The diffusion of antimony in alpha iron

Diffusion coefficients of antimony in α-iron were determined in the temperature range 700 to 900°C using the residual activity method. Specimens were large-grained polycrystals for the higher temperature measurements and single crystals for the low temperature measurements. Above 800°C the data may be represented by the equationD _sb(cm²/s) = (440 ± 200) exp [- (270,000 ± 7000)/RT]. The activation energy (reported in J/mole) is approximately equal to that measured for iron self-diffusion in this same temperature range, although the antimony diffusion coefficients are a factor of ten larger than the iron self diffusion coefficients. The potential for strongly coupled vacancy-antimony motions is demonstrated, based on the observed enhancement of iron self diffusion in dilute iron-antimony alloys. Finally molybdenum is shown to have a negligible effect on the diffusion of antimony in α-iron. These results are discussed in relation to the phenomenon of temper brittleness in steels. Embrittlement kinetics in iron-antimony alloys are shown to be consistent with an antimony diffusion controlled segregation mechanism.     

Grain refinement through thermal cycling in an Fe-Ni-Ti cryogenic alloy

A thermal cycling technique which allows the grain refinement of Fe-12 Ni-0.25 Ti alloy from 40∼60 μm (ASTM #5∼6) to 0.5 ∼ 2 μm (ASTM #1∼18) in four cycles has been developed. The process consists of alternate annealing in γ range and (α + γ) range with intermediate air cooling. The transformation behavior, the change of microstructures and cryogenic mechanical properties on each cycling step are described. Due to the ultrafine grain size, the ductile-brittle transition temperature of this ferritic alloy in Charpy impact testing was suppressed below 6 K. In fracture toughness testing at 77 K, the mode of fracture was altered from brittle quasi-cleavage to complete ductile rupture through the grain refining.     

Calculation of activation energies for defect movement during coincidence boundary migration in nickel oxide using computer simulation techniques

Two possible atomistic mechanisms of grain boundary migration in nickel oxide are examined for two coincidence boundaries using computer simulation techniques. In mechanism I, the boundary migrates by anion vacancy diffusion across it (calculated activation energy 0.64 eV in a (21̄1)/[011] boundary). In mechanism II, ions migrate across the boundary to add onto the opposite crystal lattice without the need for vacancies (activation energy 0.78 eV in a (12̄2)/[011] boundary and control by cation migration). The activation energy for an anion diffusion jump down a (21̄1)/[011] boundary is calculated as 1.57 eV. Anion vacancy supply down the boundary is therefore expected to be rate controlling for any migration mechanism requiring anion vacancies (i.e. mechanism I). There are few literature values for the grain growth activation energy in bulk NiO but values of ~0.9 eV are deduced from published data on grain sizes in NiO scales. 0.9 eV is low in comparison with literature values for a variety of ceramics. Comparison between 0.9 eV and the computer predicted activation energies for defect migration suggests that, unless the effective anion vacancy formation energy at a general grain boundary is considerably lower than expected, it is likely that anion vacancy formation is not required for boundary migration in NiO.     

Formability behavior of brass alloy sheet: the role of twins in microstructure

Quantitative understanding of the process and formability parameters involved in grain size and the formation of annealing twins after plastic straining is important in the control of the manufacturing process. There is a synergistic effect of strain and temperature on the density of annealing twins. Formability of brass alloy sheets was studied after annealing of 65% cold worked (CW) samples at different temperatures (300–600°C). Tensile, deep drawing and Erichsen tests were carried out at room temperature to evaluate formability of alloy. Effect of annealing temperature on density, distribution and size of twins is investigated. It was shown that annealing of brass alloy resulting in formation of annealing twins which at higher annealing temperature were reduced by increasing grain size. Best deep drawability would be achieved by annealing at moderate temperature 400–450°C which microstructure consists of fine grain and twin bands. Work hardening exponent of samples was calculated based on the tensile test data and correlated with stretch ability of annealed brass sheets. It was found that the sheets annealed at 600°C possess best ductility and high average n-value.     

Structure and properties of rapidly solidified dispersion-strengthened titanium alloys: Part I. Characterization of dispersoid distribution,structure, and chemistry

The feasibility of developing dispersion-strengthened powder metallurgy Ti alloys was determined in Ti-RE (RE = Ce, Dy, Er, Gd, La, Nd, or Y) alloys prepared by rapid solidification processing. The alloys were produced by electron-beam melting and splat quenching. Dispersoid precipitation and growth were studied as functions of annealing temperature, 700 to 1000 °C, for annealing times between 5 and 50,000 minutes. Dispersoid diameters, spacings, compositions, and crystal structures were characterized by transmission and scanning electron microscopy, X-ray and electron diffraction, energy-dispersive X-ray analysis, and scanning Auger microscopy. Two classes of dispersoid coarsening behavior at temperatures below theβ-transus were identified. In Ti-Ce, Ti-Gd, and Ti-Nd alloys, equilibrium rare earth sesquioxide (RE₂O₃) dispersoids form early in the annealing process and coarsen rapidly to > 1 μm diameter. The Ti-Nd alloys additionally contain large volume fractions of small (< 100 nm diameter) dispersoids. In the other Ti-RE alloys, dispersoids identified as Ti-RE-O-C compounds coarsen relatively slowly. Ti-Er is the most promising of the investigated systems for application in a multicomponent dispersion-strengthened alloy because long-time annealing at 700 to 800 °C produces stable dispersoids of 50 to 150 nm average diameter and 300 to 600 nm inter-particle spacing.     

Effect of Recovery and Recrystallization on the Hall–Petch Relation Parameters in Submicrocrystalline Metals: I. Experimental Studies

Yield strength σy, macroelastic limit σ₀, and effective grain-boundary hardening coefficient K_eff in the Hall–Petch relation (\({\sigma _y} = {\sigma _0} + {K_{eff}}/\sqrt d \)) in the submicrocrystalline (SMC) materials produced by equalchannel angular pressing are experimentally studied. It is shown that, as compared to parameter σ₀ and K in the Hall–Petch relation for coarse-grained metals, the SMC metals are characterized by higher values of σ0 and lower values of K_eff. The critical grain size (d₁) at which Keff in the σ_y–d^–1/2 relations of SMC materials changes falls in the range 0.2–0.5 μm. The dependences of macroelastic limit σ₀ and coefficient K_eff on the annealing temperature are found to be determined by recrystallization. If abnormal grain growth develops in annealing of SMC metals, anomalous hardening is detected and a nonmonotonic temperature dependence of coefficient K_eff takes place. In the case of conventional recrystallization at a high annealing temperature, SMC metals exhibit a smooth decrease in σ₀ and an increase in K_eff to the values of K characteristic of coarsegrained materials.     

Refractory metallization of green ceramic

Successful refractory metallization of green ceramic is shown to require close matching of the shrinkages of the metal layer and the ceramic substate. Selection of specific metal particle sizes is used as the prime controlling parameter for metallizing several alumina ceramic types, including commercially pure alumina. Warpage of the fired part and adhesion of the metallization are demonstrated to be dependent on and controllable by the choice of metal particle distribution. Properly selected particle distribution results in flat metallized ceramic parts and good adhesion is obtained with pure elemental particles; other additives are unnecessary. X-ray stress analysis data and warpage results are correlated with pull strength measurements.     

Kinetics of external dissolution of metals in metallic melts. (Review)

Conclusions Dissolution rate under diffusion conditions is usually controlled by three parameters, D, , and c_m. Since the dependence of D and values on the individual properties of metals (D 10^–5 cm²/sec, 10^–3 cm) is slight,dissolution rate under diffusion conditions is determined chiefly by cm, which thus constitutes the principal criterion governing the choice of a metal compatible with any given melt. Dissolution under kinetic conditions does not appear to be typical of metals, since even tungsten, which has the highest crystal lattice energy of all metals [62], dissolves under diffusion conditions [19, 20, 63–66].It thus follows that detailed researches into the dissolution kinetics of metals in metallic melts are hardly likely to reveal any new corrosion-resistant metallic materials. The existing liquid-metal corrosion inhibitors are refractory compounds such as nitrides or carbides [67]. This does not mean, of course, that investigations into the dissolution kinetics of solid metals in metallic melts serve no useful purpose, since they are concerned not only with corrosion, but also with a number of other processes referred to in the introduction to this survey.Translated from Poroshkovaya Metallurgiya, No. 8 (92), pp. 39–54, August, 1970.     

The Wear Behavior of In-Situ Al–AlN Metal Matrix Composites

Al–AlN composites are synthesized using NH₄Cl + CaO powder as a nitrogenation precursor in the melt of pure aluminum. In-situ formation of AlN to varying volume fraction is attempted using different proportion of NH₄Cl + CaO precursor into the aluminum melt held at 700 °C. Mechanical properties of synthesized metal matrix composites are evaluated for different volume fraction and distribution of AlN particles in aluminum matrix. Agglomeration of AlN is noticed with increasing precursor addition and synthesis time into the aluminum matrix. Due to heterogeneous distribution of AlN particles in aluminum matrix, marginal changes in hardness are observed. Pin on disc, dry sliding wear of metal matrix composites is carried to study wear behavior of synthesized composites. Composite with good dispersion of AlN particulates has shown higher hardness and wear resistance. Present paper discusses wear behavior of composites with different weight fraction of AlN tested under load and sliding distance as wear parameters. The shearing mechanism of agglomerate due to friction and its correlation with the wear loss is also highlighted in the present paper.     

A theory for solute impurity diffusion, which considers engel-brewer valences, balancing the fermi energy levels of solvent and solute, and differences in zero point energy

A theory that assumes the Engel-Brewer valence of elements (one for bcc structures, two for cph structures, and three for fcc structures) and considers the effects of balancing the solute and solvent Fermi energy levels and differences in zero point energy between solvent and solute atoms to calculate an “effective” relative valence for solute impurities is presented. The calculated values of relative valence and the experimental values of the differences in diffusional activation energy between solute and solvent atoms, ΔQ, are compared to the values of ΔH ₂ + ΔE calculated from the Lazarus-LeClaire theory for several solute impurities in ten solvent metals. The calculated results agree very well with the experimental values for the large majority of solutes. The theory presented adequately describes solute impurity diffusion in both α-Fe and γ-Fe, Al, Ni, and the noble metals. In particular, the low activation energies for impurity diffusion of the alkali metals (ground state valence of one) in Al (ground state valence of three) are accounted for by the theory. It is shown that the diffusion of the electronegative solute impurities (Cr, Mn, Fe, and Co) in Al is not anomalous when the relative valence is calculated by the proposed theory. The diffusion of electronegative solute impurities in the noble metals, which has been problematic in the past, is also well described by the proposed theory. The proposed theory introduces a simple method of estimating the effective electron densities of solute impurities and illustrates that the Lazarus-LeClaire theory adequately describes solute impurity diffusion in the ten solvent metals studied. It is expected that more accurate calculations of effective electron density for solute impurities would result in even better agreement between experimental and calculated results.     

Effect of the severe plastic deformation temperature on the diffusion properties of the grain boundaries in ultrafine-grained metals

A model is proposed to explain the effect of the severe plastic deformation (SPD) temperature on the diffusion properties of the grain boundaries in ultrafine-grained (UFG) metals and alloys. It is shown that an increase in the SPD temperature in UFG metals leads to an increase in the activation energy of grainboundary diffusion from (3–5)k _B T _m, which corresponds to the diffusion parameters of nonequilibrium grain boundaries, to (8–10)k _B T _m, which corresponds to the diffusion parameters of equilibrium grain boundaries (k _B is the Boltzmann constant, T _m is the melting temperature). The dependence of the activation energy of grain-boundary diffusion on the SPD temperature is found to be determined by the kinetics of the competing processes of defect accumulation at grain boundaries and the diffusion accommodation of defects.     

Rate of change of oxygen chemical potential in liquid PbO−SiO2 binary solution

The rate of the chemical potential change of oxygen in a liquid PbO?SiO₂ binary solution, with SiO₂ contents of 10, 20, and 30 mol pct, and in pure PbO, has been measured at temperatures of 900°, 950°, 1000°, 1050°, and 1100°C. The rate increased with temperature according to the Arrhenius type relation and decreased with the increase of the silica content. It is suggested that the rate-controlling step is the counter diffusion rate of Pb²⁺ and Pb⁴⁺ ions, which are considered to be the most easily movable ions in the PbO?SiO₂ solution. The relation between the rate of oxygen chemical potential change and the electrical conductivity is also discussed for the liquid PbO?SiO₂ system.     

Morphology and kinetics of cellular dissolution of the Pb−Sn alloy

Dissolution of lamellar precipitates by cell boundary migration in a Pb-5.5 at. pct Sn alloy has been studied in the temperature range between 44° and 83°C by optical microscopy. Morphological observation shows that it is a cellular mode of transformation. The cell boundary, acting as a short circuit path of diffusion, recedes, thereby dissolving the precipitates. The orientation of the transformed matrix is found to follow the same relationship as that in cellular precipitation. Measurements of the rate of dissolution are in agreement with a kinetic analysis that assumes a boundary diffusion limited process. A critical temperature, defined as the temperature at which the receding boundary ceased moving, was found to exist slightly below the solvus temperature of the alloy. By balancing driving forces at both sides of the cell boundary at the critical temperature, we evaluated the upper limit of the interlamellar surface tension of Pb?Sn alloy as 232 erg per sq cm. This value is six to ten times smaller and is believed to be more realistic than those values calculated from the precipitation kinetics.     

Structural Changes of High-Temperature Nickel Alloy Containing Rhenium and Lanthanum on Heat Treatment

The properties of high-temperature nickel alloys for manufacturing depend on the thermal stability of the structure, the particle size, the shape, the quantity of strengthening γ' phase, and the strength of the γ solid solution. Such alloys are strengthened by the addition of rhenium and lanthanum. In the present work, the structure and phase composition of high-temperature nickel alloy with added rhenium (0.4 at %) and lanthanum (0.006 at %) are qualitatively and quantitatively investigated. The methods employed are transmission diffraction electron microscopy and scanning electron microscopy. The alloy structure is considered in three states: after directed crystallization (the initial state, sample 1); after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 480 h (sample 2); and after directed crystallization, annealing at 1150°C for 1 h, and annealing at 1100°C for 1430 h (sample 3). Primary and secondary phases are observed in the superalloy. The primary phases are γ' and γ. They form the structure of the alloy and are present in the form of γ' quasi-cuboids separated by γ layers. The secondary phases due to the presence of rhenium and lanthanum are β NiAl, AlRe, NiAl₂Re, σ, χ, and Ni₃La₂. The secondary phases seriously disrupt the structure of the γ + γ' quasi-cuboids. The rhenium and lanthanum do not uniformly fill the whole alloy volume, but only appear in local sections. Therefore, in all three states of the alloy, only some volume of γ + γ' quasicuboids is disrupted. Analysis of the secondary phases’ morphology shows that the σ particles are thin needles, whereas the Ni₃La₂ particles have internal structure with characteristic contrast and are relatively thick. Interestingly, the σ phase and Ni₃La₂ are deposited at the same locations. The introduction of rhenium and lanthanum changes the phase composition of the alloy, suppressing the formation of γ phase. The particles of secondary phase are localized in individual sections of the alloy with specific periodicity. The secondary phases are refractory: the melting point is about 1600°C for β phase, 2600°C for σ phase; and 2800° for χ phase. Thanks to the formation of refractory secondary phases and their periodic distribution in the structure, the strength of the superalloy with added rhenium and lanthanum is increased.     

Structure and magnetic properties of the Nd<Subscript>9.5</Subscript>Fe<Subscript>84.5</Subscript>B<Subscript>6</Subscript> alloy subjected to severe plastic deformation and annealing

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd_9.5Fe_84.5B₆ alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd₂Fe¹⁴B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd₂Fe₁₄B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is H _c = 360 kA/m and the maximum energy product is (BH) _max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.     

The kinetics of the exchange of cobalt(II) ions between NaCl and Na2O-SiO2-Fe2O3 melts in the temperature range 1200 to 1400 K

Studies of the equilibria and kinetics of the Co²⁺ ion exchange in the Na₂O-SiO₂-Fe₂O₃/NaCl system were performed over the 1200 to 1400 K temperature range by measuring the emf of galvanic cells of the following composition: $$( - )Co\left| {\frac{{NaCl - CoCl_2 }}{{Na_2 O - SiO_2 - Fe_2 O3}}} \right.\left| {NaCl - CoCl_2 } \right.\left| {Co( + )} \right.$$ Distribution coefficients α of the Co²⁺ ions between the salt phase and silicate melt are of the l0^?2 order. Differential equations describing the transfer process of the Co²⁺ ions from the salt phase to the silicate phase were solved. The diffusion coefficients D_Co ²⁺ in the Na₂O-SiO₂-Fe₂O₃ melt were determined by substituting the Co²⁺ ion concentration change in fused NaCI into the differential equations. The values of D_Co ²⁺ are about 10^?5 cm²S^?1 and they decrease with decreasing temperature and increasing Fe_?2O_?3 content in slags. The diffusion coefficient of the cobalt (II) ions in slags determined in this way is consistent with that determined by the otating disk method.     

The self diffusion of iron in Fe2SiO4 and CaFeSiO4 melts

The self diffusion of iron in Fe₂SiO₄ and CaFeSiO₄ melts has been measured in the temperature range 1250° to 1540°C using Fe⁵⁹ as the radio tracer and the capillary-liquid reservoir method of diffusion measurement. The results obtained are represented by $$log D_{Fe} = - \frac{{3800 \pm 500}}{T} - 2.74 \pm 0.29$$ for Fe₂SiO₄, and $$log D_{Fe} = - \frac{{5450 \pm 620}}{T} - 1.93 \pm 0.37$$ for CaFeSiO₄. Excellent agreement is obtained with the self-diffusivity of iron calculated from the measured interdiffusivity of iron and oxygen in iron oxide melts.     

Kinetics of reordering of Ni3Al disordered by ball-milling

A systematic study of the kinetics of the recording process, followed by X-ray diffraction and differential scanning calorimetry, of a Ni₃Al based alloy, previously disordered by high energy ball-milling, is reported. X-ray diffraction analysis of isothermally annealed samples gives apparent activation energies of 1.57 ± 0.20 eV for reordering and 1.61 ± 0.07 eV for ordered domain growth. Good agreement is found between these values and that obtained from the calorimetric analysis of the continuous heating transformation, which gives a value for the apparent activation energy of 1.64 ± 0.21 eV. However, in order to correctly reproduce the calorimetric results upon isothermal annealing, an increasing value for the activation energy of the process is needed. As the experimental results suggest that point defect diffusion has an active role in the reordering process, a vacancy trapping mechanism via impurity is put forward to account for the slowing down of the kinetics of reordering.     

The influence of alloying,temperature, and related effects on the stacking fault energy

The present paper reviews experimental results for the magnitude of the stacking fault energy (γ) in pure fcc metals, and its variation with alloying and with temperature. Quantitative studies have principally involved electron microscopic observations of faulted defects (extended nodes, extrinsic-intrinsic fault pairs, tetrahedra) or the determination of rolling textures, while much valuable information has also been obtained from measurements of the X-ray faulting probability. Extensive measurements of the variation of γ with alloying have been made in silver, copper, and nickel base alloys and in stainless steels, from which general conclusions can be drawn regarding the composition dependence of γ with various solute types. The presence of irregular faulted configurations in samples of some high solute concentration alloys following room temperature deformation suggests that solute/dislocation pinning forces can exert considerable influence on the dislocation substructure. Annealing such samples leads to a reduction in the degree of irregularity of the substructure and generally to a decrease in mean faulted defect size. These changes appear to be due to the reduction, through a thermally activated process, of the effectiveness of the solute pinning forces rather than as a result of a strong dependence of γ on temperature. The variation of faulted defect size on annealing pure materials is likely to arise solely from the variation with temperature of γ and the elastic constants, and results in silver indicate that γ/G is approximately independent of temperature.     

The effect of the nitrogen potential on the coarsening kinetics of VN precipitates

An Fe-1.06 pct V alloy was used to study the kinetics of coarsening of VN precipitates. Nitriding was carried out at 600 °C in purified NH₃ gas. Nitrided specimens were then annealed at 820 °C in furnace atmospheres of different NH₃/H₂ ratios. The transmission electron microscopy technique was used to measure the precipitate sizes. The data on the precipitate sizes indicate that the coarsening of the plate shaped VN precipitates seems to be diffusion controlled. The precipitate coarsening rate appears to be lowered by the increase in NH₃ content in the furnace atmosphere. The particle size distributions were found to be broader than the predictions of the LSW theory.