Thermodynamic Properties of Y5Sn3 over a Wide Range of Temperature

The heat capacity and enthalpy of Y₅Sn₃ were investigated in the temperature range 58-2294 K for the first time. Values of the standard enthalpy, entropy, and reduced Gibbs energy of the stannide were calculated from the low-temperature heat capacity data. The temperature dependencies of the thermodynamic functions for the solid state of Y₅Sn₃ in the range 298.15-2300 K were found. The temperature, enthalpy, and entropy of melting of the compound were determined.     

Thermodynamic assessment of the Nb-N system

The phase equilibrium and thermodynamic information of the Nb-N system was reviewed and assessed by using thermodynamic models for the Gibbs energy of individual phases. Although there was a large amount of experimental information of the system, heat capacity data of the Nb₂N and NbN were not available either in low or high temperatures. In the present study, low-temperature heat capacity and the^o S ₂₉₈ values were estimated using estimated entropy Debye temperatures. Only the Nb₂N (hcp) and NbN (fcc) nitrides were considered to be the true binary phases and were included in the present evaluation in addition to the N₂ gas, liquid, andα-solid solution (bcc). Three thermodynamic models were used: a two-sublattice model for the solid solution phases, a substitutional model for the liquid phase, and an ideal-gas model for the N₂ gas. The model parameters were evaluated by fitting to the selected data by means of a computer program. A consistent set of parameters was obtained which satisfactorily described most of the experimental and estimated data.     

Isothermal section of the ternary Sn-Cu-Ni system and interfacial reactions in the Sn-Cu/Ni couples at 800 °C

The isothermal section of the Sn-Cu-Ni system at 800 °C has been experimentally determined. There is no ternary compound. A solid solution with a very wide compositional range, the γ phase is formed between the Ni₃Sn(H) phase and Cu₄Sn(H) phase; however, both of these two binary phases are not stable at 800 °C. The binary Ni₃Sn₂ phase also has extensive ternary solubility. The homogeneity ranges of both the γ and Ni₃Sn₂ phases are very large in parallel to the Cu-Ni side, but relatively narrow along the Sn direction. This phenomenon indicates that Cu and Ni are exchangeable in both phases. Three kinds of reaction couples, Sn-55 at. pct Cu/Ni, Sn-65 at. pct Cu/Ni, and Sn-75 at. pct Cu/Ni, were prepared and reacted at 800 °C for 5 to 20 minutes. The reaction paths are liquid/Ni₃Sn₂/γ/Ni₃Sn(L)/Ni for the Sn-55 at. pct Cu/Ni and Sn-65 at. pct Cu/Ni couples, and the reaction path is liquid/γ/Ni₃Sn(L)/Ni for the Sn-75 at. pct Ni couples.     

Microstructure and mechanical properties of as-cast and heat treated Mg-15Gd-3Y alloy

The microstructure evolution and mechanical properties of Mg-15Gd-3Y alloy were investigated in the as-cast and heat treated conditions.The microstructure evolution from as-cast to cast-T4 states involved α-Mg solid solution+Mg5(Gd,Y) phase→α-Mg supersatu-rated solid solution+rare earths compound Mg3(Gd1.26,Y0.74)→α-Mg supersaturated solid solution+rare earths compound Mg3(Gd0.745,Y1.255).It showed that 480 oC/4 h was the optimal solution treatment parameter.If the solution temperature was high or the holding time was long,such as 520 oC/16 h,an overheating phenomenon would be induced,which had a detrimental effect on the mechanical properties.When age-ing at 225 and 200 oC,the alloy would exhibit a significant age-hardening response and great long-time-age-hardening potential,respectively.The best mechanical properties were obtained at the parameters of 480 oC/4 h+225 oC/16 h,with the UTS of 257.0 MPa and elongation of 3.8%.     

Electron microscope study on martensitic transformations in Fe- Pt alloys: General features of internal structure

Martensitic transformations of Fe-Pt alloys near the composition of Fe₃Pt with various degrees of order were examined systematically mainly by transmission electron microscopy. This alloy system exhibits two types of martensitic transformations, fcc-bct (bcc) and fcc-fct. The present experimental results indicate that each transformation is independent and compctitive. As the degree of order of austenite (L1₂ superlattice) increases, the dislocation density of bct (bcc) martensite is remarkably reduced and the shape of internal twins is changed, which is closely related to the thermoelastic behavior and the reversibility of the transformation.     

Electron Microscopic Study on the Suction Cast In Situ Ti-Fe-Sn Ultrafine Composites

The current investigation reports detailed study on the microstructural evolution in the suction cast hypereutectic Ti₇₁Fe_29?x Sn _x alloys during Sn addition with x = 0, 2, 2.5, 3, 3.85, 4.5, 6, and 10 at. pct and the solidification of these ternary alloys using SEM and TEM. These alloys have been prepared by melting high-purity elements using vacuum arc melting furnace under high-purity argon atmosphere. This was followed by suction casting these alloys in the water-cooled split Cu molds of diameters, ? = 1 and 3 mm, under argon atmosphere. The results indicate the formation of binary eutectic between bcc solid solution ??-Ti and B2 FeTi in all alloys. ??-Ti undergoes eutectoid transformation, ??-Ti ?? ??-Ti + FeTi, during subsequent solid-state cooling, leading to formation of hcp ??-Ti and FeTi. For alloys x < 2, the primary FeTi forms from the liquid before the formation of eutectic with minute scale Ti₃Sn phase. For alloys with 2 ?? x ?? 10, the liquid is found to undergo ternary quasi-peritectic reaction with primary Ti₃Sn, L+Ti₃Sn ?? ??-Ti+FeTi, leading to formation of another kind of FeTi. In all the other alloy compositions (3.85 ?? x ?? 10), Ti₃Sn and FeTi dendrites are observed in the suction cast alloys with profuse amount of Ti₃Sn being formed for alloys with x ?? 4.5. The current study conclusively proves that the liquid undergoes ternary quasi-peritectic reaction involving four phases, L + Ti₃Sn ?? ??-Ti + FeTi, which lies at the invariant point Ti_69.2±0.8Fe_27.4±0.7Sn_3.4±0.2 (denoted by P). Below P, there is one univariant reaction, i.e., L ?? ??-Ti + FeTi for all alloy compositions, whereas above P, liquid undergoes one of the univariant reactions, i.e., L + ??-Ti ?? Ti₃Sn (Sn = 2, 2.5, 3, and 4.5 at. pct) or L + FeTi ?? Ti₃Sn for alloys (Sn = 6, 10 at. pct). For alloy with Sn = 3.85 at. pct, the ternary quasi-peritectic reaction is co-operated by two monovariant eutectic reactions, i.e., L ?? ??-Ti + FeTi below P and L ?? FeTi + Ti₃Sn above P. Detailed microstructural information allows us to construct liquidus projection of the investigated alloys. The results are critically discussed in the light of available literature data.     

Study on Red Long-Time Luminescent Material Y2O2S:Eu,M (M = Mg,Ca, Sr,Ba)

The red long-time luminescent material Y₂O₂S:Eu³⁺, M (M = Mg, Ca, Sr, Ba) was prepared by high temperature solid-state method. The XRD result of the sample showed that the crystal phase was Y₂O₂S, which belong to hexagonal system, and no new crystal phase were by doping different amount of Mg, Ca, Sr, Ba. The excitation spectrum was a broad band within 200 × 400 nm region, the characteristic peaks of emission spectrum were located at 583, 595, 597, 617, 627, 707 nm. There was no marked change in excitation spectra, emission spectra and maximum of their wavelengths of the luminescent materials by doping with different ions. The luminescent intensity of the phosphors were stronger when the concentration of doping ions was Mg/Y = 6%, Ca/Y = 4%, Sr/Y = 8%, Ba/Y = 2.5%, respectively. Its sequence of luminescent intensity from high to low is Sr > Ba > Mg > Ca.     

Entropy and free energy at the hcp-bcc transformation temperature in metals and alloys

It has been shown that a plot of the Φ function, defined by — (G _tr — G_o)/T_tr where G_tr andG _o are respectively the Gibb’s free energies at the hcp → bcc allotropie transformation temperature(T _tr ) and at absolute zero, vs the entropy (S_tr) of the hcp phase at T_tr is linear. This concept of the Φ function and its relation toS _tr can be extended to alloys with the aid of the ‘central atoms’ solution model. Its use has been demonstrated with respect to the Ti-Zr system where the estimated transformation temperatures are shown to be within the (hcp + bcc) phase field.     

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.     

Directional Solidification and Liquidus Projection of the Sn-Co-Cu System

This study investigates the Sn-Co-Cu ternary system, which is of interest to the electronics industry. Ternary Sn-Co-Cu alloys were prepared, their as-solidified microstructures were examined, and their primary solidification phases were determined. The primary solidification phases observed were Cu, Co, Co₃Sn₂, CoSn, CoSn₂, Cu₆Sn₅, Co₃Sn₂, γ, and β phases. Although there are ternary compounds reported in this ternary system, no ternary compound was found as the primary solidification phase. The directional solidification technique was applied when difficulties were encountered using the conventional quenching method to distinguish the primary solidification phases, such as Cu₆Sn₅, Cu₃Sn, and γ phases. Of all the primary solidification phases, the Co₃Sn₂ and Co phases have the largest compositional regimes in which alloys display them as the primary solidification phases. There are four class II reactions and four class III reactions. The reactions with the highest and lowest reaction temperatures are both class III reactions, and are L + CoSn₂ + Cu₆Sn₅  =  CoSn₃ at 621.5 K (348.3 °C) and L + Co₃Sn₂ + CoSn = Cu₆Sn₅ at 1157.8 K (884.6 °C), respectively.     

Experiments on the aging of Sn–Ag–Cu solder alloys

Abstract

The microstructural stability of the Sn–3·8%Ag–0·7%Cu solder alloy was investigated by studying microstructural changes caused by heating small samples for various times, up to 1000 h, at 150°C. The first change, evident at high magnification after heating for 1 h, occurred from the as cast lamellar plus fibrous form of the Ag₃Sn and Cu₆Sn₅ interdendritic eutectic phases to a particulate form. With further heating, coarsening of the two compound phases occurred, gradually rendering the Sn dendrite pattern less distinct. Due to the very rapid diffusion of Cu in solid Sn, the Cu₆Sn₅ phase coarsened most rapidly, growing from its originally finely divided (200 nm) size in the ternary eutectic to form many particles up to 3 m m or more in size in a time of 100 h. At that time, nearly 50% of the total Cu was contained in these particles. The Ag₃Sn phase coarsened more slowly. Approximate measurements of average particle size as a function of time suggested that coarsening occurs by Ostwald ripening, controlled by diffusion in the Sn phase.     

Thermodynamic study and the phase diagram of the Mg-Sn system

By means of concentration cells of the following type, Mg (l)MgCl2 in (LiCl-KCl)_eut (l)Mg-Sn (1), the partial thermodynamic data of Mg in Mg-Sn liquid solutions have been obtained in the composition range of 0.1 ≤X _Mg ≤ 0.75 and at temperatures from 950 to 1100 K. These values are compared with thermodynamic data reported in the literature and used for the evaluation to obtain a complete set of thermodynamic functions for phase diagram calculations and for further interpretation by the associate model. This model, which accepts the existence of ‘Mg₂Sn as-sociates’ in the liquid alloys, enables calculations of viscosity by Kucharski’s method corre-lating properly with experimental data. Mutual correlations between thermodynamic properties, physical properties, structure, and the phase diagram of the Mg-Sn system were shown to in-dicate a maximum chemical short-range order close to the composition Mg2Sn.     

Observations on the microstructure and orientation relations in the vanadium-hydrogen system

Observations on the microstructure and orientation relations in the V-H system were made using optical, X-ray, and electron microscopy techniques. In the two phase α+ β region the axes of the β (bct) vanadium hydride were shown to be slightly tilted away from the cube axes of the α (bcc) vanadium. Metallographie observations of a polished (100) crystal showed two different surface features associated with the formation of the β hydride depending on the concentration. In the two phaseβ + γ region the orientation relation between the β(bct) phase and the γ (fcc) phase is such that the (100)_γ || (110)r and [001]_γ || [001]_γ.     

Thermodynamic Properties of Si - Mn - Y System Alloys

High-temperature isoperibolic calorimetry has been used to measure the partial enthalpies of mixing for yttrium in the Si - Mn - Y ternary system at 1775 K along sections with various atomic ratios of silicon to manganese (0.85/0.15; 0.7/0.3; 0.6/0.4; 0.5/0.5; 0.3/0.7) for yttrium concentrations in the range 0 < x_Y < 0.4 together with the partial molar enthalpies of manganese for x_Si/x_Y = 0.8/0.2. The integral enthalpies of mixing have been calculated from the partial ones for yttrium by Darken’s method. The addition of yttrium to the Si - M binary system to give the ternary Si - Mn - Y system increases the exothermic effects of the alloying substantially. There is a substantial effect on the thermodynamic parameters of the ternary alloys from the atomic interactions in the Si - Y and Si - Mn binary systems.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 64–69, March–April, 2005.     

Elastic Properties,Thermal Expansion Coefficients,and Electronic Structures of Mg and Mg-Based Alloys

Ab-initio density functional theory (DFT) calculations were performed to study alloying effects on hcp Mg. The alloy solid solution strengthening represented by bond strength enhancement in alloys, elastic properties, thermal expansion coefficients, and electronic structures of Mg-based alloys was investigated. Results show that alloying additions with sp-metal Al and rare earth (RE) Y are capable of increasing the bond strength, with the addition of Y achieving a better effect. The bond strength enhancement due to an RE Y addition is associated with a hybridization between the d-orbital of Y and the p-orbital of the Mg atoms near the Fermi energy, and this was consistent with the electron localized function (ELF) evaluations showing that more localized and stronger covalent bonds are formed between Y and Mg atoms. It is also found that alloying additions of Al, Zn, and Y are not capable of increasing elastic coefficients and moduli, indicating that bond strength enhancement could play a major role in alloy solid solution strengthening in Mg-based alloys. Possible reasons for the elastic properties accompanying the alloying addition are given from the electronic point of view. Furthermore, from the calculated negative Cauchy pressure (C ₁₃ – C ₄₄ < 0), it is concluded that the chemical bonds between Y and Mg atoms show angular characteristics.     

Electrochemical co-reduction of Y(III) and Al(III) in a fluoride molten salt system and electrolytic preparation of Y–Al intermediate alloys

In this study, a molten salt co-reduction method was proposed for preparing Y–Al intermediate alloys and the electrochemical co-reduction behaviors of Y(III) and Al(III) and the reaction mechanism of intermetallic compound formation were investigated by transient electrochemical techniques. The results show that the reduction of Y(III) at the Mo electrode is a reversible electrochemical process with a single-step transfer of three electrons, which is controlled by the mass transfer rate. The diffusion coefficient of Y(III) in the fluoride salt at a temperature of 1323 K is 5.0238 × 10^?3 cm²/s. Moreover, the thermodynamic properties associated with the formation of Y–Al intermetallic compounds were estimated using a steady-state electrochemical method. Y–Al intermediate alloy containing 92 wt% yttrium was prepared by constant current electrolysis at 1323 K in the LiF–YF₃–AlF₃–Y₂O₃ (6 wt%)–Al₂O₃ (1 wt%) system at a cathodic current density of 8 A/cm² for 2 h. The Y–Al intermediate alloy is mainly composed of α-Y₂Al and Y phases. The development and application of this innovative technology have solved major technical problems, such as a long production process, high energy consumption, and serious segregation of alloy elements at this stage.     

A Comparative Study on the Microstructure and Mechanical Properties of Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> and Cu<Subscript>3</Subscript>Sn Joints Formed by TLP Soldering With/Without the Assistance of Ultrasonic Waves

In this study, the microstructure and mechanical properties of Cu₆Sn₅ and Cu₃Sn intermetallic joints, formed by the transient liquid phase (TLP) soldering process with and without the assistance of ultrasonic waves (USWs), were compared. After the application of USWs in the TLP soldering process, Cu-Sn intermetallic compounds (IMCs) exhibited a novel noninterfacial growth pattern in the molten solder interlayer. The resulting Cu₆Sn₅ and Cu₃Sn joints consisted of refined equiaxed IMC grains with average sizes of 3 and 2.3 µm, respectively. The Cu₆Sn₅ grains in the ultrasonically soldered intermetallic joints demonstrated uniform mechanical properties with elastic modulus and hardness values of 123.0 and 5.98 GPa, respectively, while those of Cu₃Sn grains were 133.9 and 5.08 GPa, respectively. The shear strengths of ultrasonically soldered Cu₆Sn₅ and Cu₃Sn joints were measured to be 60 and 65 MPa, respectively, higher than that for reflow-soldered intermetallic joints. Ultrasonically soldered Cu₆Sn₅ and Cu₃Sn joints both exhibited a combination of transgranular and intergranular fractures during shear testing.