Nd,Zn微量元素在Mg-Zn-Y-Nd血管合金支架中组织学特性和改性的变化

背景:随着材料学的不断发展,镁合金血管支架材料在心血管疾病中广泛运用,但是传统合金材料难以满足血管支架要求,因此采取有效措施完成支架表面改性,提高血管支架的组织、力学性能具有深远的意义。目的:观察血管支架在快速凝固Mg-Zn-Y-Nd合金中的组织学及表面改性情况。方法:选择具备良好力学性能、耐腐蚀性能的低锌系Mg-2Zn-0.2Y合金为基本材料,向材料中加入Nd,Zn元素完成合金支架的细化;经过对支架的挤压细化组织性能完成支架表面改性,提高合金材料的综合性能,获得血管支架用新型镁合金并完成支架表面改性。通过金相显微组织、扫描电镜能谱及射线衍射分析实验了解制备支架的组织性能;通过硬度、拉伸实验了解支架的力学性能。结果与结论:(1)金相显微镜组织观察结果显示:当不加入Y时,镁合金支架第2相为杆状,存在少许颗粒嵌入在基体中;当向镁合金支架中混入0.5%Y元素时,支架第2相中杆状物明显减少,以颗粒状为主,且均匀分布在机体中;加入1.0%的Y时,第2相数增加,晶粒中可见大量枝晶,第2相存在不连续杆状物;加入1.5%的Y时,合金组织中的大枝晶与局枝晶混合,第2相为杆状。(2)射线衍射分析实验结果表面:Mn-Zn-0.5Nd合金与Mn-Zn-1.0Nd合金中均含有相同的相(Mg4Zn7和(Nd,Y)2Zn17相)。当Nd浓度提高为1%时,合金中出现新的MgZ n2相;(3)镁合金改性材料SEM及EDS实验结果显示:镁合金改性后第2相中含有Zn元素、Nd及Y元素,并且Nd元素、Y元素含量和与Zn含量较接近。EDS分析可知:加入Zr元素后层片状第2相中Zn元素水平明显下降,Y元素、Nd元素含量提高,能获得更加稳定的性能;(4)显微硬度实验结果显示:随着镁合金含量的不断增加,合金显微硬度值不断增加;(5)拉伸实验结果显示:Mg-Zn-Y-0.5Nd-Zr支架的抗拉强度、屈服强度,显著高于Mg-Zn-Y-0.5Nd,Mg-Zn-Y-1.0Nd,Mg-Zn-Y-1.0Nd-Zr(P<0.05);Mg-Zn-Y-0.5Nd-Zr,Mg-Zn-Y-1.0Nd-Zr伸长率,高于Mg-Zn-Y-0.5Nd,Mg-Zn-Y-1.0Nd(P<0.05)。(6)结果说明:选择低锌系Mg-2Zn-0.2Y合金为核心材料,向材料中分别加入Nd,Zn等微量元素,完成材料的改性,并且经过对支架的挤压细化组织性能完成支架表面改性,改性后材料具有优良的性能。

搅拌摩擦加工对Mg-Zn-Y-Nd合金厚板组织与性能的影响

为了获得组织分布均匀且综合性能好的较大改性区,对Mg-Zn-Y-Nd合金厚板进行单面和双面搅拌摩擦加工,并对其组织和性能进行研究。结果表明:经搅拌摩擦加工后合金的微观组织均得到了显著细化,单面和双面搅拌摩擦加工后合金搅拌区的上部、中部和下部样品的平均晶粒尺寸依次分别为4.45μm、5.08μm、5.30μm和3.93μm、3.20μm、3.19μm;相比于均匀化退火态合金和单面搅拌摩擦加工态合金,双面搅拌摩擦加工态合金的组织分布更加均匀和细小,其下层搅拌区的抗拉强度和伸长率最高,分别为283.3 MPa和23.9%,且耐腐蚀性能最好,腐蚀方式由点蚀变为均匀腐蚀。

新型Mg-Zn-Y-Nd-Zr镁合金表面复合涂层的耐腐蚀性能

为了控制镁材及镁合金在人体中的生物降解速率,采用微弧氧化法、电化学沉积法及微弧氧化+电化学沉积法在新型Mg-Zn-Y-Nd-Zr镁合金表面制备了3种涂层。利用JSM-5610V扫描电子显微镜、TESCANTS5130 SB能谱分析仪、Bruker D8 ADVANCE X射线衍射仪、VS-2005涂层附着力自动划痕仪、RST200F电化学工作站对3种涂层的形貌、成分、结构、厚度、结合力以及电化学性能进行了检测。结果表明:3种涂层均能提高新型Mg-Zn-Y-Nd-Zr镁合金的电化学性能,改善其耐蚀性;微弧氧化+电化学沉积层较单一微弧氧化层及电化学沉积层在致密性、结晶度、厚度、结合力、耐腐蚀性能方面都具有更强的指标。

医用Mg-Zn-Y-Nd合金微细管材的制备及组织性能研究

通过二次热挤压、冷拉拔以及退火等方法制备外径2.46 mm、壁厚0.14 mm的Mg-Zn-Y-Nd合金微细管材。采用OM、SEM、EBSD以及拉伸试验对微细管材的显微组织、尺寸误差、表面粗糙度以及力学性能进行分析。结果表明:微细管材的外径误差、内径误差以及壁厚误差分别为0.51%、0.32%、3.35%。冷拉拔微细管材的屈服强度为342 MPa,抗拉强度为350 MPa,延伸率为0.5%。经退火处理后,微细管材发生静态再结晶,造成晶粒细化、织构弱化以及第二相颗粒的弥散分布,其综合力学性能得到显著改善。退火态微细管材的断口表现出典型的韧性断裂特征,其屈服强度、抗拉强度以及延伸率分别为246 MPa、306 MPa、18.0%。

Effects of annealing treatment on microstructure and tensile behavior of the Mg-Zn-Y-Nd alloy

In the present study,the Mg-4Zn-0.6Y-0.5Nd alloy was hot extruded and annealed at 200℃,225℃ and 250℃ for different time to optimize microstructure and mechanical properties.The results exhibit that the dual-size grain structure and linearly distributed secondary phase are the main feature of the as-extruded Mg-Zn-Y-Nd alloy,which can be described as the elongated grain is surrounded by the fine equiaxed grain.Moreover,the as-extruded alloy shows strong{011^(-)0}fiber texture feature,especially for the large elongated grains.The annealing treatment results in static recrystallization,which increases fine equiaxed grains but decreases large elongated grains.In addition,the equiaxed grains formed during the annealing treatment demonstrate relative random orientations,which weaken the{011^(-)0}fiber texture of the alloy.Moreover,during the annealing at 225℃and 250℃,the extension twins begin to form in the alloy and weaken the{011^(-)0}fiber texture of the alloy further.The annealing treatment has little influence on the linearly distributed secondary phase but promotes the coarsening of small precipitates at 250℃.The annealing treatment could increase the yield and ultimate strength,but the elongation decreases,especially at higher temperature.Such a variation can be ascribed to the evolution of texture,grain structure,twinning and precipitation during the annealing treatment.

In vitro corrosion properties of HTHEed Mg-Zn-Y-Nd alloy microtubes for stent applications:Influence of second phase particles and crystal orientation

Magnesium(Mg)alloys are promising materials for cardiovascular stent applications due to their good biocompatibility and biodegradability.However,in vitro and in vivo corrosion tests reveal that Mg alloy stents suffer from a rapid corrosion rate and severe localized corrosion,which is limiting their widespread application.To solve the problem of uneven degradation of stents,a HTHE(long-time and high-temperature heat treatment,large-reduction-ratio hot extrusion)process is used to manufacture Mg-Zn-Y-Nd alloy microtubes in this study.The heat treatment is to dissolve alloying elements and reduce the size of SPPs,and the hot extrusion is to acquire fine-grained and strongly textured microtubes.The microstructural characterization shows that coarse second phases in as-cast alloy are refined and uniformly distributed in matrix of microtubes.After hot extrusion,microtubes show strong texture with basal plain oriented parallel to the longitudinal section(LS).The corrosion testing indicates that severe localized corrosion occurs on the cross section(CS)while localized corrosion is alleviated on the LS.Based on the different corrosion properties of the LS and CS,HTHEed microtubes are promising for solving the problems of rapid corrosion rate and severe localized corrosion of Mg alloy stents.

Mn添加对挤压态Mg-Zn-Y-Nd合金微观组织和腐蚀行为的影响

通过光学显微镜,配备能量色散谱仪的扫描电子显微镜,X射线衍射仪,浸泡法和电化学测试的方法研究了Mn的添加对挤压Mg-Zn-Y-Nd合金在3.5%(质量分数)NaCl溶液中的微观组织和腐蚀行为的影响。结果表明,在研究的Mg-Zn-Y-Nd合金中添加Mn可以诱导Mg3Y2Zn3(I相)沉淀,可以抑制热挤压过程中动态再结晶(DRX)晶粒的粗化。同时,添加了Mn也可以提高合金的耐腐蚀性。不含Mn的Mg-5.6Zn-1Y-0.4Nd合金与含锰1.0%的Mg-5.6Zn-1Y-0.4Nd合金腐蚀速率分别为18.78和9.89 mm·a^(-1)。而耐腐蚀性的提高主要归因于腐蚀产物层保护性的增强。

Mg-Zn-Y-Nd-Zr合金的显微组织、织构、力学性能

对Mg-Zn-Y-Nd-Zr合金的显微组织和力学性能进行了研究。结果表明,Nd元素的加入部分取代了W相(Mg_(3)Zn_(3)Y_(2))中的Y元素,形成了新的第二相Mg_(3)Zn_(3)(Y,Nd)_(2)。热挤压后观察到由细小的等轴再结晶晶粒和粗大的细长未再结晶晶粒组成的典型双峰结构。Nd元素的加入促进了热挤压过程中的动态再结晶,随着Nd含量的增加,动态再结晶率增加,挤压态合金的整体织构强度减弱。Nd的加入细化了晶粒并改善了合金的力学性能。添加0.5%(质量分数)Nd时,挤压态合金表现出高强度和高塑性的良好结合:屈服强度为362MPa,极限抗拉伸强度为404 MPa,延伸率为10.2%。时效处理后合金的抗拉伸强度进一步提高,峰值时效极限抗拉伸强度可达421MPa。合金的高强度主要归功于超细再结晶晶粒和析出强化。

Optimizing mechanical property and cytocompatibility of the biodegradable Mg-Zn-Y-Nd alloy by hot extrusion and heat treatment

The Mg-Zn-Y-Nd alloy is a new type of degradable material for biomedical application. In the present study, Mg-6Zn-1.2Y-0.8Nd alloy was fabricated, and then extrusion and heat treatment were conducted to optimize its mechanical properties and cytocompatibility. The microstructure observation, mechanical property, degradation behavior and cytocompatibility tests were conducted on the Mg-Zn-Y-Nd alloy with three different states: as-cast(alloy C), as-extruded(alloy E) and extruded + heat treated(alloy EH).The results show that alloy C consists of coarse grains and continuous secondary phases. The extrusion process has caused incomplete recrystallization, and results in a mixed grain structure of elongated grains and small equiaxed grains(alloy E). The heat treatment process has promoted the recrystallization and homogenized the grain structure(alloy EH). Both the strength and ductility of the alloy has been improved by extrusion, but the following heat treatment has decreased the strength and increased the ductility.The degradation behavior of the alloy C and E alloys does not show much difference, but improves slightly in alloy EH, because the heat treatment has homogenized the microstructure and released the residual stress in the alloy. The directly and indirectly cell viability tests indicate that alloy EH exhibits the best cytocompatibility, which should be ascribed to its relative uniform degradation and low ion releasing rate. In summary, the combination of hot extrusion and heat treatment could optimize the mechanical property and cytocompatibility of the Mg-Zn-Y-Nd alloy together, which is beneficial for the future application of the alloy.

Microstructural characteristics and mechanical properties of the hot extruded Mg-Zn-Y-Nd alloys

A new type of Mg-Zn-Y-Nd alloy for degradable orthopedic implants was developed.In the present study,the Zn and Y content was adjusted and their influences on the microstructures and mechanical behaviors were discussed in depth.The results showed that the as-extruded Mg-Zn-Y-Nd alloys are mainly composed of fine dynamic recrystallized grains(DRXed grains),la rge unDRXed grains and linearly distributed secondary phases.The cha nge of Zn content exerts little influence on the grain structure of the extruded Mg-Zn-Y-Nd alloy,while the increase of Y content would hinder the dynamic recrystallization process and the growth of the DRXed grains,thus the size and volume fraction of the equiaxed DRXed grains decrease.The tensile and compressive properties are very little affected by Zn content because of the similar grain structure.As Y content increases,the tensile yield strength(TYS) and ultimate strength(TUS) increase while the elongation decreases,this is caused by a combined strengthening effect of grain refinement,texture,precipitation and twinning.The compressive yield strength(CYS) and ultimate strength(CUS) of Mg-Zn-Y-Nd alloy with diffe rent Y content exhibit a similar tendency as the tensile test.

Microstructure and mechanical properties of Mg-Zn-Y-Nd-Zr alloys

The microstructure and tensile properties of the as-cast and solution treatment Mg-4.5Zn-1Y-xNd-0.5Zr （x=0, 1 wt.%, 2 wt.%, 3 wt.%） alloys were investigated. The results showed that the microstructure of Mg-4.5Zn-1Y-0.5Zr alloy consisted of α-Mg, Zn-Zr, W （Mg3Y2Zn3） and I （Mg3YZn6） phases. With the addition of Nd, I-phase disappeared and Mg3Y2Zn3 phase changed into Mg3（Nd,Y）2Zn3 phase. When the content of Nd reached 3 wt.%, T phase, i.e., ternary Mg-Zn-Nd phase, formed. In addition, with the increase of Nd content in the alloys, the secondary dendritic arm spacing decreased, while the amount of intermetallic phases increased. For as-cast Mg-4.5Zn-1Y-xNd-0.5Zr alloys, after solution treatment, microsegregation was eliminated and the shape of eutectic structure of α-Mg＋W transformed from lamellar into spherical. The tensile strength and elongation of Mg-4.5Zn-1Y- 3Nd-0.5Zr alloy were increased from 219.2 MPa and 11.0% to 247.5 MPa and 20.0%, respectively.

Effect of extrusion process on the mechanical and in vitro degradation performance of a biomedical Mg-Zn-Y-Nd alloy

A new type of biomedical Mg-Zn-Y-Nd alloy was developed and thermal extruded by different processes to investigate the effect of extrusion ratio and extrusion pass on its microstructure,mechanical property and degradation performance.The results show that the increase of extrusion ratio could promote the dynamic recrystallization(DRX)process and led to the coarsening of DRXed grains.While the increase of extrusion pass also contributes to the DRX process but refines the DRXed grains.The simultaneous increasing of extrusion ratio and extrusion pass refines the secondary phases obviously.The increase of extrusion ratio has reduced the tensile strength but improved the elongation of the alloy significantly.However,the increase of extrusion pass could enhance the tensile strength and elongation simultaneously,especially the strength.The degradation performance has been optimized effectively through increasing the extrusion ratio and extrusion pass.

Mg-Zn-Y-Nd coated with citric acid and dopamine by layer-by-layer self-assembly to improve surface biocompatibility

Magnesium alloy has been generally accepted as an important biodegradable material on cardiovascular stent development for a long time. However, its limited biocompatibility, especially delayed endothelialization process restricts its further application. In this contribution, we modified the Mg-Zn-Y-Nd alloy surface with citric acid and dopamine via a layer-by-layer self-assembly assay, aiming at improving the biocompatibility of the magnesium alloy. The citric acid/dopamine(CA/PDA) layer exhibited a remarkable suppression of platelet activation/aggregation and thrombosis under 15 dyn/cm2 blood flowing. Inhibition on vascular smooth muscle cells growth and macrophages attachment/activation were also observed on this layer. In particular, the CA/PDA layer presented a promoted property for the vascular endothelial cells growth and spreading compared with the bare magnesium alloy, suggesting the pro-endotelialized function. In conclusion, this research may support potential application on surface modification of magnesium alloy based cardiovascular stents for better biocompatibility.

铸态Mg-2Nd-0.2Zn-0.4Zr-xY镁合金组织及力学性能

采用光学显微镜(OM)、扫描电子显微镜(SEM)、X线衍射分析(XRD)及力学性能测试等手段,研究不同含量稀土元素Y(4%,6%,8%,质量分数)对Mg-2%Nd-0.2%Zn-0.4%Zr镁合金铸态显微组织及力学性能的影响。结果表明:在Mg-2%Nd-0.2%Zn-0.4%Zr镁合金中添加Y可以明显细化合金晶粒,其中加入6%Y时效果最佳;合金晶粒粒径由100μm细化至35μm。未添加稀土元素的Mg-2%Nd-0.2%Zn-0.4Zr铸态合金中主要存在Mg12Nd相;加入稀土元素Y后,Nd和Y分别以Mg41Nd5和Mg24Y5化合物形式存在,合金的力学性能得到提高。其中加入6%Y的合金综合力学性能最好,抗拉强度和屈服强度分别提高至245 MPa和150 MPa,而伸长率大幅提高至16%,较未加稀土元素Y的合金提高191%;当Y含量达到8%时,合金综合力学性能下降。

Nd对Mg-Zn-Y合金显微组织与力学性能的影响

采用金相显微镜、电子探针、扫描电镜、X-射线衍射仪及电子万能拉伸试验机等设备分析研究了Nd对Mg-Zn-Y合金的显微组织和力学性能的影响。显微组织观察表明:稀土Nd能够明显起到晶粒细化的作用,改善了实验合金的显微组织。力学性能测试表明:由于稀土Nd的添加提高了合金的力学性能,并且当Nd添加量为0.5%时,合金的综合力学性能最佳,抗拉强度达到207MPa,伸长率达到16.9%,硬度达到52.8HV。

稀土元素Nd对Mg-Zn-Y合金组织结构和力学性能的影响

通过制备Mg-6Zn-1.5Y-0.8Zr-xNd(x=0、1、2、3、4)系列合金,研究了稀土元素Nd对Mg-6Zn-1.5Y-0.8Zr合金组织结构和力学性能的影响。通过金相显微镜、扫描电镜、EDS、XRD等手段,观察和分析了合金的微观形貌和组织结构,测量了合金抗拉强度、屈服强度和伸长率等力学性能。结果表明:合金中添加稀土元素Nd后晶粒明显细化,随着Nd元素含量的增加,晶粒细化效果更为明显;通过XRD分析可知,添加Nd元素后,合金中并没有出现新的含Nd的物相;扫描电镜和EDS分析表明,合金中加入的Nd置换了部分Y,形成了Mg3(NdY)2Zn3、Mg3-(NdY)Zn6的相结构,Nd元素对Y的置换主要出现在Mg3(NdY)2Zn3结构中,在Mg3(NdY)Zn6相结构中出现较少;力学性能测试结果表明,随着Nd含量增多,合金晶粒细化,细晶强化作用明显,合金屈服强度逐渐增大,而抗拉强度和伸长率在Nd含量为3%(质量分数)时达到最大,比未添加Nd元素时提高约25%以上。

镁稀土合金Mg-Gd-Y-Zr及Mg-Nd-Zn-Zr的强流脉冲电子束表面改性研究

采用强流脉冲电子束技术对Mg-Gd-Y-Zr和Mg-Nd-Zn-Zr两种镁稀土合金进行表面改性处理,并研究了处理后镁合金表层的相组成、形貌和性能变化。结果表明:Mg-Gd-Y-Zr合金经脉冲电子束处理后表层的Mg5Gd转变为Mg3Gd,而Mg-Nd-Zn-Zr合金表层的Mg12Nd相消失形成过饱和固溶体。两种稀土镁合金经脉冲电子束处理后均发生熔化和部分汽化,在快速凝固后表面形成波状形貌,且表面生成大量孪晶。脉冲电子束处理使得两种镁合金表面硬度显著提高。在模拟体液中的腐蚀测试结果显示,上述合金经强流脉冲电子束表面处理后自腐蚀电位均提高,但腐蚀电流密度有所增加。脉冲电子束处理后镁稀土合金表面组织成分均匀化、晶粒细化,稀土元素在镁中的固溶以及缺陷的生成导致表层硬度的提高和耐腐蚀性的改变。

Mg-Y-Nd-Zr-Zn铸造镁合金组织与性能研究

目的研究Mg-Y-Nd-Zr-Zn镁合金的显微组织演变和力学性能。方法采用金相显微镜(OM)、扫描电镜(SEM)、能谱(EDS)以及电子万能实验机等,研究了Mg-Y-Nd-Zr-Zn镁合金铸态及T6态的组织和性能。结果 Mg-Y-Nd-Zr-Zn铸态合金组织由含Y的镁基固溶体、网状富稀土的共晶相和颗粒状的Zr单质组成;经525℃×10 h+200℃×16 h处理后,晶界网状第二相消失,细小的Mg-RE金属间化合物从基体中析出,弥散分布于晶界及晶内。结论 T6处理后,Mg-Y-Nd-Zr-Zn合金力学性能显著提高,抗拉强度、屈服强度和断裂伸长率分别为306 MPa,230 MPa和3.5%。

Zn和Gd对Mg-4.0Y-2.8Nd-0.4Zr镁合金铸态组织和拉伸性能的影响

研究了Zn和Gd对Mg-4. 0Y-2. 8Nd-0. 4Zr镁合金铸态组织和拉伸性能的影响,结果表明:在Mg-4. 0Y-2. 8Nd-0. 4Zr试验镁合金中单独添加0. 2%Zn和1. 0%Gd(质量分数,以下同)以及复合添加0. 2%Zn+1. 0%Gd对合金铸态组织中合金相类型的影响不明显,均主要由α-Mg、Mg24Y5和Mg12Nd相组成。同时,单独添加0. 2%Zn和1. 0%Gd均能细化合金的铸态晶粒,并使合金组织中第二相的分布由连续网状向断续状转变,而复合添加0. 2%Zn+1. 0%Gd虽然具有较单独添加0. 2%Zn和1. 0%Gd更好的晶粒细化效果,但会导致第二相变得粗大并使第二相向连续状分布转变。相应地,单独添加0. 2%Zn和1. 0%Gd,使合金的抗拉强度、屈服强度和延伸率均得到改善;而复合添加0. 2%Zn+1. 0%Gd的合金,虽然具有较单独添加0. 2%Zn和1. 0%Gd更高的抗拉强度和屈服强度,但延伸率在所有试验镁合金中最低。

Zn对铸态Mg-Y-Nd-Zr合金组织和力学性能的影响

采用光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射分析及力学性能测试等研究Zn元素对Mg-Y-Nd-Zr铸态合金显微组织及力学性能的影响。结果表明:随着Zn含量的增加,Mg-Y-Nd-Zr-xZn(x=0.0%,0.5%,1.0%,1.5%,质量分数)合金的晶粒逐渐细化,平均晶粒尺寸由(57±0.8)μm细化至(30±0.3)μm,晶界处共晶相的体积分数也逐渐增加。Mg-Y-Nd-Zr铸态合金中主要存在Mg12Nd相和Mg24Y5相,加入0.5%Zn后,合金中出现Mg12YZn相。随Zn含量的增加,Mg12YZn相的体积分数不断增大,合金的力学性能逐渐提高。当Zn含量为1.0%时,合金具有最优的力学性能,其抗拉强度、屈服强度和伸长率分别为(208±5.9),(159±3.9)MPa和(7.5±0.2)%,较未加Zn的合金分别提高了18,42MPa和1.2%。