Kinematic viscosity of Mg-Al melts in the magnesium-rich portion

Kinematic viscosity ν of Mg-Al melts containing up to 14 at % second component is measured by the method of damped torsional vibrations of a crucible with a melt. The measurements are performed in the temperature t range between liquidus and 900°C upon heating of a sample after its melting and upon subsequent cooling. Kinematic viscosity isotherms and the concentration dependences of the activation energy of viscous flow are constructed.     

Dynamic viscosities of pure tin and Sn-Ag,Sn-Cu,and Sn-Ag-Cu eutectic melts

The dynamic viscosities of the melts of pure tin and eutectic Sn-Ag, Sn-Cu, and Sn-Ag-Cu alloys are studied in heating followed by cooling, and the maximum heating temperature was 1200°C. An irreversible decrease in the viscosity is found in the temperature range 800–1000°C in the polytherms of all melts. This finding is related to the loss of a local order in a melt and can be used to develop temperature regimes for the production of lead-free solders.     

Influence of crystallization conditions on the structure and modifying ability of Al–Sc alloys

The influence of the modes of thermal-and-temporal treatment and cooling rate of metallic alloys on crystallization regularities of Al–Sc alloys and their structure, properties, and modifying ability are established. Castings of Al–Sc alloy, which were prepared by the electrolysis of salt melts KF–NaF–AlF₃–Sc₂O₃ at 820–850°C, are used as the initial charge for casting. It is established that, by varying the magnitude of melt overheating and casting temperature, it is possible to vary the crystal shape, amount, and size in wide limits. The modifying action of cast and rapidly quenched master alloys, as well as the master alloy produced by electrolysis, is tested for Al–4.5% Cu alloy. The largest effect of milling the structure of the Al–4.5% Cu–0.4% Sc alloy is attained when using the rapidly quenched master alloy.     

Resonance character of polymorphic transformations for the phase transition α′<Subscript><Emphasis Type="Italic">L</Emphasis></Subscript> → β-Ca<Subscript>2</Subscript>SiO<Subscript>4</Subscript>

Experimental results are presented showing that rapid cooling of dicalcium silicate is accompanied by delay of structural processes, which leads to a decreasing in temperature of the phase transition α′ _L → β-Ca₂SiO₄. As starting materials, nepheline ore and limestone were used. In preparing the charge, the dosage of starting components was calculated for obtaining a molar ratio of CaO/SiO₂ = 2.0. From the charge, the series of samples was prepared. Each of the samples was sintered to t = 1250°C with subsequent keeping of the material at this temperature for 30 min. Then the samples were subjected to rapid cooling in air to t = 750, 650, 550, 450, 350, 250, 150, and 25°C. By means of quantitative X-ray powder diffraction analysis using a DRON-3 setup, the content of α′ _L and β-Ca₂SiO₄ was determined in the samples. The data allow us to suppose the occurring polymorphic transformations in dicalcium silicate have a resonance character.     

Effect of a high temperature and hydrostatic pressure on the structure and the properties of a high-strength cast AM5 (the 201.2 alloy type) aluminum alloy

The phase-transition temperatures of a high-strength cast AM5 aluminum alloy are determined at atmospheric pressure and an excess pressure of 100 MPa using differential barothermic analysis (DBA) and classical differential thermal analysis (DTA). An excess pressure of 100 MPa is shown to increase the critical temperatures of the alloy by 12–17°C (including an increase in the solidus temperature by 12°C), which makes it possible to increase the hot isostatic pressing (HIP) temperature above the temperature of heating for quenching. The following three barothermal treatment schedules at p = 100 MPa and τ = 3 h, which have different isothermal holding temperatures, are chosen to study the influence of HIP on the structure and the properties of alloy AM5 castings: HIP1 (t₁ = 505 ± 2°C), HIP2 (t₂ = 520 ± 2°C), and HIP3 (t₃ = 540 ± 2°C). High-temperature HIP treatment is found to increase the casting density and improve the morphology of secondary phases additionally, which ensures an increase in the plasticity of the alloy. In particular, the plasticity of the alloy after heat treatment according to schedule HIP3 + T6 (T6 means artificial aging to achieve the maximum strength) increases by a factor of ～1.5.     

Determination of the heat-transfer coefficient between the AK7ch (A356) alloy casting and no-bake mold

The heat-transfer coefficient h between a cylindrical cast made of AK7ch (A356) aluminum alloy and a no-bake mold based on a furan binder is determined via minimizing the error function, which reflects the difference between the experimental and calculated temperatures in the mold during pouring, solidification, and cooling. The heat-transfer coefficient is h _L = 900 W/(m² K) above the liquidus temperature (617°C) and h _S = 600 W/(m² K) below the alloy solidus temperature (556°C). The variation in the heat-transfer coefficient in ranges h _L = 900–1200 W/(m² K) (above the alloy liquidus temperature) and h _S = 500–900 W/(m² K) (below the solidus temperature) barely affects the error function, which remains at ~22°C. It is shown that it is admissible to use a simplified approach when constant h = 500 W/(m² K) is specified, which leads to an error of 23.8°C. By the example of cylindrical casting, it is experimentally confirmed that the heat-transfer coefficient varies over the casting height according to the difference in the metallostatic pressure, which affects the casting solid skin during its solidification; this leads to a closer contact of metal and mold at the casting bottom.     

Microstructure of high-tensile strength brasses containing silicon and manganese

The morphology, crystallography, chemistry, and distribution of the phases in commercial high-tensile strength brasses containing manganese and silicon with compositions conforming to U.S.A. Specifications C67300 (Cu-35Zn-2.5Mn-lSi) and C67400 (Cu-35Zn-2.5Mn-lSi-l.5Al) have been studied. The wrought and cast microstructures of both types of alloys consist of the copper-rich feea phase, ordered B2β’ phase, and a manganese silicide Mn₅Si₃, with the crystal structure D8₈. Particles of Mn₅Si₃ are distributed uniformly in the as-cast alloy C67300 but tend to concentrate at theβ′ boundaries in alloy C67400. Studies of the development of the microstructure show that Mn₅Si₃ particles form from the liquid and are also precipitated from solid solution. During cooling, the α phase precipitates at a higher temperature in alloy C67300 (800 °C) than in alloy C67400 (500 °C); nucleation of the α phase occurs on Mn₅Si₃ particles in alloy C67400. Tiny Mn₅Si₃ precipitates are formed in both alloys upon quenching from temperatures near the solidus. When the quenched specimens are tempered at temperatures between 400 °C and 500 CC, all of theβ′ phase transforms to α in alloy C67300, while in alloy C67400, α precipitation occurs at theβ′ boundaries and shows a Widmanstätten morphology.     

Decomposition of the LiOH · 2Al(OH)3 · nH2O compound in the presence of sulfonic cation-exchange resin

Decomposition of the LiOH · 2Al(OH)₃ · nH₂O compound (technical name hydroxy dialuminat lithium, or GDAL in Russian nomenclature) in water in temperature range t = 20?90°C is investigated. The compound was obtained by the interaction of an aluminate solution containing 130 g/L Al₂O₃ with a 2.0 caustic module (the molar ratio Na₂O: Al₂O₃) and a lithium chloride solution at t = 60°C. The complete decomposition of the starting compound is attained in water in the presence of the KU-2-8 sulfonic cationexchange resin and the weight ratio “starting substance: water: ionite” = 1: 20: 4.8 at t = 80°C. Lithium was desorbed from the KU-2-8 ionite by the 1% HCl solution at t = 70°C in dynamic conditions.     

Tensile properties and creep behavior of a new Ti-Al-Nb intermetallic alloy with an O+<Emphasis Type="Italic">α</Emphasis><Subscript>2</Subscript> microstructure

A new Ti-Al-Nb alloy with a composition of Ti-27.5Al-13Nb (at. pct) was proposed. The density of this alloy was 4.7 g/cm³, which is about 13 pct lower than that for O+B2 alloys. After hot processing, the alloy was heat treated under two conditions: directly aged at 850 °C (DA treatment), or cooled from above the β-transus temperature with a cooling rate of 3 °C/min and then aged at 850 °C (BCA treatment). Under the present heat-treatment conditions, the phase constitution was primarily O+α ₂. A very fine Widmanstätten microstructure was obtained after the DA treatment, while a microstructure with coarse O plates was obtained after the BCA treatment. The tensile properties were investigated at 20 °C to 950 °C, and the creep behavior was investigated at 650 °C to 750 °C/90 to 380 MPa. The elongation to fracture at room temperature for the DA-treated tensile specimen was as high as 2.6 pct, despite the high Al content in this alloy. In comparison with the O+B2 ternary alloys, this alloy showed higher specific proof stress at temperatures over 800 °C and higher creep strength. The stress exponent and the apparent activation energy for creep were calculated. The fracture mechanism was discussed.     

Effect of alloying by transitional refractory metals on the microstructure and thermal stability of Al–5Zn–3Mg alloys

Abstract

The effect of additions of transitional refractory metals on the structure and properties of Al–Zn–Mg alloys, made by ingot and PM routes, was investigated. The strength of the ingot alloys especially is increased by scandium and zirconium. The modifying action of scandium inhibits recrystallisation and precipitation of the fine-grained coherent Al₃(Sc_1–xZr_x) phase. The effect is weaker in PM alloys where the ultra-high cooling rate during high pressure water atomisation produces the fine-grained structure. PM semi-products of the base composition Al–5Zn–3Mg and alloys without scandium are not recrystallised during heating to 500°C, whereas cast alloys of similar composition recrystallised on the hot extrusion stage at 400–450°C. Of the Sc alloys, Al–5Zn–3Mg–0·5Mn–0·7Zr–0·3Sc showed the highest strength (UTS?=?651 MPa, YS?=?596 MPa), whereas of the PM alloys without scandium Al–5Zn–3Mg–0·85Zr–0·22Cr–0·17Ni–0·15Ti alloy showed UTS?=?618 MPa and YS?=?553 MPa. At melt cooling rates of 10⁵–10⁶ K s^–1 the total content of transitional refractory metals must not exceed 1·5–1·7 wt-% and total content (Zn+Mg) should be <8 wt-% at a Zn/Mg ratio of 5:3.     

Solidification characteristics of the Al-8.3Fe-0.8V-0.9Si alloy

Studies of solidification behavior have been conducted on cast Al-Fe-V-Si alloys. The first phase to precipitate during solidification of an Al-8.3Fe-0.8V-0.9Si alloy is Al₃Fe(V,Si), which is isostructural with the Al₃Fe phase. Thereafter, the solidification proceeds through several invariant reactions. The final invariant reaction is associated with a pronounced arrest. The temperature of this arrest is a function of the cooling rate and modification treatment, with magnesium added as an Al-20 pct Mg or Ni-20 pct Mg master alloy. The coarse iron aluminide precipitates in a slow-cooled (>1 °C/s) cast structure transform to a ten-armed, star-like morphology upon chill casting the melt (cooling rate >10 °C/s) from 900 °C or upon water quenching from above 800 °C. Treatment with magnesium refines the morphology, size, and distribution of iron aluminide precipitates in slow-cooled alloys.     

Regularities in the formation of diffusion layers in magnesium-aluminum composite

The results of metallographic investigations, micromechanical tests, and X-ray structural analysis of the layered composite of the Al-Mg system are presented. It is found that in the initial state, intermetallic phases are absent in the contact region. Starting from t = 150°C, local regions of the diffusion layers are formed. An increase in the keeping time and temperature leads to growth (towards A1) in the thickness of layers and their hardness, namely, to 2000–3000 MPa on heating to 150°C for 1 h and 4500–5000 MPa at t = 400°C for τ = 12 h. When kept for 16 h at 400°C, the layer preferentially involves the Mg₂Al₃ phase with the hexagonal lattice.     

Age Hardening of the Al0.5CoCrNiTi0.5 High-Entropy Alloy

Al_0.5CoCrNiTi_0.5 high-entropy alloy was synthesized by vacuum arc melting in a copper mold. This alloy was aged at 773 K to 1473 K (500 °C to 1200 °C) for 24 hours to investigate the microstructure and hardness. The hardness of the as-cast alloy is HV743, and it exhibits a dendritic structure, in which dendrite is composed of body-centered cubic (bcc), face-centered cubic (fcc), and σ phases, and interdendrite is an eutectic structure consisting of bcc and order bcc phases. Apparent age hardening appears at 873 K to 1173 K (600 °C to 900 °C), and no age softening occurs even after 1473 K (1200 °C) aging. The age hardening of this alloy is attributed to the transformation of the bcc phase to σ phase. Detailed variations of hardness and the microstructure of aged alloys are reported in this article.     

Characterization of Continuous and Discontinuous Precipitation Phases in Pd-Rich Precious Metal Alloys

Aberration-corrected scanning transmission electron microscopy (AC-STEM), X-ray diffraction (XRD), electron backscatter diffraction, and electron probe microanalysis were applied to characterize continuous and discontinuous phase formation in precious metal alloys used in electrical contacts. The Pd-rich Paliney^® (^®Paliney is tradename of Deringer-Ney Inc., Bloomfield, CT) alloys contain Pd, Ag, Cu, Au, Pt (and Zn or Ni). With aging at 755 K (482 °C), nanometer-scale chemistry modulation was observed indicating spinodal decomposition. An ordered body-centered tetragonal (bct) structure was also observed with AC-STEM after the 755 K (482 °C) aging treatment and another phase, tentatively identified as β-Cu₃Pd₄Zn, was found by microscopy and XRD after prolonged holds at higher temperatures. During slow cooling or isothermal holds at high temperature [755 K to 973 K (482 °C to 700 °C)], a two-phase lamellar structure develops along grain boundaries by discontinuous precipitation. XRD and AC-STEM showed that the lamellar structure was comprised of Ag-rich and Cu-rich fcc phases (α ₁ and α ₂). The phases are discussed in relation to a pseudo-ternary diagram based on Ag-Cu-Pd, which provides a simplified representation of the discontinuous phase compositions in the multi-component alloy system.     

Rheological Properties of the EP742-ID Alloy in the Context of Integrated Computational Materials Science and Engineering: Part I. Results of Experimental Investigations

Rheological properties of the EP742-ID alloy are investigated during high-temperature compression tests of cylindrical samples with various ratios of homological initial sizes of diameter and height (d₀/h₀). It is shown by the results of tests in ranges of temperature t = 1000–1150°C and initial deformation rates ε?₀= 3 × 10^–2–3 × 10^–4 s^–1 that an increase in the compression flow tension manifests itself at all temperatures and deformation rates with an increase in ratio d₀/h₀ with the linear dependence on the magnitude of ε?₀ and ratio d₀/h₀. The procedure of recalculating characteristics of the deformation resistance for the specified ratio of homological parameters is proposed. An increase in the compression flow tension is associated with an increase in the rigidity coefficient of the samples and their specific contact surfaces. The temperature dependence of the apparent activation energy of the plastic deformation (Q_def) of the alloy and its relation with the phase composition and running conditions of the dynamic recrystallization of the γ-solid solution are established. The magnitude of Q_def in temperature conditions of the development onset of the dynamic recrystallization of the γ-solid solution (1000–1050°C) is 959 kJ/mol for samples with d₀/h₀ = 0.75. The largest values of Q_def for the samples with d₀/h₀ = 0.75 equal to 1248 and 1790 kJ/mol are observed in a temperature region of the intense dissolution and coagulation of the grain-boundary γ′-phase (1050–1100°C). The value of Q_def for the samples with d₀/h₀ = 3.0 increases to 2277 kJ/mol in this temperature range. The apparent activation energy of the plastic deformation lowers to 869 kJ/mol in the temperature region of the γ-solid solution with grain-boundary primary and secondary carbides (1100–1150°C). The results of compression of alloy samples during single and repeated sequential loading with various durations of pauses between deformation actions are presented. It is shown that no metadynamic recrystallization occurs in the experimental conditions in the γ + γ′-region, while it runs slowly in the γ-region.     

Fluidity of aluminum-silicon-alumina composite

Fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet dispersed ν-A1₂O₃ particles has been studied. Spiral fluidity of Al-11.8 pet Si alloy decreases with an increase in the amount of dispersed alumina particles (for a given size) and decrease in the particle size (for a given weight percent). The spiral fluidity(F) of Al-11.8 pet Si-Al₂O₃ composite correlates well with the total surface area of dispersed A1₂O₃ particles and it can be expressed by the equation of the typeF = a − bx wherex represents the total surface area of alumina particles present in unit weight of the composite and, a and b are constants. Part of the observed decreases in fluidity could be attributed to expected increases in the effective viscosity of composite melts due to the presence of dispersed A1₂O₃ particles. However, the fluidity of Al-11.8 pct Si-5.5 pet A1₂O₃ (60μm) composite poured at 740 °C is at the same level as of Al-11.8 pet Si alloy poured at 700 °C. Hence, the fluidity of Al-11.8 pet Si alloy containing up to 5.5 wt pet A1₂O₃ particles is adequate to make variety of castings at 740 °C. Formerly with the Indian Institute of Science, Bangalore, India     

High Temperature Oxidation Behavior of Conventional and Nb-Modified MAR-M246 Ni-Based Superalloy

The present investigations focused on the thermal oxidation of two variants of MAR-M246 alloy having the same contents of Ta and Nb in at. pct, considering the effects of total replacement of Ta by Nb. The alloys were produced by investment casting using high purity elements in induction furnace under vacuum atmosphere. The alloys were oxidized pseudo-isothermally at 800 °C, 900 °C and 1000 °C up to 1000 hours under lab air. Protective oxidation products growing on the surface of the oxidized samples were mainly Al₂O₃, Cr₂O₃. Other less protective oxide such as spinels (NiCr₂O₄ and CoCr₂O₄) and TiO₂ were also detected as oxidation products. The conventional alloy exhibited slight internal oxidation at 800 °C and an enhanced resistance at 900 °C and 1000 °C. The Nb-modified alloy presented an exacerbated internal oxidation and nitridation at 900 °C and 1000 °C and an enhanced resistance at 800 °C. At 1000 °C, Nb-modified alloy was particularly affected by excessive spalling as the main damage mechanisms. From a kinetic point of view, both alloys exhibit the same behavior at 800 °C and 900 °C, with k_p values typical of alumina forming alloys (2 × 10⁻¹⁴ to 3.6 × 10⁻¹³ g² cm⁻⁴ s⁻¹). However, Ta modified alloys exhibited superior oxidation resistance at 1000 °C when compared to the Nb modified alloy due to better adherence of the protective oxide scale.

     

Effect of the structure of aging invars with a metastable austenite on the frequency dependence of their magnetic permeability

The effect of the generator current frequency f on the magnetic permeability μ of the N30K10T3 invar is studied for its various structural states formed upon the following treatments: phase naklep (i.e., the phase-transformation-induced hardening of austenite), cold plastic deformation, and cooling in liquid nitrogen. The ferromagnetic austenite of the alloy is metastable with respect to the γ → α martensite transformation upon cooling to temperatures below the temperature of the onset of the martensite transformation (M _s ≈ ?80°C) and represents a supersaturated solid solution ageable during heating. The types of treatment are shown not to change the linear character of the μ(f) dependence in the frequency range under study (15–50 kHz) and to decrease μ to a certain extent.     

Microstructure,crystallization, and coercivity of rare earth-iron-boron amorphous alloy ribbons

Amorphous alloys of rare earth-iron-boron develop high coercivity when crystallized around 650 °C to 700 °C. These alloys are located in the iron-rich corner of the ternary system, and the alloys contain 10 to 15 at. pct rare earth (R). In the amorphous state, isomorphous substitution of different rare earth atoms occurs. The short-range Fe-Fe and R-Fe environments in amorphous ribbons are similar to those in Fe₃B and R₆Fe₂₃ (within 6 Å), respectively. Beyond 6 Å, the R-Fe environment appears similar to R₂Fe₁₄B. On nonisothermal heating of these alloy ribbons, a stress-relieving process occurs around 460 °C. The crystallization of α-Fe and R₂Fe₁₄B occurs at around 520 °C and near 600 °C, respectively. The Fe₃B and R₆Fe₂₃ phases crystallize next. Depending on the alloy composition, the Fe₃B crystallizes between 600 °C and 650 °C, and R₆Fe₂₃ crystallizes between 650 °C and 680 °C. The presence of rare earth atoms, 10 to 15 at. pct, significantly raises the crystallization temperatures of a-Fe and Fe₃B. The favorable short-range Fe-Fe and R-Fe environments may be responsible for the nucleation and growth (crystallization) of Fe₃B and R₆Fe₂₃ in the ternary alloys. The high coercivity of the annealed ribbons containing 10 at. pct Tb, Dy, and Ho is related to the single magnetic domain nature of the small crystallized grains of Fe₃B and R₆Fe₂₃. For the annealed alloy ribbons with 12 to 15 at. pct rare earth, the high coercivity is related to the ternary hard phase, R₂Fe₁₄B.     

The effect of quench rate on the martensitic transformation in Fe−C alloys

The effect of very high quench rates on the transformation kinetics of a series of Fe?C and low-alloy steels and the morphology of an Fe?14Ni-0.76C alloy was investigated. TheM _S temperatures of the Fe?C and Fe?C?X alloys increased between 90° and 122°C in a sigmoidal fashion over a quench rate range from 2,750° to 24,800°C per sec. The sensitivity of theM _s temperature to the quench rate from the austenitizing temperature to 315°C was shown to be related to the influence of the third alloying element on the diffusivity of carbon in austenite. Transmission electron microscopy and optical metallography showed that the morphology of an Fe?14Ni?0.76C martensite is changed from a lath structure in slow quenched samples to a plate structure in fast quenched samples. The substructure of the untransformed austenite adjacent to the martensite plates changed from planar dislocation arrays to dislocation tangles with increased quench rate. These results were explained using a model for ferrous martensite strengthening based upon the extent of carbon segregation to imperfections in the austenite during cooling.