Comparative study of microstructure and corrosion resistance of electroless Ni-W-P coatings treated by laser and furnace-annealing

A comparative study of amorphous electroless Ni-W-P coatings on mild steel substrate treated by a high power diode laser and furnace annealing was presented.Effects of different laser operating parameters and furnace-annealing conditions on microstructures,in terms of crystallisation,pores formation and grain growth,were investigated using SEM/EDX and XRD. Corrosion behaviours of these coatings before and after various treatments were evaluated with anodic polarisation in 0.5 mol/L H2SO4 solution.The results show that the furnace-annealing produces either a mixture of nanocrystallined Ni and amorphous phases or precipitated Ni3P phase distributed in nanocrystallined Ni-based matrix,depending on annealing temperatures,whilst the laser treatment under the operating conditions only produces nanocrystallined Ni-based matrix with Ni3P precipitates.Corrosion performance of the coatings treated by both the laser and the furnace-annealing is dependent on the annealing temperature and laser operating conditions.Corrosion mechanisms of various treated-coatings were discussed in the consideration of phase constitutes and proportion,grain sizes of both Ni and Ni3P phases,pores formation and residual stresses.

Anisotropy of the crystallographic orientation and corrosion performance of high-strength AZ80 Mg alloy

A high-strength AZ80 Mg alloy was prepared through multi-direction forging,thermal extrusion,and peak-aged heat treatment.The microstructure,crystallographic orientation and corrosion performance of extrusion-direction,transverse-direction,and normal-direction specimens were investigated using scanning electron microscopy,electron backscatter diffraction,and atomic force microscopy,respectively.Experimental results showed that crystallographic orientation significantly influenced the corrosion performance of AZ80 Mg alloy.Corrosion rates largely increased with decreased(0001)crystallographic plane intensity,whereas the(10−10)and(2−1−10)crystallographic plane intensities increased.This study showed that the corrosion rates of alloy can be modified to some extent by controlling texture,thereby promoting the applications of high-strength AZ80 Mg alloys in the aerospace and national-defense fields.

PEO coating on Mg-Ag alloy:The incorporation and release of Ag species

In the present study,the distribution of Ag in the coating formed on Mg-Ag alloy by plasma electrolytic oxidation(PEO)and its ionic release kinetics when exposed to a 0.9 wt.%Na Cl solution at 37℃have been investigated.Both metallic Ag and Ag oxide particles with~5 to~40 nm in diameters were observed in the PEO coating.Further,an Ag-enriched layer of~20 nm in thickness at the substrate/coating interface was also observed.The PEO coating on the Mg-Ag alloy not only increases its corrosion resistance with the corrosion current density decreasing by up to 3 orders of magnitude from 8.04×10^(-3)to 4.03×10^(-6)A/cm^(2),but also controls the release of Ag+to the level that is sufficient for anti-infective efficacy without causing cytotoxicity to mammal cells.

Effect of air-formed film on corrosion behavior of magnesium-lithium alloys

It is recently suggested that air-formed film plays an important role in controlling corrosion resistance of Mg-Li alloys. However, the structure of the air-formed film and its effect on corrosion resistance of Mg-Li alloys has not been fully understood. Firstly, the air-formed films formed on α and β phases in a dual-phase LZ91 Mg-Li alloy after exposure to laboratory air for up to 48 h have been examined by SEM under the assistance of ultramicrotomy. Then, the effect of the air-formed film on surface potential and, consequently, corrosion/oxidation behavior of the alloy has been investigated. Finally, in order to exclude the influence from α phase, the structure of the air-formed film on β phase and its effect on corrosion/oxidation behavior of Mg-Li alloys have been studied based on a single-phase LA141 Mg-Li alloy. The results show that the air-formed film is thin and negligible on α phase but thick on β phase after prolonged exposure to laboratory air. The thick air-formed film on β phase has a multilayer structure with an inner layer consisting of Mg O/Mg(OH)_(2) and outer layer consisting of Li_(2)CO_(3), which greatly elevates the surface potential of β phase in air. Both LZ91 and LA141 Mg-Li alloys firstly undergo uniform corrosion and then filiform corrosion when immersed in Na Cl solution and the pre-existed air-formed film on β-Li phase can retard the occurrence of filiform corrosion in the alloys.

Effect of Mn Addition and Heat Treatment on the Corrosion Behaviour of Mg-Ag-Mn Alloy

The high corrosion sensitivity and the potential bio-toxicity of Mg-Ag alloys limit their wide applications for the production of implanted devices. In the present work, Mn is added into the Mg-Ag alloy to optimize its corrosion behaviour. The corrosion behaviour of Mg-Ag-Mn alloys is investigated with the underlying microstructural factors examined. The Mg-Ag alloy with 2 wt% Mn exhibits the highest corrosion resistance after post-casting heat treatment at 440 ℃. The addition of Mn results in α-Mn phase with the incorporation of Fe, which suppresses the cathodic activity of impurity Fe. Further, heat treatment of the cast alloys homogenizes the distribution of Ag and promotes the precipitation of α-Mn phase. The former removes Ag segregations as potential cathodes;the latter promotes a more uniform distribution of cathodes and, therefore, prevents localized corrosion.

Flow-accelerated corrosion behavior of 13Cr stainless steel in a wet gas environment containing CO_2

This work investigated the flow-accelerated corrosion （FAC） behavior of 13Cr in a wet CO2-containing environment at different flowing gas velocities mid impinging mlgles, with the natural-gas pipeline environment simulated by a self-assembled impingement jet sys- tem. Surface molphology determination, electrochemical measurements, mid hydromechaziics numerical analysis were cmlied out to study the FAC behavior. The results demonstrate that pitting corrosion was the primary mode of corrosion in 13Cr stainless steel. High-flow-rate gas destroyed the passive film mid decreased the pitting potential, resulting in more serious corrosion. The corrosion degree witk various im- pact mlgles showed the following order： 90~ 〉 60~ 〉 45~. The shear force and the electrolyte from the flowing gas were concluded to be the determinm^t factors of FAC, whereas the shear force was the main factor responsible for destroying the passive film.

Mechanism of Mn on inhibiting Fe-caused magnesium corrosion

In the present study,to understand the mechanism of Mn on inhibiting Fe-caused Mg corrosion,the corrosion behaviour of commercial pure Mg and Mg-6 Mn alloy in 0.6 M NaCl solution is investigated.It is found that in Mg-6 Mn alloy,Fe impurity is incorporated into Mn to form Mn(Fe)phase with Fe as solid solute.The initial galvanic corrosion cannot be reduced through converting Fe-rich phase to Mn(Fe)phase,since Mn(Fe)phase also has relatively strong cathodic activity and has much larger volume fraction than Fe-rich phase.However,the cathodic activation behaviour of pure Mg is inhibited.The cathodic activity even decreases for Mg-Mn alloy with increased exposure time,due to the reduced cathodic HER at the Mn(Fe)particles.Mn can be oxidized at the OCP of Mg-6 Mn alloy,resulting in relatively dense Mn-rich corrosion film on particle surface,which separates the particle from the electrolyte and,consequently,inhibits HER.

热机械加工对AA2099铝锂合金局部腐蚀敏感性及其扩展机理的影响（英文）

为了突出特定显微组织组成对AA2099铝锂合金严重局部腐蚀的影响,对比研究了固溶、预冷变形及人工时效状态下AA2099合金的腐蚀行为。通过浸泡和动电位极化在合金表面引入局部腐蚀;采用扫描电子显微镜和透射电子显微镜表征合金的显微组织和腐蚀形貌。研究表明:该合金的严重局部腐蚀敏感性与其热机械加工过程密切相关,且合金元素的存在方式影响腐蚀的扩展机理。T8状态合金的严重局部腐蚀敏感性比其他状态合金更高;当进行动电位极化时,固溶和T3状态合金表现为晶体学腐蚀特征而T6和T8状态合金表现为局部区域晶粒和晶界的择优腐蚀。

激光处理化学沉积Ni-P/Ni-W-P双镀层的显微组织及性能特征(英文)

采用SEM/EDX及XRD定量分析技术研究了化学沉积Ni-P/Ni-W-P双镀层激光晶化前、后的组织特征,并通过表面和截面的硬度测量以及干摩擦磨损实验评估了双镀层的硬度及耐磨性。结果表明,在两种不同的镀液中连续沉积可以制备出Ni-P/Ni-W-P双合金镀层。激光晶化处理后,化学沉积Ni-P/Ni-W-P双镀层表现出外层NiWP比内层NiP更高的晶化程度及更大的晶粒尺寸,但外层具有更高的硬度。激光处理的双镀层在给定的加工条件下,其耐磨性优于镀态镀层的。激光处理可直接在空气中进行而不需要氩气保护,这为工业化应用提供了可能性。

化学沉积Ni-P/Ni-Mo-P镀层的残余应力和腐蚀行为评价（英文）

通过化学沉积法制备Ni-P、Ni-Mo-P单镀层以及与其成分相同的Ni-P/Ni-Mo-P双镀层。采用纳米压痕法和AFM分析测量镀层表面和截面的残余应力,并用电化学法评估镀层在10%HCl溶液中的腐蚀行为,以获得镀层残余应力与腐蚀行为之间的关系。结果表明:Ni-P单镀层和Ni-P/Ni-Mo-P双镀层表现为残余压应力,分别为241和206 MPa;Ni-Mo-P单镀层呈现出257 MPa的残余拉应力。残余压应力阻止镀层中孔洞的生长,保护镀层的完整性。Ni-P/Ni-Mo-P双镀层比它们的单镀层具有更好的耐蚀性。此外,镀层的应力状态影响其腐蚀形式。

Bioleaching of zinc from gold ores using Acidithiobacillus ferrooxidans

The present work investigated microbial leaching of zinc from ore using Acidithiobacillus ferrooxidans （ATCC 14859）. The ore samples, consisted of 13wt% zinc, were obtained from a gold mine in north-eastern Thailand. A shake flask study was performed on the ore samples using a rotary shaker under the following fixed conditions （250 r·min^-1, 30℃ for 16 d）. The influence of various conditions, namely medium type （with and without iron）, particle ore size （〈20, 20-40, 40-60, 60-100, and 〉100 mesh）, ore density （20 kg·m^-3, 50 kg·m^-3, and 100 kg·m^-3）, and pH of the medium （2, 2.5, 2.8, and 3）, were investigated. The microbial leaching was assessed by determining the concentration of zinc in the medium and compared with the initial sample concentration. The results show that Acidithiobacillus ferrooxidans can successfully leach zinc by as much as 6 times compared with the control experiment （without Acidithiobacillus ferrooxidans ferrooxidans）. The maximum efficiency （92.3%） for microbial leaching is obtained in iron-containing medium, 20-40 mesh ore sizes, 20 kg·m^-3 ore density at pH 2.8, and the zinc content is found in the medium at about 120 mg·m^-1.

机加工AA7150铝合金的抗丝状腐蚀性能

采用扫描及透射电子显微技术表征机加工AA7150铝合金近表面变形层的显微组织,并结合动电位极化曲线及丝状腐蚀测试研究机加工后AA7150铝合金的丝状腐蚀行为。研究发现,机加工后AA7150铝合金近表面区域出现晶粒细化、合金元素重新分布以及晶界偏析等特征。机加工过程中强烈的塑性变形导致近表面区域显微组织的改变,从而极大地提高合金近表面变形层的腐蚀倾向。机加工使合金表面粗糙度增大,并导致形成电化学活性明显提高的近表面变形层。在二者共同影响下,机加工后AA7150铝合金的抗丝状腐蚀性能明显下降。

Hypo-toxicity and prominent passivation characteristics of 316 L stainless steel fabricated by direct metal laser sintering in a simulated inflammation environment

3D-printing is an emerging technology that challenged wrought counterparts by one-step manufacturing for complicated biological devices.However,the material properties and surface features due to manufacturing parameters play an important role on the corrosion behaviour and influence the toxicity of the material as an implant.In this paper,the improvement of pitting potential was observed by electrochemical experiments as the result of grain refinement of DMLS 316 L at 200 W laser power.The ICP results verified the supressed release of toxic cations after the formation of the passive film with enhanced characteristics.However,the pores from DMLS 316 L have the potential to develop into pits when polarised above pitting potential,promoting the risk of using 3D-printed 316 L as implant materials.