage fusion and inflammatory cytokine and chemokine secretion. At last, we performed in vivo degradation assessment via implantation of JDBM stent in an animal model, and confirmed long-term stability and structural integrity of the stent in blood vessel. Thus, the JDBM alloy with excellent biocompatibility and long-term stability and durability in vivo, represents a significant advance in the development of biodegradable implants.

To understand the possible influence of substrate degradation on the drug-loading system of magnesium alloy-based drug-eluting stents, a rapamycin drug-loading poly(lactic-co-glycolic acid) coating was prepared on Mg-Nd-Zn-Zr stents for a systematic investigation in a phosphate buffer system. Mg degradation accelerated the drug release kinetics prominently, which was mainly attributed to H2 evolution in the diffusion-controlled phase while thereafter to PLGA erosion. Although physiochemical stability of the released rapamycin was partially deteriorated by magnesium degradation, the drug-loading system on magnesium substrates exhibited a more potent long-term inhibition on smooth muscle cell proliferation in vitro as compared to drug-loaded stainless steel.

Biomedical Mg alloy is promising for its widespread use clinically. In vitro and in vivo studies showed that the degradation products of biomedical Mg alloy were composed of O, P, Ca, Mg and other alloying elements. However, little is known about the metabolism of the degradation products. In this study, the in vitro macrophage phagocytosis of the degradation products of a biomedical Mg-Nd-Zn-Zr alloy was directly observed. This result affirms the necessity to investigate the long-term fate of Mg alloy degradation products in physiological environments. Besides, an electrochemical method was proposed to prepare enough amount of degradation products in vitro efficiently.

We report hot deformation behavior of icosahedral quasi-crystalline phase reinforced Mg-1.50Zn-0.25Gd (at.%) alloys fabricated by a traditional gravity casting approach. The exponential law constitutive equation is applied to describe their flow stress behavior and the average activation energy is determined to be 187.70 kJ mol−1. We also find that I-phase forms and grows in the alloys when the deformation strain is increasingly applied and that twinning contributes to high basal texture at early stage of deformation. Basal texture is weakened when the applied strain is strong owing to the dynamic recrystallization and also to the particle stimulation nucleation (PSN) effects of I-phase at late stage of deformation. High temperature is found to contribute to recrystallization but restrain I-phase precipitation and also weaken PSN effects of I-phase. Moreover, we find that a large strain rate not only promotes non-basal dislocation glide/twinning but also contributes to basal texture randomization, while a moderate strain rate is harmful for deformation due to the generation of strong basal texture. Furthermore, I-phase is found to be more effective for basal texture randomization than other strengthening secondary phases in Mg alloys, which is due to the presence of many orientation relationships and also because the interface between I-phase and Mg matrix is coherent or semi-coherent.

Magnesium (Mg) and its alloys have been suggested as revolutionary biodegradable materials. However, fast degradation hinders its clinic application. To improve the corrosion resistance and biocompatibility of Mg–Nd–Zn–Zr alloy (JDBM), magnesium–aluminum-layered double hydroxide (Mg–Al LDH) was successfully introduced into Mg(OH)2 coating by hydrothermal treatment. The anions in the interlayer of Mg–Al LDH can be replaced by chloride ions, resulting in a relatively low chloride ion concentration near the surface of the coating. The favorable corrosion resistance of the coating was proved by polarization curves and hydrogen collection test. The Mg–Al LDH significantly promoted cell adhesion, migration and proliferation in vitro. In addition, the coating almost fulfilled the request of the clinical application in the hemolysis ratio test. Finally, in vivo results indicated that the coating offered the greatest long-lasting protection from corrosion and triggered the mildest inflammation comparing to the pur...

In this work, the long-term degradation of Mg-Nd-Zn-Zr screws in the rabbit mandible is studied. At 18 months, the screw volume has been reduced by ∼90% according to the micro-computed tomography analysis, and the averaged corrosion rate is 0.122 ± 0.042 mm/year. The bone-implant interface analysis reveals good osteointegration. The corrosion products show two-layer structure with Ca and P elements concentrated in the out layer, and the Mg12Nd particles has degraded by Mg element dissolution. Our findings contribute to a better understanding of the in vivo degradation mechanism of Mg-based implants.

We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg–3.5Zn–0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong.

Mg–1.50Zn–0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and then subjected to cyclic extrusion and compression (CEC) at 250, 300, 350 and 400 °C, respectively. The effects of CEC parameters including passes and temperatures on microstructure evolution and room temperature tensile mechanical properties were characterized and discussed. The results show that more passes are beneficial for secondary phase precipitation, grain refinement and basal texture weakening; while moderate temperature is beneficial for secondary phase precipitation and basal texture weakening by particle stimulated recrystallization nucleation (PSN), and lower temperature is beneficial for grain refinement. The alloy has the highest yield strength after CEC at 250 °C because of grain refinement and basal texture strengthening, while it has the highest elongation after being processed with 8 passes of CEC due to grain refinement and basal texture weakening. The processing passes have more important effects on microstructure evolution and mechanical properties than that of temperature during CEC. Keywords: Magnesium alloys, Cyclic extrusion and compression (CEC), Microstructure, Texture weakening, Mechanical properties

The secondary phases in quasicrystal-reinforced Mg–Zn–Gd alloys are investigated by transmission electron microscopy. The orientation relationships between the dendritic I-phase and the Mg matrix are identified to be [11 2 ¯ 0]Mg ∥[2-fold]I-phase and (0001)Mg ∥(5-fold)I-phase. We also find that the dendritic I-phase is brittle along 2-fold, 5-fold, and 3-fold atomic planes during hot extrusion. Moreover, new orientation relations [ 1 ¯ 101]Mg ∥[mirror 2-fold]I-phase and (0 1 ¯ 11)Mg ∥(5-fold)I-phase are found between nanoscale I-phase and Mg matrix. The findings have implications for our understanding of excellent mechanical properties of the I-phase-strengthened Mg alloys.

Mg–1.5Zn–0.25Gd (at.%) alloy reinforced by icosahedral quasicrystalline phase (I-phase) was fabricated and subjected to cyclic extrusion and compression (CEC) at 350 °C to investigate the microstructure evolution during CEC and its effect on the mechanical properties. It is observed that, during CEC, the microstructure of the alloy was greatly refined by dynamic recrystallization (DRX), large numbers of I-phase particles precipitated and then grew up, the texture of the alloy was obviously weakened. These changes in microstructure improved the mechanical properties of the alloy significantly and the alloy processed by 8 passes CEC exhibited outstanding plasticity of 31.4% and moderate yield strength of 161 MPa.

Plasma immersion ion implantation and deposition (PIII&D) is conducted to modify the corrosion behavior of Mg–Nd–Zn–Zr alloy. A diamond-like carbon film (DLC) with a thickness of about 200 nm is formed on the surface after acetylene PIII&D and the resulting corrosion resistance in the 0.9 wt% NaCl solution is significantly improved. The corrosion mechanism is discussed from the perspective of random defects in the DLC film.

To further improve the corrosion resistance and biocompatibility of Mg–Nd–Zn–Zr alloy (JDBM), a biodegradable calcium phosphate coating (Ca–P coating) with high bonding strength was developed using a novel chemical deposition method. The main composition of the Ca–P coating was brushite (CaHPO 4 ·2H 2 O). The bonding strength between the coating and the JDBM substrate was measured to be over 10 MPa, and the thickness of the coating layer was about 10–30 μm. The in vitro corrosion tests indicated that the Ca–P treatment improved the corrosion resistance of JDBM alloy in Hank's solution. Ca–P treatment significantly reduced the hemolysis rate of JDBM alloy from 48% to 0.68%, and induced no toxicity to MC3T3-E1 cells. The in vivo implantation experiment in New Zealand's rabbit tibia showed that the degradation rate was reduced obviously by the Ca–P treatment and less gas was produced from Ca–P treated JDBM bone plates and screws in early stage of the implantation, and at least 10 weeks degradation time can be prolonged by the present coating techniques. Both Ca–P treated and untreated JDBM Mg alloy induced bone growth. The primary results indicate that the present Ca–P treatment is a promising technique for the degradable Mg-based biomaterials for orthopedic applications.

Mg–1.5Zn–0.25Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) were fabricated to investigate the effect of heat treatment on the microstructure, mechanical properties and anisotropy of the as-extruded alloys. The results show that compared with the samples extruded without homogenized annealing, the samples extruded after homogenized annealing show larger grains, lower strength and elongation, which can be attributed to the secondary-phase particles precipitated in the matrix after homogenized annealing and to the fact that only a few volume fraction of nano-scale I-phase is precipitated in the matrix during extrusion. Moreover, the anisotropy is mitigated in the alloys extruded at as-cast condition because of the grain refinement and the I-phase precipitation. We also find that after annealing at 473 K or 673 K, yield strength decreases while the elongation increases slightly, indicating that annealing has a small effect on the improvement of room-temperature strength, especially the one at relatively higher temperature. The choice of appropriate annealing temperature only imposes a little impact on the ductility enhancement of the extruded samples.

In this study, we have developed an excellent mechanical properties of an ultrafine-grained quasicrystalline strengthened magnesium alloys by conventional extruding as-casted Mg–1.5Zn–0.25Gd (at%) ingot at 373 K with an extrusion ratio of about 9:1. After extrusion, multi-modal microstructure was formed, i.e. exhibited large deformed grains surrounded by fine dynamical recrystallization grains and the mean grain sizes smaller than 1 μm. The extruded sample shows excellent tensile properties at ambient temperature with ultimate tensile strength of 417 MPa, 0.2% proof stress of 395 MPa and elongation to failure of 8.3%. The notable improvement in strength mainly attributed to the grain refinement, dense distribution of the fine precipitates inside the fine dynamical recrystallization grains and the high intensity of typical basal texture.

In this study, in vitro blood biocompatibility of Mg-Nd-Zn-Zr (JDBM) alloy was investigated to determine its suitability as a degradable medical biomaterial. Blood biocompatibility was assessed by blood cell aggregation, platelet adhesion, and protein adsorption. A titanium alloy was used as control. The results showed that the JDBM alloy did not induce significant blood cell aggregation, platelet adhesion, and protein adsorption comparison with the titanium alloy (P>0.05). Our data indicate that the JDBM alloy has excellent in vitro blood compatibility, and thus can be considered as a potential degradable biomaterial for medical applications with respect to hemocompatibility. magnesium alloy, hemocompatibility, blood cell aggregation, platelet adhesion, protein adsorption

Biodegradable magnesium alloy with proper yield strength, high ultimate strength and elongation is a potential candidate for cardiovascular stent. Nevertheless, magnesium alloy with high ultimate tensile strength always exhibits high yield strength, which is not suitable for the plastic deformation of cardiovascular stent during implantation. Solution treatment was conducted on the as extruded Mg–2·7Nd–0·2Zn–0·4Zr alloy in order to reduce the high yield ratio, and the biocorrosion behaviour of the alloy was also evaluated in artificial plasma. The results show that the grains of the alloy grow, and the second phase reduces with increasing solution treatment temperature. The yield strength decreases gradually, and the ultimate tensile strength still keeps a high level due to the remarkable workhardening. The yield ratio of the alloy reduces from 92 to 57%. The corrosion resistance of the alloy after solution treatment is improved slightly when the temperature is

The microstructure and mechanical properties of as-cast and solution-treated Mg-xZn-yGd (x/y = 6, at.%) alloys reinforced with quasicrystals have been investigated. The results indicate that with the increase in the alloying elements contents, the dendritic microstructure is refined, the corresponding strength gradually increased, and the elongation gradually decreased as the increase in the second phase sizes leads to stress concentration under as-cast and solution-treated conditions. For as-cast alloys, micro-cracks originated in the α-Mg matrix and quasicrystals interface. The fracture mode exhibits intergranular fracture characteristics. After solution treatment, the yield strength decreased, and the ultimate tensile strength and elongation increased clearly due to the Mg2Zn3 phase dissolution and the second phase sizes decreasing. The fracture mode changes to transgranular fracture.

We have fabricated three types of Mg-Zn-Gd-based alloys containing the icosahedral quasicrystalline phase (I-phase) to investigate how volume fraction of the I-phase and extrusion ratio can have an impact on the microstructure, mechanical properties, and anisotropy of the as-extruded alloys. We find that grains are refined and that the ultimate tensile strength and elongation are improved as either the volume fraction of I-phase or the extrusion ratio is increased, which can be attributed to the secondary phase particle stimulate recrystallization nucleation and restrained grain boundary motion. Moreover, anisotropy is mitigated in all of the alloys as either the I-phase fraction or the extrusion ratio is increased owing to the coeffect of texture weakening and grain refinement as well as to the effect of I-phase on twinning. We also find that with the increase in the amount of the I-phase, the yield strength (YS) is decreased for the alloys extruded at a low ratio owing to the texture weakening, yet it is increased for the alloys extruded at high ratio owing to the strengthening originating from the I-phase and refined grains. The mechanical properties are improved for the alloys extruded at high ratio, which is due to their fine grains and uniform microstructure.

Double continuous extrusion (DCE) is proposed here as a novel thermomechanical process which means that the sample is continuously extruded twice by one process. The microstructures and mechanical properties of Mg 98 Zn 1.92 Gd 0.08 (at%, Alloy 1) and Mg 96.83 Zn 2.7 Gd 0.47 (at%, Alloy 2) after conventional extrusion and DCE at 373 K were investigated. The results show that the major secondary phase in Alloy 1 is Mg 2 Zn 3 and that in Alloy 2 is icosahedral quasicrystals phase (I-phase). After DCE, the microstructure is refined, and the average grain sizes of the both alloys are smaller than 1 μm, and this further improves the mechanical properties. Both the alloys exhibit excellent mechanical properties, and the ultimate tensile strength, yield strength and elongation to failure are 434 MPa, 410 MPa and 14.6%, respectively, for Alloy 1; and 444 MPa, 417 MPa and 13.1%, respectively, for Alloy 2. The possible strengthening mechanisms were discussed and it was found that DCE is an effective method for Mg-based alloys strengthening by grain refinement and secondary phase dispersion.

The Mg–3?08Nd–0?27Zn–0?46Zr (wt-%) alloy was hot extruded with different extrusion ratios to refine microstructure and to optimise mechanical properties and corrosion resistance as a biodegradable magnesium alloy. The microstructure was observed by optical microscopy, the mechanical properties were tested at room temperature and the corrosion resistance was evaluated in Hanks’ solution. The results show that the microstructure becomes more and more homogeneous with increasing the extrusion ratio. The mechanical properties of the as extruded alloy are much better than those of the as cast one. Higher strength is obtained with the extrusion ratio of 18, and better elongation is obtained with the extrusion ratio of 25. Corrosion results show that corrosion resistance of the as extruded alloy immersed in Hanks’ solution is better than that of the as cast one, and higher extrusion ratio results in better corrosion resistance. Both the as cast and the as extruded alloys exhibit uniform corrosion, which was interpreted by cyclic polarisation test.

Zn-based alloys have been viewed as new potential materials for biodegradable implants, such as cardiovascular stents, mainly in consideration of their lower corrosion rate when compared with that of Mg alloys. In this study we developed a new Zinc-4wt.%Copper (Zn-4Cu) alloy as a biodegradable material. Hot extrusion was applied to Zn-4Cu to refine the microstructure and consequently improve its mechanical properties and corrosion resistance. After extrusion, dendritic CuZn5 phases were broken and distributed along the extrusion direction. The grains were refined obviously due to dynamical recrystallization. The yield strength (YS), ultimate tensile strength (UTS) and elongation of the as-extruded alloy are 250±10MPa, 270±10MPa and 51±2%, respectively. The corrosion rate of the as-extruded alloy in Hank's solution is about 9.41(±1.34)μmyear(-1). In vitro evaluation shows that Zn-4Cu presents acceptable toxicity to human endothelial cells, and could effectively inhibit bacteria adhesion and biofilm formation. The present study indicates that the as-extruded Zn-4Cu alloy exhibits excellent strength and ductility, uniform and slow degradation, good biocompatibility and significant antibacterial effect, which make it an excellent candidate material for biodegradable implants, especially for cardiovascular stents application.

Magnesium alloys have been currently investigated as potential biodegradable implant materials. In this study, a patent Mg alloy Mg–Nd–Zn–Zr (Jiao Da BioMg, hereafter, denoted as JDBM) was researched as a potential biodegradable stent material in comparison with the clinical trial Mg alloy WE43. The corrosion behaviors of the as-extruded JDBM and WE43 were investigated in artificial plasma by in vitro degradation measurements and cyclic polarization tests. The results showed that the corrosion rate of JDBM was much lower than that of WE43 alloy. Most importantly, the JDBM alloy showed a uniform corrosion behavior in artificial plasma, which could avoid stress concentration as well as a rapid reduction in the mechanical integrity. The investigations indicated that the as-extruded JDBM alloy may be a promising implant material suitable for stent applications.

Mg–Nd–Zn–Zr alloy is a novel and promising biodegradable magnesium alloy due to good biocompatibility, desired uniform corrosion mode and outstanding corrosion resistance in simulated body fluid (SBF). However, the corrosion resistance and mechanical properties should be improved to meet the requirement of the biodegradable implants, such as plates, screws and cardiovascular stents. In the present study, double extrusion process was adopted to refine microstructure and improve mechanical properties of Mg–2.25Nd–0.11Zn–0.43Zr and Mg–2.70Nd–0.20Zn–0.41Zr alloys. The corrosion resistance of the alloys after double extrusion was also studied. The results show that the microstructure of the alloys under double extrusion becomes much finer and more homogeneous than those under once extrusion. The yield strength, ultimate tensile strength and elongation of the alloys under double extrusion are over 270 MPa, 300 MPa and 32%, respectively, indicating that outstanding mechanical properties of Mg–Nd–Zn–Zr alloy can be obtained by double extrusion. The results of immersion experiment and electrochemical measurements in SBF show that the corrosion resistance of Alloy 1 and Alloy 2 under double extrusion was increased by 7% and 8% respectively compared with those under just once extrusion.

Mg-Nd-Zn-Zr alloy is a promising biodegradable magnesium alloy due to higher mechanical properties and better corrosion resistance than commercial AZ31 and WE43 alloys. However, the mechanical properties and the corrosion resistance of the alloy should be further improved to meet the requirement of clinical application. In this study, cyclic extrusion and compression (CEC) processing was adopted to refine grains of Mg-Nd-Zn-Zr alloy. Mechanical properties and biocorrosion resistance of the alloy were evaluated. The results show that the yield strength, ultimate tensile strength and elongation of the alloy under CEC processing has ~ 71%, ~ 28% and ~ 154% improvement, respectively. The biocorrosion resistance of the alloy under CEC processing was also improved apparently.

Cu 46 Zr 42 Al 7 Y 5 metallic glass with nearly 100% relative density was obtained by spark plasma sintering (SPS) with a diameter of 15 mm, which was larger than the largest size of 10 mm for the as-cast specimen. The fracture strength of the sintered specimen reached 2044 MPa, which was 15% higher than that of the as-cast Cu 46 Zr 42 Al 7 Y 5 glassy specimen. The densification and compressive properties of the sintered specimens were related to sintering temperature. Structural changes of the specimens sintered at various sintering temperatures resulted in the difference of macro-mechanical properties.

Mg-10Gd-3Y-1.8Zn-0.5Zr (wt.%) alloy is prepared by permanent mold casting and further by slow solidification at cooling rate of 0.1 K s− 1. Both X phase with long period stacking ordered structure and DO3-type (Mg,Zn)3 RE phase in the alloy are observed with electron microscopy and X-ray diffraction. Three different X phase/(Mg,Zn)3 RE phases are observed in the alloy. The orientation relationship between X phase and (Mg,Zn)3 RE phase was determined by the composite diffraction patterns, which can be expressed as (0014)X phase//(110)( Mg,Zn )3RE and [110]X phase//[3 32]( Mg,Zn )3RE, (0014)X phase//(110)( Mg,Zn )3RE and [110]X phase//[1 11]( Mg,Zn )3RE, (0014)X phase//(110)( Mg,Zn )3RE and [210]X phase//[1 12]( Mg,Zn )3RE. These results show coherence between X phase and (Mg,Zn)3 RE phase and a very small mismatch in the phase boundaries.

Recently, commercial magnesium (Mg) alloys containing Al (such as AZ31 and AZ91) or Y (such as WE43) have been studied extensively for biomedical applications. However, these Mg alloys were developed as structural materials, not as biomaterials. In this study, a patented Mg-Nd-Zn-Zr (denoted as JDBM) alloy was investigated as a biomedical material. The microstructure, mechanical properties, biocorrosion behavior, and cytotoxicity of the alloy extruded at 320 °C with extrusion ratios of 8 and 25 were studied. The results show that the lower extrusion ratio results in finer grains and higher strength, but lower elongation, while the higher extrusion ratio results in coarser grains and lower strength, but higher elongation. The biocorrosion behavior of the alloy was investigated by hydrogen evolution and mass loss tests in simulated body fluid (SBF). The results show that the alloy extruded with lower extrusion ratio exhibits better corrosion resistance. The corrosion mode of the alloy is uniform corrosion, which is favorable for biomedical applications. Aging treatment on the as-extruded alloy improves the strength and decreases the elongation at room temperature, and has a small positive influence on the corrosion resistance in SBF. The cytotoxicity test indicates that the as-extruded JDBM alloy meets the requirement of cell toxicity.

In this study, in vitro degradation and biocompatibility of Mg-Nd-Zn-Zr (NZK) alloy were investigated to determine its suitability as a degradable medical biomaterial. Its corrosion properties were evaluated by static immersion test, electrochemical corrosion test, scanning electron microscopy (SEM), and energy dispersive spectroscopic (EDS) analysis, and in vitro biocompatibilities were assessed by hemolysis and cytotoxicity tests. Pure magnesium was used as control. The results of static immersion test and electrochemical corrosion test in simulated body fluid (SBF) demonstrated that the addition of alloying elements could improve the corrosion resistance. The hemolysis test found that the hemolysis rate of calcium phosphate coated NZK alloy was 4.8%, which was lower than the safe value of 5%. The cytotoxicity test indicated that NZK alloy extracts did not significantly reduce MC3T3-E1 cell viability. Hemolysis test and cytotoxicity test display excellent hemocompatibility and cytocompatibility of NZK alloy in vitro. Our data indicate that NZK alloy has excellent biocompatibility and thus can be considered as a potential degradable medical biomaterial for orthopedic applications.

The main challenge for the application of magnesium and its alloy as degradable biomaterials lies in their high degradation rates in physiological environment. In the present work, the biodegradable behavior of a patent magnesium alloy Mg–Nd–Zn–Zr (JDBM) and a reference alloy AZ31 was systematically investigated in Hank's physiological solution. The corrosion rate of JDBM (0.28 mm/year) was much slower than that of AZ31 (1.02 mm/year) in Hank's solution for 240 h. After corrosion products were removed, smooth surface of the JDBM was observed by SEM observation compared to many deep pits on the surface of AZ31. Open-circuit potential and potentiodynamic polarization results manifested that pitting corrosion did not occurred on the surface of JDBM at the early period of immersion time due to the formation of a more protective and compact film layer suggested by electrochemical impedance spectroscopy study. The corrosion rate of magnesium alloys was found to slow down in dynamic corrosion in comparison with that in the static corrosion. This provided the basis for scientific evaluation of in vitro and in vivo corrosion behavior for degradable biomagnesium alloy. The present results suggest that the new patent magnesium alloy JDBM is a promising candidate as degradable biomaterials and is worthwhile for further investigation in vivo corrosive environment.

Mg–3Nd–0.2Zn–0.4Zr alloy with good mechanical properties is a new type of biodegradable magnesium alloy. In order to improve the surface stability in the initial healing stage and foster tissue growth on biomedical implants made of this Mg alloy, oxygen plasma immersion ion implantation (O-PIII) is conducted to modify the alloy surface. Although O-PIII increases the thickness of the surface oxide, no significant improvement in the surface corrosion resistance is observed. Hence, surface alloying with Al and Cr by means of high-energy ion implantation is conducted prior to O-PIII. The electrochemical data obtained in simulated body fluids, including polarization curves and electrochemical impedance spectra (EIS), reveal that the surface corrosion resistance is improved after surface alloying. Our results show that surface alloying with Cr produces the best result in this study. The improvement stems from the formation of Al or Cr-containing oxide films in the implanted layer.

Mechanical properties at room temperature and biocorrosion behaviors in simulated body fluid (SBF) at 37 °C of a new type of patented Mg–3Nd–0.2Zn–0.4Zr (hereafter, denoted as JDBM) alloy prepared at different extrusion temperatures, as well as heat treatment, were studied. The mechanical properties of this magnesium alloy at room temperature were improved significantly after extrusion and heat treatment compared to an as-cast alloy. The results of mechanical properties show that the yield strength (YS) decreases with increasing extrusion temperature. The tensile elongation decreases a little while the ultimate tensile strength (UTS) has no obvious difference. The yield strength and ultimate tensile strength were improved clearly after heat treatment at 200 °C for 10 h compared with that at the extrusion state, which can be mainly contributed to the precipitation strengthening. The biocorrosion behaviors of the JDBM alloy were studied using immersion tests and electrochemical tests. The results reveal that the extruded JDBM alloy and the aging treatment on the extruded alloy show much better biocorrosion resistance than that at solid solution state (T4 treatment), and the JDBM exhibited favorable uniform corrosion mode in SBF.

The crystallization behaviors of Mg65Cu25Gd10, Mg65Cu20Ag5Gd10 and Mg65Cu20Ni5Gd10 metallic glasses were compared with respect to the continuous heating and the isothermal annealing. The results showed that both the partial substitution Ag and Ni for Cu in the Mg65Cu25Gd10 glass can increase the activation energy for the first crystallization and however decrease the thermal stability and the crystal growth rate during the isothermal annealing. The difference in the influence on the crystallization behaviors between Ag addition and Ni addition was analyzed in details. The examination of the crystallization product after the isothermal annealing revealed that Ag addition can effectively suppress the formation of the Mg2Cu crystalline phase of Mg65Cu25Gd10 glass while Ni addition can promote the Mg2Cu formation, which is well consistent with the larger glass-forming ability (GFA) of the Mg65Cu20Ag5Gd10 alloy than that of the Mg65Cu20Ni5Gd10 alloy. In addition, the possible relation between the crystallization features with the GFA was discussed.

In this work, we report a new Mg-based glass-forming system of Mg–Ni–(Gd,Nd), which can be produced into glassy rods with maximum diameters of 2–5 mm by copper mold casting. The Mg75Ni15Gd10–xNdx(x = 0–10) BMGs simultaneously possess a high level of glass transition temperatures, high specific strength up to 2.75 × 105 Nm/kg, and enhanced malleability with plastic strains over 1%. In particular, the Mg75Ni15Gd5Nd5 BMG with the glass-forming ability (GFA) up to 5 mm, exhibited compressive yield strength over 900 MPa and plastic strain up to 50% without failure for the specimen with an aspect ratio of 0.5. The improved GFA and malleability for the Mg75Ni15Gd10–x Ndx(x = 0–10) BMGs were discussed, which exhibited their promising potentials for the application as lightweight engineering materials.

The microstructure and mechanical properties of Mg3.5Zn0.6Gd alloy containing quasicrystals was investigated after extrusion, the role of nanoquasicrystals on the ductility of alloy was analyzed. The results indicate that nanoquasicrystal was formed and distributed along grain boundary and in the matrix for Mg3.5Zn0.6Gd alloy after extrusion. As-extruded Mg3.5Zn0.6Gd alloy containing I-phase showed one relatively random and homogeneous texture due to the local lattice rotation during deformation. The Mg3.5Zn0.6Gd alloy extruded at 673 K exhibits larger elongation about 94% at 473 K, which could been ascribed to the combination of random texture and higher content of I-phase precipitated during extrusion at higher temperature. The a + c type dislocations can be effectively active due to the existence of nanoquasicrystals. The strengthening mechanism of Mg3.5Zn0.6Gd alloy can be explained as the dislocations annihilation effect. This annihilation of dislocations can play a role in the increase of flow strain during deformation.

Microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase have been studied after extrusion at 573 K and 673 K. Extrusion significantly refined the I-phase and Laves phase, and made them exist as particles along the grain boundary and in the matrix. The strengthening effect of I-phase and Laves phase has been analyzed. The combination of I-phase and Laves phase has higher contribution to the improvement of yield strength, which made the Mg94.4Zn3.5Gd0.6Cu1.5 alloy exhibits strong heat resistance. The results show that the two alloys have different heat treatment effect due to different fraction of I-phase and Laves phase. The Mg94.4Zn3.5Gd0.6 alloy after extrusion at 673 K has higher elongation about 94% at 473 K due to higher fraction of I-phase.

The microstructure and mechanical properties of Mg95.9Zn3.5Gd0.6 and Mg94.4Zn3.5Gd0.6Cu1.5 alloys reinforced by icosahedral quasicrystalline phase (I-phase) and Laves phase has been studied after extrusion at 573K. Extrusion can significantly refined the I-phase and Laves phase, and the strengthening effect of I-phase and Laves phase has been analyzed. Large volume of icosahedral phase in Mg95.9Zn3.5Gd0.6 has important role in its high UTS and elongation due to strong bonding effect at the I-phase/matrix interface for low interface energy. The Laves phase with cubic topological and close-packed structure in Mg94.4Zn3.5Gd0.6Cu1.5 alloy result in the higher heat resistance at elevated temperatures.

Mg–Zn–Gd and Mg–Zn–Gd–Cu alloys, reinforced with quasicrystal (I-phase) and Laves phases, have been produced by extrusion process. The deformation behavior of these two alloys at room temperature and at elevated temperatures was investigated, respectively. The Mg–Zn–Gd alloy has high UTS of 305 MPa and elongation of 14.6% due to the strengthening effect of I-phase, while Mg–Zn–Gd–Cu alloy with Laves phases has higher yield stress of 217 MPa due to more strengthening particles and lower elongation of 11.9% resulting from the low content of I-phase and low symmetry of Laves phase due to which it cleaves easily (while the I-phase has a very high symmetry and therefore isotropic in nature). At high temperatures, Mg–Zn–Gd alloy shows large strain due to the excellent plastic compatibility coming from low interfacial energy of I-phase/matrix; Mg–Zn–Gd–Cu alloy has higher level of flow stress, strain exponent and more stable microstructure than Mg–Zn–Gd alloy due to better heat-resistance supplied by collaboration of Laves phases and quasicrystal phase, which can provide more effective pinning effect and suppress grain growth during deformation.

Magnesium (Mg) alloys have revolutionized the application of temporary load-bearing implants as they meet both engineering and medical requirements. However, rapid degradation of Mg alloys under physiological conditions remains the major obstacle hindering the wider use of Mg-based implants. Here we developed a simple method of preparing a nanoscale MgF2 film on Mg-Nd-Zn-Zr (denoted as JDBM) alloy, aiming to reduce the corrosion rate as well as improve the biological response. The corrosion rate of JDBM alloy exposed to artificial plasma is reduced by ∼20% from 0.337 ± 0.021 to 0.269 ± 0.043 mm·y(-1) due to the protective effect of the MgF2 film with a uniform and dense physical structure. The in vitro cytocompatibility test of MgF2-coated JDBM using human umbilical vein endothelial cells indicates enhanced viability, growth, and proliferation as compared to the naked substrate, and the MgF2 film with a nanoscale flakelike feature of ∼200-300 nm presents a much more favorable environment for endothelial cell adhesion, proliferation, and alignment. Furthermore, the animal experiment via implantation of MgF2-coated JDBM stent to rabbit abdominal aorta confirms excellent tissue compatibility of the well re-endothelialized stent with no sign of thrombogenesis and restenosis in the stented vessel.

This paper investigates the microstructure, mechanical properties and creep behavior of Mg–Al–Ca alloys with different Ca content. SEM and EDAX analyses show that the dominant second phase in the as-cast Mg–Al–Ca alloys is Al2Ca, which distributes at the grain boundaries and disperses in the grain interior as well. Both the elevated tensile strength and the creep resistance of Mg–Al–Ca alloys obviously increased with increasing Ca at high temperature. TEM analyses reveal that finer Al2Ca particles with an average size of 0.02 µm precipitated dynamically during the creep process. Selected area electron diffraction (SAD) patterns show that the dynamic Al2Ca precipitates have a coherent interface with matrix as (0110) Mg // (220) Al2Ca, [2110] Mg // [112] Al2Ca. The strengthening mechanism of Mg–Al–Ca alloys at elevated temperature was discussed.

Mg-8Zn-4Al-xY base alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were prepared by casting into a copper mould at moderate cooling rates. The Y addition was effective for decreasing the size of i-phase and the more homogeneousness of its dispersed state. The mechanical properties at room temperature were much superior to those of AZ91 alloy. The creep tests indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg-Zn-Al-Y cast alloy. The dislocation characteristic in crept specimens which containing i-phase and no i-phase was analyzed and strengthening mechanism was discussed.

A new type of Mg–Zn–Cu–Gd-based alloy strengthened by quasicrystal and Laves phase was developed. This alloy exhibits much better creep properties compared to AE42(Mg–4 wt% Al–2 wt% rare-earth) alloy, which is the benchmark creep-resistant magnesium die-casting alloy under the compressive creep condition of 180 °C and80 MPa. The new alloy also exhibits high room-temperature mechanical properties close to that of AZ91 alloy. The good mechanical properties are attributed to the special microstructure; the thermally stable icosahedral quasicrystals phase (i-phase) and Laves phase distributed along the grain boundary as a hard skeleton, and some fine β′1 precipitates distributed homogenously on the matrix. The dislocation morphology after the creep test was studied, and the strengthening mechanism was proposed.

The structural relaxation and glass-forming ability (GFA) of Mg–Cu–Gd-based glassy alloys and the effect of Ni addition on the glass-forming ability, structural relaxation and mechanical properties were studied by thermal analysis, X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The medium-range order (MRO) zones of about 1–2 nm size were observed in the Mg 65 Cu 25 Gd 10 glassy alloy after structural relaxation caused by annealing for 180 s at 305 K. The structural relaxation resistance increased with decreasing Cu content, although the GFA also decreased in Mg–Cu–Gd-based alloys. Appropriate substitution of Cu by Ni in Mg 75 Cu 15 Gd 10 -based alloy not only improved the glass-forming ability and mechanical properties, but also increased the stability against structural relaxation.

Bulk metallic glasses with a maximum diameter of 2.5–5 mm were formed in Mg75Cu5Ni10Gd10, Mg70Cu15Ni5Gd10, and Mg65Cu20Ni5Gd10 systems by copper mold casting. There is a clear tendency for glass-forming ability (GFA) to increase with increasing solute content. These bulk glassy alloys exhibit a large supercooled liquid region (ΔTx) of 44–64 K, indicating high thermal stability of the supercooled liquid. The Young’s modulus, fracture strength, elastic elongation limit, and plastic strain are in the range of 54–59 GPa, 854–904 MPa, 1.50–1.55%, and 0.10–0.20%, respectively. The Mg65Cu20Ni5Gd10 alloy exhibited the highest values of Young’s modulus and strength, while the largest plastic strain was obtained for the Mg75Cu5Ni10Gd10 alloy. The bulk Mg–Cu–Ni–Gd-based metallic glasses exhibited distinct enhanced corrosion resistance compared to Mg65Cu25Gd10 glassy alloy in NaCl aqueous solutions. The fabrication of the Mg-based bulk glassy alloys exhibiting a high strength level of about 900 MPa and plastic strains of ∼0.2%, in conjunction with good corrosion resistance, indicates that the Mg-based bulk glassy alloys may be used as a new generation of structural material.

The effect of substitution of Ni for Cu on the glass forming ability and mechanical properties was studied in Mg 65 Cu 25− x Ni x Gd 10 ( x = 0, 5, 10, 15, 20, 25) alloys by thermal analysis and X-ray diffractometry (XRD). With increasing x from 0 to 25 at.%, the glass transition temperature, T g, of Mg 65 Cu 25− x Ni x Gd 10 alloys increases from 417 to 450 K, and the onset temperature of crystallization, T x , decreases slightly, resulting in a decrease in the supercooled liquid region. However, an appropriate substition of Cu by Ni (5 at.%) in Mg 65 Cu 25 Gd 10 significantly improves mechanical properties, especially improves the ductility of Mg-based bulk metallic glass (BMG) while keeping good glass forming ability (GFA). The Mg 65 Cu 20 Ni 5 Gd 10 BMG sample of 5 mm in diameter is fabricated by the conventional Cu-mold casting method in an argon atomsphere.

The structure and mechanical properties of Mg–Zn–Al–Y base cast alloys containing an icosahedral quasicrystal phase (i-phase) as a main strengthening phase were investigated. Mg–8Zn–4Al–xY base bulk alloys containing the i-phase were prepared by casting into a copper mold at moderate cooling rates. The Y addition was effective for decreasing the size of the i-phase and the increasing the homogeneity of its dispersed state. The mechanical properties examined by compression tests at room temperature were much superior to those of a conventional AZ91 Mg alloy. The creep tests at elevated temperatures indicated a promising high temperature creep resistance of the quasicrystal-reinforced Mg–Zn–Al–Y cast alloy. The strengthening mechanism was also discussed.

Effects of solid solution treatment on microstructure and mechanical property of AM60B alloy with rare earth additions were studied. The experimental results indicated that the ultimate tensile strength and yield strength of alloys were obviously improved by addition of RE no more than 1.6%, while their elongation were not decreased much, microstructure of AM60B+xRE alloys consisted of following phases: delta (Mg) solid solution, rod-like Al11RE3 phase, particle-like Al10Ce2Mn7 phase, and net-like and/or insular Mg17Al12 phase. After solid-solution treated(T4) for 20hr, 35hr, and 50hr at 410degreesC respectively, the Mg17Al12 phase almost dissolved in Mg matrix, but the rare earth compounds Al11RE3 and Al10Ce2Mn7 phases didn';t dissolve and their morphology was slightly changed. When the content of RE reached 1.6%, the alloys'; UTS reached peak.

The effect of a Mg–Nd–Zn–Zr (JDBM) alloy as a degradable biomedical material on chondrocytes was investigated. Chondrocytes were isolated from rabbit articular cartilage. Direct adhesion experiments show good cell spreading and adhesion on JDBM, CaHPO 4 -coated JDBM (C-JDBM), and pure Mg. A significantly higher amount of cells was found on C-JDBM compared with the uncoated samples. Indirect cytotoxicity and RT-PCR test results show that C-JDBM has higher absorbance and relative expression levels of collagen II mRNA and aggrecan mRNA compared with JDBM and Mg ( p p > 0.05). The results indicate that the JDBM alloy exhibits an in vitro cytocompatibility with chondrocytes that is similar to that of pure Mg, and that the addition of a CaHPO 4 coating provides further protection and improves the performance of the material.

The Mg-3.5Zn-0.6Gd (at. %) alloy was prepared and homogenized at 673 K for 8 h, and then extruded at 523 K with an extrusion ratio of 9:1. The microstructure and mechanical properties of the extruded alloy have been investigated. Icosahedral quasicrystalline phase (I-phase) existed in extruded Mg–Zn–Gd-based alloys in two morphologies: (1) micron-scale I-phase formed in the solidification, (2) nano-scale ellipsoid-shape I-phase particles precipitated in the extrusion process. A definite orientation relationship and good atomic match between I-phase and α-Mg matrix were directly observed by conventional and high-resolution transmission electron microscopy (HRTEM), which contribute to the high tensile strength of 308 MPa and the large plasticity of 16.4%.