Discussion of “effects of tensile stress on microstructural change of eutectoid Zn-AI alloy”

In a recent contribution,[1] Zhu and Orozco presented a phase transformation of the ternary alloy Zn-20.2 wt pct Al-1.8 wt pct Cu, studied under tensile stress by using X-ray diffraction and scanning electron microscopy techniques. The authors report the existence of three phases in the alloy at room temperature after furnace cooling,α,ε, and a newη _′ ^T instead of the zinc-rich solid solutionη, as appears in the phase diagrams. The reported parameters for this hcp metastable phase are^[1,2] a = 0.2663 andc = 0.4873 nm; these values are close to the parameters of pure zinc,^[3] witha = 0.2664 nm andc = 0.4946 nm. The difference betweenη _′ ^T and zinc in thea parameter is around 0.03 pct, and it is 1.47 pet for thec parameter. When zinc is saturated with aluminum in the Zn-AI alloys, thea parameter shrinks^[3] to 0.2660 nm. It is possible to see that the value ofa of theη _′ ^T phase lies in-between the values of pure zinc and zinc-aluminum solid solution. The solubility of Al and Cu in Zn^[4] at 100 °C is 0.3 wt pct Cu and 0.06 wt pct Al. The covalent radius of Cu (0.117 nm) is smaller than the covalent radius of Al (0.118 nm) and Zn (0.125 nm), so the introduction of Cu in the zinc structure can result in a reduction of thec parameter. These values suggest that the metastable phaseη _′ ^T could be the hcp zincrich solid solution with low aluminum and copper contents. The article of Zhu and Goodwin,^[5] cited by Zhu and Orozco in their Reference 14, is related not to the eutectoid alloy, as they argue, but to an alloy with 27 wt pct Al, and no reports about the transformation ofε intoT′ were found. The presence of the metastable e phase (CuZn₄, sometimes called CuZn₅) at room temperature and its transformation to the stable phaseT′ (rhombohedral intermetallic phase, Al₄Cu₃Zn) have been observed by other authors.^[6,7] Y.H. ZHU and E. OROZCO:Metall Mater. Trans. A, 1995, vol. 26A, pp. 2611-15.     

Data interpretation of “vapor pressure measurement of Zn-Fe intermetallic compounds”

It was with great interest that the article published by Mita et al. ^[1] was studied. In the article, experimental measurements of vapor pressures of various Zn-Fe intermetallic compounds were reported. Zinc activities were derived from the vapor pressure measurements. Such thermodynamic data, albeit indispensable for phase diagram construction, are scarce and often outdated as many researchers today opt to work on computation over experimentation for quick results. Data on zinc-related systems are even scarcer in comparison to other common metals such as iron, aluminum, or copper. It is certainly encouraging to see this experimental work on the Zn-Fe system.     

Phase equilibria and intermetallic phases in the Ni-Si-Mg ternary system

The Ni-Si-Mg ternary phase diagram has been established after homogenization and slow cooling to room temperature. The chemical compositions of the alloys and their phases were obtained using fully quantitative energy dispersive X-ray spectroscopy (EDS) with standard spectrum files created from intermetallic compounds Mg₂Ni and Ni₂Si. The following intermetallic phases have been observed: (a) four new ternary intermetallic phases, designated as ν, ω, μ, and τ, (b) a ternary intermediate phase Mg(Ni,Si)₂ based on the binary MgNi₂ phase containing Si; (c) three ternary intermetallic phases, η, κ, and ζ, previously reported by the present authors;[10] and (d) Mg₂SiNi₃ (Fe₂Tb type),^[9] previously reported by Noreus et al. ^[8] The MgNi₆Si₆ phase, which was also previously reported,^[7] was not observed at the corresponding composition in the present work. However, the MgNi₆Si₆ phase reported as being of hexagonal symmetry (Cu₇Tb type),^[9] with the lattice parameters a=0.4948 nm and c=0.3738 nm, possibly corresponds to the μ phase (Mg(Si_0.48Ni_0.52)₇) discovered in the present work. The lattice structure of the newly discovered ω phase was determined with the help of the X-ray indexing program TREOR (developed by Werner et al. ^[13]) to be a hexagonal structure of the Ag₇Te₄ type ((Mg_0.52Ni_0.48)₇Si₄) with the lattice parameters a=1.3511 nm and c=0.8267 nm.     

Creep Behavior of Nickel-Copper Solid Solution Alloys below 0. 55 Tm

In two recent creep studies of inhomogeneous nickelcopper solid solution alloys,i.e. cast weld metal with solidification-induced composition gradients^[1] and nickelcopper laminate composites with controlled composition gradients across the layers,^[2] the creep rates at an intermediate temperature (500 °C) were shown to decrease with an increase in homogenization. The creep behavior in inhomogeneous alloy systems reflects the composite effects of position-dependent creep properties as controlled by solid solution alloy content. To utilize composite modeling techniques in creep analyses of materials with composition gradients, creep data of homogeneous materials as a function of alloy content are required. Therefore, this study was undertaken to evaluate the creep behavior of nickel-copper solid solution alloys at intermediate temperatures and to provide a base set of data to evaluate the effect of gradients described above.^[1,2] I. D. CHOI, formerly Graduate Research Assistant, Colorado School of Mines.     

Kinetics of Ammonia Leaching of Multimetal Sulphides

This paper briefly describes the studies carried out on oxidative ammonia leaching of Cu-Zn-Pb multimetal sulphides. Kinetics of zinc and copper dissolution were studied with ? 200 + 300 mesh BSS fraction and 1% solids in the slurry. It is observed that the dissolution of sphalerite proceeds by a phase boundary reaction model and that of copper via diffusion through product layer in the temperature range of 70-100°C. The rate equations for zinc and copper dissolution are given by:

1 ? (1 ? α)^1/3 = k _Zn[NH₃][pO₂]^1/2

1 ? 2/3α ? (1 2/3α )^2/3 = k^Cu[NH₃]²[pO₂]^1/2

where the symbols have the usual meanings.

Activation energies for zinc and copper dissolution reactions are estimated to be 66.5 and 55.4 kJ/mole, respectively. Activation energy values thus obtained are also comparable to those obtained using a differential approach.

The leaching results obtained with 10% solids using a wide range of particle size (? 140 + 500 mesh) indicate that copper dissolution is chemically controlled in ammonia as well as ammonia-ammonium sulphate medium in the temperature range of 115-135°C. However, at lower temperature (?55°C). the leaching reaction follows a diffusion model. Zinc dissolution data show deviations from the shrinking core model due to high extractions in the initial stages.     

Role of yield criteria and hardening laws in the prediction of forming limit diagrams

Forming limit diagrams (FLDs) are calculated based on an extension of previous analyses by Jones and Gillis,^[1] Choi et. al. ^[2] and Pishbin and Gillis.^[3] They considered the plastic behavior of sheet metals in three deformation phases using a generalized flow law and using the commonly used power hardening law to describe the stress-strain behavior. In the present study, however, the yield criterion proposed by Hosford is used in conjunction with both power-law and Voce material constitutive equations to develop a model. This model is capable of predicting the forming limit strains achievable during sheet metal forming operations for sheets having planar isotropy. The predictions from Voce and power-law equations have been compared with the experimental forming limits determined by hemispherical punch stretching of gridded blanks of AA3105 and AA8011 aluminum alloys. The results indicate good prediction of limit strains for the two alloys when the Voce equation is applied.     

Crack-tip behaviors of stationary and growing cracks in Al-Fe-X alloys: Part II. Crack opening profile

The crack opening behaviors of monotonically loaded stationary and growing cracks in Al-Fe-X alloys have been examined using the stereoimaging technique. Crack opening displacements (COD’s) have been measured as a function of distance behind the crack tip at different load levels. By comparing with existing asymptotic solutions, the experimental COD results confirm the dominance of the HRR (Hutchinson,^[4,6] and Rice and Rosengren^[5]) singularity in a stationary crack, the logarithmic singularity in a growing crack, and the transition from the HRR to the logarithmic singularity when a stationary crack extends by a small increment. In addition to the In (r) singularity, experimental evidence suggests the presence of a In² (r) singularity in plane stress cracks growing into intense shear bands.     

Lattice imperfections studied by x-ray diffraction in deformed aluminum-base alloys: Al-Ge alloy

In the present analysis, which is part of a series on a study that has been undertaken on aluminum-base alloys, a detailed X-ray diffraction study of deformation^[1–5] is made on aluminum-base germanium alloys in four different compositions: Al-3.10 at. pct Ge, Al-3.80 at. pct Ge, Al-4.16 at. pct Ge, and Al-4.60 at. pct Ge. The alloys were prepared from spectroscopically pure metals supplied by Johnson-Matthey and Co. Ltd., London, by melting them in graphite crucibles sealed under vacuum in quartz capsules. The alloys were homogenized for 15 days at 400 °C in the face-centered cubic phase (Figure 1), and cold working was performed by careful hand filing at room temperature. The diffractometer samples were prepared in the usual manner,^[3,4] and X-ray diffraction profiles were recorded in a Siemens Kristalloflex-4 X-ray diffractometer using Cu K_α radiation. A portion of the powder obtained by hand filing from each alloy was annealed at 400 °C to relieve strain and was taken as standard for line shift, line asymmetry, and line shape analyses in light of recent developments.^[3,4,6–8] The microstructural parameters, such as coherent domain size (D _e, microstrain 〈∈_L〉, stacking faults α′ and a" (both intrinsic and extrinsic), deformation twin fault β, dislocation density ρ, and stacking fault energy parameter γ/μ, were determined by adopting the same method of analysis and following the same equations that were used before.^[3–7]     

Raman studies of the phase separation mechanism of CaO-Al2O3-SiO2 glasses in an electric field

The effects of an electric field on phase separation in CaO-Al₂O₃-SiO₂ (CAS) has been studied by Raman spectroscopy. It was discovered that an electric field can promote the process of phase separation in CAS glasses. The droplet phase is the enriched section for Ti⁴⁺ and Ca²⁺ ions. The continuous matrix is the enriched section for Si⁴⁺. The results of Raman spectroscopy indicate that the electric-field treatment can increase the concentrations of Q^[2] and Q^[4] in CAS glasses and that increase in concentration near the cathode is higher than that near the anode. The increase in Q^[2] and Q^[4] units is due to the increase of the concentration of O_f and O_b. On the basis of experimental results, the mechanism of phase separation of CAS glass in an electric field has been proposed.     

Studies on the removal of phosphorus and sulfur from Fe-C and Fe-C-Mn melts at 1350°C

Laboratory studies have been performed on simultaneous dephosphorization and desulfurization of Si-free Fe-4.5 % C melts with [P]_o = 0.11 wt.% and [S]_o = 0.04 wt.% in MF induction furnaces at 1 350°C. In these investigations, CaO- or Na₂CO₃-based fluxes were used and the techniques of powder injection or single top slag addition were applied. The following results have been obtained:

• – The effectiveness of lime and soda-based fluxes with regard to dephosphorization is practically the same. But a lower sulfur level is attained when Na₂CO₃-based fluxes are used.
• – In the injection experiments, efficiencies of η_P = 80% for dephosphorization and η_s = 90% for desulfurization are easily reached at a powder consumption of 50 to 60 g/kg. But a further increase of the η values requires a remarkable increase in the amount of injected powder. Top slag addition instead of powder injection is less effective, in general.
• – Apparent rate constants k_[P] and k_[S] from 0.05 to 0.3 min^?1 have been determined in the initial stage of injection depending on the relative amount of injected flux. In the top slag experiments, the k_[P] and k_[S] values were practically constant at a level of 0.1 min^?1.

Furthermore, dephosphorization of molten Fe-C-Mn alloys at 1 350°C has been studied at variable Mn content. It is predicted from thermodynamic data and confirmed by experiments that dephosphorization lessens with increasing Mn content in the range from 0 to 15 wt.%.     

A15 Compound Deformation and Secondary Slip in V3Si

The plastic deformation of A15 compounds has been the subject of a number of investigations. Cold working is possible only under high hydrostatic pressure, and Nb₃Sn, V₃Si, and V₃Ga polycrystals have been cold worked under hydrostatic pressures in the 1790 to 6000 MPa range.^[1,2,3] Hot deformation has been more widely evaluated, starting with the work of Greiner and Buehler in 1962.^[4] V₃Si single crystal deformation has been studied in the 1200 to 1800 °C range,^[4–10] and V₃Ga polycrystal deformation has recently been evaluated in the range from 1000 to 1300 °C.^[11,12] The hot deformation of Nb₃Sn polycrystals has been extensively studied in the 1150 to 1650 °C range.^[12–15]     

An assessment of studies on homogeneous diffusional nucleation kinetics in binary metallic alloys

A critical review is presented of all studies on homogeneous nucleation kinetics in crystalline binary metallic alloys located in the literature. Emphasis was first placed upon examining the data on the number of precipitates per unit volume of matrix phase,N _v , recorded as a function of isothermal reaction or aging time. With the exception of the results of a few studies on Cu-rich Cu-Co alloys, all of these data were extensively “contaminated” by significant overlapping of the diffusion fields of adjacent precipitates and especially by concurrent coarsening. The use of the “nucleation window” concept was advocated as a means of finding a range of alloy compositions and reaction temperatures in a particular alloy system within which sufficient data onN _v vs time can be collected to evaluate the steady-state nucleation rate,J _s ^* without significant intervention by either disturbing effect. Transmission electron microscopy (TEM) was identified as a particularly valuable experimental tool for measuringN _v . However, smallangle neutron scattering (SANS) is also proving useful for this purpose, and the combination of SANS with FIM-AP (field ion microscope-atom probe) has uncovered information of crucial importance to understanding the transformation sequence in Cu-Co alloys. Wagner and co-workers^{[52,62,63,64-78-79]} have demonstrated the presence of precursor Co segregations large in extent but small in amplitude, of which the most successful lead to the formation of identifiable precipitates (within which segregation is very much larger in amplitude but considerably smaller in extent). The Wagneret al. work suggests that the supersaturations at which they formed were insufficient to permit the fluctuations which did not eventually fulfill exactly the specifications for critical nuclei to evolve into precipitates. While classical, the Cahn-Hilliard continuum nonclassical [su2] and Cook-deFontaine discrete lattice point nonclassical nucleation theories^[25,26,27] yield nearly identical results in the temperature-Co concentration range experimentally studied, theJ* _s values thus calculated are a few orders of magnitude smaller than the experimentally measured rates when the concentration of vacancies present at the reaction temperature is (reasonably) assumed operative. On the basis of theoretical and computer simulation studies by Binderet al. ^{[84,87,89,90]} and Kleinet al.,^[91–94] the observed precursor concentration fluctuations are indicative of relatively long-range interactions among adjacent atoms in Cu-Co alloys, whereas the solution thermodynamics so far applied to this system is based upon the use of short interaction distances. This is suggested to be the principal source of the discrepancy between measured and calculated nucleation kinetics in Cu-Co alloys. Suggestions are offered for future research intended to clarify some of the complexities which have recently become apparent in studies of homogeneous nucleation kinetics in binary metallic alloys. This paper is based on a presentation made in the “G. Marshall Pound Memorial Symposium on the Kinetics of Phase Transformations” presented as part of the 1990 fall meeting of TMS, October 8–12, 1990, in Detroit, MI, under the auspices of the ASM/MSD Phase Transformations Committee.     

The composition of the solid solution,structure, and contact fatigue of the case-hardened layer

One result of contact fatigue of metals, due to the high stress in surface contact zones, is the appearance of dimples on the surface of the case-hardened layer. Contact fatigue depends on a series of factors, the most important of which are thought to be the carbon concentration in the layer, the amount of retained austenite, and the morphology of the carbide phase.^[1-4] The literature data concerning the quantitative effect of retained austenite on contact fatigue are contradictory. Vinokuret al.^[5] have shown that the temperature of heating before quenching was the greatest influence on contact fatigue, since it determines the solution of carbides, the degree of alloying of the solid solution, and the amount and ratio of structural components. There are almost no data on the critical points for the carburized case or their variation with the carbon content of the case.     

The Elastic Modulus and Flow Stress of Nb3Sn at Elevated Temperatures

The plastic deformation of Nb₃Sn has been the subject of a number of investigations, and the hot deformation of Nb₃Sn polycrystals has been extensively studied in the 1150 to 1650 °C range.^[1–4] The hot deformation stress-strain rate-temperature relationships are largely those of “power law creep”, with activation energies for creep roughly in the 400 to 500 kJ/mol range.^[2,3] Grain size refinement increases flow stress in the power law creep regime.^[3] Hot deformed Nb₃Sn displays polygonized dislocation structure.^[5]     

The leaching kinetics of chalcopyrite (CuFeS2) in ammonium lodide solutions with iodine

The leaching kinetics of chalcopyrite (CuFeS₂) in ammonium iodide solutions with iodine has been studied using the rotating disc method. The variables studied include the concentrations of lixiviants, rotation speed, pH of the solution, reaction temperature, and reaction product layer. The leaching rate was found to be independent of the disc rotating speed. The apparent activation energy was measured to be about 50 kJ/mole from 16 °C to 35 °C, and 30.3 kJ/mole from 35 °C to 60 °C. The experimental findings were described by an electrochemical reaction-controlled kinetic model: rate =k [NH₃]^0.69[OH⁻]^0.42[I ₃ ⁻ ]^0.5.     

Ballistic impact behavior of multilayered armor plates processed by hardfacing

Hardfacing is a type of surface treatment for the extension of service life of worn parts or structures and the improvement of the surface properties through deposition of the alloys using arc welding or laser cladding.^[1,2] Among the hardfacing alloys, the high chromium hardfacing alloys have been used most extensively for dies or parts in various industrial areas because of their excellent hardness, corrosion resistance, and wear resistance as well as inexpensiveness.^[2-6] These properties are obtained from the large volume fraction of hard chromium carbides.^[3-8] The recent works on these alloys have focused on the property enhancement, the microstructural modification, and the high-temperature application.^[1,7,8]     

Density measurements of the lithium fluoride/lithium sulfide eutectic at high temperature

A straightforward and reliable method to determine densities of molten salts at high temperatures was de-veloped by Janz and Lorenz several years ago.^[1] This method was followed in order to determine the density of the LiF/Li₂S eutectic^[2] over the temperature range of 1176 to 1355 K in which the eutectic is liquid. The rel-ative lack of data for this eutectic is surprising given its potential usefulness in the study of advanced batteries'31 and electrowinning of metals from molten sulfides.^[41] The method is based on the fact that a solid piece of metal of known volume suspended from a pan balance into a molten salt will weigh less than if it were sus-pended in air at the same temperature. This difference in weight measured in grams will be equal to the buoyant force of the liquid at that temperature. The density of the salt bath can then readily be determined by dividing this difference by the volume of the solid piece of metal that is immersed in the bath. The procedure can be re-peated to give density values over a range of temperatures.     

Thermodynamic Calculation on Calcium Treatment for 26CrMo4S/2 Steel

Because CaSi core wire was not fed in external refining process for 26CrMo4S/2 steel making, it was found that the molar ratio of calcium versus alumina was very low and subsequently resulted in generation of much more non-metallic inclusions. Hence, it was reasonable to sugguest feeding appropriate amount of Ca core wire. Before the performance, the thermodynamic calculation had been carried out to obtain the theoretical amount of Ca wire to be fed. According to the practical data from steel plant and the thermodynamic data, it was calculated that only when 1.38 × 10^–4[%Al]_T^2/3 ≥ [%Ca]_T ≥ 4.97×10^–5[%Al]_T^2/3 in molten steel the Al₂O₃ inclusions could be properly modified.     

Cathodic copper deposition at 65 °C in the absence and presence of Bi3+ and Sb3+ additives in acidified CuSO4 aqueous solutions

An electrochemical study by cyclic voltammetry and potentiostatic pulse method of the cathodic deposition of copper on polycrystalline copper electrode was carried out in acidic aqueous copper sulfate solution. Comparative electrochemical investigations were performed in electrolytes in the absence and presence of Bi³⁺ and Sb³⁺ ions. All experiments were performed at 65 °C. For bulk copper deposition, the results indicate that in the presence or absence of additive ions, the charge transfer at the Cu/Cu²⁺ electrode occurs in two consecutive one-electron steps, with Cu⁺ being formed as an intermediate. The addition of Bi³⁺ to the electrolyte retarded the copper deposition process, while the introduction of Sb³⁺ caused a depolarization effect. The kinetic studies in the potential range which characterizes the deposition of bismuth show that this reaction takes placevia a stepwise electron transfer mechanism. In the case of antimony-containing electrolyte, the cathodic reduction was found to proceedvia a two-electron transfer pathway. The presence of Sb³⁺ and Bi³⁺ in potentiostatic studies shows that the additive ions behave in a manner consistent with that observed by cyclic voltammetry. The nucleation and growth of bulk copper deposition appears to occurvia aninstantaneous three-dimensional (3-D) nucleation and growth mechanism. However, in the presence of Bi³⁺ or Sb³⁺, copper is deposited by aprogressive 3-D nucleation and growth pattern. X-ray photoelectron spectroscopic surface analyses revealed strong incorporation of both antimony and bismuth within the copper deposit.     

Effect of reduced graphene oxide-supported copper addition on electrochemical properties of La0.7Mg0.3Ni2.8Co0.5 electrodes

The reduced graphene oxide-supported copper(Cu@rGO) nanocomposite was introduced to improve the electrochemical properties of La_(0.7)Mg_(0.3)Ni_(2.8)Co_(0.5)alloy electrodes.Experimental results show that adding Cu@rGO nanocomposite with mass fractions of x wt%(x=0,3,6 and 9) to the alloy electrodes provides electrodes with maximum discharge capacities of 368.9 mAh/g(x=0),373.2 mAh/g(x=3),407.3 mAh/g(x=6) and 398.6 mAh/g(x=9),and high-rate dischargeabilities at a discharge current density of1200 mA/g of 40.5%(x=0),64.0%(x=3),82.0%(x=6) and 76.0%(x=9).The addition of Cu@rGO nanocomposite also provides alloy electrodes with hydrogen diffusion coefficients of 3.7×10~(-10) cm~2/s(x=0),4.1×10~(-10) cm~2/s(x=3),4.2×10~(-10) cm~2/s(x=6) and 4.0×10~(-10) cm~2/s(x=9).Clearly,the addition of 6 wt%Cu@rGO nanocomposite not only increases the electrochemical capacity of La_(0.7)Mg_(0.3)Ni_(2.8)Co_(0.5) alloy electrodes,but also improves their electrochemical kinetic properties.