Effects of Ni addition on mechanical properties and corrosion behaviors of coarse-grained WC-10(Co,Ni) cemented carbides

The effects of the Ni content on the mechanical properties and corrosion behavior of coarse-grained WC-10Co cemented carbide, with a grain size of 3.5 μm, were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electrochemical measurements, and mechanical property tests. The results indicate that the strength and toughness are improved with the addition of 2 wt% Ni without sacrificing hardness. Furthermore, the existence of Ni can decrease the corrosion current density (i_corr) of WC-10Co cemented carbide in both 0.1 M HCl and 0.1 M NaOH solutions. The SEM and XPS results reveal that only a minor amount of WO₃ formed in the corroded surface in HCl solution. The corrosion behavior was determined by the dissolution of the binder phase, and Ni can develop the charge-change resistance (R_ct). Contrarily, the Co binder phase were oxidized to a dense passive film (Co(OH)₂ and Co₃O₄) in NaOH solution, and the addition of Ni was conducive to the enhancement of the diffusion resistance (R_f). This may give insights into adding an appropriate Ni content in coarse-grained WC-Co cemented carbide, in which the wear and corrosion of the components coexist.     

不同晶粒尺寸的Cu-40Ni合金在酸性介质中的耐蚀性能

采用电弧熔炼(CA)和机械合金化(MA)通过热压烧结工艺制备了晶粒尺寸差别较大的Cu-40Ni合金,借助于PARM273A和M5210电化学综合测量仪,利用动电位扫描法和交流阻抗技术对比研究了上述合金在酸性介质中的腐蚀电化学性能以及腐蚀机理。结果表明:随着H 浓度的增加,CA Cu-40Ni合金的自腐蚀电位负移,而MA Cu-40Ni合金则正移,两种合金的动电位扫描极化曲线均未出现钝化现象;随着H 浓度的增加,CA Cu-40Ni合金的极化电阻增大,腐蚀电流减小,合金的耐蚀性能增加,而MA Cu-40Ni合金的极化电阻减小,腐蚀电流增加,合金的耐蚀性能降低。两种合金的交流阻抗谱均由双容抗弧组成,腐蚀过程受电化学反应控制。晶粒细化后,合金中存在大量晶界,参与腐蚀反应的活性原子数增加,促使MA Cu-40Ni合金的腐蚀速度高于CA Cu-40Ni合金。     

Corrosion performance of high pressure die-cast Al-6Si-3Ni and Al-6Si-3Ni-2Cu alloys in aqueous NaCl solution

The corrosion performance of high pressure die-cast Al-6Si-3Ni (SN63) and Al-6Si-3Ni-2Cu (SNC632) alloys in 3.5% (mass fraction) NaCl solution was investigated. X-ray diffraction (XRD) and microstructural studies revealed the presence of single phase Si and binary Al₃Ni/Al₃Ni₂ phases along the grain boundary. Besides, the single Cu phase was also identified at the grain boundaries of the SNC632 alloy. Electrochemical corrosion results revealed that, the SNC632 alloy exhibited nobler shift in corrosion potential (?_corr), lower corrosion current density (J_corr) and higher corrosion resistance compared to the SN63 alloy. Equivalent circuit curve fitting analysis of electrochemical impedance spectroscopy (EIS) results revealed the existence of two interfaces between the electrolyte and substrate. The surface layer and charge transfer resistance (R_ct) of the SNC632 alloy was higher than that of the SN63 alloy. Immersion corrosion test results also confirmed the lower corrosion rate of the SNC632 alloy and substantiated the electrochemical corrosion results. Cu addition improved the corrosion resistance, which was mainly attributed to the absence of secondary Cu containing intermetallic phases in the SNC632 alloy and Cu presented as single phase.     

Corrosion behavior of electrodeposited Ni with normal and bimodal grain size distribution

The corrosion behavior of electrodeposited Ni with normal and bimodal grain size distribution was investigated. The microstructure of samples was researched by SEM, EBSD, TEM and XRD. The corrosion behavior was studied by potentiodynamic tests and electrochemical impedance. Nanocrystalline Ni with (100) and (111) textures was prepared by an electrodeposition method. The Ni samples with different grain size distributions and twins were then obtained by heat treatment of nanocrystalline Ni at different temperatures. The effect of grain size on corrosion behavior of the sample depends on the ability of the environment to passivate. In the case where passive film forms on the sample surface, the corrosion resistance of the sample increases with decreasing grain size. Conversely, the corrosion resistance decreases with decreasing grain size when there is no passivation. The corrosion behavior of samples with bimodal grain size distribution obeys the rule of mixture.     

Corrosion behavior of Ti(C,N)-Ni/Cr cermets in H2SO4 solution

The effects of partial substitution of Ni with Cr on the microstructure and corrosion resistance of Ti(C,N)-based cermets in H₂SO₄ solution were investigated in this paper. The results showed that partial substitution of Ni with Cr had a minor effect on the microstructure, whereas the hardness of the Ti(C,N)-based cermets could be improved for dissolution of Cr in Ni binder. The corrosion behavior of Ti(C,N)-based cermets with different Cr content in 0.2 mol/L H₂SO₄ solution was also studied via potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and corrosion test. The tested Ti(C,N)-Ni/Cr cermets had three typical passive regions. The current of the first passive region was reduced and the passive range was enlarged with the increase of Cr content in binder attributed to the synergistic effect of Ti-based and Cr-based passive layers. But the remaining passive regions were pseudopassive regions. The EIS results also demonstrated that the impendence of the reaction rose with the increase of Cr content in binder. Moreover, the corrosion resistance of cermets in H₂SO₄ solution was improved remarkably by Cr dissolving in the binder, which gave rise to the enhanced passivation ability.     

Ni对Zr-Cu-Al系非晶合金在NaCl溶液中腐蚀性能的影响

利用动电位极化和电化学阻抗谱研究了Ni元素对Zr-Cu-Al系非晶合金在3.5wt.%NaCl中性溶液中的电化学腐蚀行为的影响规律。结果表明：含Ni元素的Zr₅₅Cu₃₀Ni₅Al₁₀比Zr₅₅Cu₃₅Al₁₀非晶合金在NaCl溶液中具有更优异的耐腐蚀性能。Zr-Cu-Al系非晶合金在NaCl溶液中发生点腐蚀,圆形腐蚀坑内布满泡沫状孔洞。通过腐蚀前后的元素分布对比,发现Zr-Cu-Al非晶合金在Cl^_-作用下合金元素选择性溶解。含Ni元素的非晶合金形成致密的钝化膜,抑制了金属元素的选择性溶解,从而提高了耐腐蚀性能。研究结果可为耐Cl^_-环境腐蚀非晶合金成分设计及其应用提供参考。     

The effect of processing gas on corrosion performance of electroless Ni-W-P coatings treated by laser

An investigation of the microstructural and corrosion characteristics of electroless Ni-5.5 W-6.5P coatings on steel substrates after laser treatment in argon and air is presented. The microstructural characteristics of the coatings, in terms of crystallisation, grain size, microstrain, porosity as well as surface chemistry, were examined using quantitative X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical tests, using potentiodynamic polarisation in 0.5 M H₂SO₄ solution and electrochemical impedances spectroscopy (EIS) in 3.5% NaCl solution, were undertaken to evaluate the corrosion behaviour of the coatings. The results indicated that the laser-treated coatings consisted of nanocrystalline Ni and Ni₃P phases, along with retained amorphous phase; further, the dimensions of the Ni crystallites were larger than those of Ni₃P. The laser-treated coating in argon revealed the presence of submicron scale porosity, while no porosity was evident in the coating surface treated by laser in air. The uniform corrosion revealed in 0.5 M H₂SO₄ solution is mainly determined by the microstructural characteristics of the coating. Pitting corrosion in 3.5% NaCl solution depended on the amount of porosity on the surface. The laser-treated coating in air exhibited better corrosion resistance in both acidic and chloride environments than that laser-treated in argon.     

WC-Co-(Ni)-(Cr)硬质合金在中性溶液中的腐蚀行为

以WC粉、Co粉、Ni粉及Cr3C2粉为原料,采用粉末冶金方法制备了3组不同粘结相成分的WC-Co-(Ni)-(Cr)硬质合金,通过极化曲线测试和浸泡实验研究了3组合金在中性溶液中的腐蚀行为,并采用扫描电镜、能谱分析、X射线光电子能谱(XPS)和EBSD等手段对其腐蚀机理进行了探讨。结果表明,WC-Co和WC-Co-Cr硬质合金在中性溶液中主要发生粘结相Co的腐蚀,浸泡产生的腐蚀产物主要是Co(OH)2;添加Cr将提高WC-Co硬质合金在中性溶液中的耐腐蚀性能,这可能与Cr的添加明显降低了粘结相中密排六方Co的含量有关;同时添加Ni和Cr可进一步提高WC-Co合金在中性溶液中的耐腐蚀性能,在pH=7的Na2SO4溶液中浸泡480 h后,WC-Co-Ni-Cr合金发生很少量的腐蚀。     

Laser nanocrystallisation and corrosion behaviour of electroless Ni–W–P coating with high phosphorus content

This paper reports an investigation of microstructural characteristics in electroless Ni–3·9W–13·4P (wt.%) coating by laser nanocrystallisation using a quantitative X–ray diffraction (XRD) method and scanning electron microscopy (SEM) with energy dispersive X–ray spectroscopy (EDX). The corrosion resistance of the coatings before and after laser treatment has been evaluated in 0·5 M H₂SO₄ solution by potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. The results show that the laser treatment improves the corrosion resistance of the coatings. The corrosion mechanism has been studied and correlated to the microstructural characteristics including volume fraction of I_Ni3P/I_total, microstrain, and the crystallite size of the Ni and Ni₃P phases.     

Erosion–corrosion characteristic of nano‐particulates reinforced Ni–Cr–Mo–Cu surface alloying layer in acidic flow and acidic slurry flow

In order to improve the corrosion and erosion–corrosion resistance of 316L stainless steel in engineering application, two kinds of composite alloying layers were prepared by a duplex treatment, consisting of Ni/nano‐SiC and Ni/nano‐SiO₂ predeposited by brush plating, respectively, and a subsequent surface alloying with Ni–Cr–Mo–Cu by double glow process. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were performed on the two kinds of composite alloying layer using 10 wt% HCl solution to assess the corrosion behavior. Erosion–corrosion tests were carried out by erosion–corrosion test rig in acidic flow and acidic slurry flow for test time of 20 h at four different rotational speeds. Results of electrochemical tests indicated that the corrosion resistance of composite alloying layer with brush plating Ni/nano‐SiO₂ particles interlayer approximated to that of single Ni‐based alloying layer, whereas the corrosion resistance of the composite alloying layer with brush plating Ni/nano‐SiC particles interlayer was apparently inferior to that of Ni‐based alloying layer in 10 wt% HCl solution at static state. Under the conditions of acidic flow and acidic slurry flow, the mass losses of tested samples increased with increase in the time of erosion–corrosion tests and the rotational speeds of samples. The mass losses of composite alloying layer with brush plating Ni/nano‐SiO₂ particles interlayer were lower than that of single Ni‐based alloying layer at all rotational speeds, except at 1.88 m/s in acidic flow. The mass losses of composite alloying layer with brush plating Ni/nano‐SiC particles interlayer were higher than that of single Ni‐based alloying layer at all rotational speeds, but were obviously lower than that of AISI 316L stainless steel. The influences of second phase on the corrosion and erosion–corrosion of the two kinds of composite alloying layer were discussed in this paper.     

Corrosion behavior of ultra-fine grained industrial pure Al fabricated by ECAP

Corrosion behavior of ultra-fine grained(UFG) industrial Al fabricated by equal channel angular pressing(ECAP) for 16 pass times was investigated by potentiodynamic polarization test, potentiostatic polarization test, electrochemical impedance spectroscopy(EIS) measurement, immersion test and surface analyses (OM and SEM). The microstructures including grain size, grain boundaries and dislocations were also observed by TEM. The results show that the UFG industrial pure Al has more positive pitting potential, less corrosion current density and five times larger passive film resistance compared with the coarse grained(CG) one. It was found that the increased pitting resistance is profited from the more stable passive film kept in the Cl⁻ aggressive solution due to more grain boundaries, larger fraction of non-equilibrium grain boundaries and residual stress of the UFG industrial pure Al.     

Ni/Cu定向结构涂层在不同浓度H2SO4中的耐蚀性能

为了研究Cu元素对Ni基合金定向结构涂层耐腐蚀性能的影响,向Ni60合金粉末中添加了5%Cu(质量分数,下同),制备了定向结构Ni60/Cu复合涂层。采用电化学试验和浸泡试验,评估了涂层在不同浓度H₂SO₄溶液中的电化学腐蚀特性和浸泡腐蚀性能,探讨了涂层在不同浓度H₂SO₄溶液中的腐蚀行为。结果表明,涂层在不同浓度H₂SO₄溶液中的腐蚀均表现为活化-钝化-过钝化的过程,电化学阻抗谱在整个时间常数内具有典型的容抗特征,H₂SO₄溶液浓度从5%增至80%时,电荷转移电阻先减小后增大,涂层的耐腐蚀性呈现先降低后升高的趋势。随着H₂SO₄溶液浓度的增加,涂层表面的腐蚀程度先加剧后逐渐减缓,且在H₂SO₄溶液浓度为40%时,腐蚀电位移至最负,腐蚀电流密度增至最大。但在H₂SO₄溶液浓度达到80...     

Grain growth effects on the corrosion behavior of nanocrystalline NdFeB magnets

Isotropic nanocrystalline Nd₁₄Fe₈₀B₆ magnets with different grain sizes in the range of 100-600 nm have been produced from melt-spun materials by hot pressing at 700 °C and subsequent annealing at 800 °C for 0.5-6 h. The microstructures have been characterized using XRD, SEM, EDX and Kerr microscopy. The effect of grain size on the corrosion behavior of nanocrystalline magnets has been examined in N₂-purged 0.1 M H₂SO₄ electrolyte by in situ inductively coupled plasma solution analysis, gravimetric and electrochemical techniques and hot extraction [H]-analysis. The corrosion resistance increases with increasing grain size of the hard magnetic phase. Nanocrystalline magnets showed an increase in absorbed hydrogen by anodic polarization and abnormal dissolution by cathodic polarization. The corrosion behavior of the magnets in relation to their microstructure is discussed in terms of dissolution, hydrogenation and mechanical degradation.     

Effect of nanocrystalline grain size on the electrochemical and corrosion behavior of nickel

Nanocrystalline nickel of different grain sizes (8–28 nm) was produced by electrodeposition using Watt's bath. Saccharine addition to the bath and pulsed current deposition were effective in lowering the grain size of the deposits. The grain size and microstrain of deposits was determined by X-ray diffraction analysis. The microhardness of nanocrystalline Ni ranged between 572 and 724 kg/mm². The electrochemical behavior of nanocrystalline Ni was evaluated in 1 mol/l H₂SO₄ and compared with that of coarse-grained nickel. All the nickel samples exhibited active–passive potentiodynamic polarization behavior. The zero current potential, passive current density and breakdown potential generally increased with decrease in grain size. The increased passive current density for nanocrystalline nickel confirmed the defective nature of passive film that forms on nanocrystalline nickel. The tendency for localized corrosion was lower in case of nanocrystalline nickel as indicated by increased breakdown potential. Tafel and linear polarization tests revealed that the corrosion rate of freshly exposed surfaces of Ni decreased with grain size, thereby indicating greater hindrance to anodic dissolution in nanocrystalline Ni. The magnitude of compressive microstrain in the Ni deposits increased with decrease in grain size.     

Evaluation of corrosion resistance of electrodeposited nanocrystalline Ni–Fe alloy coatings

Nickel–iron alloys with a compositional range of 24–80?wt-% iron were electrodeposited on a copper substrate from a sulphate-based bath and using a stirring rate of 100?rev?min^?1. The effect of applied current density and Ni²⁺/Fe²⁺ metal ion ratio of plating bath on the properties of alloy coatings was examined. Crystal structure and grain size of Ni–Fe alloy coatings were investigated using X-ray diffraction technique. Field emission scanning electron microscopy and energy dispersive X-ray spectroscopy were used to analyse the surface morphology and chemical composition of coatings. Microhardness test was applied to evaluate the hardness of the coatings. Finally, the electrochemical behaviour of the Ni–Fe alloy coatings was studied by a polarisation test in 10?wt-% H₂SO₄ solution. Results revealed that current density and plating bath composition had a strong effect on the characteristics of coatings. As the iron content of alloys produced increased, their corrosion resistance improved with the best corrosion resistivity being achieved at a metal ion ratio of 0.5 and applied current density of 2.5?A?dm^?2.     

Corrosion Behavior of Magnesium Alloy AP65 in 3.5% Sodium Chloride Solution

Magnesium alloy AP65 was prepared by melting and casting. The corrosion behavior of the as-cast and solid solution (T4)-treated AP65 alloys in 3.5% sodium chloride solution was investigated by corrosion morphology observation, immersion test, and electrochemical measurements. The results show that the second phase Mg₁₇Al₁₂ surrounded by a lead-enriched area distributes discontinuously along the grain boundaries in the as-cast AP65 alloy. The lead-enriched areas with high activity are susceptible to be attacked during immersion test and can act as places for preferential anodic dissolution. The corrosion resistance of the as-cast AP65 alloy can be improved after T4 treatment and the T4-treated alloy suffers general corrosion.     

The corrosion behavior of porous Ni3Al intermetallic materials in strong alkali solution

Porous Ni₃Al alloys was prepared by cold pressing and reactive synthesis of Ni and Al elemental powders via the Kirkendall effect. Corrosion behavior of porous Ni₃Al alloys was investigated by electrochemical tests and weight change measurements. Polarization resistance indicated that porous Ni₃Al had more positive free corrosion potential and lower corrosion current than porous Ni and porous Ti and exhibited a wider passive region. The immersion test revealed that after 2000 h immersion, the weight change and pore structure of porous Ni₃Al stayed stable in KOH solution. The influence of temperature on corrosion behavior and corrosion mechanism of porous Ni₃Al were also discussed.     

Synthesis and passivation behavior of electroless Ni–P‐CNT composite coating

Carbon nanotubes (CNTs) have high chemical stability, unique hollow nanotube structure, and are believed to be ideal materials for fabricating composites. In this study, Ni–P and Ni–P‐CNT composite coatings were fabricated by electroless plating. Scanning electron microscopy was used to characterize the coatings. The corrosion behavior of Ni–P and Ni–P‐CNT coated samples were evaluated by polarization curves and electrochemical impedance spectroscopy in 3.5 wt% NaCl and 0.1 M H₂SO₄ aqueous solutions at room temperature. The results indicated that incorporation of CNTs in the coating significantly increased corrosion resistance. The role of CNTs in improvement of corrosion resistance of the coating was also discussed.     

Corrosion behavior of nanostructured Ni‐Si3N4 composite films: A study of electrochemical impedance spectroscopy

Ni‐Si₃N₄ nanocomposite films with both the consecutive Ni crystallites and dispersed Si₃N₄ particles in the nanometer range have been fabricated using DC electroplating technique, and characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), and X‐ray diffraction (XRD). The corrosion resistance of the Ni‐Si₃N₄ nanocomposite film has been compared to that of pure Ni coating through polarization. Meanwhile, the corrosion process of Ni‐Si₃N₄ nanocomposite film in neutral 3.5% NaCl solution has been investigated using electrochemical impedance spectroscopy (EIS). The results show that the Ni‐Si₃N₄ nanocomposite film is more resistant to corrosion than the pure Ni coating. The corrosion of Ni‐Si₃N₄ nanocomposite film is controlled by electrochemical step, and the whole corrosion process is divided into two sequential stages. The main corrosion type of Ni‐Si₃N₄ nanocomposite films in neutral 3.5% NaCl solution is pitting.     

Deposition and corrosion resistance of electroless Ni-PCTFE-P nanocomposite coatings

The present work deals with the process of electroless deposition and electrochemical corrosion behavior of nickel-polychlorotrifluoroethylene-phosphorous (Ni-PCTFE-P) nanocomposite coatings. The process of autocatalytic-catalytic reduction of Ni in nickel sulfate and sodium hypophosphate solution with PCTFE suspended particles has been employed for the formation of the electroless Ni-PCTFE-P composite coatings. Surface morphology and composition of the composite coatings are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) measurements and X-ray diffraction (XRD) analysis. Corrosion behavior of coatings is evaluated using open-circuit potential (E_OCP) measurements, electrochemical impedance spectroscopy (EIS) and polarization techniques in 3.5 wt.% NaCl solution. The study reveals significant shift in corrosion potential towards the noble direction, decrease in corrosion current density, increase in charge transfer resistance and decrease in double‐layer capacitance values with the incorporation of PCTFE particles in the Ni-P matrix. The significant improvement in corrosion resistance observed for Ni-PCTFE-P nanocomposite coatings (25.3 kΩ cm²) compared to Ni-P (16 kΩ cm²) could have resulted from the microstructural differences of pure Ni-P with Ni-PCTFE-P nanocomposite coatings.