Microstructure and corrosion behavior of Zr–1.0Cr–0.4Fe–xMo alloys

Possibility of using Mo as an alloying element in Zr-based alloys was attractive in terms of microstructure refinement and mechanical properties strengthening. In this research, Zr–1.0Cr–0.4Fe–xMo(0, 0.2, 0.4, and 0.6) alloys with different Mo contents were prepared by vacuum arcmelting method, the microstructure and the corrosion resistance of these alloys were investigated. Addition of Mo has a refinement effect on the microstructure; with the increase of Mo content, the a-laths in the as-cast samples and the grain size in the annealed samples decrease. Zr–1.0Cr–0.4Fe–xMo alloys have large numbers of fine second-phase particles(SPPs) in the matrix, the area fraction of the SPPs is more than 10 %. With the increase of Mo content, the population density of the SPPs increases significantly, while the average diameter of the SPPs decreases. Mo addition also affects the texture; the intensity of basal pole texture aligning normal direction decreases with the increase of Mo content in the alloys.Compared with Zr-4 and Zr–1Nb, Zr–1.0Cr–0.4Fe–xMo alloys have excellent corrosion resistance in 500 °C/10.3 MPa steam. The corrosion rates of Mo-containing alloys are higher than that of Mo-free alloy, which is mainly attributed to the solute Mo atoms in the Zr matrix.Change of the SPPs features due to the increase of Mo content alleviates the degradation of corrosion resistance in some degree, but it is not the dominant factor.     

Effect of Zr Addition on Resistance to High Temperature Softening and Resistivity of 6082 Al-Mg-Si Alloys

The influence of zirconium on the resistance to high temperature softening of 6082 Al-Mg-Si alloys has been researched. The softening process of 6082 alloys with Zr and without Zr, isothermally conditioned at 250℃, has been investigated. The results show the inclusion of Zr inhibits the decrease of HB in hardness(HB) compared with the alloys without Zr. This is due to the Zr and Al forming coherent dispersoid-Al3Zr, and Al3Zr particles within an Al matrix, which effectively restricts grain boundary movement. A study is also carried out to investigate the changes in resistivity, which occurs during the ageing of alloys containing Zr, compared to those without Zr. It is found that in both cases there is an initial rapid rise in resistivity followed by a slower rise in resistivity as ageing proceeds. The value of resistivity is lower for 6082 alloys with Zr compared with 6082 alloys without Zr; this is explained in terms of the role of Zr in the 6082 alloys.     

Effect of Sub-T_g Annealing on the Corrosion Resistance of the Cu–Zr Amorphous Alloys

Despite the economy of material cost and excellent toughness of Cu-based amorphous alloys, especially Cu_(50)Zr_(50), their poor corrosion resistance to a chloride medium limits their widespread applications. In this study, corrosion tests were performed on the Cu_(50)Zr_(50) amorphous alloy with different degrees of short-range order, which were prepared by annealing below the glass transition temperature(T_g). It was found that the corrosion resistance of amorphous alloys is improved to a significant level when the alloys were heated below T_g. Calorimetric studies showed that thermally activated relaxation process of created disorder, which occurs during sub-T_gannealing, is responsible for the improvement in the corrosion resistance. Molecular dynamics simulations performed on the Cu–Zr amorphous alloys demonstrated that the relaxation process of the alloys is associated with the formation of energetically stable icosahedra and icosahedron-like structures. Our study highlights the effects of sub-T_gannealing on the improvement in the corrosion resistance of the amorphous alloys from the viewpoint the relaxation process of the short-range orders.     

Corrosion of New Zirconium Claddings in 500 ℃/10.3 MPa Steam: Effects of Alloying and Metallography

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions, six new zirconium alloys(named N1–N6) have been designed.The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water, and Fe, Cr, V, Cu or Mo elements were added to the alloys to adjust the corrosion behavior.The current work focused on the rapid corrosion behavior in 500 ℃/10.3 MPa steam for up to 1960 h, aiming to test the corrosion resistance at high temperature.The structure of matrix and properties of second-phase particles(SPPs) were characterized to find the main differences among these alloys.All the six alloys exhibited better corrosion resistance than N36, and N1 was shown to have the best performance.A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition.Elements Fe, Cr, V, Cu or Mo aggregated into SPPs with different concentrations and structures.This was demonstrated to be the main reason for different corrosion resistance.Due to good processing control, all alloys had a uniform structure and a uniform distribution of SPPs.As for N4, N6 and N36, the existing of large-size SPPs(450 nm) might be a contributing factor of the relatively poor corrosion resistance.     

Wear and corrosion properties of laser cladded Cu47Ti34Zr11Ni8/SiC amorphous composite coatings on AZ91D magnesium alloy

To improve the wear and corrosion properties of AZ91D magnesium alloys, Cu-based amorphous composite coatings were fabricated on AZ91D magnesium alloy by laser cladding using mixed powders of Cu47Ti34Zr11Ni8 and SiC. The wear and corrosion behaviours of the coatings were investigated. The wear resistance of the coatings was evaluated under dry sliding wear condition at room temperature. The corrosion resistance of the coatings was tested in 3.5% （mass fraction） NaCl solution. The coatings exhibit excellent wear resistance due to the recombined action of amorphous phase and different intermetallic compounds. The main wear mechanisms of the coatings and the AZ91D sample are different. The former is abrasive wear and the latter is adhesive wear. The coatings compared with AZ91D magnesium alloy also exhibit good corrosion resistance because of the presence of the amorphous phase in the coatings.     

Effect of cooling rate and composition on microstructures and properties of Zn-Mg alloys

The Zn-Mg alloys with Mg additions of 35%, 40% and 45%（mass fraction） were prepared by conventional casting method, with the aim to develop new biodegradable materials. The effects of cooling rate and composition on the microstructures, hardness and corrosion resistance were studied by XRD, SEM, microhardness and corrosion testing techniques. The corrosion behaviors of experimental alloys in simulated body fluids were analyzed. The results show that the amount of the petal-like MgZn2 phase decreases, as well as the hardness of the alloys, but that of the polygonal MgZn2 phase increases with the increase of Mg content when the cooling rate is constant. When the alloy composition is constant, the MgZn2 phase changes easily from petal-like to polygon, and the hardness decreases with the decrease of the cooling rate.     

Corrosion behaviors for peak-aged Mg-7Gd-5Y-lNd-0.5Zr alloys with oxide films

The corrosion behaviors of T5(225℃,6.5 h)and T6(460℃,2 h + 225℃,12 h) peak-aged Mg-7Gd-5Y-lNd-0.5Zr alloys with oxide films were investigated by optical microscope(OM),scanning electron microscopy(SEM),and energy-dispersive spectroscopy(EDS).The weight loss rates and electrochemical tests were also analyzed.The thicknesses of T5 and T6 oxide films are roughly 0.6 and1.0 μm,respectively.The components of oxide films mainly consist of O,Mg,Y,Nd,and Gd,and the T6 oxide film results in surfaces with larger peaks than T5 oxide film.In addition,Y,Nd,and Gd peaks are all higher than those of Mg-7Gd-5YlNd-0.5Zr alloys,but Mg peak is consistently far below than that of the alloys.The specimens could be arranged in decreasing order of corrosion rates and corrosion current densities:T6 oxide film T5 oxide film T6 without oxide film T5 without oxide film.The oxide films are compact to increase the corrosion resistance for Mg-7Gd-5Y-lNd-0.5Zr alloys,which will provide a guiding insight into the corrosion and protection of Mg-RE alloys in atmospheric environments.     

Preparation of Ti–Nb–Ta–Zr alloys for load-bearing biomedical applications

Ti–Nb–Ta–Zr alloys for biomedical applications were successfully fabricated by arc melting(AM) and diffusion bonding.The microstructure, mechanical properties and electrochemistry behavior in a simulated body fluid(SBF) were studied.It shows that melted Ti–Nb–Ta–Zr alloy mainly contains β phase although there are a few Ti-rich phases and micropores, the number of which is lower than that in sintered sample with a few Ti-rich and Ta-rich phases.The melted alloys present higher strength(1224 MPa), Young's modulus(15.3 GPa) and corrosion potential(-0.34 V) in SBF, while total recovery strain ratio(67.5%) and pseudoelastic strain ratio(8.4%) of sintered Ti–Nb–Ta–Zr alloy keep higher value than 35.7%and 5.0% for melted Ti–Nb–Ta–Zr.The reasons were discussed based on the microstructure of the Ti–Nb–Ta–Zr alloys.     

Effect of Cr on high temperature oxidation of TiAl

The oxidation behavior of TiAl-Cr（mole fraction of Cr：0-20%） was investigated at 1 173 K in air. The microstructure and composition of the oxide scale were studied by X-ray diffractometry（XRD）, scanning electron microscopy（SEM） and electro-probe micro-analyses（EPMA）. The results show that with the addition of Cr content from 0 to 8%, the oxidation resistance decreases, especially at 3%, which is mainly attributed to the doping effect of Cr^3＋. TiAI-Cr（mole fraction of Cr： 15%-20%） has good oxidation resistance, and the protective alumina layer is preferentially formed on the surface of TiAI alloy, which is due to an increase of mole ratio of Al to Ti in TiAl-Cr alloys.     

Corrosion resistance of Zr-Al-Ni-Cu（Nb） bulk amorphous alloys

The corrosion resistance of Zr-Al-Ni-Cu(Nb) bulk amorphous alloys was systematically investigated. The experimental results show that the corrosion resistance of Zr-based bulk amorphous alloys can not be considered to be excellent at any situation, whereas it is affected by many factors such as the kind of corrosive medium, solution concentration and the alloy composition. It is found that Zr-Al-Ni-Cu bulk amorphous alloys are seriously corrodedin HCl solution in comparison with their excellent corrosion resistance at other acid, alkali and salt circumstances for passivating. Its resistance ability against the chlorine ion induced pitting corrosion can be greatly improved by the addition of Nb element.     

Hydrogen permeation resistance and characterization of Si–Al and Si–Zr composite sol oxide coating on surface of zirconium hydride

The hydrogen permeation resistance of Si–Zr(SZ) and Si–Al(SA) composite sol oxide coating on zirconium hydride blocks(Zr H_(1.8)) was studied. SZ and SA composite sol were prepared by sol–gel method. SZ and SA composite oxide coatings were prepared on the surface of Zr H_(1.8)(in situ oxidized or not) in turns by dip-coating and heat treatment. Hydrogen permeation of Zr H_(1.8)with and without composite oxide coating was compared.Hydrogen desorption experiments in thermal vacuum show that hydrogen permeation resistance of SA composite oxide coating is better than that of SZ, to a certain extent,which could decrease hydrogen thermal loss. Experimental results in the working condition show that the SA composite oxide coating can not only prevent hydrogen permeation, but also retard contact and reaction between CO_2 and Zr H_(1.8)matrix, which could mitigate excessive oxidation of in situ oxide film. Differential scanning calorimetry and thermogravimetry(DSC–TG) analysis was performed to investigate the decomposition behavior of SA and SZ liquid sol in heat treatment process. X-ray diffraction(XRD) and scanning electron microscopy(SEM) analysis were employed to characterize the phase composition,surface and cross-section morphology of the coatings.     

Corrosion behavior of NiCr alloys in HCl-containing oxidation atmosphere at 700-800℃

Corrosion behaviors of pure Ni and three NiCr alloys were investigated in an HCl-containing oxidizing at-mosphere at 700℃ and 800℃. All materials suffer from accelerated corrosion at both temperatures. NiCr alloys show an initial mass loss due to the formation of volatile CrCl3 and CrO2Cl2. Some chlorides are detected at the scale/substrate interface and many voids are also found there. NiCr alloys with higher chromium content have better corrosion resistance. However, Ni50Cr is inferior to Ni25Cr due to its two-phase structure, which makes it easy for chlorine to diffuse along grain boundary and to occur inner oxidation. The relevant corrosion mechanism was also discussed.     

Corrosion property of copperized layer on Zr formed by double glow plasma surface alloying technique

Zr and its alloys have excellent mechanical properties as new structural material,but in specific application environment,its corrosion resistance still needs to be further explored.In this work,double glow plasma surface alloying technique was used for copperizing on pure Zr surface.Besides,X-ray diffraction(XRD),scanning electron microscope(SEM) and energy dispersion spectrum(EDS) were employed to characterize the samples.Furthermore,research was also conducted on the polarization curve of the samples in different solutions.Copperizing on surface can improve corrosion resistance of pure Zr in 3.5 % Na Cl and 0.5 moláL-1Na OH solutions.Especially in 0.5 moláL-1Na OH solution,the corrosion resistance can achieve significant improvement.However,copperizing has no influence on the improvement of corrosion resistance of pure Zr in 0.5 moláL-1H2SO4 solution.The results may provide new insight into way for improving the corrosion property of zirconium alloys.     

Improvement of corrosion resistance of AZ91D magnesium alloy by gadolinium addition

Based on the previous investigation on beneficial introduction of holmium into magnesium alloy, the effect of gadolinium, an adjacent rare earth element, on corrosion resistance was examined. The corrosion behavior of two Mg-9Al-Gd alloys （Mg-9Al-0.45Gd and Mg-9Al-l.43Gd） was evaluated and compared with that of Mg-9Al alloy without Gd by means of specimen mass loss and hydrogen evolution in 3.5% NaCl solution saturated with Mg（OH）2. The Gd-containing alloys exhibit enhanced corrosion resistance with respect to the plain Mg-9Al alloy. The microstructures of Mg-9Al alloy and Mg-9Al-0.45 Gd alloy were observed by electron probe microanalysis （EPMA） and energy dispersion spectroscopy （EDS）. The alloys with Gd addition show a microstructure characterized by a phase solid solution, surrounded by minor amount of β phase and more grain-like Gd-containing phase. To illustrate the involved mechanism their polarization curves were recorded. The electrochemical investigations reveal that Gd addition shifts the corrosion potential of the alloy towards active, as Gd containing phase is more active and hence less cathodic. As a result, the micro-galvanic corrosion is suppressed. Moreover corrosion product films formed on the Gd containing alloys are more compact and provide a better protective effectiveness than that on the alloy without Gd against corrosion. Repassivation measurements in mixture solution of 0.21 mol/L K2CrO4＋0.6 mol/L NaCI also verify the beneficial role of Gd addition. Based on the present preliminary analysis, both the deposited Gd-containing phases and corrosion product films are believed to be responsible for the improved corrosion behaviour due to Gd addition.     

Effects of Pd substitution for Ni on corrosion performances of Mg0.9Ti0.1Nil-xPdx hydrogen storage alloys

The Mg0.9Ti0.1Ni1-xPdx （x= 0, 0.05, 0.1, 0.15） hydrogen storage electrode alloys were prepared by mechanical alloying. The main phases of the alloys were determined as amorphous by X-ray diffraction（XRD）. The corrosion potentials of the alloys were measured by open circuit potential measurements and the values are -0.478, -0.473, -0.473 and -0.471 V （vs Hg/HgO electrode） for x=0, 0.05, 0.1, 0.15, respectively. The corrosion currents of the studied alloys were obtained by non-linear fitting of the anodic polarization curve using Bulter-Volmer equation and Levenberg-Marquardt algorithm, which were obtained after different cycles. The initial corrosion currents of the alloys are decreased with the increasing of Pd content. The increasing of Pd content in the alloys inhibits the corrosion rates of the electrode alloys with the progress of cycle number. The electrochemical impedance spectroscopy（EIS） was conducted after open circuit potential of the alloys stabilizing. The impedance data fit well with the theoretical values obtained by the proposed equivalent circuit model. The corrosion resistances and the thickness of surface passive film of the alloys, which were deduced by the analyses of EIS, are enhanced with the increasing of Pd content in the alloys, which are consistent with the results of corrosion rates obtained from anodic polarization measurements.     

Corrosion behavior of Mg-Zn-Ca amorphous alloys with Nd addition in simulated body fluids

The effects of Nd addition on corrosion behavior of Mg66Zn30Ca4 amorphous alloys in simulated body fluids （SBF） were studied in this paper. Electrochemical properties of the samples before and after corrosion were determined. Surface morphologies of samples after immersion in SBF at 37 ℃ for different times were observed under scanning electron microscope （SEM）. Results show that the corrosion resistance of Mg-based alloys in SBF is improved with the addition of Nd element. The electrochemical properties indicate that microalloying Nd element to the alloys leads to an ennoblement in the open circuit potentials of the alloys and a decrease in the anodic current density in SBF, especially for the Mgee66-xZn30Ca4Ndx alloys with Nd content of 1.0at.%-1.5at.%. It was observed that the surface morphologies of the alloys immersed in SBF change with the Nd addition. A flake- like structure parallel to the alloy substrate formed on the surface of 1.0at.% Nd-containing alloy immersed in SBF for 7 days improves the corrosion resistance of the amorphous alloys by blocking the corrosion liquid from attacking the alloys.     

Effect of crystallization on corrosion resistance of Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy

The effects of crystallization on the corrosion resistance of a Cu52.5Ti30Zr11.5Ni6 bulk amorphous alloy in 1 mol/L HCI, and 6 mol/L NaOH solutions were studied. The amorphous alloy was identified by differential thermal analysis（DSC） and by X-ray diffraction（XRD）. The partially and fully crystallized alloys were prepared by controlling the annealing temperatures at 738 and 873 K for 1 and 12 min, respectively, and the corrosion resistances of those annealed alloys were compared with that of the amorphous alloy by immersion test and potentiodynamic measurements in 1 mol/L HCl and 6 mol/L NaOH solutions. The results show that the partially crystallized alloy exhibits high corrosion resistance, whereas full crystallization results in deteriorated corrosion resistance compared with that of the as-cast amorphous alloy.     

Enhanced Mechanical Properties,Corrosion Behavior and Bioactivity of Ti-based Bulk Metallic Glasses with Minor Addition Elements

In this research, corrosion behavior, mechanical properties and bioactivity of Ti–Zr–Cu–Pd–Sn bulk metallic glasses with minor addition of Au, Pt, Nb or Ta elements were investigated. The results revealed that minor additions of the elements were beneficial to enhancing mechanical properties and corrosion resistance of Ti-based bulk metallic glasses.Minor addition of the element(especially with Nb and Ta addition) results in the improvement in plastic deformation ability due to the existing of nanoparticles with a size smaller than 10 nm in glassy matrix, inhibiting the deformation of the shear bonds. Enrichments of Ti and Zr elements in oxide layer were responsible for high corrosion resistance. The bioactivity of Ti-based bulk metallic glasses was also investigated. The best combination of large plastic deformation ability, good corrosion resistance and bioactivity in Ti_(40)Zr_(10)Cu_(33)Pd_(14)Sn_2Ta_1 BMG was obtained.     

Tribological behaviour of biomedical Ti–Zr-based shape memory alloys

The tribological behaviour of Ti–30Zr, Ti–20Zr–10Nb and Ti–19Zr–10Nb–1Fe alloys was investigated using reciprocating friction and wear tests. X-ray diffraction(XRD) results indicate that Ti–30Zr, Ti–20Zr–10Nb and Ti–19Zr–10Nb–1Fe alloys are composed of hexagonal a'-martensite, orthorhombic a'-martensite and bcc β phases,respectively. Ti–30Zr alloy has the highest hardness of HV(273.1 ± 9.3), while Ti–20Zr–10Nb alloy exhibits the lowest hardness of HV(235.2 ± 20.4) among all the alloys.The tribological results indicate that Ti–30Zr alloy shows the best wear resistance among these alloys, corresponding to the minimum average friction coefficient of 0.052 and the lowest wear rate of 6.4x10~(-4)mm3·N~(-1)·m~(-1). Ti–20Zr–10Nb alloy displays better wear resistance than Ti–19Zr–10Nb–1Fe alloy, because the iron oxide is easy to fall off and less Nb_2O_5 films form on the worn surface of the latter.Delamination and abrasive wear in association with adhesive wear are the main wear mechanism of these alloys.     

Oxidation and hot corrosion behavior of Ti2AlNb-based alloy with and without enamel coating at 800℃

The oxidation and hot corrosion behavior of Ti2AlNb-based alloy with and without enamel coating at 800 ℃ was investigated. The results indicated that Ti-22Al-25Nb alloy exhibited poor oxidation resistance at 800 ℃. The constitution of oxide scale had the effect on its oxidation rate. Because of the S and Cl accelerating the corrosion process, Ti-22Al-25Nb alloy suffered severe hot corrosion and exhibited very poor hot corrosion resistance, Enamel coating could remarkably improve the high temperature oxidation resistance of Ti-22Al-25Nb alloy because it had good chemical stability and matched thermal expansion coefficient with the substrate. In （Na,K）2SOa＋NaCl molten salts at 800 ℃, chemical reactions between molten salts and enamel coating occurred and complicated products formed on the surface of the enamel coating; Cl in the molten salts could penetrate through the coating and induced the substrate corrosion, but enamel coating still had good hot corrosion resistance.