Improving corrosive wear resistance of Mg-Zn-Y-Zr alloys through heat treatment

The wear behavior of an as-received Mg-Zn-Y-Zr alloy before and after a facile heat treatment was investigated under sliding in air and 0.5 wt.%NaCl solution.Results revealed that the wear resistance of the alloy was remarkably enhanced after the heat treatment,irrespective of testing condition.The wear mechanism was predominantly abrasive wear accompanied by oxidation under the dry sliding condition,while corrosive wear was dominant under sliding in the NaCl solution.The superior corrosive wear resistance was attributed to the homogenous distribution of fine I-phase precipitates in the alloy by the heat treatment,leading to a reduction in wear,corrosion as well as wear-corrosion synergy.The wear-accelerated corrosion rate was remarkably alleviated after the heat treatment.

Investigation of a novel self-sealing pore micro-arc oxidation film on AM60 magnesium alloy

Micro-arc oxidation(MAO)is one of the promising methods to improve the corrosion resistance of magnesium alloys.However,there are plenty of micro-pores in the traditional MAO films,deteriorating their protection property.A novel self-sealing pore MAO film was developed in this paper.The morphologies and chemical composition of the film were detected by scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDX).The corrosion behavior was investigated by electrochemical and salt spray tests.The possible film formation and corrosion mechanisms were proposed.The self-sealing pore film presents a blue appearance.Most of the micro-pores in the surface of the film are sealed during the film formation process.The chemical composition of the film mainly contains Mg,O,Ti,F and P.The self-sealing pore film exhibits better corrosion resistance compared with the traditional silicate film.Especially,the self-sealing pore film keeps intact after salt spray test for 2000 h,which can be attributed to its high compactness.

Influence of yttrium element on the corrosion behaviors of Mg-Y binary magnesium alloy

The influence of yttrium on the corrosion behavior of Mg–Y alloys has been investigated by electrochemical measurements,scanning electron microscope(SEM)observation,X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS)analysis in NaCl solution.The corrosion resistance decreased with increasing Y content due to increasing Y-rich zone.The solid-dissolved Y improved the chemical activity of the substrate which promoted the corrosion reaction by forming Y2O3.The corrosion resistance was improved by increasing the Y concentration of matrix and proper net Y-rich structure.The sample has the best corrosion resistance when all the Y element was dissolved into the matrix of Mg–5Y in 0.1 M NaCl.

Comparison of the corrosion behavior of AM60 Mg alloy with and without self-healing coating in atmospheric environment

Coatings on the surface of Mg alloys are inevitably damaged during their practical applications,and corrosion can easily initiate from the damaged areas to accelerate the failure of Mg parts.A dual self-healing coating has already been developed to solve this problem in our previous work.Considering the practical application of this coating,it is necessary to investigate its service behavior in atmospheric environment.Thus,the corrosion behavior of AM60 Mg substrate with and without the self-healing coating was compared in Shenyang industrial atmospheric environment.The results show that the enrichment of sediments and rainwater on the scratch areas can accelerate the corrosion of the exposed Mg substrate.The inhibitors can be released from the damaged coating to inhibit corrosion.The dual self-healing coating shows better inhibition ability to narrow scratches due to the higher inhibitor concentration and less resumption.Also,the coating with wide scratches displays enough inhibition ability as well.The dual self-healing coating is a good alternative for Mg alloy parts in the practical applications.

Effect of hydrogen on the corrosion behavior of the Mg-xZn alloys

Hydrogen evolution reaction is inevitable during the corrosion of Mg alloys.The effect of hydrogen on the corrosion behavior of the Mg-2Zn and Mg-5Zn alloys is investigated by charging hydrogen treatment.The surface morphologies of the samples after charging hydrogen were observed using a scanning electron microscopy(SEM)and the corrosion resistance was evaluated by polarization curves.It is found that there are oxide films formed on the surface of the charged hydrogen samples.The low hydrogen evolution rate is helpful to improve the corrosion resistance of Mg alloys,while the high hydrogen evolution rate can increases the defects in the films and further deteriorates their protection ability.Also,the charging hydrogen effect is greatly associated with the microstructure of Mg substrate.

The preferential growth and related textural evolution during static recrystallization in a cold-rolled Mg-Zn-Gd alloy

The grain growth process plays an important role in the texture formation in magnesium alloys.The microstructural and micro-textural evolution of a cold-rolled Mg-Zn-Gd alloy during annealing at 350℃for 60-190 min were tracked by quasi-in-situ electron backscatter diffraction method.The results show that grain growth takes place gradually with the annealing time increasing.Moreover,the TD-split texture maintains the texture type but alters in three aspects-the increased tilting angle,the decreased pole intensity and the widened distribution of high-intensity area.Grains with their c-axis tilting 45-70°from normal direction show preferential growth which is closely associated with the texture changes.The original grain size advantage is one of the important factors leading to the growth advantage,some grain boundaries,such as 50-60°[1^(-)21^(-)0],50-60°[2750],60-70°[1^(-)21^(-)0](18b),and 70-80°[1^(-)01^(-)0](10)are also considered to be related to this preferential growth.

Effects of Hydrogen Charging Time and Pressure on the Hydrogen Embrittlement Susceptibility of X52 Pipeline Steel Material

The effects of hydrogen charging time and pressure on the hydrogen embrittlement(HE)susceptibility of X52 pipeline steel material are studied by slow strain rate tensile tests.The fracture morphologies of the specimens are observed by scanning electron microscopy.The HE susceptibility of the X52 pipeline steel material increases with an increase in both hydrogen charging time and hydrogen pressure.At a charging time of 96 h,the HE susceptibility index reaches 45.86%,approximately 3.6 times that at a charging time of 0 h.Similarly,a charging pressure of 4 MPa results in a HE susceptibility index of 31.61%,approximately 2.5 times higher than that at a charging pressure of 0.3 MPa.

Enhanced tensile properties in a Mg-6Gd-3Y-0.5Zr alloy due to hot isostatic pressing(HIP)

Hot isostatic pressing (HIP) was applied to Mg-6Gd-3Y-0.5Zr (GW63) alloy to reduce shrinkage porosity, thus, to enhance the integrity and reliability of castings. During HIP process, shrinkage porosity was closed by grain compatible deformation and subsequent diffusion across the bonding interface. The amount of initial shrinkage porosity was the key factor for shrinkage porosity closure. HIP was testified to be effective on shrinkage porosity reduction in GW63 alloy due to its relatively narrow solidification range and resultant low content of initial shrinkage porosity in most sections, leading to higher tensile properties both in as-cast and cast-T6 condition. The improvement in tensile properties was mainly because of shrinkage porosity reduction and resultant effective rare-earth (RE) elements homogenization and precipitation strengthening.

Microstructure, Mechanical Properties, and Corrosion Behavior of MoNbFeCrV, MoNbFeCrTi, and MoNbFeVTi High-Entropy Alloys

The development of high-entropy alloys(HEAs)has stimulated an ever-increasing interest from both academia and industries.In this work,three novel MoNbFeCrV,MoNbFeCrTi,and MoNbFeVTi HEAs containing low thermal neutron absorption cross section elements were prepared by vacuum arc melting.The microstructure,mechanical properties,and corrosion behaviors were investigated.A dominant body-centered cubic(BCC)phase was present in all these three HEAs.In addition,an ordered Laves phase was found to be another major phase in both MoNbFeCrV and MoNbFeCrTi alloys,whereas an ordered BCC(B2)phase was observed in the MoNbFeVTi alloy.The phase formation in these three alloys was discussed.It is found that the formation of the secondary phase in these alloys is mainly ascribed to the large atomic size difference and electronegativity difference.All the three HEAs show high hardness,high yield strength but limited plasticity.Moreover,the MoNbFeCrV,MoNbFeCrTi and MoNbFeVTi alloys exhibit excellent corrosion resistance in both deaerated 1mol/L NaCl and 0.5 mol/L H2SO4 solutions at room temperature.However,further composition adjustment and/or thermomechanical processing is required to enhance the mechanical properties of the three alloys.

Effect of Nb Content on Microstructure and Mechanical Properties of Mo_(0.25)V_(0.25)Ti_(1.5)Zr_(0.5)Nbx High-Entropy Alloys

High-entropy alloys(HEAs)have significant application prospects as promising candidate materials for nuclear industry due to their excellent mechanical properties,corrosion resistance and irradiation resistance.In this work,the Mo_(0.25)V_(0.25)Ti_(1.5)Zr_(0.5)Nb_(x)(x=0,0.25,0.5,0.75 and 1.0)HEAs were designed and fabricated.The alloys were prepared by vacuum arc melting,and all the ingots were annealed at 1200℃ for 24 h.The microstructures,crystal structures,hardness and mechanical properties of Mo_(0.25)V_(0.25)Ti_(1.5)Zr_(0.5)Nb_(x) HEAs were investigated.The as-cast alloys are composed of single BCC phase.Moreover,the single BCC phase is retained after annealing at 1200℃ for 24 h.The compressive and microhardness tests show that the strength and hardness of the alloys decrease gradually with the increase of Nb content,while the plasticity increases and the fracture mode of the alloy changes from brittle fracture to ductile fracture,which is mainly owing to the decrease of grain size.The addition of Nb significantly improves the plasticity of the Mo_(0.25)V_(0.25)Ti_(1.5)Zr_(0.5)Nb_(x) alloys.In particular,Nb1.0 alloy can reach 28.32%strain without fracture,which exhibits promising potential in industrial application.

Corrosion Behavior and Mechanism of Irradiated 304 Nuclear Grade Stainless Steel in High-Temperature Water

Corrosion behavior and mechanism of irradiated 304 nuclear grade stainless steel were studied in simulated pressurized water reactor primary water.The microstructure of the oxide formed on the steel irradiated to different doses over an exposure period range of 25–1500 h was analyzed and compared.It was found that the general and intergranular corrosion rates of the steel were increased with irradiation dose,in correspondence with an evolution of the general oxide and the oxide formed at the grain boundary.Correlation of the oxide evolution with the corrosion kinetics and mechanism has been discussed in detail.

Fretting wear behavior of Zr alloy cladding tube mated with Zr alloy dimple under mixed fretting regime in simulated primary water of PWR

The fretting wear behavior of Zr alloy cladding tube under mixed fretting regime in a high-temperature pressurized water was investigated.The main wear mechanism is adhesive wear,with characters of small-scale delamination at the center of worn area and serious delamination on the worn edge.A long crack throughout the worn area and other cracks propagated towards the substrate are observed.The cross-sectional microstructure of worn area can be divided into a thick third-body layer,thin inner oxide layer and thick tribologically transformed structure layer,and their formation mechanisms are analyzed in detail.Finally,the mixed fretting regime process and the microstructural evolution during fretting wear are discussed.

Effect of Normal Force on Fretting Wear Behavior of Zirconium Alloy Tube in Simulated Primary Water of PWR

The effect of normal force on fretting wear behavior of zirconium alloy tube mated with grid dimple in simulated primary water of pressurized water reactor nuclear power plant was investigated.Results showed that the maximum wear depth,wear volume and wear coefficient of Zr alloy tube in simulated primary water at 315℃ gradually increased with increasing normal force,while the friction coefficient gradually decreased.Fretting process could be divided into four stages according to the variation of friction coefficient during test.When normal force exceeds 30 N,the fretting regime would transition from gross slip regime to partial slip regime after 3×10^(7 )cycles.Delamination was aggravated with increasing normal force,while abrasive wear became slighter.A thicker third-body layer with monoclinic ZrO_(2) was formed by the tribo-sintering mechanism under higher normal force.In addition,the schematic evolution processes of delamination and third-body layer formation were displayed according to morphology observation.

Effect of phosphate conversion film on fatigue and corrosion fatigue behavior of an as-rolled Mg–3.08Zn–0.83Al(in wt.%)alloy

Through investigating and comparing the fatigue behavior of an as-rolled Mg–3.08Zn–0.83Al(in wt.%)alloy performing surface phosphate conversion film treatment,it revealed that the determined fatigue strength of surface treated samples at 106 cycles in air was 65 MPa,whereas the fatigue strength was only 35 MPa when tested in 3.5 wt.%NaCl solution.Failure analysis demonstrated that in air,the fatigue crack initiation was mainly dominated by the interaction between the retarding effect of phosphate conversion film on cyclic slips occurring in the underneath substrate.When the matrix cannot endure the accumulated stress concentration due to the irreversibility of cyclic slips,the fatigue crack will preferentially initiate at sample subsurface.Since the phosphate conversion film cracked easily under the cyclic loading and lost its protectiveness on the substrate in 3.5 wt.%NaCl solution,fatigue cracks were preferentially nucleated at the localized corrosion pits.

Effect of tannic acid on corrosion behavior of carbon steel in NaCl solution

Corrosion behavior of unrusted Q235 carbon steel was investigated in 3.5% NaCl solutions with 1–5 wt%tannic acid addition, using electrochemical methods including electrochemical impedance spectra(EIS),potentiodynamic polarization and scanning vibrating electrode technique(SVET) combined with surface analysis. Results show that the corrosion rate decreases with increasing tannic acid concentration. As compared with tannic acid-free solution, 1% tannic acid does not provide inhibition effect during the whole immersion, while inhibition effect is observed for 3% tannic acid after 8 h and for 5% tannic acid after 4 h. The inhibition efficiency by weight loss measurements(áw) for 1%, 3%, and 5% tannic is around-17.2%, 40.3%, and 51.5%, respectively. Corrosion of unrusted carbon steel in the presence of tannic acid is attributed to the joint effect of tannic acid adsorption and pH decrease. Formation of ferric-tannates is verified by X-ray photoelectron spectroscopy(XPS) and Raman spectra. The reaction mechanism between tannic acid and unrusted carbon steel is proposed.

Corrosion Behavior of X52 Anti-H_2S Pipeline Steel Exposed to High H_2S Concentration Solutions at 90℃

Initial corrosion kinetics of X52 anti-H_2S pipeline steel exposed to 90℃/1.61 MPa H_2S solutions was investigated through high temperature and high pressure immersion tests.Corrosion rates were obtained based on weight loss calculation.The corrosion products were analyzed by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and electron probe micro-analysis(EPMA).The initial corrosion kinetics was found to obey the exponential law.With increasing immersion time,the main corrosion products changed from iron-rich mackinawite to sulfur-rich pyrrhotite.The corrosion films had two layers:an inner fine-grained layer rich in iron and an outer columnar-grained layer rich in sulfur.The corrosion film formed through the combination of outward diffusion of Fe^(2+)ions and inward diffusion of HS^-ions.The variation of the corrosion products and compaction of the corrosion layer resulted in a decrease in the diffusion coefficient with increasing immersion time.The double-layered corrosion film formed after long time immersion acted as an effective barrier against diffusion.

Research Progress on the Corrosion Behavior of Magnesium-Lithium-Based Alloys: A Review

In this review paper, the research progress on corrosion behavior of hexagonal close-packed(HCP) singular phase, body cubic-centered(BCC) singular phase and(HCP + BCC) duplex-structured Mg–Li alloys has been summarized and reviewed, and the future trend about the studies on corrosion behavior of Mg–Li-based alloys and possible solving methods for the improvement in corrosion resistance are discussed also.

Effect of corrosive media on galvanic corrosion of complicated tri-metallic couples of 2024 Al alloy/Q235 mild steel/304 stainless steel

Galvanic corrosion of tri-metallic couples is more complicated than that of bi-metallic couples. In this study, the effect of the pH of corrosive media on the galvanic corrosion of 2024 A1 alloy/Q235 mild steel/304 stainless steel tri-metallic couples was investigated using potentiodynamic polarization, scanning electron microscopy, scanning vibrating electrode technique and a multi-channel galvanic corrosion meter. The results show that 2024 always acts as the only anode in 3.5 wt% NaCl at pH 5.56,9.72 and 12.0, while both Q235 and 2024 act as anodes at pH 2.39 in the initial stage and then the role of Q235 changes at longer coupling time, which can be attributed to the effect of pH on the surface film of 2024. It is also found that the galvanic current density of a tri-metallic couple is the superposition of two bi-metallic couples when cathodic reactions are controlled by the diffusion of oxygen, otherwise it is smaller than that of the sum of two bi-metallic couples. The localized corrosion instead of uniform corrosion of anodic metal is accelerated by galvanic corrosion.

New insights into the effect of Tris-HCl and Tris on corrosion of magnesium alloy in presence of bicarbonate,sulfate,hydrogen phosphate and dihydrogen phosphate ions

In vitro degradation is an important approach to screening appropriate biomedical magnesium(Mg) alloys at low cost. However, corrosion products deposited on Mg alloys exert a critical impact on corrosion resistance. There are no acceptable criteria on the evaluation on degradation rate of Mg alloys. Understanding the degradation behavior of Mg alloys in presence of Tris buffer is necessary. An investigation was made to compare the influence of Tris-HCl and Tris on the corrosion behavior of Mg alloy AZ31 in the presence of various anions of simulated body fluids via hydrogen evolution, p H value and electrochemical tests.The results demonstrated that the Tris-HCl buffer resulted in general corrosion due to the inhibition of the formation of corrosion products and thus increased the corrosion rate of the AZ31 alloy. Whereas Tris gave rise to pitting corrosion or general corrosion due to the fact that the hydrolysis of the amino-group of Tris led to an increase in solution p H value, and promoted the formation of corrosion products and thus a significant reduction in corrosion rate. In addition, the corrosion mechanisms in the presence of Tris-HCl and Tris were proposed. Tris-HCl as a buffer prevented the formation of precipitates of HCO_3^-, SO_4^(2-),HPO_4^(2-) and H_2PO_4^- ions during the corrosion of the AZ31 alloy due to its lower buffering p H value(x.x).Thus, both the hydrogen evolution rate and corrosion current density of the alloy were approximately one order of magnitude higher in presence of Tris-HCl than Tris and Tris-free saline solutions.