大型真空感应熔炼炉VIDP的发展

VIDP炉(Vacuum Induction Degassing and Pouring Furnace)的熔炼室体积比同等容量常规VIM炉(Vacuum Induction Melting Furnace)小,缩短了抽真空时间和熔炼周期。小体积熔炼室便于温度压力控制、回收易挥发元素和准确控制合金成分。较长的流道也是VIDP炉的重要部件,具有精炼功能。VIDP炉的模块化设计和装配,可连接各种浇注设备,包括常规锭浇注,电极浇注或连铸。     

Enhancing strength and ductility in back extruded WE71 magnesium alloy cylindrical parts by introduction of multi-direction forging process

Magnesium cylindrical parts have relatively poor mechanical properties and distinct anisotropy of microstructure,which hinder their application as structural components.To improve the performance of WE71 cylindrical parts,multi-direction forging(MDF) was introduced before back extrusion,and the microstructure and mechanical properties were investigated.Results of microstructure show that the grain size in the outer of the cylindrical bottom is refined from 30.1 to 27.7 μm,the micro structure is ...     

Tb~(3+) substituted strontium hexaferrites:Structural,magnetic and optical investigation and cation distribution

In this study,SrFe_(12-x)Tb_xO_(19)(0.00≤x≤0.1) hexaferrites(HFs) were prepared successfully by citrate solgel approach.X-ray powder diffraction analyses affirm the hexagonal structure of products.Impurity phase starts to appear for x≥0.04.The crystallites sizes were estimated to be in the range of 33-46 nm.All the products exhibit inhomogeneous distribution of grain size detected through SEM.The analyses of magnetization versus applied magnetic field,M(H),were performed.Magnetization measurements were done at room(300 K;RT) and low(10 K) temperatures.The different magnetic parameters including saturation magnetization M_s,remanence M_r,squareness ratio(SQR=M_r/M_s),coercivity H_c,and magnetic moment n_B are deduced and discussed in detail.At both considered temperatures,M(H) results show ferrimagnetic nature for all compositions.It is shown that the Tb substitutions significantly affect M(H)data.A significant increase in the M_s,M_r,and n_B is observed for x=0.02 sample.The SQR values are around 0.5 indicating the single domain nature with uniaxial anisotropy.The obtained magnetic results were investigated deeply with relation to structural and microstructural properties.Mossbauer spectroscopy results were also investigated.According to Mossbauer results,the Tb~(3+) ions preferentially occupy 12 k and 4f_2 sites.     

贝氏体区等温时间对低硅TRIP钢组织和力学性能的影响

研究了0.15C-1.5Mn-1.5Al-0.3Si TRIP钢820℃2 min加热后快冷至450℃盐浴中保温5～300s空冷的组织和力学性能。结果表明,随在贝氏体转变区450℃等温时间的增加,该钢的屈服强度和伸长率增加,抗拉强度降低,等温时间60s时强塑积最佳,为23 000MPa%;等温时间≤60s时随等温时间增加钢中残余奥氏体含量增加,>60s时随等温时间的增加钢中残余奥氏体含量降低,60s时钢中残余奥氏体达到最高值,为14%。     

Thermochemical Study on Coordination Complex of Samarium with Salicylic Acid and 8-Hydroxyquinoline

It is knownthat rare earthions ,8-hydroxyquino-line and salicylic acid are antibacterial[1 ～5].Synthesisand characterization of the rare earth complexes withsalicylic acid were reported by Sun[6].Synthesis andcharacterization of the rare earth complexes …     

Effect of thulium substitution on conductivity and dielectric belongings of nanospinel cobalt ferrite

The CoTm_x Fe_(2-x) O_4(x≤0.1) NPs were synthesized sonochemically.X-ray powder diffraction patterns and TEM images of the samples prove their chemical purity and cubic structure-morphology,respectively.Some substitution ratio of thulium ions to cobalt ferrites have an important effect on the characteristic evaluation of both electrical and dielectric characteristic measured at frequencies up to 3.0 MHz between room temperature and 120℃.Since the thulium substitution has a very strong effect on the characteristic evaluation of both electrical and dielectric properties of cobalt-ferrite samples,four substitutio nal ranges-none,small,medium and high were determined for the interpretation of contribution of thulium ratio to ac/dc conductivity,dielectric constant,dielectric loss and tangent loss.Conductivity increases with the incremental frequencies,in general depending on a variety of tendencies of both temperature and substitutional Tm ratios while the activation energy varies with a high dependency to the regional level of Tm substitution in Co-ferrites NPs.The Arrhenius graph appears to provide us with a single activation energy much higher than 400 meV for x=0.02,which can be attributed to electron hopping mechanisms,apart from other substituted spinel ferrites.     

Determination of the Phase Equilibria in the Mn-Sn-Zn System at 500 °C

The isothermal section of the Mn-Sn-Zn system at 500 °C was determined with 20 alloys. The alloys were prepared by melting the pure elements in evacuated quartz capsules. The alloy samples were examined by means of X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. A new ternary phase Mn₄Zn₈Sn (λ) was found to have a bcc structure with a lattice parameter a = 0.92508 (5) nm. Its composition range spans 25 to 35 at. pct Mn, 4 to 8 at. pct Sn, and 55 to 70 at. pct Zn. The Zn is substituted for Mn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂. The solubility of Zn in Mn₃Sn, Mn₂Sn, and Mn₃Sn₂ was measured to be about 17, 12, and 4 at. pct, respectively. The phase boundaries of the liquid and β-Mn phases were well established. The following 3 three-phase equilibria were well determined: (1) β-Mn + ε-MnZn₃ + Mn₃Sn, (2) λ + Mn₃Sn + Mn₂Sn, and (3) L + λ + Mn₂Sn. The additional 5 three-phase equilibria, which are ε-MnZn₃ + λ + Mn₃Sn, ε ₁-MnZn₃ + ε-MnZn₃ + λ, ε ₁-MnZn₃ + λ + L, Mn₂Sn + L + MnSn₂, and Mn₃Sn₂ + MnSn₂ + Mn₂Sn, were deduced and shown with dashed lines in the present isothermal section.     

Thermodynamic modeling of binary and ternary metallic solutions

A model is proposed for describing heat of mixing behavior in binary and ternary metallic solutions. The binary model, which has the form, ΔH ^M =α₁ X _A ² X _B +α₂ X _A X _B ² −α₃ X _A ² X _B ² , whereX _A andX _B are mole fractions of componentsA andB and α₁, α₂, and α₃ are constants, is applied to the heat of mixing values for 84 solid and liquid systems and the results are compared with the subregular model. The ternary model, which is composed of the sum of the binary equations and a ternary interaction term of the form α _ABC X _A X _B X _C , was applied to the Bi−Cd−Pb, Cd−Pb−Sn, and Cd−Pb−Sb systems. There was excellent agreement both as to the shapes of the isoenthalpy of mixing curves and as to the heat of mixing values in the ternary systems when the model was used to predict the experimental values.     

模拟控轧控冷过程含Nb超低碳钢的组织演变

用Thermecmastor-Z型热模拟机模拟试验了成分(%)为:0.03C-1.05Mn-0.6Cr-0.08Nb的Nb超低碳钢加热1 200℃后冷至850℃压缩变形50%,并在850℃下保温20~1 000 s后快冷至450℃,再空冷的过程中的组织演变。试验结果表明,随50%变形后保温时间的延长,钢中针状铁素体及贝氏体数量减少,多边铁素体数量增加,马氏体-奥氏体(M-A)岛尺寸增大,组织中位错密度降低;当50%变形后,保温时间>50 s时,显微硬度(Hv10)值快速下降,保温时间≥500 s时,Hv10值下降较慢。     

Preparation and thermoelectric properties of ternary rare earth sulfide γ-Ce3–xEuxS4

The effect of Eu-substitution on the density and thermoelectric properties of ternary sulfide Ce_3–xEu_xS₄ (0≤x≤0.8) compacts was investigated. Ce_3–xEu_xS₄ powders were prepared via the sulfurization of the oxide using CS₂ gas at 1473 K. The pressureless sintered Ce_3–xEu_xS₄ compacts in the atmosphere were crystallized in the γ-phase. The density of the Ce_3–xEu_xS₄ compacts increased with the increasing of Eu-substitution. Eu-substitution yielded a higher Seebeck coefficient and lower electrical resistivity. The highest value of the thermoelectric power factor of 1.41×10⁻⁴ W/K²m was obtained for the Ce_2.2Eu_0.8S₄ compact at 673 K. It indicated that Eu-substitution was effective for improving thermoelectric properties of Ce_3–xEu_xS₄.     

High temperature thermodynamic properties of the chromium carbides Cr7C3 and Cr3C2 determined using a galvanic cell technique

The standard free energies of formation of Cr₇C₃ and Cr₃C₂ have been obtained from emf measurements on the following galvanic cells with BaF₂-BaC₂ solid solutions as the electrolyte: Cr,Cr₂₃C₆∣BaF-BaC₂∣Cr₂₃C₆,Cr₇C₃ (920 to 1250 K) (A) Cr₂₃C₆, Cr₇C₃ ∣BaF₂-BaC₂∣W, WC (900 to 1200 K) (B) WC, W∣BaF₂-BaC₂∣Cr₃C₂, Cr₇C₃ (973 to 1173 K) (C) Combining the results of this study with a previous work¹⁵ and those of Kulkarniet al. and Dawsonet al., the following equations for ΔG _f ^ℴ of Cr₇C₃ and Cr₃C₂ have been determined: from cell (A): ΔG _Cr7C3 ^o (±2300) = −155410(±173) − 35.8(±0.1)T joules; from cell (B): ΔG _Cr7C3 ^o (±2000) = −155585(±385) − 35.8(±0.4)T joules for the reaction 7Cr + 3C = Cr₇C₃; from cell (C): ΔG _Cr3C2 ^o , (±1200) = −92860(±210) − 19.4(±0.2)T joules for the reaction 3Cr + 2C = Cr₃C₂.     

Isothermal Phase Transformation in Biomedical Co-29Cr-6Mo Alloy without Addition of Carbon or Nitrogen

The isothermal phase transformation behavior in a biomedical Co-29Cr-6Mo alloy without carbon or nitrogen was investigated during aging at temperatures between 973 K and 1273 K (700 °C and 1000 °C) for up to 90 ks. Transformation from the γ to the ε phase did not occur at 1273 K (1000 °C) as the γ phase was more stable than the ε phase, and the σ phase precipitated at the γ grain boundaries. At 1173 K (900 °C), a γ → ε ₁ phase transformation occurred by massive precipitation. Prolonged annealing at 1173 K (900 °C) led to a lamellar structure of ε ₂ and σ phases at ε ₁/ε ₁ boundaries by a discontinuous/cellular reaction, expressed by the reaction equation ε ₁ → ε ₂ + σ. After decreasing the aging temperature to 973 K (700 °C), transformation from the γ to the ε phase occurred mainly by isothermal martensitic transformation, but a lathlike massive ε ₁ phase and ε ₂/σ lamellar colonies were also observed at the original γ-grain boundaries. It is likely that not adding carbon results in the promotion of the massive transformation and the precipitation of the σ phase during isothermal aging in the Co-29Cr-6Mo alloy system, whose composition corresponds to the ASTM F75 standard for metallic materials for surgical implantation. The resultant isothermal transformation behavior of the present alloy is described on the basis of thermodynamic calculations using Thermo-Calc.     

Ductile and High Strength White Cast Iron of Ultrafine Interconnected Network Morphology

Fe_100–x C _x melts (x = 18 to 24) can be cast under B₂O₃ flux into solids of interconnected network morphology, with a wavelength in the submicron range. There are two major constituent subnetworks, which are a brittle Fe₃C subnetwork and a ductile αFe subnetwork. The Fe_100–x C _x network alloys, therefore, are white cast iron of novel microstructure. Fe_100–x C _x specimens of x = 18 to 21 are ductile and the yield strength can be as large as ~3200 MPa. Fe_100–x C _x specimens of x = 22 to 24 are in the regime of a ductile-to-brittle transition. The compressive strength is high, at ~2700 MPa. Microstructural analysis indicates that the ultrafine network morphology and the ductile αFe subnetwork are responsible for the ductility exhibited in Fe_100–x C _x network alloys of x = 17 to 21. They are also responsible for the high compressive strength in Fe_100–x C _x network alloys of x = 22 to 24.     

The C.L.m-δ equation of superplasticity

In the fundamental equation of superplastic flow, σ = kέ^m, έ is the strain rate, σ is the flow stress,m is the strain-rate sensitivity index of flow stress, andk is a material constant. Bothm andk vary with increase in strain (δ). Therefore, we can have m0 (≠0), m_I (m_I1,m,_I2,m_I3,....), m_F; k₀ (≠0), k_I (k_I1,k_I2,k_I3,.... ), k_F values corresponding to the initial strain δ₀ (= 0.00 pct), the strain at any instant during stretching, δ_I (δ_I1, δ_I2, 8δ_I3,....), and the total elongation, δ_F, at fracture, respectively. The curves expressing the dependence ofm andk on δ can be called them-k- δ orm-C- δ or simply them- δ curves. All these curves can be classified into types and can be expressed by the C. L.m- δ equation derived by the present author: δ(pct) = [Cέ^{(m- m0} - 1] × 100 whereC = k₀ + dk₀/k₀,m = m₀ andC = k₀/k₀ = 1, when δ = δ₀;m = m_I, andC = C_I = k_I/k₀ when δ= δ_I;m = m_F andC = C_F = k_F/k₀, when δ = δ_F. By means of this equation, not only the total elongation at fracture but also the strains at any instant during stretching of a material can be predicted, if the correspondingm values are known.     

Tetragonal distortion field of hydrogen atoms in iron

The difference between the chemical potentialμ _σ of hydrogen atoms producing a nonspherical symmetry strain in a solid sample under stress and that μ₀ corresponding to the state without stress has been calculated. It is shown that μ_σ - μ₀ = -VΣiσ_iε _ii ^′ =U whereσ _i stands for principal stress,ε _ii ^′ for the strain component along the direction of the principal stress,V for volume, andU is the interaction energy between the strain field and external stress field. The hydrogen atoms producing the tetragonally symmetric strain are preferentially ordered in samples under stress. As a result, the variation of hydrogen concentration with tensile stress σ will be different from that with compressive stressσ*. For a general polycrystal the formulas are, respectively,C _ten =C ₀ exp[(0.70089ε₁₁ + 0.2991lε₂₂)Vσ/RT]andC _com =C ₀ exp[(0.14956ε₁₁ + 0.85044ε₂₂)Vσ*/RT], whereC _ten.,C _com., andC ₀ are, respectively, the hydrogen concentrations under tensile stress, compressive stress, and without stress; R stands for the gas constant andT for absolute temperature. Hence, ε₁₁/ε₂₂ may be determined in terms ofC _ten/C _com which can be obtained by hydrogen permeation measurement. For example, according to Bockris' data ε₁₁/ε₂₂ = 1.27 at temperature of 27 °C which implies that the strain field of hydrogen atoms inα-Fe is nonspherical symmetry. For a torsional stressτ,U _tor = -0.55133V _τ(ε₁₁ ε₂₂. The interaction can result in the enrichment of hydrogen atoms on and hydrogen induced delayed cracking along the planes inclined at an angle ofα = 45 deg to torsional axis, which was observed in precharged smooth torsional or type III cracked specimens made of ultra-high strength steel.     

Electrical conductivity of REF_3-LiF(RE=La and Nd) molten salts

The electrical conductivity of REF3-LiF(RE=La and Nd) molten salts(xREF_3=5 mol%-40 mol%) was systematically measured over the temperature range from 1223 to 1423 K by using continuously varying cell constant(CVCC) method.Electrical conductivity values of LaF3-LiF and NdF_3-LiF molten salts within the studied ranges are 4.11-9.39 and 3.62-9.51 S/cm,respectively.The composition and temperature dependences of electrical conductivity and the factor of RE_2 O_3 on electrical conductivity were investigated.The electrical conductivity nonlinearly decreases with the increasing mole percent of REF_3 for the changing of structural ion in molten salts.A good linear relationship between the natural logarithm of electrical conductivity(lnκ) and the reciprocal of the absolute temperature(T~(-1)) can be interpreted by the trend that electrical conductivity linearly increases with increasing temperature.Although it is an important factor of RE_2 O_3 on electrical conductivity,the influence of RE_2 O_3 on conductivity is small for the very limited solubility of RE_2 O_3 in REF_3-LiF molten salts.The results of this work supplement the present electrical conductivity data of rare earth fluoride electrolyte.