The introduction of biodegradable implant materials has significantly improved the postoperative subjective feelings of patients within the past few decades,among which magnesium alloy is widely considered a favorable...The introduction of biodegradable implant materials has significantly improved the postoperative subjective feelings of patients within the past few decades,among which magnesium alloy is widely considered a favorable choice as its appropriate biodegradability and evident antibacterial activity.Here,we reveal a semisolid rheo-formed Mg–Zn–Sr alloy ureteral implant that displayed suitable degradability and biocompatibility in a pig model.Refined non-dendritic microstructure was observed in the rheo-formed alloy,which led to ca.47%increase in ultimate tensile strength(from 195.0 MPa to 288.1 MPa)and more homogeneous degradation process compared with the untreated alloy.No post-interventional inflammation or pathological changes of the test animals were observed during the implantation period,and the corrosion rate(0.22±0.04 mm·y^(-1))perfectly fitted the clinical ureteral stent indwelling time.The urine bacteria numbers decreased from 88±13 CFU·mL^(-1)at 7 weeks post operation to 59±8 CFU·mL^(-1)at 14 weeks post operation,which confirmed the evident antibacterial activity of the alloy.Our study demonstrates that the Mg–Zn–Sr alloy is clinically safe for urinary system,enabling its efficacious use as ureteral implant materials.展开更多
In this work,the shear model of metal melt flowing on vibration surface is established,and coupling effects of vibration and shear on the distribution of shear stress in melt and melt solidification microstructure are...In this work,the shear model of metal melt flowing on vibration surface is established,and coupling effects of vibration and shear on the distribution of shear stress in melt and melt solidification microstructure are analyzed.Calculation results show that the transition of melt from laminar flow to turbulent flow occurs earlier with increasing vibration frequency and vibration amplitude.In the laminar flow melt,shear stress in melt decreases with increasing vertical length,but it decreases firstly and then stabilizes with increasing flow length.In the turbulent flow melt,shear stress decreases firstly and then stabilizes with increasing vertical length,but it increases with increasing flow length.With the increase in vibration frequency and amplitude,shear stress along flow direction in laminar flow melt increases,while shear stresses along both flow direction and vertical direction in turbulent flow melt increase.Shear stress in melt decreases with increasing length along vertical direction.With the increase in flow length,shear stress decreases firstly and then stabilizes in laminar flow melt,while it increases in turbulent flow melt.With the increase in vibration frequency and amplitude,shear stress increases in laminar flow melt,while it stabilizes in turbulent flow melt.Based on theoretical calculation,the maximum shear stress in melt during vibration shear flow is always much lower than the yield strength of a-Al grain,so the shear stress induced by vibration shear flow cannot break columnar crystal,which agrees with the experiment result.So,the model can explain the shear constitutive relation of melt flow on vibration surface relatively well.展开更多
Al-Mg-Si alloys(6000 series)exhibit a promising prospect as conductive materials due to their high specific strength,high electrical conductivity,excellent formability,good weldability,corrosion resistance and relativ...Al-Mg-Si alloys(6000 series)exhibit a promising prospect as conductive materials due to their high specific strength,high electrical conductivity,excellent formability,good weldability,corrosion resistance and relatively low cost[1-3].These optimum properties are largely attributed to the formation of small-sized,coherent or semi-coherent and metastable phases brought by aging treatment[1,4].展开更多
Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging,building transportation and electrical materials due to its rich resource, light weight, good mechanical propertie...Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging,building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry.Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows: grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.展开更多
Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl_3 and TiB_2 in Al-5Ti-1B alloy are the main secondary-phase particles fo...Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl_3 and TiB_2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing(ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope(SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl_3 particles and then gradually expanded, which resulted in continuous refinement of TiAl_3 particles. In addition, micro-distribution uniformity of TiB_2 particles was improved due to the impingement of TiAl_3 particles to TiB_2 clusters during deformation. Excessively large sizes of TiAl_3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl_3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18-22 μm for TiAl_3 particles was suggested.展开更多
A biodegradable metallic ureteral stent with suitable mechanical properties and antibacterial activity remains a challenge.Here we reveal the scientific significance of a biodegradable Mg-Sr-Ag alloy with a favorable ...A biodegradable metallic ureteral stent with suitable mechanical properties and antibacterial activity remains a challenge.Here we reveal the scientific significance of a biodegradable Mg-Sr-Ag alloy with a favorable combination of balanced mechanical properties,adjustable indwelling time in urinary tract and evident antibacterial activity via in vivo experiments in a swine model.Attributed to the rheo-solidification process,equiaxial microstructure and significantly refined grains(average grain size:27.1μm)were achieved.Mg17Sr2 and Mg4Ag were found as the primary precipitates in the matrix,due to which the alloy obtained ca.111%increase in ultimate tensile strength in comparison to pure magnesium.Both the in vitro and in vivo results demonstrated the satisfactory biocompatibility of the alloy.Histological evaluation and bioindicators analysis suggested that there was no tissue damage,inflammation and lesions in the urinary system caused by the degradation process.The stent also improved the post-operative bladder functions viewed from the urodynamic results.Our findings highlight the potential of this alloy as antibacterial biodegradable urinary implant material.展开更多
基金National Natural Science Foundation of China(grant numbers 51771045 and U1764254)the Fundamental Research Funds for the Central Universities(grant number N2002016)for the financial supports。
文摘The introduction of biodegradable implant materials has significantly improved the postoperative subjective feelings of patients within the past few decades,among which magnesium alloy is widely considered a favorable choice as its appropriate biodegradability and evident antibacterial activity.Here,we reveal a semisolid rheo-formed Mg–Zn–Sr alloy ureteral implant that displayed suitable degradability and biocompatibility in a pig model.Refined non-dendritic microstructure was observed in the rheo-formed alloy,which led to ca.47%increase in ultimate tensile strength(from 195.0 MPa to 288.1 MPa)and more homogeneous degradation process compared with the untreated alloy.No post-interventional inflammation or pathological changes of the test animals were observed during the implantation period,and the corrosion rate(0.22±0.04 mm·y^(-1))perfectly fitted the clinical ureteral stent indwelling time.The urine bacteria numbers decreased from 88±13 CFU·mL^(-1)at 7 weeks post operation to 59±8 CFU·mL^(-1)at 14 weeks post operation,which confirmed the evident antibacterial activity of the alloy.Our study demonstrates that the Mg–Zn–Sr alloy is clinically safe for urinary system,enabling its efficacious use as ureteral implant materials.
基金supported financially by the National Natural Science Foundation of China (Nos. 51474063, 51674077)the Fundamental Research Funds for the Central Universities (No. N150204016)
文摘In this work,the shear model of metal melt flowing on vibration surface is established,and coupling effects of vibration and shear on the distribution of shear stress in melt and melt solidification microstructure are analyzed.Calculation results show that the transition of melt from laminar flow to turbulent flow occurs earlier with increasing vibration frequency and vibration amplitude.In the laminar flow melt,shear stress in melt decreases with increasing vertical length,but it decreases firstly and then stabilizes with increasing flow length.In the turbulent flow melt,shear stress decreases firstly and then stabilizes with increasing vertical length,but it increases with increasing flow length.With the increase in vibration frequency and amplitude,shear stress along flow direction in laminar flow melt increases,while shear stresses along both flow direction and vertical direction in turbulent flow melt increase.Shear stress in melt decreases with increasing length along vertical direction.With the increase in flow length,shear stress decreases firstly and then stabilizes in laminar flow melt,while it increases in turbulent flow melt.With the increase in vibration frequency and amplitude,shear stress increases in laminar flow melt,while it stabilizes in turbulent flow melt.Based on theoretical calculation,the maximum shear stress in melt during vibration shear flow is always much lower than the yield strength of a-Al grain,so the shear stress induced by vibration shear flow cannot break columnar crystal,which agrees with the experiment result.So,the model can explain the shear constitutive relation of melt flow on vibration surface relatively well.
基金financially supported by the National Key Research and Development Program(No.2018YFB2001800)the National Natural Science Foundation of China(Nos.51871184 and 51974083)。
文摘Al-Mg-Si alloys(6000 series)exhibit a promising prospect as conductive materials due to their high specific strength,high electrical conductivity,excellent formability,good weldability,corrosion resistance and relatively low cost[1-3].These optimum properties are largely attributed to the formation of small-sized,coherent or semi-coherent and metastable phases brought by aging treatment[1,4].
基金supports of the National Natural Science Foundation of China under Grant Nos.51474063,51674077 and 51504065
文摘Aluminum becomes the most popular nonferrous metal and is widely used in many fields such as packaging,building transportation and electrical materials due to its rich resource, light weight, good mechanical properties, suitable corrosion resistance and excellent electrical conductivity. Grain refinement, which is obtained by changing the size of grain structure by different techniques, is a preferred method to improve simultaneously the strength and plasticity of metallic materials. Therefore, grain refining of aluminum is regarded as a key technique in aluminum processing industry.Up to now, there have been a number of techniques for aluminum grain refining. All the techniques can be classified as four categories as follows: grain refining by vibration and stirring during solidification, rapid solidification, the addition of grain refiner and severe plastic deformation. Each of them has its own merits and demerits as well as applicable conditions, and there are still some arguments in the understanding of the mechanisms of these techniques. In this article, the research progresses and challenges encountered in the present techniques and the future research issues and directions are summarized.
基金financial support provided by the National Natural Science Foundation of China(Nos.51674077 and 51474063)
文摘Addition of Al-5Ti-1B alloy to molten aluminum alloys can refine α-Al grains effectively and thereby improve their strength and toughness. TiAl_3 and TiB_2 in Al-5Ti-1B alloy are the main secondary-phase particles for refinement, while the understanding on the effect of their sizes on α-Al grain refinement continues to be fragmented. Therefore, Al-5Ti-1B alloys with various sizes and morphologies of the secondary-phase particles were prepared by equal channel angular pressing(ECAP). Evolution of the secondary-phase particles during ECAP process and their impact on α-Al grain refinement were studied by X-ray diffraction and scanning electron microscope(SEM). Results show that during the ECAP process, micro-cracks firstly appeared inside TiAl_3 particles and then gradually expanded, which resulted in continuous refinement of TiAl_3 particles. In addition, micro-distribution uniformity of TiB_2 particles was improved due to the impingement of TiAl_3 particles to TiB_2 clusters during deformation. Excessively large sizes of TiAl_3 particles would reduce the number of effective heterogeneous nucleus and thus resulted in poor grain refinement effectiveness. Moreover, excessively small TiAl_3 particles would reduce inhibitory factors for grain growth Q and weaken grain refinement effectiveness. Therefore, an optimal size range of 18-22 μm for TiAl_3 particles was suggested.
基金This work was supported by National Natural Science Foundation of China(grant numbers 51771045 and U1764254)Special thanks are due to the instrumental analysis from Analytical and Testing Center,Northeastern University.The authors sincerely acknowledge the Animal Experimental Center of China Medical University for the in vivo experiments.
文摘A biodegradable metallic ureteral stent with suitable mechanical properties and antibacterial activity remains a challenge.Here we reveal the scientific significance of a biodegradable Mg-Sr-Ag alloy with a favorable combination of balanced mechanical properties,adjustable indwelling time in urinary tract and evident antibacterial activity via in vivo experiments in a swine model.Attributed to the rheo-solidification process,equiaxial microstructure and significantly refined grains(average grain size:27.1μm)were achieved.Mg17Sr2 and Mg4Ag were found as the primary precipitates in the matrix,due to which the alloy obtained ca.111%increase in ultimate tensile strength in comparison to pure magnesium.Both the in vitro and in vivo results demonstrated the satisfactory biocompatibility of the alloy.Histological evaluation and bioindicators analysis suggested that there was no tissue damage,inflammation and lesions in the urinary system caused by the degradation process.The stent also improved the post-operative bladder functions viewed from the urodynamic results.Our findings highlight the potential of this alloy as antibacterial biodegradable urinary implant material.
