Deformation and fracture of Cu-SiO2 bicrystals with [011] twist boundaries

Several kinds of Cu-SiO₂ bicrystals having [011] twist boundaries with different misorientation angles were tensile tested at various temperatures from 473–1023 K at strain rates from 4.2 × 10⁻⁵–4.2 × 10⁻³ s⁻¹ in vacuum. Most of bicrystals fractured intergranularly. The grain-boundary strength and fracture behavior of the Cu-SiO₂ bicrystals strongly depended on the grain-boundary character, temperature and strain rate. As the misorientation angle or grain-boundary energy increases, grain-boundary fracture takes place more easily at lower temperatures with lower fracture stresses. Furthermore, fracture stress and elongation to fracture decrease almost monotonically with increasing temperature and decreasing strain rate. The observed grain-boundary character and test condition dependence of grain-boundary strength can be understood reasonably by considering the occurrence of stress-concentration sites around the grain-boundary SiO₂ particles to form voids and cracks caused by grain-boundary sliding.     

Sliding of copper [001]-twist grain boundaries detected by shear deformation of liquid B2O3 particles on the grain boundaries

From a Cu–0.065mass%B solid solution alloy, bicrystals having [001]-twist grain boundaries with various misorientation angles were prepared by the Bridgman method. Cu bicrystals containing B₂O₃ particles were made from the bicrystals by internal oxidation treatment. The Cu–B₂O₃ bicrystals were tensile tested at high temperatures, where B₂O₃ particles become liquid. The amount of grain-boundary sliding was measured from the amount of shear deformation of the liquid B₂O₃ particles on a sliding grain boundary. Shear deformation of voids where the B₂O₃ particles was embedded was also utilized to measure the amount of grain-boundary sliding. The temperature and misorientation-angle dependence of the grain-boundary sliding is discussed for the Cu–B₂O₃ bicrystals. Since the liquid B₂O₃ particles easily deform at high temperatures, the measured amount of grain-boundary sliding is considered to reflect the inherent nature of the Cu [001]-twist grain boundaries. Using the present method of measurements, up to 2 μm grain-boundary sliding can be measured with an accuracy of about 0.1 μm.     

The inclination dependence of gold tracer diffusion along a Σ3 twin grain boundary in copper

Grain boundary impurity diffusion of Au in diffusion bonded Σ3〈011〉 Cu bicrystals has been studied by the radiotracer serial-sectioning technique using the ¹⁹⁵Au isotope with high specific activity. The dependence of the grain boundary diffusion parameter sδD_b on the inclination angle Φ of the grain boundary plane with respect to the close-packed (111) plane of the coherent twin boundary has been determined for the temperatures of 673 and 773 K (here s, δ and D_b are the segregation factor, the grain boundary width and the grain boundary diffusion coefficient, respectively). At both temperatures sδD_b exhibits a minimum at Φ=70.5° and a maximum at Φ=82.0°. It is shown that there is no direct correlation between the energy and diffusivity of the grain boundaries in this system and that the periodicity in the grain boundary plane has a significant influence on the grain boundary diffusivity.     

Microanalytical study of discontinuous precipitation and dissolution in Ni–4 at.% Sn: local and global characterization of the reactions

The morphology and kinetics of the discontinuous precipitation (DP) and discontinuous dissolution (DD) reactions have been studied in a Ni–4 at.% Sn alloy. High spatial resolution energy-dispersive X-ray microanalysis has been used to determine the Sn concentration profiles left behind the moving reaction front for the individual cells of the Sn-depleted α lamellae and Ni₃Sn compound. These data, combined with the local values of the reaction front velocity and the thickness of the α lamellae, have been used to evaluate the local sδD_b values (D_b is the grain-boundary chemical diffusion coefficient, δ is the grain-boundary thickness and s is the segregation factor). The obtained results have been compared with those calculated by the global approach to the DP and DD reactions, which is relevant for the whole population of the cells. It has been shown that the application of the local characterization of the DP and DD reactions removes essentially the differences between the sδD_b values calculated by the Petermann–Hornbogen equation and the equations of Cahn and Zięba–Pawłowski. Moreover, both sets of data do not show any substantial differences from the sδD_b values obtained from measurements of the tracer diffusion of tin along stationary grain boundaries in nickel.     

Bismuth segregation at copper grain boundaries

The dependence of Bi segregation on the grain-boundary (GB) geometry for various Bi concentrations in Cu at different temperatures is investigated systematically. The GB segregation of Bi in Cu(Bi) bicrystals was determined quantitatively using energy dispersive X-ray spectroscopy (EDS) in a dedicated scanning transmission electron microscope (STEM). The Miller indices of the corresponding GB planes were determined by high resolution transmission electron microscopy (HRTEM). The energies of all experimentally investigated GBs were calculated by atomistic computer simulations. Gibbs segregation free energies were determined from the experimentally measured amount of Bi segregation using the classical McLean segregation theory. The free energies decrease monotonically with increasing calculated GB energies. The Fowler–Guggenheim segregation theory yields an attractive interaction between the segregated Bi atoms. No Bi-induced changes in the bonding at the GBs could be detected by electron energy loss spectroscopy (EELS).     

Kinetics of diffusion induced grain boundary migration of [100] twist boundaries in the Cu(Zn) system

The kinetics of diffusion induced grain boundary migration (DIGM) in the Cu(Zn) system was experimentally studied for [100] twist boundaries using Cu bicrystals annealed at 693 K for various times between 5.4×10⁴ and 1.73×10⁵ s. The experiment was carried out for bicrystal specimens with misorientation angles of 15, 20, 23 (Σ13), 25, 28 (Σ17), 32, 37 (Σ5), 40, 44 (Σ29) and 45°. During DIGM, the grain boundary migrates rather unidirectionally towards one of the crystal grains for most of the specimens and becomes wavy with increasing annealing time. The migration distance at 5.4×10⁴ s is smaller for coincidence site lattice (CSL) boundaries with low energy than for random boundaries with high energy. The migration rate of the moving boundary was observed to be almost constant independent of the annealing time between 5.4×10⁴ and 1.73×10⁵ s. The steady state migration rate is larger for low-energy CSL boundaries than for high-energy random boundaries. The experimental results were quantitatively analyzed using the energy balance model proposed by Kajihara and Gust. In this analysis, the effective driving force for DIGM was calculated as a function of the migration rate. The calculation indicates that 75–93% of the chemical driving force is consumed by the volume diffusion of Zn in the untransformed Cu matrix ahead of the moving boundary under the given experimental conditions. Considering the energy consumption, the mobility M of the moving boundary was evaluated for the steady state stage. The evaluation yields M=6.6×10⁻¹⁷ m⁴/J s as the mobility of the random boundary for DIGM in the Cu(Zn) system at 693 K.     

Characteristic features of diffusion induced grain boundary migration for Σ9 [110] asymmetric tilt boundaries in the Cu(Zn) system

The characteristic features of diffusion induced grain boundary migration (DIGM) in the Cu(Zn) system were experimentally studied for [110] asymmetric tilt boundaries using Cu bicrystals annealed at 693 K for various times by a capsule zincification technique. The experiment was carried out for the boundaries with inclination angles of φ=0, 20, 35, 55, 65 and 90° and with a constant misorientation angle of θ=39° (Σ9). During annealing, the grain boundary migrates towards a crystal grain of larger coherency strain energy with higher probability due to DIGM. Taking elastic anisotropy of each crystal grain into consideration, the difference between the probabilities of grain boundary migration towards both side grains can be accounted for by the coherency strain model proposed by Hillert. The migration rate v of the moving boundary is almost constant regardless of the annealing time t between t=72 and 384 h (2.59×10⁵ and 1.38×10⁶ s). The value of v monotonically decreases with increasing inclination angle. This implies that the boundary diffusion coefficient of Zn in Cu is a monotone decreasing function of the inclination angle. The experimental results on the kinetics at the steady state stage were theoretically analyzed using the energy balance model proposed by Kajihara and Gust (Scripta mater., 1998, 38, 1621. The analysis indicates that the effective driving force Δ^efG for the grain boundary migration is merely one-thirtieth of the chemical driving force, whereas it still remains three times greater than the minimum value corresponding to the coherency strain energy during DIGM under the present experimental conditions. The mobility of the moving boundary was evaluated to be M=3.77×10⁻¹⁷ m⁴/Js from the values of v and Δ^efG according to the relationship M=v/Δ^efG. This value of M is close to the results estimated by Yamamoto et al. (Acta mater., 1999, 47, 1757) for the [100] twist and random boundaries in the Cu(Zn) system.     

Atomic-scale structure and chemistry of ceramic/metal interfaces—II. Solute segregation at MgO/Cu (Ag) and CdO/Ag (Au) interfaces

The first quantitative measurements of solute segregation at ceramic/metal (C/M) heterophase interfaces are presented for the MgO/Cu (Ag) and CdO/Ag (Au) systems. Interfaces are produced by internal oxidation of ternary alloys. Solute segregation at C/M interfaces is induced by intermediate-temperature annealing treatments. The Gibbsian interfacial excess of solute, Γ_solute, at these interfaces is determined in a direct, quantitative manner by atom-probe field-ion microscopy (APFIM). These measurements are complemented in the MgO/Cu (Ag) system by a composition analysis of this interface employing electron energy loss spectroscopy (EELS). Analyses of 15 {222} MgO/Cu (Ag) interfaces by APFIM show an average segregation level of (4.0±1.9)×10¹⁴ atoms/cm² or 0.22±0.10 effective monolayers at 500°C. Analyses of three {222} CdO/Ag (Au) interfaces show an average segregation level of (3.0±1.0)×10¹⁴ atoms/cm² or 0.22±0.07 effective monolayers at 400°C. Whereas {222} CdO/Ag (Au) interfaces in unannealed specimens show no evidence of gold segregation. These results are discussed in view of recent models of interfacial segregation.     

Structure and electronic properties of SiC thin-films deposited by RF magnetron sputtering

SiC thin-films were prepared by RF-magnetron sputtering technique(RMS) with the target of single crystalline SiC and then annealed. The surface morphology of thin-films was characterized by AFM. The result shows that the surface of the thin-films is smooth and compact; XRD analysis reveals that the thin-films are amorphous. The thickness, square-resistance and curves of resistance—temperature were measured. The results show that the curves of lnR versus 1/kT both before and after annealing satisfy the expression of lnR∝△W/kT, where ?W is electron excitation energy in the range of 0.014 2-0.018 5 eV, and it has a trend of increasing when the temperature is increased. After synthetical analysis we get the conclusion that the electronic mechanism of the thin-films is short distance transition between the localized states in the temperature range of 25-250 ℃. The resistivity is in the range of 2.4×10-3-4.4×10-3 Ω·cm and it has the same trend as electron excitation energy when annealing temperature is increased, which further confirms the electronic mechanism of thin-films and the trend of electron excitation energy versus annealing temperature.     

Structural evolution and grain growth kinetics of the Fe–28Al elemental powder during mechanical alloying and annealing

The structural evolution and grain growth kinetics of the Fe–28Al (28 at.%) elemental powder during mechanical alloying and annealing were studied. Moreover, the alloying mechanism during milling the powder was also discussed. During mechanical alloying the Fe–28Al elemental powder, the solid state solution named Fe(Al) was formed. The lattice parameter of Fe(Al) increases and the grain size of Fe(Al) decreases with increasing milling time. The Fe and Al particles were first deformed, and then, the composite particles of the concentric circle-like layers were generated. Finally, the composite particles were substituted by the homogeneous Fe(Al) particles. The continuous diffusion mixing mechanism is followed, mainly by the diffusion of Al atoms into Fe. During annealing the milled Fe–28Al powder, the order transformation from Fe(Al) to DO₃-Fe₃Al and the grain growth of DO₃-Fe₃Al occurred. The grain growth kinetic constant, K = 1.58 × 10⁻⁹ exp(−540.48 × 10³/RT) m²/s.     

Iron grain boundary diffusion in pure and in Cr,Fe and Zr-doped Ni3Al alloys

The grain-boundary diffusion (GBD) of ⁵⁹Fe in pure and in Cr-, Fe- and Zr-doped Ni₃Al alloys was studied at temperatures between 873 and 1273 K using the serial sectioning method. The grain-boundary diffusivities P (P is a product of grain-boundary width δ, and the diffusion coefficient in the grain-boundary D_b) were obtained from the penetration profiles using both the Le Claire’s analysis and direct fit of Suzuoka’s solution. The activation enthalpies of ⁵⁹Fe GBD were somewhat lower in comparison with analogous values for ⁵¹Cr GBD, reported in our previous paper.     

Comparison of interfacial reactions of Ni and Ni–P in extended contact with liquid Sn–Bi-based solders

A time dependence of the form t^1/n with n > 3 was observed for the thickening kinetics of the Ni₃Sn₄ scallops formed in both the Sn–58Bi/Ni and Sn–58Bi/Ni–P systems, which can be attributed to the radial growth kinetics of the Ni₃Sn₄ scallops and grain boundary diffusion due to the existence of molten channels between the previously formed Ni₃Sn₄ scallops. Evidence is presented suggesting that highly scattered pores within the Ni₃P layer play an important role in the seemingly random fluctuations of the Ni₃Sn₄ thickness in the Sn–58Bi/Ni–P system with respect to reaction temperature and time. By contrast, the thickness of the Ni₃Sn₄ layer in the Sn–58Bi/Ni system increased with increasing reaction temperature and time. Addition of 1 wt.% Cu into the basic Sn–58Bi solder led to the formation of (Cu,Ni)₆Sn₅, instead of Ni₃Sn₄, and hence significantly reduced the consumption rates of both the Ni and Ni–P layers during high-temperature storage. Pure electroplated Ni will not survive appreciably longer than electroless Ni–P when in contact with either molten Sn–58Bi or Sn–Bi–Cu.     

Cu基板退火处理的Cu/Sn58Bi/Cu钎焊接头界面微结构

研究了铜基板退火处理对Cu/Sn58Bi界面微结构的影响. 结果表明,在回流以及时效24 h后Cu/Sn58Bi/Cu界面只观察到Cu₆Sn₅. 随着时效时间的增加,在界面形成了Cu₆Sn₅和Cu₃Sn的双金属间化合物(IMC)层,并且IMC层厚度也随之增加. 长时间时效过程中,在未退火处理的铜基板界面产生了较多铋偏析,而在退火处理的铜基板界面较少产生铋偏析. 比较退火处理以及未退火处理的铜基板与钎料界面IMC层生长速率常数,发现铜基板退火处理能减缓IMC层生长,主要归因于对铜基板进行退火处理能够有效的消除铜基板的内应力与组织缺陷,从而减缓Cu原子的扩散,起到减缓IMC生长的作用.     

Influence of Zinc on Coarsening of δ-Ni<Subscript>2</Subscript>Si Particles,Aging Behavior and Hardness in a Cu-Ni-Si Alloy

In the present paper, the aging precipitation and coarsening of disk-like δ-Ni₂Si particles in Cu and Cu-10Zn alloys aged at 450 °C have been investigated by hardness, electric resistivity measurement and transmission electron microscopy observation. The coarsening dynamics of the average diameter of the δ-Ni₂Si particles coincides with the t ^1/3 time law for both alloys. The coarsening of the diminution of supersaturation related to aging time t coincides with the t ^?1/3 time rule. Adding Zn to the Cu-Ni-Si alloy increases the growth and coarsening rate of the particles mainly because of the increased diffusivity D of the δ-Ni₂Si particles in the matrix. The value of D of the δ-Ni₂Si particles in the Cu-xZn (x = 0, 10 wt.%) matrix and the Cu/δ-Ni₂Si interfacial energy γ are independently calculated by using the Lifshitz–Slyozov–Wagner theory which was extended to include disk-like particles by Boyd and Nicholson. The values of D and γ increase from 0.77 × 10^?19 to 2.21 × 10^?19 m²/s and 0.19 to 0.63 J/m², respectively, when Zn is added to the Cu-Ni-Si alloy. These calculations and the analysis show that the properties of Cu-Ni-Si-Zn alloy can significantly be enhanced by reducing the aging temperature.     

Effect of adding 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder alloy on the intermetallic formations with Cu-substrate during soldering and isothermal aging

Intermetallic compound (IMC) formations of Sn–2.8Ag–0.5Cu solder with additional 1 wt% Bi were studied for Cu-substrate during soldering at 255 °C and isothermal aging at 150 °C. It was found that addition of 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder inhibits the excessive formation of intermetallic compounds during the soldering reaction and thereafter in aging condition. Though the intermetallic compound layer was Cu₆Sn₅, after 14 days of aging a thin Cu₃Sn layer was also observed for both solders. A significant increase of intermetallic layer thickness was observed for both solders where the increasing tendency was lower for Bi-containing solder. After various days of aging, Sn–2.8Ag–0.5Cu–1.0Bi solder gives comparatively planar intermetallic layer at the solder–substrate interface than that of the Sn–2.8Ag–0.5Cu solder. The formation of intermetallic compounds during aging for both solders follows the diffusion control mechanism and the diffusion of Cu is more pronounced for Sn–2.8Ag–0.5Cu solder. Intermetallic growth rate constants for Sn–2.8Ag–0.5Cu and Sn–2.8Ag–0.5Cu–1.0Bi solders were calculated as 2.21 × 10⁻¹⁷ and 1.91 × 10⁻¹⁷ m²/s, respectively, which had significant effect on the growth behavior of intermetallic compounds during aging.     

Sb(V) removal from copper electrorefining electrolyte: Comparative study by different sorbents

Removal of Sb(V) from copper electrolyte by different sorbents such as activated carbon, bentonite, kaolin, resin, zeolite and white sand was investigated. Adsorption capacity of Sb(V) removal from copper electrolyte was as follows: white sand < anionic resin < zeolite < kaolin < activated carbon < bentonite. Bentonite was characterized using FTIR, XRF, XRD, SEM and BET methods. The results show specific surface area of 95 m²/g and particles size of 175 nm for bentonite. The optimum conditions for the maximum removal of Sb are contact time 10 min, 4 g bentonite and temperature of 40 °C. The adsorption of Sb(V) on bentonite is followed by pseudo-second-order kinetic (R²=0.996 and k=9×10^?5 g/(mg·min)). Thermodynamic results reveal that the adsorption of Sb(V) onto bentonite from copper electrolyte is endothermic and spontaneous process (ΔG^Θ=–4806 kJ/(mol·K). The adsorption data fit both the Freundlich and Langmuir isotherm models. Bentonite has the maximum adsorption capacity of 10000 mg/g for adsorption of Sb(V) in copper electrolyte. The adsorption of Zn, Co, Cu and Bi that present in the copper electrolyte is very low and insignificant.     

Deformation mechanisms in Cr20Ni80 alloy at elevated temperatures

The mechanisms of plastic deformation of Cr20Ni80 nichrome with an initial grain size of 80 μm were studied in the temperature range 600–950°C and the strain-rate range 1.5 × 10^?6?5 × 10^?2s^?1. Nichrome is shown to exhibit anomalously high values of stress exponent n and a high deformation activation energy Q. These unusual properties were found to be caused by “threshold” stresses below which deformation does not occur. An analysis of the deformation behavior with allowance for threshold stresses reveals the regions of hot, warm, and cold deformation in nichrome. At normalized strain rates \(\dot \varepsilon \) kT/D _{1 Gb} < 10^?8, the true values of n and Q are ～4 and 285 ± 30 kJ/mol, respectively. In the normalized-strain range 10^?8?10^?4 n ～ 6 and the deformation activation energy decreases to 175 ± 30 kJ/mol. This change in the deformation-behavior characteristics is explained by the transition from high-temperature dislocation climb, which is controlled by lattice self-diffusion, to low-temperature dislocation climb, which is controlled by pipe diffusion, as the temperature decreases. At \(\dot \varepsilon \) kT/D _{1 Gb} = 10^?4, a power law break-down takes place and an exponential law (which describes the deformation behavior in the range of cold deformation) becomes operative.     

Grain boundary diffusion and segregation of Ni in Cu

Grain boundary (GB) diffusion of ⁶³Ni in polycrystalline Cu was investigated by the radiotracer technique in an extended temperature interval from 476 to 1156 K. The independent measurements in Harrison’s C and B kinetic regimes resulted in direct data of the GB diffusivity D_gb and of the so-called triple product P = s · δ · D_gb (s and δ are the segregation factor and the diffusional GB width, respectively). Arrhenius-type temperature dependencies for both the D_gb and P values were measured, resulting in the pre-exponential factors $D_{\mathrm{gb}}^0=6.93\times {10}^{-7}$ m² s⁻¹ and P₀ = 1.89 × 10⁻¹⁶ m³ s⁻¹ and the activation enthalpies of 90.4 and 73.8 kJ mol⁻¹, respectively. Although Ni is completely soluble in Cu, it reveals a distinct but still moderate ability to segregate copper GBs with a segregation enthalpy of about −17 kJ mol⁻¹.     

High temperature oxidation of LaB6–ZrB2 eutectic in situ composite

LaB₆–ZrB₂ eutectic in situ composites are interesting candidates for manufacture of turbine blades because of their excellent mechanical properties. The oxidation behavior of LaB₆–ZrB₂ eutectic in situ composites prepared by electric arc melting was studied in a temperature range of 916–1223°C and in a pressure range of 1.5×10⁴–7.2×10⁴ Pa. The specific weight change of the LaB₆–ZrB₂ eutectic obeys the Arrhenius equation below the oxidation temperature of 1094°C and appears to obeya paralinear equation above this temperature. The rate of weight change is described by k_p=9.71×10⁻³ exp(−31 000/RT) mg²/cm⁴ min in the range 916–1094°C. Above 1094°C, rapid oxidation kinetics were observed, La₂O₃·B₂O₃ and La₂O₃·3B₂O₃ being the primary scale constituent with ZrO₂ deficiency in the outer scale. The oxidation increases with P_O2 up to 3.9×10⁴ Pa, above which the trend is reversed due to the active oxidation of ZrB₂. The oxidation appears to be controlled by oxygen diffusion through the scale and the oxidized layers consist mainly of La₂O₃·B₂O₃, La₂O₃·3B₂O₃ and trace of ZrO₂.     

Transformation and leaching kinetics of silicon from low-grade nickel laterite ore by pre-roasting and alkaline leaching process

The mineralogical phase transformation of a low-grade nickel laterite ore during pre-roasting process and the extraction of silicon during alkaline leaching process were investigated. The results indicate that the reaction activity of nickel ores is effectively improved by pre-roasting at 650 °C for 2 h, because of the transformation of lizardite into magnesium olivine and protoenstatite. When finely ground ore samples (44–61 μm) pre-roasted firstly react with sodium hydroxide solution (60 g/L) with a solid/liquid ratio of 1:5 at 140 °C for 120 min, the extraction of silicon can reach 89.89%, and the other valuable elements of magnesium, iron and nickel are accumulated in the solid residues. The leaching kinetics of nickel laterite ore can be described successfully by the diffusion through the product layer control model. The activation energy is calculated to be 11.63 kJ/mol and the kinetics equation can be expressed as 1–3(1–x)^2/3+2(1–x)=13.53×10^?2exp[–11.63/(RT)]t.