镁合金激光重熔后微弧氧化膜的微观组织和耐蚀性能

为了改善WE43镁合金的耐蚀性能,采用激光重熔(LSM)和微弧氧化(MAO)复合工艺对其表面进行了改性。通过扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)研究了WE43镁合金及其激光重熔层、微弧氧化膜层和激光重熔-微弧氧化膜层的微观组织、表面形貌和物相;通过GAMARY-Reference 600电化学工作站研究了其腐蚀行为,重点研究了镁合金激光重熔后微弧氧化膜层的微观组织、成分和耐蚀性能。结果表明:激光重熔使WE43镁合金晶粒细化、网状的β-Mg41Nd5相均匀分布和表面稀土元素Y及Nd增加,有效地改善了其耐蚀性能;微弧氧化膜和激光重熔后的微弧氧化膜层都可以显著提高WE43镁合金的耐蚀性能,但后者优于前者。     

Structural characteristics and corrosion behavior of biodegradable Mg–Zn, Mg–Zn–Gd alloys

In this research, binary Mg–Zn (up to 3 wt% Zn) and ternary Mg–Zn–Gd (up to 3 wt% Gd, 3 wt% Zn) alloys were prepared by induction melting in an argon atmosphere. The structures of these alloys were characterized using light and scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction and X-ray fluorescence. In addition, Brinell hardness measurements were taken to supplement these studies. Corrosion behavior was evaluated by immersion tests and potentiodynamic measurements in a physiological solution (9 g/l NaCl). Depending on the composition, structures of the as-cast alloys contained α-Mg dendrites, MgZn, Mg₅Gd and Mg₃Gd₂Zn₃ phases. Compared to pure Mg, zinc improved the corrosion resistance of binary Mg–Zn. Gadolinium also improved the corrosion resistance in the case of Mg–1Zn–3Gd alloy. The highest corrosion rate was observed for Mg–3Zn–3Gd alloy. Our results improve the understanding of the relationships between the structure and corrosion behavior of our studied alloy systems.     

Influence of Rare-Earth Elements on ElectricalProperties of Pd

The influence of RE (RE = La, Ce. Pr. Nd, Sm, Eu, Gd. Tb. Dy, Er, Yb) additives with dilute concentrations on the electrical properties of Pd has been studied. All RE elements increase the specific resistivity (ρ) and decrease the resistance temperature coefficient (α) of Pd. and (ρ.α) Pd-RE ls equal to (ρ· α)Pd.The RE elements before Gd reduce the thermo-emf of Pd on Cu. other heavy RE enhance the thermo-emf.The experimental data of normalized Pd-0.1 at.-%RE alloys indicate that the effect of light RE additives on the specific resistivity of Pd is larger than that of heavy RE and Ce. Eu and Yb show anomalous strong effect. The valence and atomic size are main factors influencing the electrical properties.     

时效态Mg-Gd-Y-Nd合金的组织结构及耐腐蚀性能

镁合金中加入Gd、Y、Nd等元素能提高其耐蚀性能,但目前对同时加入3种元素的情况研究较少。采用熔炼法制备了Mg-10Gd-3Y-Nd合金,并对其进行时效处理。利用金相显微镜、扫描电镜、X射线衍射仪等研究了时效态Mg-10Gd-3Y-Nd合金的微观组织及物相。通过静态失重法研究了时效态合金在不同浓度NaCl溶液中的耐腐蚀性能。结果表明:时效态合金主要由基体α-Mg和晶间共晶相(Mg_5Gd、Mg_(24)Y_5)组成,Gd能够良好地固溶于镁合金基体中;随着NaCl溶液浓度的增加,时效态合金的腐蚀速率增加,腐蚀深坑严重,颗粒状腐蚀物逐渐转为粉状;第二相颗粒的存在能阻止腐蚀过程向更深的晶粒区域发展,降低了腐蚀程度,提高了合金的耐腐蚀性。     

Reline低温熔盐体系中Gd-Mg-Co合金膜的制备及表征

为了得到附着力好、耐腐蚀性强的稀土镁合金,在353 K油浴条件下,采用循环伏安法分别研究了Gd(Ⅲ)、Mg(Ⅱ)、Co(Ⅱ)在氯化胆碱-尿素低温熔盐体系中的电化学行为。结果表明:Co(Ⅱ)→Co为一步不可逆反应,其在Pt电极的传递系数为0.41,扩散系数为1.32×10~(-6)cm~2/s,Mg(Ⅱ)、Gd(Ⅲ)在此体系中不能单独还原为单质,可被Co(Ⅱ)诱导共沉积。由恒电位法电沉积得到的Gd-Mg-Co合金中Gd的含量随沉积电位、沉积时间、Gd~(3+)/Mg~)(2+)/Co~(2+)浓度比的改变而改变,在-1.15 V电位下,Gd~(3+)/Mg~)(2+)/Co~(2+)摩尔比为4∶3∶4、沉积20 min时,得到表面均匀的黑色合金膜。在此沉积条件下得到的合金膜经扫描电镜(SEM)、X射线衍射仪(XRD)、能谱仪(EDX)等手段进行形貌、成分分析可知,此合金膜为非晶态,在碱性溶液中具有较好的耐腐蚀性能,合金膜中Gd的质量分数高达62.41%。     

Preparation and characterization of bismuth rare earth tungstate (BiREWO6) dielectric ceramics

BiREWO₆[RE=La, Nd, Pr, Sm, Gd, Dy, Tb, Yb, Y] ceramics have been prepared by the conventional solid-state ceramic route. The sintered samples are characterized by X-ray diffraction and SEM methods. The ceramics have high dielectric constants in the range 25–55 depending on the rare earth element. The dielectric losses of these ceramics increase with increase in the frequency and with increase in the rare earth crystal radii.     

Corrosion Behavior of Reactive Sputtered Al_2O_3 and ZrO_2 Thin Films on Mg Disk Immersed in Saline Solution

Magnesium has attracted a lot of attention over the last few decades due to its light weight and potential use as biomaterial. However, the poor corrosion resistance of magnesium restricts its practical use for application where exposure to aggressive aqueous media is unavoidable. This paper describes the growth,characterization and corrosion analyses of Al2O3 and ZrO2 thin film coatings aimed at slowing down the fast degradation of Mg in saline solution. In this study, different thicknesses of Al2O3 and ZrO2 were deposited on pure magnesium(99.95%) disk using pulsed-DC reactive sputtering process. The microstructure and phase analyses were performed using scanning electron microscopy(SEM) and X-ray diffraction(XRD),respectively. The corrosion protection behavior of the Al2O3 and ZrO2 coated magnesium samples immersed in 0.9 wt% NaC l solution were evaluated using electrochemical measurement techniques, such as open-circuit potential(OCP), potentiodynamic polarization(PD) and electrochemical impedance spectroscopy(EIS). The microstructural analyses showed that the Al2O3 thin film coatings have circular grains between5 and 25 nm, while the ZrO2 coatings have bigger ellipsoidal grains. The results from the electrochemical corrosion analyses showed that the Al2O3 coated Mg disk had corrosion resistance of approximately 3 times that of ZrO2 coated Mg disk. It was also observed that increasing the thickness of the Al2O3 coating improved the corrosion resistance of the Mg disk. These results suggest that Al2O3 and ZrO2 coating can be used to effectively control the fast degradation of magnesium for medical implant applications.     

Susceptibility of rare earth bromates between 1 and 4.2 K

AC magneitic susceptibilities measured between 1 and 4.2 K are reported for a series of rare earth bromate hydrates, RE(BrO₃)₃ · 9H₂O, for the rare earths Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Yb. Results for Pr, Tb, Dy, and Er are in good agreement with a previous determination. New results are reported for Nd, Sm, Gd, Ho, and Yb, some of which show interesting differences from the structurally similar rare earth ethylsulfates and anhydrous trichlorides.     

添加元素对Mg-3Si合金组织影响

采用扫描电镜、X射线衍射对合金组织进行观察,研究在Mg-3Si(质量分数/%,下同)合金陆续添加Zn,Nd,Gd,Y元素后微观组织演变规律。结果表明:Mg-3Si合金中Mg_2Si粒子具有初生和共晶两种明显不同的形貌;添加3%Zn元素后的Mg-3.0Si-3.0Zn合金中,初生Mg_2Si粒子粗化,共晶Mg_2Si粒子完全消失;在Mg-2.0Nd-3.0Zn-3.0Si合金中,Nd元素的加入能有效地细化初生Mg_2Si粒子并生成少量的Mg_(41)Nd_5粒子;继续添加Gd,Y元素后,在Mg-8.0Gd-4.0Y-2.0Nd-3.0Zn-3.0Si合金中的Gd_5Si_3和YSi等粒子急剧增加而Mg_2Si粒子含量大大减少。通过Thermo-Calc热力学软件的热力学计算表明:Gd_5Si_3,YSi的吉布斯自由能低,Gd,Y原子与Si更容易形成化合物。在Mg-8Gd-4Y-2Nd-3Zn-3Si合金中,Gd_5Si_3,YSi,Mg_2Si三种化合物的室温吉布斯自由能分别为-9.56×10~4,-8.72×10~4,-2.83×10~4J/mol,粒子的质量分数分别为8.07%,5.27%,1.40%。     

Effects of rare-earth element substitution on magnetostrictive properties of polycrystalline Tb-Dy-Fe alloys

Magnetostrictive properties of (Tb/sub 0.5/Dy/sub 0.5/)/sub 1-x/RE/sub x/Fe/sub 1.9/ (x=0-0.05, RE=Y, Ce, Sm, Gd, Ho, Yb) polycrystalline compounds were studied. Each rare-earth element formed a RE-Fe/sub 2/ Laves compound with a different lattice spacing. Corresponding to this difference, (Tb/sub 0.5/Dy/sub 0.5/)/sub 0.95/RE/sub 0.05/Fe/sub 1.9/ alloys showed a variation in lattice spacing as a result of the substitution of rare-earth elements and the prestress dependence of magnetostriction changed noticeably. In the case of Y, Sm, and Gd substitution, which showed greater lattice spacing than that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the case of Ce, Ho, and Yb substitution, which showed a decrease in lattice spacing, the conspicuous prestress dependence was the same as that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy and the maximum magnetostriction was greater than that of the latter alloy.     

Structure,superconductivity and magnetism of new rare earth-rhodium silicides RE2Rh3Si5 of U2Co3Si5-type

New ternary silicides RE₂Rh₃Si₅ (RE = Y, La, Nd, Sm, Gd, Tb, Dy, Ho, Er) have been prepared. They crystalize in the U₂Co₃Si₅-type structure. Only the silicides containing the diamagnetic rare earths Y and La show a superconducting transition at T_Cr = 4.4 ± 0.2K and T_Cr = 2.7 ± 0.1K respectively, those with magnetic rare earths order antiferromagnetically at low temperature.     

稀土元素对富Ni的Ti-Ni形状记忆合金马氏体相变的影响

在本文中,向Ti-50.7at.%Ni合金分别加入1at.%的稀土元素Ce、Dy、Gd和Y,并利用X射线和示差扫描热分析研究了稀土掺杂对富Ni的Ti-Ni合金马氏体相变行为的影响.结果表明:向富Ni的Ti-Ni合金中添加稀土元素能使合金的马氏体相变温度显著增加,且添加稀土Ce使合金相变温度的增幅最大.此外,Ti-50.2Ni-1Gd和Ti-50.2Ni-1Y合金中发生两步马氏体相变,而添加Ce和Dy的Ti-Ni合金中仍只发生一步马氏体相变.     

Hydrogenation and Anisotropic Expansions in R3Fe29-xTx (R = Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

1.IntroductionIntensiveinvestigatiOnsontheR-Fe-T(R=rareearth,T=transitionmetalasastabilizingelement)phasediagrams,locatedattheironrichcorner,ledtothediscoveryofthenovelR2(Fe,T)l9phase[1l2]duetothegreatinterestinhighperfOrmanceper-manentmagneticmaterials.ItsrealstoichiometriccompOsitionandcrystallographicstructurewerede-terminedasaNd3(Fe,Ti)29-typestructurewithmon-oclinicsymmetry[3]andtheA2/mspacegrOup[4]byX-rnypowderdiffractiOn(XRD)andthenthiswasconfirmedbyneutrOnpOwderdiffraction[5'6…     

A CALPHAD study on the thermodynamic stability of calcium-, zinc-, and yttrium-doped magnesium in aqueous environments

Magnesium has attracted the attention of the biomaterials community as a potential biodegradable metallic candidate for use in stents and orthopedic applications. Alloying of Mg with metals such as Ca, Y and Zn, etc., to form alloy precursors is important to optimize its corrosion rate in electrolytic and aqueous environments to understand the alloy response in body fluid environments. In the current study, the chemical reactions of Mg-Me alloys (Me = Ca, Y, and Zn) with pure water have been investigated using the CALPHAD technique. A qualitative agreement between CALPHAD and first-principles results has been obtained. The CALPHAD method has also been employed to study the reactions of Mg alloys in the human blood fluid environment. The effects of alloying elements and compositions on the reaction enthalpies, reaction products, amount of gas release and gas compositions as well as the pH of the fluids have been systematically discussed and reported.     

Patterning corrosion‐susceptible metallic alloys for digital image correlation in a scanning electron microscope

We investigate the self‐assembly of gold nanoparticles on the surface of magnesium functionalized with 3‐(aminopropyl)trimethoxysilane or 3‐(mercaptopropyl)trimethoxysilane. These nanoparticles served as a speckle pattern for high magnification deformation tracking via digital image correlation combined with scanning electron microscopy. Controlling the pH of the gold nanoparticle suspension to a specific basicity passivated corrosion in magnesium and in three of its alloys to enable proper nanoparticle bonding and self‐assembly. Magnesium was used as a model material as it is particularly difficult to modify for self‐assembly because of its propensity to quickly form a thick oxide, hydroxide, and carbonate layer in the presence of oxygen, water, and carbon dioxide, respectively. Moreover, it corrodes in acidic and slightly basic solutions, further complicating the self‐assembly process. Due to these difficulties, the successful self‐assembly of nanoparticles on magnesium has not previously been reported, to the best of the authors' knowledge. This technique is potentially amendable to other corrosion‐susceptible materials. Gold nanoparticles were self‐assembled in a uniformly dispersed random distribution on pure cast magnesium, cast AM60 (Mg‐6Al‐0.5Mn), rolled WE43 (Mg‐4Y‐3Nd/Gd), and extruded ZE20 (Mg‐2Zn‐0.2Ce).     

含N稀土－黄长石固溶体

研究了由通式Ｒ２Ｓｉ３－ｘＡｌｘＯ３＋ｘＮ４－ｘ（Ｒ＝Ｎｄ，Ｓｍ，Ｇｄ，Ｄｙ和Ｙ）表示的含Ｎ稀土（及Ｙ）－黄长石固溶体的形成和固溶度，在１６００～１７５０°Ｃ温度范围内，由热压和无压烧结制备了０＜ｘ＜１．５含不同稀土的黄长石固溶体样品，相分析结果表明：稀土－黄长石相（包括固溶　体）在轻稀土系统中较易形成，它们的固溶范围随稀土元素离子半径减小而变窄，Ｎｄ－黄　长石固溶体具有最大固溶度ｘ＝１．     

(Gd,Y)相对GW103K时效合金局部腐蚀的影响

对Mg-10Gd-3Y-0.4Zr(GW103K)合金进行193 h时效处理,使用扫描电子显微镜(SEM)和透射电子显微镜(TEM)观测块状和链状相的微观结构和腐蚀形貌,使用扫描开尔文探针显微镜(SKPFM)测试块状相和链状相与基体之间的相对电势差,研究了这些相对GW103K合金局部腐蚀的影响。结果表明：分布在晶内和晶界的单独块状相为Mg₂(Gd, Y)相,(Gd, Y)固溶体与Mg₂(Gd, Y)相交替排列形成链状相。(Gd, Y)固溶体和Mg₂(Gd, Y)相的相对电势均高于基体,与相邻基体形成微电池,(Gd, Y)固溶体和Mg₂(Gd, Y)相作为阴极促进了周围基体的腐蚀。尽管(Gd,Y)固溶体与基体之间的相对电势差更大,但是与基体的相界面为共格界面,界面能低、化学稳定性高,因此对基体腐蚀没有更强烈的影响。     

Corrosion studies of modified organosilane coated magnesium–yttrium alloy in different environments

Magnesium (Mg) and its alloys have numerous potential applications as biodegradable implants, but the fast degradation rate of Mg alloys at the initial implanted stage could be a problem. This paper describes the modification of the water-based bis-[triethoxysilyl] ethane (BTSE) silane applied to the surface of magnesium–yttrium (Mg–4Y) to increase its corrosion resistance. Surface characterization by SEM, FTIR, and EDX showed that the hydrolysis and condensation of the silane resulted in a covalent bonding to the Mg–4Y surface. Corrosion behavior of the uncoated and coated Mg–4Y alloy was evaluated in different environments by using a novel self-developed corrosion probe. Based on the electrochemical results of DC polarization and electrochemical impedance spectroscopy (EIS), we conclude that the epoxy-modified BTSE silane coating successfully increases the corrosion resistance at the initial stage of implantation. The corrosion rates in the flesh of dead mice environments such as body cavity and subcutaneous tissue of the mice were lower than the corrosion rates in in vitro environments.     

Effect of rare earth metals on microstructure and corrosion resistance of Zn–0·18Al coatings

Abstract

Effect of rare earth (RE) metals addition on the microstructure, formation of Fe–Zn intermetallics and corrosion resistance of the batch galvanising Zn–0·18Al coating were studied. Microstructure of the coating was observed using optical microscopy, scanning electron microscopy and transmission electron microscopy. Salt spray test and surface potential measurement were employed for corrosion resistance determination. The results show that the addition of RE can improve bath liquidity, refine surface spangles, stabilise the Fe₂Al₅ inhibition layer, decrease coating thickness and enhance corrosion resistance of the coating. However, corrosion resistance of the coating did not increase continuously with increasing RE content and the optimum RE content lies between 0·045 and 0·069% in the experiment. Mechanism of RE on the corrosion resistance of the galvanised coating was briefly analysed.     

Development of high mechanical properties and moderate thermal conductivity cast Mg alloy with multiple RE via heat treatment

A new cast Mg–2 Gd–2 Nd–2 Y–1 Ho–1 Er–0.5 Zn–0.4 Zr(wt%) alloy was prepared by direct-chill semicontinuous casting technology. The microstructure, mechanical properties and thermal conductivity of the alloy in as-cast, solid-solution treated and especially peak-aged conditions were investigated. The as-cast alloy mainly consists of β-Mg matrix,(Mg, Zn)_3 RE phase and basal plane stacking faults. After proper solid-solution treatment, the microstructure becomes almost Mg-based single phase solid solution except just very few RE-riched particles. The as-cast and solid-solution treated alloys exhibit moderate tensile properties and thermal conductivity. It is noteworthy that the Mg alloy with 8 wt% multiple RE exhibits remarkable age-hardening response( HV = 35.7), which demonstrates that the multiple RE(RE = Gd, Nd, Y, Ho, Er) alloying instead of single Gd can effectively improve the age-hardening response.The peak-aged alloy has a relatively good combination of high strength/hardness(UTS(ultimate tensile strength) 300 MPa; TYS(tensile yield strength) 210 MPa; 115.3 HV), proper ductility(ε≈ 6%) and moderate thermal conductivity(52.5 W/(m K)). The relative mechanisms mainly involving aging precipitation of β￠ and β' phases were discussed. The results provide a basis for development of high performance cast Mg alloys.