The effects of Ni3Al binder content on the electrochemical response of melt-infiltration processed TiC–Ni3Al cermets

TiC–Ni₃Al samples were successfully fabricated with varying amounts of the Ni₃Al intermetallic binder (alloy IC-50), ranging from 10 to 40?wt-%, through a simple melt-infiltration method. Each sample was then tested to determine the degree of resistance of that composition to electrochemical corrosion in an aqueous solution containing 3.5?wt-% NaCl, using a range of testing procedures including open-circuit potential, potentiodynamic polarisation and cyclic polarisation. Results indicate that the lowest binder content results in greater potential to resist corrosion. It is demonstrated that the Ni₃Al binder undergoes dissolution for the examined conditions, which was confirmed through the high amount of Al and Ni in the electrolyte solutions following testing. It was also confirmed from the electrochemical experiments and the SEM that localised corrosion was visible.     

Low temperature microwave sintering of Cu0.7Ni0.3(Al2O3) nanocomposite

In the present study, the effects of microwave sintering (MWS) on microstructural, tribological and corrosion properties of Cu_0.7Ni_0.3-5?wt-% Al₂O₃ nanocomposites were evaluated. The Cu and Ni powders along with Al₂O₃ nanopowder were mixed in a high-energy ball mill. The XRD patterns indicating formation of Cu_0.7Ni_0.3 solid solution alloy during mechanical alloying process. The mechanically alloyed powders were compacted by coldpress, and sintered samples at 200 and 300°C for 30 and 60?min by means of conventional sintering and MWS. Tribological properties of sintered samples were evaluated by ball-on-disk wear test. For MWS, results indicate that increasing the MWS temperature decreased the wear rate about 30%. Corrosion behaviour of nanocomposites were studied by cyclic potentiodynamic polarisation in 1?M NaOH solution and was found that corrosion current density of microwave sintered sample was decreased almost 35 times of that for conventional sintered sample.     

Corrosion study of Al–Fe (20 wt-%) alloy in artificial sea water with NaOH additions

The corrosion behaviour of the Al–Fe (20?wt-%) alloy was investigated by electrochemical methods in an artificial sea water solution at various alkaline pH values adjusted by a NaOH solution. The electrochemical results showed lower current density values at a temperature of 23°C, varying from 0.008 to 0.873?mA/cm². The potentiodynamic polarisation results suggest the formation of a sensitive layer, which decreases with increasing pH. EIS results showed a corrosion mechanism control governing by diffusion of the solution ions across the permeable scale. SEM characterisation showed a scale formation composed of hydroxides as the main corrosion products; this was associated with increases in both the pH and the immersion time.     

Corrosion Behavior of Alloy 625 in PbSO4-Pb3O4-PbCl2-ZnO-10?Wt?Pct CdO Molten Salt Medium

Corrosion behavior and degradation mechanisms of alloy 625 under a 47.288 PbSO₄-12.776 Pb₃O₄-6.844PbCl₂-23.108ZnO-10CdO (wt pct) molten salt mixture under air atmosphere were studied at 873?K, 973?K, and 1073?K (600?°C, 700?°C, and 800?°C). Electrochemical impedance spectroscopy (EIS), open circuit potential (OCP) measurements, and potentiodynamic polarization techniques were used to evaluate the degradation mechanisms and characterize the corrosion behavior of the alloy. Morphology, chemical composition, and phase structure of the corrosion products and surface layers of the corroded specimens were studied by scanning electron microscopy/energy-dispersive X-ray (SEM/EDX) and X-ray map analyses. Results confirmed that during the exposure of alloy 625 to the molten salt, chromium was mainly dissolved through an active oxidation process as CrO₃, Cr₂O₃, and CrNbO₄, while nickel dissolved only as NiO in the system. Formation of a porous and nonprotective oxide layer with low resistance is responsible for the weak protective properties of the barrier layer at high temperatures of 973?K and 1073?K (700?°C and 800?°C). There were two kinds of attack for INCONEL 625, including general surface corrosion and pitting. Pitting corrosion occurred due to the breakdown of the initial oxide layer by molten salt dissolution of the oxide or oxide cracking.     

Influence of aluminium addition on oxidation resistance of Ta-W alloy

ABSTRACT

Alloys with composition of Ta-10?wt.% W and Ta-10?wt.% W-6?wt.% Al, respectively, were prepared by the hot-press sintering process. The oxidation behaviour at 900°C and 1000°C was studied. The oxidation weight gain curves of the Ta–10%W alloy followed the linear law and the final oxidation product was Ta₂O₅ solid solution. Meanwhile, due to the addition of Al, the oxidation weight gain curves of the Ta–10%W–6%Al alloy followed the parabolic law. The final oxidation products at 900°C formed a dense outer layer Al₂O₃ and an inner layer. However, after being oxidised at 1000°C, the oxidation products included Al₂O₃, AlTaO₄ and Ta₂₂W₄O₆₇. Since the dense Al₂O₃ oxide film was consumed by the generation of AlTaO₄, the inward diffusion of oxygen cannot be prevented. The oxidation resistance degraded at 1000°C. The addition of Al significantly improved the oxidation resistance of the Ta-W-based alloy system.     

Corrosion and mechanical properties of AM50 magnesium alloy after being modified by 1 wt.% rare earth element gadolinium

In order to improve the corrosion and mechanical properties of AM50 magnesium alloy, 1 wt.% Gd was used to modify the AM50 magnesium alloy. The microstructure, corrosion and mechanical properties were evaluated by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS), electrochemical and mechanical stretch methods. The results indicated that β-Mg17Al12 phase decreased and Al2Gd3 and Al0.4GdMn1.6 phase existed after Gd addition. Because of the Gd addition, the grain of AM50 magnesium alloy was refined significantly, which improved the tensile strength of AM50 magnesium alloy. The decreasing of β phase improved the corrosion resistance of the magnesium alloy. The fracture mechanism of the Gd modified AM50 magnesium alloy was quasi-cleavage fracture. The corrosion residual strength(CRS) of AM50 magnesium alloy was improved after 1 wt.% Gd addition.     

Electrochemical Characterization of a Novel Mg70Al18Zn6Ca4Y2 Low Entropy Alloy in Different Aqueous Environments

In the present investigation, design and development of a novel Mg-based multicomponent low entropy alloy (Mg LEA-Mg₇₀Al₁₈Zn₆Ca₄Y₂) was carried out using Disintegrated Melt Deposition (DMD) technique. Various electrochemical techniques such as potentiodynamic polarization test (PDP) and electrochemical impedance spectroscopy (EIS) are used to investigate the electrochemical behaviour of the present Mg-LEA alloy at different molar concentrations in acidic (HCl), neutral (NaCl) and alkaline (NaOH, at different pH levels) solutions. The results show that, this alloy easily gets corroded with the increase of Cl⁻ ion concentration due to the breakdown of the Mg(OH)₂ passive layer in both acidic and neutral solutions. However, in the case of alkaline solution, the corrosion resistance of the alloy increases due to the formation of a stable Mg(OH)₂ layer along with AlMg₂Zn and Al₂Y phases, which is more stable than αMg. The ranking of Mg-LEA alloy’s corrosion rate is as HCl> NaCl> NaOH. The impedance measurements have correlated well with polarizations results and the data obtained according to the equivalent circuit provide insights between electrode and electrolyte interface. Through SEM analysis, pitting corrosion was observed in Mg-LEA alloy in acidic and neutral solutions and their chemical compositions were obtained using energy-dispersive X-ray spectroscopy (EDS).

     

Effect of solid-solution treatment on corrosion and electrochemical behaviors of Mg-15Y alloy in 3.5 wt.% NaCl solution

The effect of solid-solution treatment on corrosion and electrochemical mechanisms of Mg-15Y alloy in 3.5 wt.% NaCl solution was investigated by electrochemical testing,immersion testing and SEM observation.The results indicated that the corrosion resistance of Mg-15Y sample gradually deteriorated with immersion time increasing,which was consistent with the observation of corrosion morphologies.The solid-solution treatment decreased the amounts of second phase Mg24Y5.The Ecorr and corrosion rate of as-cast samples were both lower than those of solid solution-treated samples,and both increased with increment of solid solution-treated time.The corrosion mechanism was proposed for the galvanic,pitting and filiform corrosion which varied with the immersion time and solid-solution treatment.     

Effect of samarium on microstructure and corrosion resistance of aged as-cast AZ92 magnesium alloy

The effects of samarium（Sm） on microstructure and corrosion resistance of AZ92 magnesium alloy were characterized and analyzed by scanning electronic microscopy, X-ray diffraction, mass loss test, electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy and potentio-dynamic polarization test. The results showed that the added Sm could promote continuous precipitation of β-Mg17Al12 phase in grains, and meanwhile restrain discontinuous precipitation of the same phase along the grain boundaries. Thus, the precipitations distributed more uniformly in the aged AZ92 magnesium alloys. When the content of Sm was 0.5 wt.%, the corrosion resistance of aged AZ92 alloy tended to be the best, which was due to the β-phase distributes more homogeneous reducing the galvanic corrosion. The corrosion product film had more integrality and compactness than AZ92 alloys without Sm. However, it resulted in worse corrosion resistance of AZ92 alloy because of the formation of mass cathodic Al2 Sm phase coming from excess Sm in AZ92 alloy.     

Behavior of MgO· Al2O Based Inclusions in Alloy Steel During Refining Process

The transformation of MgO ? Al₂O₃ based inclusions in alloy steel during refining has been studied by industrial trials. Besides Factsage software is used to study the formation and modification of spinel inclusions in alloy steel using calcium treatment during refining process. The results show that the transformation sequence of inclusions is: MgO ? Al₂O₃→CaO-Al₂O₃-MgO complex inclusions→MgO ? Al₂O₃, and under present experimental condition, in order to avoid forming MgO ? Al₂O₃ inclusions the content of dissolved Ca in the molten steel has to reach 1×10^?6. Also the results show that when more calcium was added to molten steel, the content of Al₂O₃ and MgO will be lower. Besides, increasing the content of CaO in the inclusions will increase even if the content of SiO₂ changes little.     

Sb含量对Sn–Sb合金焊料电化学腐蚀行为的影响

为了评估Sn-Sb合金焊料的电化学可靠性，以Sn-xSb(x=0.5%,3%,5%,10%,质量百分数)合金为工作电极，Pt片为对电极，饱和甘汞电极（SCE，饱和KCl溶液）为参比电极，中性5% NaCl溶液为腐蚀溶液，采用电化学腐蚀试验方法，研究了Sb含量对Sn-Sb合金焊料的电化学腐蚀行为的影响。通过对合金样品的动电位极化曲线和电化学交流阻抗谱（EIS）的分析，得出Sn-Sb合金焊料耐腐蚀性下降的趋势为Sn-10Sb > Sn-5Sb > Sn-3Sb > Sn-0.5Sb。     

High-temperature phase equilibria of Cu–O–Al2O3 system in air

Phase equilibria of Cu–O–Al₂O₃ system were experimentally investigated in a temperature range of 1100–1400°C under 0.21?atm oxygen pressure. The experiments were conducted employing a high-temperature equilibration and quenching method. Microstructures of the quenched samples were observed with scanning electron microscope. The phase compositions in the samples were analysed with electron probe microanalysis technique. Measured solubility of Al₂O₃ into the molten oxide ranged from 0.0 to 1.8?wt-%. A small solubility of Cu₂O into Al₂O₃ was also observed ranging from 1.20 to 1.58?wt-%.     

Corrosion protection of magnesium alloys anode by cerium-based anodization coating in magnesium-ait battery

CeN₃O₉·6H₂O(0.5,1.0,1.5,and 2.0 g/L) was added into an 8.0% NaCl electrolyte solution to investigate this electrolyte for use in a Mg-air battery.The effects of the amount of CeN₃O₉-6H₂O on the corrosion resistance of an AZ31 Mg alloy anode and battery performance were investigated using microstructure,electrochemical(dynamic potential polarization method and electrochemical impedance spectroscopy),and battery measurements.The re ...     

Effects of Duty Cycle,Current Frequency,and Current Density on Corrosion Behavior of the Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Artificial Seawater

In this study, the effects of duty cycle, current frequency, and current density on corrosion behavior of the plasma electrolytic oxidation (PEO) coatings on 6061 Al alloy in artificial seawater (3.5 wt pct NaCl solution) were investigated. To serve this purpose, the electrical parameters of a unipolar pulsed current were applied during the PEO process on 6061 Al alloy in alkaline silicate electrolyte with and without Al₂O₃ nanoparticles. The coating morphology and microstructure were characterized by the scanning electron microscopy. The corrosion behavior and electrochemical response of the specimens treated by plasma electrolytic oxidation were analyzed by the electrochemical impedance spectroscopy and the potentiodynamic polarization in artificial seawater. It was found that PEO coatings formed in the presence of Al₂O₃ nanoparticle had lower porosity and exhibited better corrosion behavior compared with the coatings formed in the absence of Al₂O₃ nanoparticle in the structure. This can be attributed to the nanoparticles’ incorporation and penetration through the PEO coatings. On the other hand, the decrease in the current density and increases in the duty cycle and frequency lead to further reduction of the nanoparticles’ incorporation and distribution on the coating surface.

     

Effect of plasma nitriding parameters on corrosion performance of 17-4 PH stainless steel

This study investigates the effect of plasma nitriding parameters on corrosion susceptibility of 17-4 PH stainless steel in 3.5?wt-% NaCl solution. In this regard, 17-4 PH stainless steel was plasma nitrided at 400°C for 5 and 10?h, 450°C for 5?h and 500°C for 5?h. Cross-sectional images after nitriding process showed that a uniform nitrided layer has been formed on steel substrate. Depending on the temperature and time of the nitriding process, different phases were formed in the nitrided layer. This affected general corrosion and pitting corrosion performance of 17-4 PH stainless steel in 3.5?wt-% NaCl solution. While precipitation of chromium nitrides for nitrided specimens at 450°C and higher increased the susceptibility to pitting and general corrosion, formation of expanded martensite (EM) in nitriding at 400°C improved the pitting corrosion resistance of 17-4 PH stainless steel. This is believed to be due to the release of nitrogen atoms from EM phase to form ammonium ions and increase the pH of the solution, supressing pit growth.     

Corrosion behavior of zirconium diboride-based ceramics and electrospark coatings in 3% NaCl solution

The paper examines the corrosion behavior of AlN-ZrB₂, AlN-TiN, and ZrB₂-LaB₆ composite materials and associated electrospark coatings based on aluminum alloy AL9 in 3% NaCl solution. It is shown that the electrochemical corrosion resistance of composites is close to that of titanium nitride. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 54–57, 2007.     

Corrosion Behavior of Cu-Cr Alloy in 3.5% NaCl + NH3 Solution

The corrosion behavior of Cu-Cr alloy in 3.5% NaCl NH3 solution had been studied, and the influences of the concentration of NH3 on corrosion resistance discussed by means of Metallograph, XRD, SEM and electrochemical method. The results show that the Cu is easier to corrosion than Cr, and the corrosion rate increases with the increasing of the concentration of NH3, and deformation worsen the corrosion resistance of the alloy in such corrosive environment.     

Electrochemical co-reduction of Y(III) and Al(III) in a fluoride molten salt system and electrolytic preparation of Y–Al intermediate alloys

In this study, a molten salt co-reduction method was proposed for preparing Y–Al intermediate alloys and the electrochemical co-reduction behaviors of Y(III) and Al(III) and the reaction mechanism of intermetallic compound formation were investigated by transient electrochemical techniques. The results show that the reduction of Y(III) at the Mo electrode is a reversible electrochemical process with a single-step transfer of three electrons, which is controlled by the mass transfer rate. The diffusion coefficient of Y(III) in the fluoride salt at a temperature of 1323 K is 5.0238 × 10^?3 cm²/s. Moreover, the thermodynamic properties associated with the formation of Y–Al intermetallic compounds were estimated using a steady-state electrochemical method. Y–Al intermediate alloy containing 92 wt% yttrium was prepared by constant current electrolysis at 1323 K in the LiF–YF₃–AlF₃–Y₂O₃ (6 wt%)–Al₂O₃ (1 wt%) system at a cathodic current density of 8 A/cm² for 2 h. The Y–Al intermediate alloy is mainly composed of α-Y₂Al and Y phases. The development and application of this innovative technology have solved major technical problems, such as a long production process, high energy consumption, and serious segregation of alloy elements at this stage.     

Hot Corrosion Behaviour of Refractory and Rare Earth Oxide Reinforced CoCrAlY APS Coatings at 700 °C

This paper investigates cyclic hot corrosion of plasma sprayed CoCrAlY?+?Al₂O₃?+?YSZ (C1) and CoCrAlY?+?CeO₂ (C2) composite coatings on MDN 321 and Superni 76 substrates in molten salt (Na₂SO₄-60%V₂O₅) environment exposed to 700 °C. Weight change technique is used to evaluate the corrosion performance. Both C1 and C2 coatings showed better corrosion resistance than uncoated alloy. Both the coatings showed linear weight gain during the initial cycles and parabolic weight gain nature with subsequent hot corrosion cycles. The parabolic rate constant (K_p) of C1 and C2 coating was observed to be in the range 0.29–0.32?×?10^?10 g² cm^?4 s^?1 and 1.0–1.13?×?10^?10 g² cm^?4 s^?1 respectively. In C1 coating, the globular and continuously packed structure on the corroded surface having CoO, Cr₂O₃, CoCr₂O₄ and CoAl₂O₄ spinel oxides provided superior hot corrosion resistance. While in case of C2 coating, the outward growth of CeVO₄ irregular crystals as a corrosion product of CeO₂ and V₂O₅ salt deteriorated the oxide scales resulting in higher corrosion rate.     

The role of solution heat treatment on corrosion and mechanical behaviour of Mg–Zn biodegradable alloys

The mechanical properties and bio-corrosion behaviours of T4 solid solution heat-treated Mg–1.5Zn and Mg–9Zn alloys at 340°C under different heat treatment durations were investigated. In vitro corrosion behaviour of the heat-treated alloys immersed in simulated body fluid (SBF) were measured by electrochemical, hydrogen evolution and mass loss tests. Surface examination and analytical studies were carried out using optical and scanning electron microscopy, EDX, and X-ray diffractometry. The results show that the grains size of both the alloys apparently remained unchanged after T4 treatment. T4 treatment at 340°C for 6?h slightly increased the strength and elongation of Mg–1.5Zn alloy while it significantly improved the strength and elongation of the Mg–9Zn alloy because of the presence of residual Mg₅₁Zn₂₀ and Mg₁₂Zn₁₃ secondary phase at the grain boundary. The results of electrochemical tests show that the corrosion rate of both the alloys decrease with increasing treatment temperature. The result also shows corrosion resistance of both the T4 tread alloys much better than that of as-cast samples. The corrosion mechanism exhibited that the occurrence of galvanic and pitting corrosion, which varied with the alloy composition and treatment time.