Molecular dynamics study of primary radiation damage in TiVTa concentrated solid-solution alloy

The primary radiation damage in pure V and TiVTa concentrated solid-solution alloy(CSA)was studied using a molecular dynamics method.We have performed displacement cascade simulations to explore the generation and evolution behavior of irradiation defects.The results demonstrate that the defect accumulation and agglomeration in TiVTa CSA are significantly suppressed compared to pure V.The peak value of Frenkel pairs during cascade collisions in TiVTa CSA is much higher than that in pure V due to the lower formation energy of point defects.Meanwhile,the longer lifetime of the thermal spike relaxation and slow energy dissipation capability of TiVTa CSA can facilitate the recombination of point defects.The defect agglomeration rate in TiVTa CSA is much lower due to the lower binding energy of interstitial clusters and reduced interstitial diffusivity.Furthermore,the occurrence probability of dislocation loops in TiVTa CSA is lower than that in pure V.The reduction in primary radiation damage may enhance the radiation resistance of TiVTa CSA,and the improved radiation tolerance is primarily attributed to the relaxation stage and long-term defect evolution rather than the ballistic stage.These results can provide fundamental insights into irradiation-induced defects evolution in refractory CSAs.

Effects of Ni content on the cast and solid-solution microstructures of Cu-0.4wt% Be alloys

The effects of Ni content（0–2.1wt%）on the cast and solid-solution microstructures of Cu-0.4wt%Be alloys were investigated,and the corresponding mechanisms of influence were analyzed.The results show that the amount of precipitated phase increases in the cast alloys with increasing Ni content.When the Ni content is 0.45wt%or 0.98wt%,needle-like Be_（21）Ni_5 phases form in the grains and are mainly distributed in the interdendritic regions.When the Ni content is 1.5wt%or greater,a large number of needle-like precipitates form in the grains and chain-like Be_（21）Ni_5 and Be Ni precipitates form along the grain boundaries.The addition of Ni can substantially refine the cast and solid-solution microstructures of Cu-0.4wt%Be alloys.The hindering effects of both the dissolution of Ni into the matrix and the formation of Be–Ni precipitates on grain-boundary migration are mainly responsible for refining the cast and solid-solution microstructures of Cu-0.4wt%Be alloys.Higher Ni contents result in finer microstructures;however,given the precipitation characteristics of Be–Ni phases and their dissolution into the matrix during the solid-solution treatment,the upper limit of the Ni content is 1.5wt%–2.1wt%.

Effect of component substitution on the microstructure and mechanical properties of MCoCrFeNiTi_x (M = Cu, Al) solid-solution alloys

MCoCrFeNiTix （M = Cu, Al; x： molar ratio, x = 0, 0.5） alloys were prepared using the new alloy-design strategy of equal-atomic ratio and high entropy. By the component substitution orAl for Cu, the microstructure changes from the face-centered cubic solid solution of original CuCoCrFeNiTix alloys to the body-centered cubic solid solution of AlCoCrFeNiTix alloys. Compared with original CuCoCrFeNiTix alloys, AlCoCrFeNiTix alloys keep the similar good ductility and simultaneously possess a much higher compressive strength, which are even superior to most of the reported high-strength alloys like bulk metallic glasses.

Effect of solid-solution temperature on the microstructure of Fe-Ni based high strength low thermal expansion (HSLTE) alloy

The influence of solid-solution temperature on the dissolution of carbide precipitates, the average grain size and the microhardness of the austenite matrix in an Fe-Ni based high strength low thermal expansion （HSLTE） alloy was investigated to obtain the proper temperature range of the solid-solution process. The XRD analysis, microstructure observations, and the theoretical calculations showed that the Mo-rich M2C-type precipitates in the Fe-Ni based HSLTE alloy dissolve completely at about 1100℃. The average grain size of the studied alloys increases from 14 to 46 μm in the temperature range of 1050 to 1200℃. The microhardness of the matrix decreases gust for the sake of solid-solution treatment, but then increases later with increasing solution temperature because of the solution strengthening effect.

Effect of low concentration electrolytes on the formation and corrosion resistance of PEO coatings on AM50 magnesium alloy

In this paper,the formation process,morphology,and electrochemical performance of PEO coatings on AM50 magnesium alloy prepared in low concentration phosphate,aluminate,and phosphate-aluminate electrolytes were systematically studied.The results show that the coatings prepared from the phosphate electrolytes have a higher thickness and better corrosion resistance properties compared to the other electrolytes.The coatings prepared from low concentration phosphate-aluminate mixed electrolytes have slightly thinner thickness,a similar coating structure and an order of magnitude lower value of electrochemical impedance compared with phosphate electrolyte coatings.The Coatings prepared from low concentration aluminate electrolytes have the lowest thickness and the worst corrosion resistance properties which gets close to corrosion behavior of the bare AM50 under the same test conditions.Considering application,coatings prepared from single low concentration phosphate electrolytes and low concentration phosphate-aluminate electrolytes have greater potential than single low concentration aluminate coatings.However,reducing the electrolyte concentrations of coating forming ions too much has negative influence on the coating growth rate.

Effect of Gd on neutron absorption properties and electrochemical corrosion behavior of Zr-Gd alloy in boiling concentrated HNO3

A Zr-Gd alloy with neutron poisoning properties and resistance to boiling concentrated HNO3 corrosion was developed based on a corrosion-resistant Zr-702 alloy to meet the demand for neutron shielding in the closed-loop treatment of spent fuel and the nuclear chemical industry.In this study,1 wt.%,3 wt.%,5 wt.%,7 wt.%,and 9 wt.%Zr-Gd alloys were designed and fabricated with Zr-702 as the control element.The electrochemical behavior of the Zr-Gd alloys in boiling concentrated HNO3 was investigated,and the neutron shielding effect on plate thickness and Gd content was simulated.The experimental results demonstrate that the corrosion resistance of the alloy decreased slightly before~7-9 wt.%with increasing Gd content;this is the inflection point of its corrosion resistance.The alloy uniformly dissolved the Gd content that could not be dissolved in the Zr lattice,resulting in numerous micropores on the passivation coating,which deteriorated and accelerated the corrosion rate.The MCNP simulation demonstrated that when the Gd content was increased to 5 wt.%,a 2-mm-thick plate can shield 99.9%neutrons;an alloy with a Gd content≥7 wt.%required only a 1-mm-thick plate,thereby showing that the addition of Gd provides an excellent neutron poisoning effect.Thus,the corrosion resistance and neutron shielding performance of the Zr-Gd alloy can meet the harsh service requirements of the nuclear industry.

Influence of temperature and alloying elements on the threshold displacement energies in concentrated Ni-Fe-Cr alloys

Concentrated solid-solution alloys(CSAs)have demonstrated promising irradiation resistance depending on their compositions.Under irradiation,various defects can be produced.One of the most important parameters characterizing the defect production and the resulting defect number is the threshold displacement energies(Ed).In this work,we report the results of Ed values in a series of Ni-Fe-Cr concentrated solid solution alloys through molecular dynamics(MD)simulations.Based on several different empirical potentials,we show that the differences in the Ed values and its angular dependence are mainly due to the stiffness of the potential in the intermediate regime.The influences of different alloying elements and temperatures on Ed values in different CSAs are further evaluated by calculating the defect production probabilities.Our results suggest a limited influence of alloying elements and temperature on Ed values in concentrated alloys.Finally,we discuss the relationship between the primary damage and Ed values in different alloys.Overall,this work presents a thorough study on the Ed values in concentrated alloys,including the influence of empirical potentials,their angular dependence,temperature dependence,and effects on primary defect production.

Corrosion behavior of micro-arc oxidation coating on AZ91D magnesium alloy in NaCl solutions with different concentrations

Ceramic oxide coatings were prepared on AZ91D magnesium alloys in alkaline silicate solution using micro-arc oxidation（MAO） technique.The corrosion behavior of MAO coating on AZ91D magnesium alloys in NaCl solutions with different concentrations（0.1%,0.5%,1.0%,3.5% and 5.0% in mass fraction） was evaluated by electrochemical measurements and immersion tests.The results showed that the corrosion rate of the MAO coated AZ91D increased with increasing chloride ion concentration.The main form of corrosion failure was localized corrosion for the MAO coated AZ91D immersed in higher concentration NaCl solutions（1.0%,3.5% and 5.0%）,while it was general corrosion in dilute NaCl solutions（0.1% and 0.5%）.Two different stages of the failure process of the MAO coated AZ91D could be identified：1） occurrence of the metastable pits and 2） growth of the pits.Different equivalent circuits were also proposed based on the results of electrochemical impedance spectroscopy（EIS） for the MAO coated AZ91D immersed in different concentrations of NaCl solutions for 120 h.

CALCULATING MODEL OF MASS ACTION CONCENTRATIONS FOR Cd-Sb ALLOY MELT

According to the Cd-Sb alloy phase diagram, resistivity, heat capacity, partial molar entropy and viscosity,the structural units of this alloy melt have been determined as Cd and Sb atoms as well as Cd3Sb2, Cd4Sb3 and CdSb compounds.Based on these structural units and the coexistence theory of metallic melt structure involing compound formation,a calculating model of mass action concentrations has been deduced.The calculated mass action concentrations Ncd are in good agreement with measured activities acd. The Gibbs standard free energy of formatioin for above three compunds have been obtained too.

Influence of chloride ion concentration on immersion corrosion behaviour of plasma sprayed alumina coatings on AZ31B magnesium alloy

Corrosion attack of aluminium and magnesium based alloys is a major issue worldwide.The corrosion degradation of an uncoated and atmospheric plasma sprayed alumina(APS)coatings on AZ31B magnesium alloy was investigated using immersion corrosion test in NaCl solutions of different chloride ion concentrations viz.,0.01 M,0.2 M,0.6 M and 1 M.The corroded surface was characterized by an optical microscope and X-ray diffraction.The results showed that the corrosion deterioration of uncoated and coated samples were significantly influenced by chloride ion concentration.The uncoated magnesium and alumina coatings were found to offer a superior corrosion resistance in lower chloride ion concentration NaCl solutions(0.01 M and 0.2 M NaCl).On the other hand the coatings and Mg alloy substrate were found to be highly susceptible to localized damage,and could not provide an effective corrosion protection in solutions containing higher chloride concentrations(0.6 M and 1 M).It was found that the corrosion resistance of the ceramic coatings and base metal gets deteriorated with the increase in the chloride concentrations.

The Role of Nd Solid-Solution and Grain-Boundary Segregation in Binary NiAl Intermetallic Compound

The role of Nd solid-solution and grain-boundary segregation in binary NiAl alloy was studied based on microhardness and compressive macrostrain. X-ray and Auger spectra studies indicate that Nd not only is soluble in grain interiors, but also segregates to the grain boundaries. Nd solid-solution induces an increase of the microhardness from 269 to 290 HV in grain interiors and segregation results in an enhancement of hardness from 252 to 342 HV on grain boundaries. Thus, the cohesion of grain boundaries is enhanced by Nd segregation, which make the alloy doped with 0.05 wt pct Nd exhibit more compressive microstrain, i.e. the higher the compressive ductility at room temperature, the better the final surface condition at elevated temperature. Finally, a discussion was made on the reason that Nd strengthens the grain boundaries in NiAl intermetallic alloy.

CONCENTRATION DISTRIBUTION OF ALLOYING ELEMENTS IN SURFACE LAYER OF Ti ALLOY MELTS

The concentration distribution of alloying elements such as Al,Sn,V,Si and Mo in surface layer of quenched Ti alloy melts(TC4,TA 7 and TC9)has been determined by EPMA.Ti al- loy samples were melted and evaporized by electron beam in water cooled copper curcible.The activity coefficient of alloy elements in Ti alloy melts are:γ_(Al)=0.009—0.018 and γ_(Sn)=0.066 —0.123 at 1921—2106℃;γ_V=0.713 at 2021℃;γ_(Si)=0.020 and γ_(Mo)=0.913 at 1921℃.The rate controlling steps of the evaporation of alloying elements Al,Sn,V,Si and Mo from Ti al- loy melts have been discussed with the data of evaporation activation energies of such alloy el- ements.

Effect of Ni and vacancy concentration on initial formation of Cu precipitate in Fe–Cu–Ni ternary alloys by molecular dynamics simulation

In the present work, the effects of Ni atoms and vacancy concentrations （0.1%, 0.5%, 1.0%） on the formation process of Cu solute clusters are investigated for Fe-1.24%Cu-0.62%Ni alloys by molecular dynamics （MD） simulations. The presence of Ni is beneficial to the nucleation of Cu precipitates and has little effect on coarsening rate in the later stage of aging. This result is caused by reducing the diffusion coefficient of Cu clusters and the dynamic migration of Ni atoms. Additionally, there are little effects of Ni on Cu precipitates as the vacancy concentration reaches up to 1.0%, thereby explaining the embrittlement for reactor pressure vessel （RPV） steel. As a result, the findings can hopefully provide the important information about the essential mechanism of Cu cluster formation and a better understanding of ageing phenomenon of RPV steel. Furthermore, these original results are analyzed with a simple model of Cu diffusion, which suggests that the same behavior could be observed in Cu-containing alloys.

Effect of Impurities and Cerium on Stress Concentration Sensitivity of Al-Li Based Alloys

A notch sensitivity factor was derived in order to evaluate the stress concentration sensitivity of Al Li based alloys. The factor values for the Al Li alloy sheets containing various contents of impurities and cerium addition were evaluated by determining the mechanical properties. It is found that the impurities Fe, Si, Na and K significantly enhance the stress concentration sensitivity of the alloys 2090 and 8090, whereas cerium addition reduces the stress concentration sensitivity to a certain degree for the high strength alloys. However, an excess amount of cerium addition in the high ductility alloy 1420 can significantly increase the stress concentration sensitivity. As compared with conventional aluminum alloys, the Al Li based alloys generally show high stress concentration sensitivity. Therefore, a special attention must be paid to this problem in the practical application of Al Li based alloys.

Electron Concentration Dependence of Transformation Temperature in Different NiMnGa Alloys with First Order Magnetic Transition

Composition and electron concentration dependence of transformation temperature in Ni2＋x＋y Mn1-xGa1-y, Ni2＋x Mn1-x Ga alloys with first order magnetic transition were studied. For Ni2 ＋ x ＋ y Mn1- x Ga1-y alloys, martensitic transformation temperature TM increases and Curie temperature Tc decreases with the increase of electron concentration e/a, they intercept at e/a = 7.68. TM and Tc decrease when continue to increase electron concentration. While for Ni2＋x Mn1-xGa alloys, they cross at e/a = 7. 635. Before their crossing, the change tendency with e/a is the same as Ni2＋x＋yMn1-xGa1-y alloys;, after their crossing, both TM and Tc increase slowly. The different relations between TM and Tc and e/a within two NiMnGa alloys show that TM and Tc depend not only on e/a, but also on composition.

Novel Insight into the Preparation of Ti-6Al-4V Alloy Through Thermite Reduction Based on the Mass Action Concentration

Based on the mass action concentration theory,a novel thermodynamic analysis for the raw material ratio in the procedure of preparing Ti-6Al-4V alloy by aluminothermic reduction process is proposed in this paper,which is originated from TiO_(2),Al particles,and V_(2)O_(5) as feedstocks,and the relevant equilibrium thermodynamics was calculated through this new method.The results show that the range of aluminum addition coefficient in raw material to experiment should be controlled within 61.5%-100%,which can significantly reduce the number of experimental groups.This method is ready to regulate the matter of excessive aluminum content in reactants for materials preparation,especially for those reactions including elements that are effortless to combine with aluminum to form the corresponding intermetallics or alloys.In addition,it can also be used in general metallurgy or material preparation process to effectively predict the composition and proportion of equilibrium components under certain conditions.

Relationships between the precipitation of α_2 ordered phase and alloying elements/electron concentration in α+α_2 titanium alloys

Some experimental α+α2 alloys were prepared by the addition of tin or aluminum elements into Ti-55 alloy. These alloys were designed with varied electron concentration values and named as Sn-rich alloys and Al-rich alloys, respectively. The precipita- tion and growth of α2 ordered phase in the tested alloys under various heat treatment conditions were investigated. Some compari- sons among the experimental results were performed and discussed in detail. Stronger precipitation and growth of α2 ordered phase were caused in Al-rich alloys but relatively weak change in Sn-rich alloys with increasing the electron concentration. The precipita- tion of α2 ordered phase in Al-rich alloys is stronger than that in Sn-rich alloys when the electron concentration value is the same for the two alloys.

The Role of Valence Electron Concentration on the Structure and Properties of Rapidly Solidified Sn-Ag Binary Alloys

A group of binary Sn-xAg alloys (x = 0.5, 1.5, 2.5, 3.5, 4.5, 5.5 and 6.5 wt%) has been produced by a single copper roller melt-spinning technique. In this study the interaction between Fermi sphere and Brillouin zone and Hume-Rothery condition of phase stability have been verified. It is found that by increasing valence electron concentration VEC the diameter of Fermi sphere 2kF increases which leads to the increase in the diameter of Brillouin zone which arises from the decrease in volume of the unit cell. It is found that the electrical resistivity increases by increasing VEC due to the decrease in relaxation time τ with increasing VEC. Also it has been confirmed that the correlation between Young’s modulus and the axial ratio c/a of β-Sn unit cell.

Tailoring microstructures and mechanical properties of Zr_(45)Ti_(15)Nb_(30)Ta_(10)refractory complex concentrated alloy using

Compared with cold rolling,warm rolling can significantly reduce or completely eliminate microstruc-ture damage to regulate the microstructure of the material,which is an effective method to improve the mechanical properties of the material.However,the effect of warm rolling on refractory complex concen-trated alloys(RCCAs)has rarely been reported.This research examines how warm rolling influences the microstructure,texture,and mechanical properties of the Zr_(45)Ti_(15)Nb_(30)Ta_(10)RCCA.The RCCA was warm-rolled to a 75%reduction in thickness at 650℃(two-phase zone)and then annealed at 1000°C for 1 h.To highlight the advantages of warm rolling,a comparison was conducted with similarly deformed and annealed cold-rolled RCCA.The warm-rolled RCCA exhibits a layered heterogeneous structure and induces the precipitation of the(Nb,Ta)-enriched bcc2 phase.The deformation texture of warm-rolled RCCA is weaker than that of cold-rolled RCCA,which is attributed to localized deformation inhomogene-ity.After annealing,warm rolling resulted in a remarkable increase in the yield strength of the RCCA,i.e.,from 861 MPa to 1071 MPa;meanwhile,moreover,the tensile plasticity was almost identical.Warm rolling leads to a change in plastic deformation of the RCCA from dislocation cross-slip to one dominated by the interaction of dislocations with subgrain boundaries as well as the bcc2 phase.The back tress gen-erated by the heterogeneous structure induced by warm rolling is also effective in increasing the yield strength of the RCCA.The remarkably layered heterogeneous structure,subgrain boundaries and textures result in warm-rolled RCCA with optimal strength-ductility combination.Our results provide an effective processing approach for tailoring the microstructure and mechanical properties of RCCAs.

Effect of one-step and two-step homogenization treatments on distribution of Al_3Zr dispersoids in commercial AA7150 aluminium alloy

Semi-quantitative electron probe microanalysis （EPMA） mapping, scanning electron microscopy （SEM） and transmission electron microscopy （TEM） were employed to study the effect of one-step and two-step treatments on the Zr distribution and Al3Zr dispersoid characteristics in as-cast commercial AA7150 aluminum alloy. It is shown that the Zr concentration in the dendrite centre regions is higher than that near the dendrite edges in the as-cast condition, and that homogenization at 460 °C for 20 h is insufficient to remove these concentration gradients. After homogenizing at 460-480 °C, a high number density of larger dispersoids can be observed in dendrite centre regions but not near dendrite edges. Furthermore, the dispersoid size increases with increasing the temperature during both one-step and two-step homogenization treatments.