The effect of alloying molybdenum additives on the hyperfine structure and corrosion-electrochemical behavior of Fe-Cr alloys

With the use of Mössbauer spectroscopy, the effect of alloying molybdenum additives on the hyperfine magnetic and electronic structure of iron alloys containing ～21 and 28% chromium is studied. Probability distribution functions of hyperfine magnetic fields P(H _eff), intensities of the effective magnetic field H _eff, isomer (chemical) shifts δ, second-to-third spectral line area ratios (W ₂₃), and other spectral parameters are calculated with the use of the Normos program package. The data of Mössbauer spectroscopy are compared to the corrosion-electrochemical behavior of the alloys.     

Methanol electro-oxidation and surface characteristics of amorphous Pt-Zr alloys doped with tin or ruthenium

Methanol electro-oxidation on electrodes of amorphous Pt-Zr alloys doped with tin or ruthenium was studied in 0.5 M H₂SO₄ by means of potentiostatic polarization and the results were correlated with surface characteristics determined by surface area measurements, scanning electron microscopy observations and X-ray photoelectron spectroscopy (XPS) analyses. The electrocatalytic activity was considerably enchanced by brief treatment with aqueous HF, which yielded a porous surface layer on the alloy electrodes. The layer was effectively in a higher state of dispersion than ordinary platinum black. The XPS analyses indicated that Raney-type porous platinum layers are formed in the surface region, and that a suitable concentration of tin or ruthenium dopant is essential in realizing a high electrocatalytic activity.     

Effect of Extrusion and Annealing Regimes on Mechanical Properties of Powder Alloys of the Mo – Zr – B System

The effect of extrusion and heat treatment regimes on mechanical properties of rods 40 – 45 mm in diameter fabricated from powder molybdenum alloys is investigated. The alloys are fabricated from a mixture of Mo and 0.1 – 2.0% ZrB₂. A deformed alloy of molybdenum with 2% ZrB₂ is shown to be hardened effectively. An optimum composition is chosen for a high-temperature molybdenum alloy possessing good ductility at 20°C in deformed and recrystallized states.     

Potentialities of Mössbauer Spectroscopy for Studying Zirconium Alloys and Their Oxide Films

A brief review and an analysis of results of a study of iron- and tin-bearing zirconium alloys and their oxide films by the method of Mössbauer spectroscopy (MS) are presented. The potentialities of MS for studying the phase composition of zirconium alloys are described and the changes in the states of iron and tin atoms are presented as a function of additional alloying and thermomechanical treatment. The conditions of formation of Zr₂Fe and Zr₃Fe intermetallic compounds and chromium- and niobium-bearing compounds are considered. It is shown that some intermetallic compounds transform into other compounds at room temperature. Metallic iron and tin are shown to be present in oxide films of zirconium alloys, and their concentration is shown to affect the corrosion resistance of zirconium alloys.     

The microstructural engineering of Mo-Si-B alloys produced by reaction synthesis

Mo-Si-B alloys are candidate materials for next-generation jet engine turbine blades and have the potential to increase the service temperature of the base metals 200°C higher than nickel superalloys. These refractory alloys form a composite microstructure of molybdenum solid Solution (Mo_ss and two intermetallic phases, Mo₃Bi and Mo₅SiB₂, where the Mo_ss phase enhances toughness and the intermetallic phases provide oxidation resistance. The properties of the alloys are highly dependent on the morphology of the microstructure. A powder processing approach has been developed to synthesize the three-phase alloys through the reaction of molybdenum, Si₃N₄ and BN powders. Electron backscatter diffraction imaging has been used to map the location of individual phases and provide a method for quantifying the Cluster size distribution of a secondary phase to examine the effect of BN reactant powders on the dispersion of the intermetallic phases.     

Microstructure and mechanical properties of the intermetallic alloy Ti-45Al-6(Nb, Mo)-0.2B

The microstructure and tensile properties of the intermetallic γ-TiAl + α₂-Ti₃Al alloy Ti-45Al-6(Nb, Mo)-0.2B are studied after various heat and thermomechanical treatments. Its cast state is found to be characterized by a homogeneous, relatively fine-grained structure in the cases of both a model 30-g ingot and a bulk laboratory ?120 × 180-mm ingot. The cast material subjected to heat treatment with furnace cooling and aging at T = 1100°C exhibits strength properties at T = 20–900°C that are relatively high for cast γ + α₂ alloys. Due to the rational choice of the alloy, its thermomechanical treatment is facilitated, a fine-grained structure can easily be formed upon hot deformation, and a superplastic state with elongations in the test-temperature range T = 900–1000°C that are very large for γ + α₂ alloys is reached. However, the high contents of niobium and molybdenum in the Ti-45Al-6(Nb, Mo)-0.2B alloy hinder the formation of an equilibrium lamellar structure upon heat treatment, and an increase in the aging temperature to T = 1100°C leads to the development of the α₂ → ß(B2) phase transformation, which makes it impossible to reach a high level of the mechanical properties in the temperature range of the potential application of γ + α₂ alloys. Our study has revealed that the compositions of the γ + α₂ alloys need further optimization of the way of refining the niobium and molybdenum contents.     

Fabrication of simulated DUPIC fuel

Simulated DUPIC fuel provides a convenient way to investigate the DUPIC fuel properties and behavior such as thermal conductivity, thermal expansion, fission gas release, leaching, and so on without the complications of handling radioactive materials. Several pellets simulating the composition and microstructure of DUPIC fuel are fabricated by resintering the powder, which was treated through OREOX process of simulated spent PWR fuel pellets, which had been prepared from a mixture of UO₂ and stable forms of constituent nuclides. The key issues for producing simulated pellets that replicate the phases and microstructure of irradiated fuel are to achieve a submicrometre dispersion during mixing and diffusional homogeneity during sintering. This study describes the powder treatment, OREOX, compaction and sintering to fabricate simulated DUPIC fuel using the simulated spent PWR fuel. The homogeneity of additives in the powder was observed after attrition milling. The microstructure of the simulated spent PWR fuel agrees well with the other studies. The leading structural features observed are as follows: rare earth and other oxides dissolved in the UO₂ matrix, small metallic precipitates distributed throughout the matrix, and a perovskite phase finely dispersed on grain boundaries.     

Electrodeposition of lead–tin alloy from methanesulphonate bath containing organic surfactants

The article discusses the process of electrodeposition of lead-tin alloy (tin content in the deposit up to 10–12 wt %) from methanesulfonate electrolytes. A composition was proposed of organic additives to the electrolyte providing attainment of high quality microcrystalline coatings with the alloy of predetermined composition at relatively low content of Sn²⁺ in the solution. It has been shown that the tin content in the deposit increases at an increase in current density and decrease in the electrolyte temperature. For production of anti-frictional Pb-Sn alloys with the tin content of about 10% the electrolysis should be performed at a current density of about 4 A/dm² and the temperature not exceeding 25°C. The effect of a decrease in the discharge rate of the Sn²⁺ ions into the alloy at deposition from electrolyte without organic additives was discovered, that is stipulated by deceleration of crystallization stage of tin on foreign substrate. When the alloy is deposited from electrolyte containing a composition of organic additives, the effect of super-polarization of discharge of Sn²⁺ ions is reduced.     

Bond Characterization of Plasma Sprayed Zirconium on Uranium Alloy by Microcantilever Testing

The future production of low enriched uranium nuclear fuel for test reactors requires a well-adhered diffusion barrier coating of zirconium (Zr) on the uranium/molybdenum (U-Mo) alloy fuel. In this study, the interfacial bond between plasma sprayed Zr coatings and U-Mo fuel was characterized by microcantilever beam testing. Test results revealed the effect of specific flaws such as cracks and pores on the bonding of interfaces with a sampling area of approximately 20 μm². TEM examination showed the Zr/U-Mo interface to contain rows of very fine grains (5-30 nm) with the Zr in contact with UO₂. Bond characteristics of plasma sprayed samples were measured that are similar to those of roll bonded samples showing the potential for plasma sprayed Zr coatings to have high bond strength.     

Development of advanced research reactor fuels using centrifugal atomization technology

Rotating disk centrifugal atomization technology has been utilized to fabricate uranium silicide (U₃Si, U₃Si₂) and U-Mo nuclear fuel powders having high uranium content per unit volume for high performance research reactor fuels. Atomized nuclear fuel powders have characteristics of a spherical shape with narrow size distribution, small specific surface area and high purity. The heat treatment time for the formation of U₃Si by a peritectoid reaction was reduced from about 72 hours for comminuted powders to about 6 hours for atomized powders due to more rapid solidification of atomized powder with a finer microstructure. The homogeneity of fuel particles in fuel meats was improved by mixing atomized fuel powders with Al powders using a V-shaped tumbler mixer. The atomized powders with a spherical shape and smooth surface were extruded under lower force than the comminuted powders with angular rough surfaces. The dispersed fuel meat with atomized powders resulted in an increased fuel powder loading density and higher thermal conductivity in the heat flow direction. The thermal swelling of dispersed fuel meat decreased due to the reduced specific surface area of spherical atomized nuclear powder. The atomized U-10wt.%Mo dispersion fuel showed less bubble formation than the comminuted fuel after an irradiation test with 40% burnup.     

Reaction mechanisms of low-grade molybdenum concentrate during calcification roasting process

The effects of Ca-based additives on roasting properties of low-grade molybdenum concentrate were studied. The results show that calcium-based additives can react with molybdenum concentrate to form CaSO₄ and CaMoO₄. The initial oxidation temperature of MoS₂ is 450 °C, while the formation of CaMoO₄ and CaSO₄ occurs above 500 °C. The whole calcification reactions are nearly completed between 600 and 650 °C. However, raising the temperature further helps for the formation of CaMoO₄ but is disadvantageous to sulfur fixing rate and molybdenum retention rate. Calcification efficiency of Ca-based additives follows the order: Ca(OH)₂>CaO>CaCO₃. With increasing the dosage of Ca(OH)₂, the molybdenum retention rate and sulfur-fixing rate rise, but excessive dosages would consume more acid during leaching process. The appropriate mass ratio of Ca(OH)₂ to molybdenum concentrate is 1:1. When roasted at 650 °C for 90 min, the molybdenum retention rate and the sulfur-fixing rate of low-grade molybdenum concentrate reach 100% and 92.92%, respectively, and the dissolution rate of molybdenum achieves 99.12% with calcines being leached by sulphuric acid.     

Electrochemical Behavior of Nickel and Electroplating with Nickel–Molybdenum (Tungsten) Alloys in Oxide Melts

The electrochemical behavior of nickel in tungstate melts and the effect of electrolysis conditions on the composition and structure of nickel–molybdenum (tungsten) alloys in tungstate–molybdate melts are studied. It is shown that with an increase in the molybdenum (tungsten) concentrations and a decrease in the nickel concentration in the melt, the phase composition of cathodic deposits changes from nickel through nickel–molybdenum (tungsten) alloys of different composition to pure molybdenum (tungsten).     

Performance studies of bare and Co-plated titanium alloy as cathode current collector in Molten Carbonate Fuel Cell (MCFC)

The corrosion characteristics of bare, heat treated and cobalt coated titanium alloys were studied and compared with that of SS 316 in molten carbonates (Li/K = 62/38 vol.%) at 650 °C under oxygen atmosphere using electrochemical and surface characterization techniques. Immersion test of titanium alloys conducted in cathode environment followed by atomic absorption spectroscopy (AAS) indicated leaching of molybdenum from the alloy. Coating the alloy with Co was found to decrease the molybdenum dissolution rate. X-ray diffraction results showed the formation of LiTiO₂ and Li₂TiO₃ on the surface of the titanium alloys and formation of LiFeO₂ and Fe₂O₃ in the case of SS 316. SEM and EDAX analysis of the post-test samples revealed the loss of Mo, Sn and Zr from the titanium alloys and loss of Cr and Ni from SS 316. Electrochemical studies showed that the conductivity of the corrosion scale was higher for cobalt electroplated alloy when compared to other titanium alloys and lower than that of SS 316. Cobalt coated titanium alloy exhibited higher polarization resistance than other alloys. The present study confirmed that the surface modification of titanium alloy lead to the formation of a protective layer with better corrosion barrier properties and better electronic conductivity in molten carbonate fuel cell cathode operating conditions.     

Corrosion behavior of rapidly solidified Mg-Zn-rare earth element alloys in NaCl solution

Rapidly solidified flaky powder metallurgy (RS FP/M) processing was applied for preparation of corrosion-resistant bulk Mg alloys with Zn and rare earth elements. The corrosion behavior of the melt spun Mg-Zn-La and Mg-Zn-Yb alloy ribbons in 1% NaCl solution was investigated in order to determine optimum composition of corrosion-resistant Mg alloys. The effect of heat-treatment on the corrosion behavior of RS Mg-Zn-La and Mg-Zn-Yb alloys also was studied. In the Mg-Zn-La alloys, as-quenched alloys showed good corrosion resistance in the NaCl solution, but heat-treatment led to degradation due to microstructure change, that is, reduction in dispersion of the Mg₁₇La₂-type intermetallic compound. In the Mg-Zn-Yb alloys, both as-quenched and heat-treated Mg_97.5Zn_0.5Yb₂ alloys exhibited low corrosion rates because fine distribution of Mg₂Yb-type intermetallic compound in α-Mg matrix was not largely changed by heat treatment.     

A study of superplasticity of alloy ATs6N4

The structure and elongation of aluminum alloys of type V95 with additives of Ni, Zr, and Cr, which bear about 10% Al₃Ni phase of eutectic origin, are studied after different modes of deformation and heat treatment with the aim of determining optimum conditions for manifestation of superplasticity. The alloys were fabricated with different rates of crystallization of ingots. The ingots were subjected to two-stage homogenizing annealing and hot rolling. In order to determine optimum strain rates flat specimens were tested for tensile strength with a step increase in the deformation rate. The sizes of the grains and of particles of the Al₃Ni phase were evaluated.     

Structure and properties of cast and splat-quenched high-entropy Al–Cu–Fe–Ni–Si alloys

The effect of the composition and cooling rate of the melt on the microhardness, phase composition, and fine-structure parameters of as-cast and splat-quenched (SQ) high-entropy (HE) Al–Cu–Fe–Ni–Si alloys was studied. The quenching was performed by conventional splat-cooling technique. The cooling rate was estimated to be ~10⁶ K/s. Components of the studied HE alloys were selected taking into account both criteria for designing and estimating their phase composition, which are available in the literature and based on the calculations of the entropy and enthalpy of mixing, and the difference between atomic radii of components as well. According to X-ray diffraction data, the majority of studied Al–Cu–Fe–Ni–Si compositions are two-phase HE alloys, the structure of which consists of disordered solid solutions with bcc and fcc structures. At the same time, the Al_0.5CuFeNi alloy is single-phase in terms of X-ray diffraction and has an fcc structure. The studied alloys in the as-cast state have a dendritic structure, whereas, after splat quenching, the uniform small-grained structure is formed. It was found that, as the volume fraction of bcc solid solution in the studied HE alloys increases, the microhardness increases; the as-cast HE Al–Cu–Fe–Ni–Si alloys are characterized by higher microhardness compared to that of splat-quenched alloys. This is likely due to the more equilibrium multiphase state of as-cast alloys.     

Irradiation-induced amorphized state of rapidly quenched R 12Fe82B6 alloys (R = Nd, Er)

Rapidly quenched (RQ) alloys R ₁₂Fe₈₂B₆ (R = Nd, Er) have been prepared by melt spinning. Their magnetic properties, structure, and phase composition have been studied before and after fast-neutron irradiation to a fluence of 1.2 × 10²⁰ n/cm². Before irradiation, it is the Nd₂Fe₁₄B-type phase (space group P4₂/mnm) that is mainly present in the RQ alloys at 295 K. In the Nd₁₂Fe₈₂B₆ alloy, this phase has a ferro-magnetic structure with magnetic moments at the Nd and Fe atoms oriented parallel to the c axis; the Er₂Fe₁₄B phase found in the Er₁₂Fe₈₂B₆ alloy is characterized by a ferrimagnetic order of Er and Fe magnetic moments parallel to the basal plane. After irradiation, the crystalline state of both RQ alloys transforms into an amorphous state. The ferro- and ferrimagnetic orders are retained in them, but the Curie temperature of the alloys with Nd and Er decreases by 100 and 200 K, respectively. The spontaneous magnetization of the irradiated alloys at 5 K is approximately equal to their magnetization in the crystalline state, whereas their coercive force is lower than that for the alloys before irradiation by two orders of magnitude. The effects observed are explained by the dispersion of Fe-Fe exchange interactions resulting from the dispersion of interatomic spacings in the amorphous alloys.     

The electrochemical behavior of Sn–Ag binary alloys in sulfate solutions

The corrosion and passivation behavior of four binary xSn–Ag (x = 26, 50, 70, and 96.5 wt%) alloys and their pure metal components was investigated in sodium sulfate solutions using electrochemical techniques. The influence of two different electrolytic parameters, namely, concentration (0.01–1.0 M ) and pH (3.0–11.0) were studied while the specimens were potentiodynamically polarized between ?1000 and 500 mV versus saturated calomel electrode (SCE). The results showed that the corrosion current density (i_corr) increases with increasing either the tin content in the alloy or the ions concentration in the electrolyte. Increasing the pH value of a constant composition sulfate solution was found to improve the corrosion resistance of the tin‐richer alloys (x = 50–96.5 wt%), and decreases a little the stability of the silver‐rich one (74 wt% Ag). Impedance measurements at the free corrosion potential (E_corr) give good support for these results, where a small addition of tin to silver up to the intermetallic ratio (x = 26 wt%) gives an alloy with better corrosion resistance to the aggressive sulfate medium. In terms of the tin ratio, the order of surface film stability on the tested samples, generally follows the ranking: 26 > 96.5 > 50 > Ag > 70 > Sn. The good corrosion resistance of the tin‐rich alloy (x = 96.5 wt%), surpassing those for the pure constituents tin and silver can be attributed to the homogenous phase structure of this eutectic mixture.     

镀锡AgCuZnSn钎料熔化特性的热力学分析

以BAg50CuZn钎料为基材,采用电镀热扩散组合工艺制备了镀锡AgCuZnSn钎料。为了揭示镀锡银钎料的热力学特性,借助差示扫描量热仪(DSC)测定了镀锡银钎料的熔化温度,运用热分析动力学中的非等温微分法和积分法分析了镀锡银钎料的相变热力学特性,并利用金相显微镜和X射线衍射仪(XRD)对钎料熔化后润湿界面的显微组织和物相进行了分析。研究表明,随着Sn含量升高,在吸热峰镀锡银钎料由固态向液态转变的温度区间变窄,非等温微分法和积分法得到的钎料相变活化能均逐渐增大。在Sn含量为7.2%时,镀锡银钎料的相变活化能和指前因子最大,分别为555.56kJ/mol、1.41×10~(32),此时镀锡银钎料相变速率方程的表达式为:k=1.41×10~(32)exp(-5.56×10~5/RT)。7.2%Sn含量的镀锡银钎料在304不锈钢表面熔化后,润湿界面组织主要由Ag相、Cu相、CuZn相、Cu_5Zn_8相、Cu_(41)Sn_(11)相、Ag_3Sn相组成。     

Effect of the deviation of the chemical composition from the stoichiometric composition on the structural and phase transformations and properties of rapidly quenched Ti50 + xNi25 ? xCu25 alloys

Methods of X-ray diffraction, transmission and scanning electron microscopy, and electron diffraction have been used to study phase composition and structure of an almost stoichiometric alloy Ti₅₀Ni₂₅Cu₂₅. The alloys of the quasi-binary section TiNi-TiCu to be studied, which exhibit in the initial ascast state thermoelastic martensitic transformations B2 ↔ B19 and related shape-memory effects, have been produced by rapid quenching of the melt (melt spinning technique). The chemical composition of the Ti_{50 + x} Ni_{25 − x} Cu₂₅ alloys was varied with respect to titanium and nickel within x ≤ ±1% (from Ti₄₉Ni₂₆Cu₂₅ to Ti₅₁Ni₂₄Cu₂₅). It has been shown that the rapid quenching from the melt at a cooling rate of 106 K/s provides amorphization for all the alloys under consideration. Heating to 723 K or higher temperatures leads to the devitrification of the amorphous alloys with the formation of a polycrystalline structure of the B2 austenite. The mechanical properties of the alloys have been measured in the initial amorphous state and after subsequent heat treatment. It has been established that, depending on the degree of deviation of the alloy from the stoichiometric composition, which leads to solid solution decomposition in the process of nanocrystallization upon heat treatment, there occur regular changes in the mechanical properties and shape-memory effects of the alloys. The characteristic temperatures of the onset and finish of the process of crystallization from the amorphous and amorphous-crystalline states and the critical temperatures of the onset and finish of the forward and reverse thermoelastic martensitic transitions have been determined by measuring temperature dependences of the electrical resistivity of the alloys. The diagram of the dependence of the critical temperatures on the chemical composition of the alloy has been constructed.