Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegrad-ability,biocompatibility,low density and adequate mechanical properties.Neverthel...Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegrad-ability,biocompatibility,low density and adequate mechanical properties.Nevertheless,there is a need to further improve these properties either by alloying or through the use of appropriate processing.Among the different biodegradable Mg alloys now in use,the Mg-Zn series are of special interest and have been the subject of many research investigations.This is primarily because Zn is an essential element for the human body in addition to its positive effects in improving the mechanical strength and lowering the degradation rate of the implant.The properties of Mg-Zn alloys may be further improved both through the addition of third and fourth alloying elements such as Ca,Ag,Sn or Sr and/or by thermo-mechanical processing where the latter is more environmentally and economically favorable.In practice,procedures based on the application of severe plastic deformation(SPD)are especially suited to produce fine-grained microstructures with improved mechanical,degradation and cell behavior.Equal-channel angular pressing(ECAP)is a popular SPD technique that has the capability of pro-ducing bulk materials that are sufficiently large for use as typical implants.Accordingly,this review is designed to provide a comprehensive summary of the research that has been undertaken on ECAP-processed biodegradable Mg-Zn alloys.展开更多
Biodegradable magnesium(Mg)alloys exhibit great potential for use as temporary structures in tissue engineering applications.Such degradable implants require no secondary surgery for their removal.In addition,their co...Biodegradable magnesium(Mg)alloys exhibit great potential for use as temporary structures in tissue engineering applications.Such degradable implants require no secondary surgery for their removal.In addition,their comparable mechanical properties with the human bone,together with excellent biocompatibility,make them a suitable candidate for fracture treatments.Nevertheless,some challenges remain.Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue.Among different methods used to improve the performance of the biodegradable Mg alloys to address these challenges,it appears that heat treatment is the most effective way to modify the microstructure and thus the corrosion behavior and mechanical properties without changing the composition or shape of the alloys.A desirable combination of corrosion and mechanical properties can be obtained through a precise control of the heat treatment parameters.In this report,the effects of different heat treatments(T4 and T6)on the microstructure,corrosion behavior,and mechanical properties of some of the most important heat-treatable biodegradable Mg alloys(Mg-Zn,Mg-Gd,Mg-Y,Mg-Nd,Mg-Al and Mg-Ag)are examined as well as new perspectives to enhance their clinical implementation.展开更多
Magnesium and its alloys have gained significant popularity due to their light weight and their potential for use as bioresorbable materials.However,their application is limited in practice due to their relatively poo...Magnesium and its alloys have gained significant popularity due to their light weight and their potential for use as bioresorbable materials.However,their application is limited in practice due to their relatively poor corrosion resistance.Several methods are available for improving the corrosion resistance of Mg alloys for bio-applications such as using different coatings,alloying,and modifying the microstructural parameters such as the grain size and the crystallographic texture.This review provides a comprehensive summary of the effects of crystallographic texture and twinning,as one of the most important deformation mechanisms of Mg and Mg alloys,on the corrosion behavior.Regarding the crystallographic texture,it is shown that theoretically the basal planes should exhibit a lower corrosion rate but in some cases,such as when there is a galvanic effect or when corrosion films control the overall corrosion behavior,different results may take place.Also,there are contradictory results concerning the effect of twinning on the corrosion behavior.Thus,in some cases twinning may provide preferential sites for corrosion due to the higher energies of atoms located in the twin region by comparison with normal atomic positions in the crystalline lattice whereas there are also other examples where experiments show that twins produce more protective films than in the surrounding matrix.展开更多
Nanoscale metallic multilayers(NMMs)have attracted significant attention owing to their enhanced me-chanical properties and excellent thermal stability.However,the underlying deformation mechanisms of the high-tempera...Nanoscale metallic multilayers(NMMs)have attracted significant attention owing to their enhanced me-chanical properties and excellent thermal stability.However,the underlying deformation mechanisms of the high-temperature annealed microstructures have not been well clarified.In this study,the effect of annealing temperatures(500,600,700,800,and 1000℃)on the microstructural evolution and mechan-ical properties of Cu/Nb NMMs was investigated systematically.The results show that when the anneal-ing temperature is lower than 800℃the Cu/Nb NMMs maintain their initial continuous nanolayered structure.As the annealing temperature reaches 1000℃,a thermal instability,driven by thermal grain boundary grooving and a Rayleigh instability,leads to the pinching offof the nanolayered structure and even a complete disintegration into an equiaxed grain structure.Uniaxial tensile tests show that 1000℃annealed samples exhibit an enhanced strain hardening capability compared to as-rolled NMMs and this imparts superior ultimate tensile strength(∼492 MPa)and a high elongation(∼20%).TEM observations demonstrate that high-density entangled dislocations exist in the Cu-Nb interface and layers after tensile testing of the high-temperature annealed samples.The dislocation tangles lead to stable and progres-sive strain hardening which is the dominant factor in determining the superior combination of strength and ductility of the high-temperature annealed samples.Thus,this study offers a promising strategy for evading the strength-ductility dilemma and instead promotes a more in-depth understanding of the de-formation mechanisms of heterostructured materials.展开更多
基金supported by the European Research Council under Grant Agreement No.267464-SPDMETALS(TGL).
文摘Magnesium alloys are of considerable current interest for use as degradable implants due to their unique properties including biodegrad-ability,biocompatibility,low density and adequate mechanical properties.Nevertheless,there is a need to further improve these properties either by alloying or through the use of appropriate processing.Among the different biodegradable Mg alloys now in use,the Mg-Zn series are of special interest and have been the subject of many research investigations.This is primarily because Zn is an essential element for the human body in addition to its positive effects in improving the mechanical strength and lowering the degradation rate of the implant.The properties of Mg-Zn alloys may be further improved both through the addition of third and fourth alloying elements such as Ca,Ag,Sn or Sr and/or by thermo-mechanical processing where the latter is more environmentally and economically favorable.In practice,procedures based on the application of severe plastic deformation(SPD)are especially suited to produce fine-grained microstructures with improved mechanical,degradation and cell behavior.Equal-channel angular pressing(ECAP)is a popular SPD technique that has the capability of pro-ducing bulk materials that are sufficiently large for use as typical implants.Accordingly,this review is designed to provide a comprehensive summary of the research that has been undertaken on ECAP-processed biodegradable Mg-Zn alloys.
基金the European Research Council under Grant Agreement No.267464SPDMETALS(TGL)。
文摘Biodegradable magnesium(Mg)alloys exhibit great potential for use as temporary structures in tissue engineering applications.Such degradable implants require no secondary surgery for their removal.In addition,their comparable mechanical properties with the human bone,together with excellent biocompatibility,make them a suitable candidate for fracture treatments.Nevertheless,some challenges remain.Fast degradation of the Mg-based alloys in physiological environments leads to a loss of the mechanical support that is needed for complete tissue healing and also to the accumulation of hydrogen gas bubbles at the interface of the implant and tissue.Among different methods used to improve the performance of the biodegradable Mg alloys to address these challenges,it appears that heat treatment is the most effective way to modify the microstructure and thus the corrosion behavior and mechanical properties without changing the composition or shape of the alloys.A desirable combination of corrosion and mechanical properties can be obtained through a precise control of the heat treatment parameters.In this report,the effects of different heat treatments(T4 and T6)on the microstructure,corrosion behavior,and mechanical properties of some of the most important heat-treatable biodegradable Mg alloys(Mg-Zn,Mg-Gd,Mg-Y,Mg-Nd,Mg-Al and Mg-Ag)are examined as well as new perspectives to enhance their clinical implementation.
基金the European Research Council under Grant Agreement No.267464-SPDMETALS(TGL)。
文摘Magnesium and its alloys have gained significant popularity due to their light weight and their potential for use as bioresorbable materials.However,their application is limited in practice due to their relatively poor corrosion resistance.Several methods are available for improving the corrosion resistance of Mg alloys for bio-applications such as using different coatings,alloying,and modifying the microstructural parameters such as the grain size and the crystallographic texture.This review provides a comprehensive summary of the effects of crystallographic texture and twinning,as one of the most important deformation mechanisms of Mg and Mg alloys,on the corrosion behavior.Regarding the crystallographic texture,it is shown that theoretically the basal planes should exhibit a lower corrosion rate but in some cases,such as when there is a galvanic effect or when corrosion films control the overall corrosion behavior,different results may take place.Also,there are contradictory results concerning the effect of twinning on the corrosion behavior.Thus,in some cases twinning may provide preferential sites for corrosion due to the higher energies of atoms located in the twin region by comparison with normal atomic positions in the crystalline lattice whereas there are also other examples where experiments show that twins produce more protective films than in the surrounding matrix.
基金supported by the National Natural Science Foun-dation of China under Grant No.51635005the Program of Introducing Talents of Discipline to Universities under grant num-ber B18017Partial support was provided by the European Research Council underERC GrantAgreementNo.267464-SPDMETALS(TGL).
文摘Nanoscale metallic multilayers(NMMs)have attracted significant attention owing to their enhanced me-chanical properties and excellent thermal stability.However,the underlying deformation mechanisms of the high-temperature annealed microstructures have not been well clarified.In this study,the effect of annealing temperatures(500,600,700,800,and 1000℃)on the microstructural evolution and mechan-ical properties of Cu/Nb NMMs was investigated systematically.The results show that when the anneal-ing temperature is lower than 800℃the Cu/Nb NMMs maintain their initial continuous nanolayered structure.As the annealing temperature reaches 1000℃,a thermal instability,driven by thermal grain boundary grooving and a Rayleigh instability,leads to the pinching offof the nanolayered structure and even a complete disintegration into an equiaxed grain structure.Uniaxial tensile tests show that 1000℃annealed samples exhibit an enhanced strain hardening capability compared to as-rolled NMMs and this imparts superior ultimate tensile strength(∼492 MPa)and a high elongation(∼20%).TEM observations demonstrate that high-density entangled dislocations exist in the Cu-Nb interface and layers after tensile testing of the high-temperature annealed samples.The dislocation tangles lead to stable and progres-sive strain hardening which is the dominant factor in determining the superior combination of strength and ductility of the high-temperature annealed samples.Thus,this study offers a promising strategy for evading the strength-ductility dilemma and instead promotes a more in-depth understanding of the de-formation mechanisms of heterostructured materials.
