Repassivation rates of surgical implant alloys by rotating‐disk scratching measurements

As the dissolution of metals ions in living tissues is an issue of primary importance in the field of surgical implant alloys, a rotating disk scratch technique has been used to examine this aspect by studying the potentiostatic repassivation behavior of pure titanium of commercial grade 11 and AISI 316L Stainless Steel (SS) samples in aqueous chloride solutions. By evaluating the effects of applied potential, pH and surface treatment on the current decay transients in the millisecond regime the higher tendency to passivate of titanium with respect to the stainless steel has been clearly demonstrated. An analysis conducted to estimate the efficiency of the oxide formation process has led to the conclusion that the majority of the measured transient current goes to the anodic dissolution process on both the materials investigated. Moreover, a repetitive process of film formation/breakdown on the AISI 316L surface related to pitting corrosion has been observed to strongly increase the ion release in the vicinity of the characteristic pitting potentials.     

Repassivation behaviour of 316L stainless steels using new type of abrading electrode technique

Abstract

In this paper, a novel electrode abrading technique is designed to improve the conventional methods. By employing the new depassivation method, 316L stainless steel has been tested in 0.05M H₂SO₄ solution with and without chloride ion. The repassivation kinetics has been analysed in terms of the current density flowing through the abraded surface bare metal surfaces. The results are described by the linear relationship of log i(t) versus log t. At potentials within the passive region, the passive film grew according to the high field ion conduction model in which log i(t) is linearly proportional to 1/q(t). The repassivation process was analysed in three stages according to different kinetics. The effect of applied potential and chloride ion concentration on repassivation kinetics was also discussed, and the change of calculated film thickness is more sensitive to applied potential than chloride ion concentration.     

Effect of an Mg-rich matrix on the corrosion behavior of As-cast magnesium-aluminum alloys

In the present study, the corrosion behavior of as-cast Mg-Al and Mg-Al-Zn alloys was studied as a function of the Al content in the matrix. Corrosion properties such as the corrosion rate, corrosion potential, and repassivation tendency were estimated through immersion and electrochemical tests. The corrosion potential and corrosion rate of a solutionized alloy depend mainly on the Al content of the as-cast alloy. The variation of Al content in the Mg-rich matrix influences the stability of the passive film and the repassivation tendency, i.e., as the Al content of the matrix increases, the repassivation tendency of the surface protective film after its breakage deteriorates. Also, it was proven that the enhancement of corrosion resistance by heat treatment, as in T6, is due to the decrease of solute concentration in the matrix, in addition to the effect of the precipitate, which plays the role of a barrier against corrosion.     

Effect of temperature on corrosion and semiconducting properties of oxide films formed on M5 zirconium alloy

Nuclear fuel cladding for pressurised water reactors is commonly manufactured with zirconium alloys. The M5 alloy is a relatively new cladding material for in-reactor used with enhanced performance compared to traditional zircaloys. In this work, the influence of temperature on the corrosion resistance and semiconducting properties of the passive film formed on the M5 alloy in a borate buffer solution has been evaluated. The electrochemical behaviour of the zirconium alloy was assessed by potentiodynamic polarisation tests, electrochemical impedance spectroscopy and Mott–Schottky plots. The results indicated that the corrosion resistance of the M5 alloy decreased with temperature due to the formation of a less stable and more defective passive film. The Mott–Schottky approach used in combination with polarisation tests and impedance measurements was effective to reveal the protective state of the passive film on the M5 alloy.     

等离子体循环刻蚀镀膜提高锆膜的水汽阻隔性

为了提高以锆金属镀层封闭聚氨酯泡沫塑料表面对水气的阻隔性,采用了等离子体循环刻蚀和中频磁控溅射镀膜相结合的方法改变锆膜晶粒的生长模式。结果表明,等离子体循环刻蚀以后,锆膜表面的晶粒呈现出非晶化趋势,无等离子体循环刻蚀时锆膜横截面晶粒的生长方式是法向柱状晶模式,而刻蚀后薄膜呈现的是一种柱状晶和细小球晶团的混合生长模式。水气阻隔实验表明,等离子体循环刻蚀的方法可明显提高锆膜的水气阻隔性。等离子体循环刻蚀抑制了锆膜的法向柱状晶生长,使晶粒更加细化,膜呈现非晶化趋势,这是膜致密性、水气阻隔性增加的根本原因。     

Electrochemical behavior of zirconium in the LiCl-KCl molten salt at Mo electrode

The electroreduction process of Zr(IV) was studied at molybdenum electrode in LiCl-KCl-K₂ZrF₆ molten salt. The transient electrochemical techniques, such as cyclic voltammetry and chronopotenimetry were used. The experimental results showed that the electrochemical reduction of Zr(II)/Zr and Zr(IV)/Zr(II) were both diffusion-controlled process. In the 773-973 K range, the diffusion coefficients of Zr(ii) and Zr(IV) were determined: D_Zr(II) = 0.15567exp{−69.65 × 10³RT(K)} cm²/s, D_Zr(IV) = 1.09 × 10⁻⁴ exp{−44.39 × 10³RT(K)} cm²/s. The activation energy values for the diffusion process were 69.65 kJ/mol and 44.39 kJ/mol, respectively.     

锆合金电解渗氢工艺及组织演变研究

对新型Zr-Sn-Nb系SZA-4锆合金管材进行电解渗氢处理,研究了渗氢时间对SZA-4锆合金吸氢量和氢化物类型及分布的影响规律,以及均匀化退火对氢化物类型及分布的影响规律。结果表明,随着电解渗氢时间延长,SZA-4锆合金管材的吸氢量增加,吸氢量与渗氢时间之间符合抛物线关系。显微组织分析表明,锆合金电解渗氢后在样品表面形成一层氢化物层,而内部仍为锆合金基体。随着渗氢时间延长,该氢化物层的厚度增加。对氢化物层的相结构分析表明,渗氢时间较短时,氢化物层由δ-ZrH_1.66相组成;随着渗氢时间延长,氢化物层中的δ-ZrH_1.66相含量增加;渗氢24 h后,氢化物层由ε-ZrH_1.801相和δ-ZrH_1.66相组成。对渗氢试样400 ℃/6 h均匀化退火处理后,发现氢化物层厚度进一步增加,且在样品内部沿周向有条状氢化物析出。相结构分析显示,此时氢化物层中ε-ZrH_1.801相消失,原来的δ-ZrH_1.66氢化物转变为δ-ZrH_1.5氢化物。而经400 ℃/96 h均匀化退火处理后,氢化物层消失,细小条状氢化物均匀分布于试样中。     

316L不锈钢微动磨蚀过程表面钝化膜自修复行为研究

采用球－平面接触设备,对轧制固溶３１６Ｌ不锈钢不不同ＮａＣｌ溶同动过程中,表面钝化膜的自修复行为进行了研究,讨论了溶液腐蚀特性及缝隙腐蚀行为对微动过程的影响,结果表明,溶液腐蚀特性的改变引起材料钝化膜自修复行为的差异,但不显著,在去离子水溶液中,３１６Ｌ不锈钢表面钝化膜保护了较高的自修复能力,稳定阶段表面钝化膜自修复约占平衡态下钝化膜厚度的１７％,说明３１６Ｌ不锈钢表面钝化膜在微动过程并能长期有效     

Plasma electrolytic oxidation of a zirconium alloy under AC conditions

The microstructures of zirconia coatings formed by plasma electrolytic oxidation of a zirconium alloy, Zirlo, under AC conditions in an alkaline silicate electrolyte have been examined by scanning and transmission electron microscopies. The coatings are shown to consist of three layers. The innermost barrier layer is relatively thin, up to 500 nm in a 100 µm-thick coating formed for 3600 s. The intermediate layer, constituting the main part of the coatings, consists primarily of monoclinic and tetragonal zirconia. The outer, loose layer is rich in silicon species and constitutes a reduced proportion of the coating thickness at increased time of treatment. The porous intermediate and outer layers are readily permeated by the electrolyte. The formation of the coating accounts for < 27% of the anodic charge passed during the treatment.     

Repassivation of steel in carbonated concrete induced by cathodic protection

The paper discusses the peculiarities of cathodic protection applied to steel in carbonated concrete, which are strictly connected to the production of alkalinity at the steel surface. Results of a research on the application of cathodic protection to specimens with steel bars in carbonated concrete are discussed. A thin layer of concrete was realkalized within a period of 4–5 months by applying a current density of 10 mA/m² and steel could repassivate even in the presence of small contents of chlorides. A lower current density of 5 mA/m² could only maintain steel passive when the concrete in the vicinity of the steel had been previously realkalized through the application of a start‐up current density of 70 mA/m² for one month. Protection mechanisms are investigated and design of cathodic protection of steel in carbonated concrete is outlined. The possibility of obtaining protection on deeper rebars is also considered.     

A study of the chemical composition of the passive film on a Ti-Mo alloy in HCI and H2SO4

The composition of the passive film on Ti-15Mo alloy, formed in 1 mol/L and 4mol/L HCI and 2 mol/L H₂SO₄ solutions at 70 °C (160 °F) under anodic polarization is investigated by XPS and electrochemical techniques. Anodic polarization potential is found to have an obvious influence on the content of Mo in the film. At lower anodic polarization potentials, the surface of the passive film is enriched in Mo. However, at higher anodic polarization potentials, the surface is diluted in Mo. The anions of the electrolytes influence the composition of the passive film. In HCI solution, chloride ions are incorporated with the passive film during its formation. The passive film consists of a compound containing chloride and oxide ions. While in H₂SO₄ solution, the passive film only consists of titanium-molybdenum oxide. Sulfide ions and other sulfur are not incorporated. Ti-Mo alloys have a better passivity than pure Ti in HCI and H₂SO₄ solutions. This passivity is related to the enrichment of Mo in the surface of the passive film.     

Hydrogen pulverization of refractory metals,alloys and intermetallics

Hydrogen-induced pulverization allows the production of fine powders with high purity and low cost in refractory metals, alloys, and intermetallics. In this paper, their hydrogen pulverization behavior has been investigated in order to further utilize hydrogen pulverization as a new powder fabrication process. Hydrogen pulverization was examined by the following three methods: (i) hydrogenation in an arc-melting chamber for NbCr₂ and Ta₂Ni alloys; (ii) measurement of hydrogen absorption-desorption curves in a Sieverts-type apparatus for Nb₃Al alloys; and (iii) heat treatment in a hydrogen furnace for pure Ta. Two-phase alloys of NbCr₂/Nb_ss, Nb₃Al/Nb_ss, Nb₃Al/Nb₂Al, Ta₂Ni/Ta_ss and Ta_ss/Ta₂H (Nb_ss and Ta_ss denote Nb and Ta solid solutions, respectively) are pulverized by absorbing a large amount of hydrogen. It is suggested that cracking leading to pulverization is initiated at brittle intermetallic regions or hydrides, which are fractured by lattice expansion of Nb_ss or Ta_ss due to hydrogen absorption. This article is based on a presentation made in the symposium “The 3rd KIM-JIM Joint Symposium on Advanced Powder Materials”, held at Korea University, Seoul, Korea, October 26–27, 2001 under auspices of The Korean Institute of Metals and materials and The Japan Institute of Metals.     

锆丝电爆炸法制备氧化锆纳米颗粒及其特征

在空气中采用锆丝点爆炸法合成了纳米二氧化锆颗粒,根据实测电流、电压和由此计算得到的能量沉积波形分析了电爆炸和纳米颗粒形成过程。发现锆丝气化后在锆丝蒸汽和空气中形成电击穿现象诱发电爆炸并截断锆丝中的能量沉积。通过扫描电镜和透射电镜对产物进行了分析,发现纳米二氧化锆颗粒形貌呈近球形,粒度分布在30.6-69.4纳米之间。X射线衍射分析表明产物由单斜晶型(m- ZrO2)和四方晶型(t- ZrO2)二氧化锆组成,随着充电电压的提高,四方晶型二氧化锆含量增加而单斜晶型含量变小,二者粒度都呈变大趋势。     

锆合金热变形过程中的织构演变研究

本文选取了一种热轧退火态的锆合金板材沿着其板材法向(0°样品)及横向(90°样品)在700 ℃温度下以1/s应变速率进行压缩试验。利用电子背散射衍射(EBSD)技术对变形后样品的微观组织及织构进行表征,并利用粘塑性自洽模型(VPSC)确定了在低应变条件下的各滑移系及孪晶的相对开启量。微观组织揭示了在两种样品中均有动态再结晶的发生。再结晶晶粒的织构变化与变形晶粒的织构变化相似,表明了再结晶过程中的优先形核及长大过程不会影响织构的形成及变化。在0°样品中,基面滑移、柱面滑移和锥面滑移在变形初期阶段同时开启,但是在90°样品中,只有少量的锥面滑移在变形初期阶段开启。在90°样品中存在的高强度的<10-10>//RD 织构组分是由大量开启的柱面滑移造成的。此外,700 ℃温度下大量基面滑移的开启对织构形成起重要作用。     

铌-铬复合溅射膜对锆合金基体的附着性

研究了铬膜和铌膜的复合对锆合金基体上制备的商流磁控溅射薄膜附着性的影响。使用扫描电镜(SEM)观察了膜层界面，用原子力显微镜(AFM)观察了膜层表而，用划痕法测定了薄膜的附着性。结果表明：膜／基界面结合良好，界面成分升降区狭窄；铬膜与铌膜组成的复合薄膜结合紧密；铬膜的组织为致密、边界孔洞少的纤维状晶粒，铬膜厚度为2μm时，晶粒仍为业微米级，但晶粒顶而已出现拱形；膜厚同为2μm时，外层1μm铌膜 内层1μm铬膜组成的复合膜的附着性分别是外层1μm铬膜 内层1μm铌膜组成的复合膜的2．35倍、2μm铬膜附着性的3倍，其原因在于膜层组织及力学性能变化、铌膜韧性好和复合顺序。因此，依靠铬膜厚度的增加米提高铬膜保护性的方法具有较大局限性，通过在一定厚度的铬膜外复合铌膜的方法则有较好的可行性。     

用正电子湮没技术研究Zr和Nb在TiAl合金中的行为

测量了ＴｉＡｌ,Ｔｉ５０Ａｌ４８Ｚｒ２和Ｔｉ５０Ａｌ４８Ｎｂ２的正电子寿命谱,并利用正电子寿命参数分别计算了合金基体和缺陷态的自由电子密度。ＴｉＡｌ合金基体的自由电子密度比金属Ｔｉ和金属Ａｌ基体的低,当Ｔｉ和Ａｌ组成ＴｉＡｌ合金时,Ｔｉ原子和Ａｌ原子的部分价电子被局域化,ＴｉＡｌ合金中金属健和共键共存。ＴｉＡｌ合金晶界缺陷的开空间较大,晶界缺陷处的自由电子密度较低,金属键结合力较弱,材料易发生沿晶     

氢化物对N18锆合金原位拉伸变形的影响

采用扫描电镜下原位拉伸方法,观察研究了电解渗氢后的N18锆合金中氢化物的变形过程和基体的滑移行为,分析了氢化物对拉伸性能的影响。研究发现,锆合金基体的塑性变形是由多滑移引起的,氢化物可随基体发生较大变形。稀疏分布的带状氢化物簇对滑移的阻碍小,滑移线能够穿过而不改变方向,但尺寸较大的氢化物簇会阻碍滑移带的穿过而改变滑移方向。氢化物使抗拉强度略有增加,伸长率显著下降,但氢含量达到623μg/g的N18锆合金的伸长率仍然达到了13.1%,具有较好的塑性。     

Corrosion behaviour of zirconium electrode in sodium azide electrolyte as compared to the alkali halide solutions

The kinetics of open circuit growth of an oxide film on zirconium electrode in NaN₃ solution of various concentrations was investigated using potential and capacitance measurements. The protective oxide film formed in azide solutions was found to thicken with time in two steps, the rate of oxide growth was found to decrease as the azide concentration increased. The corrosion behaviour of the electrode was characterized by ac impedance measurements to obtain detailed information about the effect of azide ion concentration on the electrical properties of the Zr electrode surface. The impedance response for the metal‐metal oxide‐electrolyte system was modeled with a transfer function. The potentiodynamic oxidation of Zr was also studied as a function of the azide ion concentration. The polarization curves showed the peak‐shaped active‐to‐passive transition and the corrosion rate was found to increase with increase of azide ion concentration. The activation energy of corrosion was calculated according to Arrhenius plot and found to be 14.5 kJ mol^?1. The polarization results in azide solutions were compared to those obtained in solutions of different halide ions, namely, F^?, Cl^?, Br^? and I^? ions. The rate of corrosion was found to decrease in the order Br^? > Cl^? > F^?, I^? > azide. Opposite to the behaviour in azide solutions, the halide ions do not show the active‐passive transition.     

Ta12W合金表面离子束沉积薄膜与U-Nb合金之间的摩擦性能

采用离子束沉积方法在Ta12W合金表面制备了Sn,In软金属薄膜,Al2O3陶瓷薄膜和In/Al2O3复合薄膜.利用销盘摩擦磨损试验机并结合SEM观察分析了对偶销为U-Nb合金时,试样的摩擦学性能并讨论了摩擦磨损机理.当用SiC对偶进行评价时,Sn,In软金属薄膜降低了Ta12W合金摩擦系数.然而当对偶销改为工程状态的U-Nb合金时,由于用离子束溅射沉积法制备的Sn薄膜太薄、In薄膜与U-Nb合金发生粘着,Sn,In软金属薄膜与In/Al2O3复合薄膜均未降低Ta12W合金的的摩擦系数.当Sn薄膜增加到一定厚度时,摩擦性能得到明显改善.Al2O3陶瓷薄膜与U-Nb合金对偶销摩擦时,与Ta12W合金表面直接摩擦结果一样,由于U-Nb合金容易被磨损而使磨屑转移到试样表面,摩擦系数没有下降.