Improved Corrosion Behavior of Biodegradable Mg-4Zn-1Mn Alloy Modified by Sr/F co-doped CaP Micro-arc Oxidation Coatings

The Sr/F co-doped CaP(Sr/F-CaP)coatings were prepared by micro-arc oxidation(MAO)under different voltages to modify the microstructure and corrosion behavior of Mg-4Zn-1Mn alloy.The surface and interface characteristics investigated using scanning electron microscopy(SEM)and energy dispersive X-ray spectrometer(EDS)showed that the MAO coatings displayed uneven crater-like holes and tiny cracks under lower voltage,while they exhibited relatively homogeneous crater-like holes without cracks under higher voltage.The thickness of MAO coatings increased with increasing voltage.The corrosion behavior of Mg-4Zn-1Mn alloy was improved by the MAO coatings.The MAO coatings prepared under 450 V and 500 V voltages possessed the best corrosion resistance with regard to the electrochemical corrosion tests and immersion corrosion tests,respectively.The MAO coatings fabricated under 450-500 V could provide a better corrosion protection effect for the substrate.

钨粉制备及其对钨合金性能影响的研究进展

金属钨因具有高熔点、高硬度、耐腐蚀、耐磨和热膨胀系数小等优点而被广泛应用于制备各种合金材料。本研究综述了钨粉的制备方法,如熔盐电解法、溶胶凝胶法、高能球磨法和氢气还原法。针对钨粉均匀性问题,重点阐述了目前使用最广泛的氢气还原法的研究现状,其中,调控氢气中水蒸气分压有利于提高钨粉均匀性;气流磨和球化等钨粉的处理工艺有助于提高钨粉均匀性和分散性。另外,介绍了钨粉粒度和分散性等对钨合金性能的影响,均匀分散的钨粉对制备组织均匀的钨合金优势巨大。针对钨粉和钨合金中钨晶粒之间的相关性介绍了晶粒细化的相关研究。简要介绍了钨粉性能对增材制造钨合金性能的影响。

Improvement of microstructure,mechanical properties,and corrosion resistance of WE43 alloy by squeeze casting

The WE43 magnesium alloy was prepared by squeeze casting,and the influence of squeeze casting parameters on mechanical properties and corrosion resistance was studied and compared with gravity casting.The gravity cast WE43 alloy shows uneven grain size distribution,and some grains even greater than 90μm.While,the grain size of the squeeze cast WE43 alloy is mainly distributed in 20-50μm.The Mg12Nd2Y phase morphology changes from large lamellar to strips after squeeze casting,whereas Mg_(24)Y_(5) phase exhibits no obvious change.The yield strength,tensile strength,and elongation of the gravity cast WE43 alloy are 127 MPa,157 MPa,and 6%,respectively,and 145 MPa,193 MPa,and 9.1%for squeeze cast alloy.For the squeeze cast WE43 alloy,the average corrosion rate is 0.6056 mm·year^(-1) according to immersion test results,and according to electrochemical measurements,the corrosion current density is 78.13μA·cm^(-2),which is better than that of the gravity cast WE43 alloy.Compared with gravity casting,the grains and second phase of the WE43 alloy by squeeze casting are refined,and the mechanical properties and corrosion resistance are improved.This may expand the applications of the WE43 alloy.

金属镁的氧化及氧化机理研究进展

镁合金作为目前最轻的商用金属结构材料,在航空航天、汽车、3C产品等领域具有广泛的应用前景。同时,面对全球铁铝资源日趋紧缺和我国大量进口铁铝矿石的困境,推广应用镁合金材料具有重要的战略意义。与常用的钢铁材料和铝合金相比,镁合金的研究与开发还不充分,应用也受限。镁合金的耐腐蚀性能差,部分原因是镁的化学活性高,且表面生成的保护膜不具备保护作用。尤其在高温下,镁及其合金极易氧化,甚至燃烧,释放大量的热,这成为限制镁合金大量推广应用的瓶颈之一。针对镁及其合金极易氧化的问题,近年来研究学者围绕其氧化机制和影响因素开展了大量的研究,认为镁合金的氧化受氧化膜P-B值、镁的蒸发、扩散等因素影响。目前,大多通过合金化的方式来提高镁的抗氧化性。镁合金抗氧化性研究为高抗氧化性镁合金的研发提供了理论支持,同时扩大了镁合金的高温应用前景,并将为镁合金行业带来巨大的经济效益。本文归纳总结了国内外镁及其合金氧化特征及氧化机理的研究进展。首先,简述了镁的氧化;然后,分析了镁氧化的机理和影响因素,重点讨论了P-B值、扩散、蒸发、金相组织、合金元素对镁及其合金氧化行为的影响规律及作用机理;最后,总结了目前研究中的不足,提出了镁抗氧化性研究方向的建议。

Mg-1.4Gd-1.2Y-0.4Zn-0.1Zr合金挤压板材的组织与力学性能

制备了Mg-1.4Gd-1.2Y-0.4Zn-0.1Zr(at%)合金挤压板材,并进行了时效处理。采用XRD、OM、SEM和TEM分析了不同状态合金的相组成和微观组织,并测试了其室温硬度和拉伸力学性能。结果表明,铸态组织由α-Mg基体、Mg_(3)(RE,Zn)共晶相、长周期堆垛有序(LPSO)结构以及Mg-RE颗粒组成。经固溶处理后,晶界处的Mg_(3)(RE,Zn)共晶相固溶于基体中,并且富集的RE和Zn元素从晶粒内部的堆垛层错处析出。经热挤压后,板材组织呈现典型的双峰晶粒分布,粗大未变形晶粒周围分布大量破碎的LPSO结构,且这些第二相的分布限制了动态再结晶晶粒长大,其抗拉强度、屈服强度和伸长率分别为380 MPa、327 MPa和8.0%。再经200℃时效48 h后,基体内部析出大量纳米尺度的β’相,合金的抗拉强度和屈服强度分别提高至435 MPa和380 MPa,伸长率降为5.0%。

热处理对Mg-Zn-Sr合金组织与性能的影响

研究了少量Sr(0、0.2%、0.5%、1.0%)的加入对铸态Mg-4Zn合金组织和力学性能的影响,以及热处理对Mg-Zn-Sr合金显微组织与力学性能的影响。结果表明,添加0.5%Sr的铸态合金具有最佳的力学性能,其抗拉强度为161 MPa,屈服强度为82 MPa,伸长率为10.30%。合金经过440℃×18 h固溶处理后,第二相基本固溶进基体中,其抗拉强度为192 MPa,屈服强度为99 MPa,伸长率为14.77%。随着时效时间的增加,MgZn相数量增加,且弥散分布,时效8 h,合金性能较好,其抗拉强度为223 MPa,屈服强度为118 MPa,伸长率为12.06%。时效12 h,Mg17Sr2相开始大量析出,影响合金性能。

Nd对压铸AZ91D合金组织与性能的影响

传统压铸获得AZ91D和AZ91D-1.11Nd两种合金试样,采用光学金相显微镜、扫描电子显微镜和X射线衍射仪分析了压铸态微观组织和相组成,并测试了其拉伸力学性能、硬度、导热性能和流动性能。结果表明,在AZ91D合金中添加1.11%Nd后,压铸态晶粒有所细化,形成较多弥散分布的细小颗粒状Al2Nd和少量针状Al_(11)Nd_(3),原有的半连续网状分布的β-Mg_(17)Al_(12)数量有所减少。压铸态AZ91D-1.11Nd合金呈现良好的综合性能,室温抗拉强度、伸长率和热导率分别为272 MPa、12.0%和69.5 W/(m·K),与AZ91D合金相比分别提高14%、100%和14%;同时呈现与AZ91D合金相当的优异铸造工艺性能,流动长度达到1161 mm。

Mg-3.52Sn-3.32Al合金轧制板材的组织和力学性能

采用同步轧制工艺对Mg-3.52Sn-3.32Al合金挤压板材在603 K进行了小变形轧制实验,用XRD、OM、SEM和TEM分析了挤压板材和轧制板材的相组成和微观组织,并测试了室温拉伸性能。结果表明:热轧后,合金板材的相组成未发生变化,仍由α-Mg基体、颗粒Mg_(2)Sn相和块状Mg_(17)Al_(12)相组成。但第二相大量析出,且发生明显的动态再结晶,晶粒尺寸为5~10μm。在细晶强化、加工硬化和第二相强化的共同作用下,轧制板材的综合拉伸力学性能显著提高,抗拉强度和屈服强度分别由挤压板材的270、193 MPa提高至332、297 MPa,提高幅度分别为23%和54%。此时,伸长率为5.0%。

选区激光熔化Al-Zn-Mg-Sc合金组织与性能研究

采用选区激光熔化(SLM)技术成形Al-Zn-Mg-Sc合金。研究了激光打印参数及热处理工艺对Al-Zn-Mg-Sc合金显微组织与力学性能的影响。研究结果表明,打印态Al-Zn-Mg-Sc合金组织具有显著的各向异性特征:建造面熔池为鱼鳞状,晶粒为大尺寸柱状晶;扫描面熔池则为条带状,晶粒为小尺寸柱状晶与等轴晶。SLM成形的Al-Zn-Mg-Sc合金存在大量热裂纹,严重影响合金力学性能。但热处理后,Al-Zn-Mg-Sc合金力学性能显著提高。经过热处理后合金的维氏(HV)硬度由91.70提升至144.27,抗拉强度由183.71 MPa提升至257.53 MPa。

Mg-6.4La-4.87Al镁合金的金属型和压铸组织与性能

制备铸态与压铸态Mg-6.48La4.87Ar两种合金试样,采用OM、SEM和XRD分析其微观组织和相组成,并测试室温拉伸与压缩力学性能、导热性能和流动性能。结果表明:铸态晶粒粗大,第二相分布不均匀;经传统压铸后,晶粒变得细小,第二相分布均匀。两者试样微观组织均主要由a-Mg基体、点状Al_(11)La_(3)相和少量针状Mg_(12)La相组成。铸态试样抗拉强度、抗压强度和伸长率分别为157MPa、263MPa和4.0%,经压铸后试样抗拉强度、抗压强度和伸长率分别提高至236MPa、345MPa和4.5%,较铸态值分别提高63%、31%和13%,同时呈现较好的流动性能,流动长度为1374mm。铸态试样导热系数达到113.2W/(m·K),经压铸后仍能保持较高的导热系数,为90.9W/(m·K)。

晶体取向及析出相对Al-Cu-Li单晶腐蚀行为的影响

通过扫描电子显微镜、透射电子显微镜、光学显微镜、剥落腐蚀溶液浸泡实验和电化学测试研究晶体取向和析出相对Al-Cu-Li单晶腐蚀行为的影响。结果表明,时效态Al-Cu-Li合金不同取向的腐蚀速率按(001)<(101)<(111)的顺序增加,与淬火态合金的腐蚀速率按(111)<(001)<(101)的顺序增加明显不同。T1相的析出恶化了Al-Cu-Li合金的耐蚀性,且不同晶面取向的恶化程度不同。时效态合金的严重局部腐蚀沿着晶体学方向扩展,并以腐蚀带的形式沿{111}Al面扩展。

Degradation and biological properties of Ca-P contained micro-arc oxidation self-sealing coating on pure magnesium for bone fixation

Poor corrosion resistance is one of the main disadvantages for biodegradable magnesium-based metals,especially applied for bone fixation,where there is a high demand of bio-mechanical strength and stability.Surface coating has been proved as an effective method to control the in vivo degradation.In this study a Ca-P self-sealing micro-arc oxidation(MAO)coating was studied to verify its efficacy and biological properties by in vitro and in vivo tests.It was found that the MAO coating could effectively retard the degradation according to immersion and electrochemical tests as well as 3D reconstruction by X-ray tomography after implantation.The MAO coating exhibited no toxicity and could stimulate the new bone formation.Therefore,the Ca-P self-sealing MAO coating could be a potential candidate for application of biodegradable Mg-based implant in bone fixations.

Deformation behavior of a TiZr-based metallic glass composite containing dendrites in the supercooled liquid region

The deformation behavior of a TiZr-based bulk metallic glass composite(BMGC)was characterized in the supercooled liquid region(SLR)from 623 K to 693 K.It was observed that the alloy exhibits the deformation behavior from work softening at low temperatures to work hardening at high temperatures.The yield stress and overshoot stress decrease remarkably with the increase of temperature,accompanied by superplasticity.The results showed that the crystallization occurred in the amorphous matrix for the post-deformation samples and the volume fraction of the corresponding crystallization products increased with increasing testing temperature.It is implied that the work hardening behavior was closely associated with the crystallization of the amorphous matrix.The tensile stress can accelerate the crystallization of amorphous matrix and the martensitic transformation of dendrite phases,which implies that the thermal stability of the alloy decreases under tension.These findings shed light on designing new BMGCs with high mechanical performance as well as the good SLR formability.

Fabrication and Characterization of Ca-Mg-P Containing Coating on Pure Magnesium

A biodegradable Ca-P coating mainly consisting of β-tricalcium phosphate （β-TCP） was fabricated on pure magnesium via the chemical deposition in a simulated Hank’s solution. The method significantly accelerated the coating formation on magnesium. Moreover, the morphology, phase/chemical composition, the coating formation mechanism as well as degradation behavior in phosphate buffered saline （PBS） solution were in- vestigated. Scanning electron microscopy （SEM） images showed that the coating had three layers and X-ray diffraction （XRD） patterns showed that the coating mainly contained Ca3（PO4）2 and （Ca,Mg）3（PO4）2. Elec- trochemical test showed that the corrosion current density （Icorr） of the coated Mg was decreased by about one order of magnitude as compared to that of pure magnesium. The immersion test indicated that the coating could obviously reduce the degradation rate.

Fe-based metallic glass:An efficient and energy-saving electrode material for electrocatalytic degradation of water contaminants

Excessive consumption of electrical energy has hampered the widespread application of electrochemical technology for degradation of various contaminants. In this paper, a Fe-based metallic glass(MG) was demonstrated as a new type of electrocatalyst to effectively and economically degrade an azo dye. In comparison to other typical electrodes, Fe-based MG electrodes exhibit a minimized degradation time, and the specific energy is 4-6 orders of magnitude lower than that of dimensionally stable anode(DSA), metal-like boron-doped diamond(BDD) and other electrodes. As sacrificial electrode materials, Fe-based MGs have less specific electrode mass consumption than iron electrodes. The use of Fe-based MGs will promote the practical application of electrochemical technology and the use of MGs as functional materials.

Corrosion mechanisms of Zr-based bulk metallic glass in NaF and NaCl solutions

So far,some investigations related to the corrosion mechanism of Zr-based metallic glasses in solutions containing Cl-have been developed.However,few attentions have been paid to the situation in F--containing solution.This paper describes the corrosion behaviours of Zr52Al10Ni6Cu32 bulk metallic glass(BMG)in Na F and Na Cl aqueous solutions.The corrosion mechanism of Zr-based BMG in F–containing solution was proposed for the first time.It was found that in Na Cl solutions,Zr-based BMG samples underwent typical pitting corrosion.Selective dissolution of Zr,Al and enrichment of Cu were observed in corrosion pits.However,corrosion occurred in the form of general breakdown of passive film in Na F solutions.Such difference is interpreted in terms of the binding ability of anions to surrounding molecules,i.e.,Cl-with loose surrounding water passes through the passive film to cause pitting;F-with a tight surrounding molecules layer absorbs on passive film then coordinates with cations from matrix.

Deformation behavior of Ta wire-reinforced Zr-based bulk metallic glass composites

A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.

High-temperature Mechanical Properties and Dynamic Recrystallization Mechanism of in situ Silicide-reinforced MoNbTaTiVSi Refractory High-entropy Alloy Composite

The hypoeutectic composite material composed of BCC phase and in situ precipitated Ti_(5)Si_(3) was prepared by adding Si into MoNbTaTiV high-entropy alloy.The obvious oriented in situ Ti_(5)Si_(3) phase formed eutectic phase with BCC phase in the inter-dendritic area,which leads to excellent properties of the composite.The alloy exhibits ultra-high yield stress of 718 MPa at 1200℃ and obvious compression plasticity.After reaching the maximum strength,dynamic recovery(DRV)and dynamic recrystallization(DRX)caused soften phenomena.The DRX mechanism of the dual-phase eutectic structure is analyzed by electron backscatter diffraction.The DRX of the BCC phase conforms to the discontinuous DRX and continuous DRX mechanisms,while the Ti_(5)Si_(3) phase has a geometric DRX mechanism in addition to the above two mechanisms.The high performance of this composite has enough potential high-temperature applications such as nuclear and aero engine.

Evaluation of the performance of Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating on biodegradable high-purity magnesium in a femoral condyle defect model in rabbits

The two most critical factors in promoting the clinical translation of magnesium(Mg)are reducing its degradation rate and improving its osteogenesis.In this study,a Ca-deficient hydroxyapatite(CDHA)/MgF_(2)bilayer coating was prepared on high-purity magnesium(HP Mg)rods by fluorination and hydrothermal treatment.Scanning electron microscope showed that the thickness of the bilayer coating was 3.78 lm and that the surface morphology was nanoscale.In an in vivo experiment on femoral condyle defects in rabbits,the serum magnesium ion levels of rabbits were always in the normal range after surgery,and the liver and kidney functions were not abnormal,which indicated that the CDHA/MgF_(2)bilayer coating has good biosafety.Micro-CT showed that the CDHA/MgF_(2)bilayer coating significantly reduced the degradation rate of the HP Mg rods and enhanced the promotion of bone formation.Hard tissue sections showed that the CDHA/MgF_(2)bilayer coating gave the bone tissue a tight contact interface with the HP Mg rod and improved the bone mass.Immunohistochemistry showed that the expression of vascular endothelial growth factor and BMP-2 was more obvious.These results confirm that the CDHA/MgF_(2)bilayer coating can improve the properties of HP Mg and provide a basis for the further transformation of HP Mg in the future.It also provides a new reference for the surface modification of magnesiummetal.

表面活性剂对金属铜微切削过程中微沟槽显微形貌影响机制的研究

本研究对微沟槽横截面微观组织进行了观察,阐明了表面活性剂对纯铜微切削加工表面的机理影响。研究结果表明:添加表面活性剂后,切削力和推力明显降低,并发现具有物理化学效应的微沟槽表面粗糙度为12nm,没有物理化学效应的微沟槽表面粗糙度为17nm。受物理化学效应影响的样品的微沟槽区内的平均晶粒尺寸为67.9μm,而无物理化学效应影响的样品平均晶粒尺寸为48.3μm,此外,还发现无物理化学效应影响微沟槽附近晶粒尺寸大于远离微沟槽表面的晶粒尺寸。通过电子背散射衍射显微镜观察,受物理化学效应影响的横截面表面晶粒呈各向异性,而无物理化学效应影响的横截面表面晶粒取向主要为{101}方向。通过对几何必要位错计算和分析,推断出在微切削过程中,具有物理化学效应的样品中残余应力和温度较高,可以为再结晶提供足够的驱动能量。