High temperature plastic deformation of two V-Ga alloys with A15 structure

A study of high temperature plastic deformation has been undertaken on alloys of V-18 at. pct Ga and V-23 at. pct Ga. The materials were prepared by arc melting, homogenizing, and transformation annealing, resulting in polycrystalline A15 structure. Through compression testing and load-relaxation testing, plastic deformation has been studied over a strain rate range from 10^-6 to 10^-2/s and a temperature range from 1000 to 1300 °C. Flow stress decreases with increased temperature and decreased strain rate. Stress-strain rate relations may be fitted with a power law creep expression. The flow stress is influenced by the length of the 1150 °C transformation anneal; longer anneals result in a decrease in flow stresses projected from load relaxation testing. Analysis of compressive yield strength data places the activation energy for A15 V-Ga creep roughly in the 400 kJ/mol range.     

Metallurgical processing,structure and superconducting transition temperature of V3Ga

Alloy compositions, spanning the A15 phase field and the adjacent two phase fields, were arc melted and cast as rods for the study of metallurgical processing, resultant microstructures and superconductivity of V₃Ga. In cast materials, dendritic segregation was observed by metallographic examination and a radial Ga gradient was revealed by inductive super conducting transition temperature measurement. A brief heat treatment at temperatures in the bcc-phase field eliminated the dendritic segregation, decreased the radial Ga gradient, and produced very similar microstructures in the full range of compositions. The fine scale segregation generated in the bcc-to-A15 transformation was removed by an anneal at 1000 to 1150°C. The series of annealed specimens were uniform in microstructure and also in hardness. The lattice parameter-composition plot defined two lines intersecting near the stoichiometric composition. These data and density measurements show that the compositional adjustment is by substitution of V and Ga atoms on lattice sites. The superconducting transition temperature drops rapidly from a maximum as the composition deviates from stoichiometry. Measured values of the zero field transition temperature are somewhat higher than theT _o determined by extrapolating low fieldT _c measurements to zero field. R. W. HUBER, presently retired was with Electronics Technology Division, Naval Research Laboratory, Washington, DC 20375     

Crystallographic textures in rolled and annealed Fe-Ga and Fe-Al alloys

The feasibility of obtaining [001] preferred texture in polycrystalline Fe₈₅Ga₁₅ and Fe₈₅Al₁₅ magnetostrictive alloys containing 1 mol pct NbC using a low-cost conventional thermomechanical processing approach is shown in this work. Thermomechanical processing conditions examined consisted of a sequence of hot rolling, two-stage warm rolling at 400 °C with intermediate anneal at 900 °C and texture anneal in the temperature range of 900 °C to 1300 °C for time periods up to 24 hours. Textures present prior to and after texture annealing were characterized using orientation imaging microscopy in a scanning electron microscope. In the case of Fe₈₅Ga₁₅ alloy with 1 mol pct NbC, the deformation-induced texture after a two-stage warm rolling consists of mixed {100} 〈110〉 and {111} 〈110〉 type partial textures. Texture annealing of the Fe₈₅Ga₁₅ alloy with 1 mol pct NbC at 1150 °C for 2 hours changes the texture to a predominant texture that is close to {001}〈100〉. On increasing the annealing time to 24 hours, the texture shifts toward {110}〈100〉. While texture anneal at both 1150 °C and 1300 °C produces a [001] or near-[001] preferred orientation along the rolling direction in the Fe₈₅Ga₁₅ alloy with 1 mol pct NbC, 1150 °C-24 hour treatment was found to provide the strongest [001] orientation among the conditions examined. Similar trends are observed for the case of Fe₈₅Al₁₅ alloy with 1 mol pct NbC.     

The effects of deformation and pre-heat-treatment on abnormal grain growth in RENÉ 88 superalloy

When an extruded strain-free RENé 88 Ni-base superalloy about 1 to 2 μm in grain diameter is heattreated at 1150°C, abnormal grain growth (AGG) begins after 50 hours. When heat-treated at 1200 °C, AGG occurs at 15 minutes. Some of the grain boundaries are faceted with hill-and-valley structures when observed in transmission electron microscopy (TEM), and the occurrence of AGG is consistent with the boundary step and dislocation mechanism for the migration of singular boundaries with faceted shapes, as observed and proposed in other pure metals and alloys. The dissolution of abundant γ′ precipitates (with a solvus temperature of 1107 °C), which are coherent with the matrix and hence strongly pin the grain boundaries, does not cause AGG during early stages of heat-treatment at 1150 °C. Small deformations drastically alter the AGG behavior. When deformed to 4 pct, AGG begins after heat-treating for 10 minutes at 1150 °C, compared to the apparent incubation time of 50 hours for an undeformed specimen, and very large abnormal grains are produced. With increasing deformation to 6 and 9.2 pct, the abnormal grain size decreases. These results are qualitatively similar to those observed in Cu. This deformation effect on AGG is attributed to the absorption of lattice dislocations in the grain boundaries, which produces nonequilibrium structures that, in turn, can apparently cause rapid boundary migration. When heat-treated at 1200 °C, the largest abnormal grains are found in the specimens deformed to 2 pct. When the initial grain size is increased to about 14 μm by heattreating the extruded alloy at 1150 °C for 30 minutes, similar low deformation effects on AGG are observed. When these specimens are deformed to 10, 13, and 15.2 pct, primary recrystallization occurs during the heat-treatment at 1150 °C, and large abnormal grains are again produced because of the small recrystallized grain size. Therefore, there are two peaks in the grain size vs deformation curve after heat-treating at 1150 °C for 1 hour. A pre-heat-treatment of this alloy at 1050 °C below the solvus temperature of the γ′ phase greatly reduces the size of the abnormal grains obtained in the specimen deformed to 4 pct after the heat-treatment at 1150 °C, probably because some recovery of the dislocations takes place at grain boundaries during the pre-heat-treatment. The deformation effect on AGG observed in this alloy is qualitatively similar to that previously observed in Cu and appears to be consistent with the boundary step and dislocation mechanism for AGG. An erratum to this article is available at .     

The effect of double austenitization on the microstructure and fracture toughness of AISI M2 high speed steel

In this study, the effect of double austenitization on microstructure and toughness of AISI M2 high speed steel was investigated. For double austenitization treatment, the specimens, which are hardened initially at 1220°C and quenched in air, were hardened for a second time in the temperature range 1150 – 1050°C. For comparison purposes, another set of specimens is austenitized singly in the temperature range 1150 – 1050°C. Tempering process was carried out between 500 – 640°C. A double austenitization causes a fine carbide precipitation in the matrix, having sizes in the range of 0.10 ± 0.05 μm and volume fractions of between 1 and 6%. It is shown that a double austenitization treatment causes a decrease in fracture toughness (K_Ic), when compared with single austenitized ones. The reason for the lower K_Ic values of double austenitized specimens are attributed to these fine carbide precipitates: It is suggested that they limit the plastic deformation capability of the matrix and yield lower fracture toughness values.     

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]     

Hot Deformation Behavior of As-Cast 2101 Grade Lean Duplex Stainless Steel and the Associated Changes in Microstructure and Crystallographic Texture

The hot deformation behavior of 2101 grade lean duplex stainless steel (DSS, containing ~5 wt pct Mn, ~0.2 wt pct N, and ~1.4 wt pct Ni) and associated microstructural changes within δ-ferrite and austenite (γ) phases were investigated by hot-compression testing in a GLEEBLE 3500 simulator over a range of deformation temperatures, T _def [1073 K to 1373 K (800 °C to 1100 °C)], and applied strains, ε (0.25 to 0.80), at a constant true strain rate of 1/s. The microstructural softening inside γ was dictated by discontinuous dynamic recrystallization (DDRX) at a higher T _def [1273 K to 1373 K (1000 °C to 1100 °C)], while the same was dictated by continuous dynamic recrystallization (CDRX) at a lower T _def (1173 K (900 °C)]. Dynamic recovery (DRV) and CDRX dominated the softening inside δ-ferrite at T _def ≥ 1173 K (900 °C). The dynamic recrystallization (DRX) inside δ and γ could not take place upon deformation at 1073 K (800 °C). The average flow stress level increased 2 to 3 times as the T _def dropped from 1273 to 1173 K (1000 °C to 900 °C) and finally to 1073 K (800 °C). The average microhardness values taken from δ-ferrite and γ regions of the deformed samples showed a different trend. At T _def of 1373 K (1100 °C), microhardness decreased with the increase in strain, while at T _def of 1173 K (900 °C), microhardness increased with the increase in strain. The microstructural changes and hardness variation within individual phases of hot-deformed samples are explained in view of the chemical composition of the steel and deformation parameters (T _def and ε).

     

A sintering study on the β-spodumene-based glass ceramics prepared from gel-derived precursor powders with LiF additive

Beta-spodumene (Li₂O·Al₂O₃·4SiO₂, LAS) powders were prepared by a sol-gel process using Si(OC₂H₅)₄, Al(OC₄H₉)₃, and LiNO₃ as precursors and LiF as a sintering aid agent. Dilatometry, X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and electron diffraction (ED) were utilized to study the sintering, phase transformation, microstructure, and properties of the β-spodumene glass-ceramics prepared from the gel-derived precursor powders with and without LiF additives. For the LAS precursor powders containing no LiF, the only crystalline phase obtained was β-spodumene. For the pellets containing less than 4 wt pct LiF and sintered at 1050 °C for 5 hours the crystalline phases were β-spodumene and β-eucryptite (Li₂O·Al₂O₃·2SiO₂). When the LiF content was 5 wt pct and the sintering process was carried out at 1050 °C for 5 hours, the crystalline phases were β-spodumene, β-eucryptite (triclinic), and eucryptite (rhombohedral (hex.)) phases. With the LiF additive increased from 0.5 to 4 wt pct and sintering at 1050 °C for 5 hours, the open porosity of the sintered bodies decrease from 30 to 2.1 pct. The grains size is about to 4 to 5 μm when pellect LAS compact contains LiF 3 wt pct as sintered at 1050 °C for 5 hours. The grains size grew to 8 to 25 μm with a remarkable discontinuous grain growth for pellet LAS compact contain LiF 5 wt pct sintered at 1050 °C for 5 hours. Relative densities greater than 90 pct could be obtained for the LAS precursor powders with LiF > 2 wt pct when sintered at 1050 °C for 5 hours. The coefficient of thermal expansion of the sintered bodies decreased from 8.3 × 10⁻⁷ to 5.2 × 10⁻⁷/°C (25 °C to 900 °C) as the LiF addition increased from 0 to 5 wt pct.     

The effect of plastic deformation on Al2CuLi (T 1) precipitation

The enhancement ofT ₁ precipitation in Al-Li-Cu alloys by plastic deformation prior to aging (that is, cold work) and the subsequent increase in alloy strength is investigated. The increased understanding of the role of matrix dislocations in the nucleation and growth ofT ₁ plates, discussed in the previous paper,^[1] permits a detailed study of the phenomenon. In this paper, the effect of different levels of plastic strain on theT ₁ particle distributions as a function of aging time at 190 °C is quantified, and the subsequent influence on tensile properties is thereby described. The effect of plastic deformation is shown to decrease theT ₁ plate length and thickness, increase the number density by almost two orders of magnitude, increase the yield strength by 100 MPa, while simultaneously reaching peak strength in 20 pct of the time required without plastic deformation. Formerly Graduate Student, Department of Materials Science, University of Virginia,     

Observation of the crystallization behavior of a slag containing 46 wt pct CaO, 46 wt pct SiO<Subscript>2</Subscript>, 6 wt pct Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and 2 wt pct Na<Subscript>2</Subscript>O using the double hot thermocouple technique

In this work, isothermal crystallization of a synthetic slag containing 46 wt pct CaO, 46 wt pct SiO₂, 6 wt pct Al₂O₃, and 2 wt pct Na₂O has been investigated by means of double hot thermocouple technique (DHTT). The effect of Na₂O content on crystallization time was confirmed. Two different types of calcium silicate crystals were observed. Calcium di-silicate forms at temperatures above 1150 °C and calcium tri-silicate precipitate at temperatures below 1050 °C. A mixture of the two types of calcium silicate has been observed between the two temperatures. The tendency of crystals to become richer in calcium at low temperatures that has also been observed in previous published works has been confirmed. No effect of the cooling rate on crystallization start time was confirmed in the range of cooling rates applied in this investigation.     

Structure and properties of a β solution treated,quenched, and aged si-bearing near-α titanium alloy

The microstructure, tensile properties, and fractographic features of a near-α titanium alloy, IMI 829(Ti-6.1 wt pct Al-3.2 wt pct Zr-3.3 wt pct Sn-1 wt pct Nb-05 wt pct Mo-0.32 wt pct Si) have been studied after aging over a temperature range of 550°C to 950°C for 24 hours following solution treatment in the β phase field at 1050°C and water quenching. Transmission electron microscopy studies revealed that aging at 625°C and above produced discrete silicides at α′ interplatelet boundaries. However, aging at 900°C and above has also resulted in the precipitation of β phase along the lath boundaries of martensite. The silicides have been found to have a hexagonal structure withc=0.36 nm anda=0.70 nm (designated as S₂ by earlier workers). There is a significant improvement in yield and ultimate tensile strength after aging at 625°C, but there is less improvement at higher aging temperatures. The tensile ductility is found to be drastically reduced. While the fracture surface of the unaged specimen shows elongated dimples, the aged samples show a mixed mode of fracture, consisting of facets, featureless parallel bands, and extremely fine dimples.     

Metallurgical considerations for optimizing the superconducting properties of Nb3Al

The effects of heat treatment and composition on the superconducting transition temperature of Nb₃Al were studied in conjunction with an X-ray diffraction investigation of ordering and other structural effects. It was determined that an ordering anneal of 750°C for at least 48 hr achieved a maximum midtransitionT _c of 18.5 K in arc-melted samples of Nb₃Al. The changes in lattice parameter and order parameter during heat treatment indicate that theβ-tungsten crystal structure becomes more ordered as the maximumT _c is approached. Further, theT _c of 18.5 K could not be reached in Nb₃Al material having nonstoichiometric composition. In such material, there was a direct correlation between increasing percentage of second-phase Nb₂Al present and decreasingT _c after the maximumT _c had been obtained. The information obtained during this investigation led to the development of a simple empirical model to explain the change in theT _c of Nb₃Al. Also based on this work, a method was evolved for producing conductor material based on the highT _c Nb₃Al alloy (Appendix I). J. G. KOHR, formerly Research Assistant, Department of Metallurgy and Materials Science, Massachusetts Institute of Technology, Cambridge, Mass.     

The influence of Al3Zr dispersoids on the recrystallization of hot-deformed AA 7010 alloys

The recrystallization of AA 7010 alloys (Al-6 pct Zn-2.4 pct Mg-1.6 pct Cu-Zr) during solution treatment is investigated as a function of Zr content after deformation under conditions simulating hot rolling. The respective roles of the volume fraction and size of Al₃Zr dispersoids are characterized by additions of 0.05 to 0.12 pct Zr and suitable heat treatments. Plane strain compression (channeldie) tests at temperatures of 320 °C and 440 °C were conducted to strains of 1, and the samples subsequently solution-annealed at 470 °C. Recrystallization during this anneal was characterized by optical and electron microscopy and X-ray diffraction. The fraction recrystallized decreases with increasing Zr content, higher deformation temperature, and finer particle size. An original model based on the concept of the recrystallizable volume fraction is presented to predict the degree of recrystallization in materials characterized by spatially heterogeneous microstructures.     

The niobium (columbium)-platinum constitution diagram

The Nb-Pt system was investigated over the entire composition range by metallography and X-ray diffraction analysis. The solubility limits of terminal and intermediate phases and solidus temperatures were determined. α-Nb dissolves ≈12 at. pct Pt at 2040 °C and ≈5 at. pct Pt at 1150 °C; α-Pt dissolves ≈20 at. pct Nb at 2000 °C and ≈ 18 at. pct Nb at temperatures below 1700 °C. The presence of six intermediate phases, Nb₃Pt (Cr₃O, A15 or β-W type), σ(≈Nb₂Pt, β-U type), Nb_1−xPt_1+x (AuCd type), α′-Pt (undetermined structure), NbPt₂ (MoPt₂ type), α-NbPt₃ (TiCu₃ type), and β-NbPt₃ (β-NbPt₃ type) was confirmed. The phase NbPt₃ melts congruently at ≈2040 °C, and σ forms peritectically at ≈1800 °C. By analogy with related systems, the high-temperature phase α′-Pt is probably an extension of and isomorphous with α-Pt solid solution. Eight three-phase reactions are described, the mean atomic volumes are given, and crystal chemical relationships among the six homologous T₅-T₁₀ systems (T₅ = V, Nb, Ta; T₆ = Pd, Pt) are discussed.     

Reaction sequences in the formation of silico-ferrites of calcium and aluminum in iron ore sinter

Complex silico-ferrites of calcium and aluminium (low-Fe form, denoted as SFCA; and high-Fe, low-Si form, denoted as SFCA-I) constitute up to 50 vol pct of the mineral composition of fluxed iron ore sinter. The reaction sequences involved in the formation of these two phases have been determined using an in-situ X-ray diffraction (XRD) technique. Experiments were carried out under partial vacuum over the temperature range of T=22 °C to 1215 °C (alumina-free compositions) and T=22 °C to 1260 °C (compositions containing 1 and 5 wt pct Al₂O₃) using synthetic mixtures of hematite (Fe₂O₃), calcite (CaCO₃), quartz (SiO₂), and gibbsite (Al(OH)₃). The formation of SFCA and SFCA-I is dominated by solid-state reactions, mainly in the system CaO-Fe₂O₃. Initially, hematite reacts with lime (CaO) at low temperatures (T ∼ 750 °C to 780 °C) to form the calcium ferrite phase 2CaO·Fe₂O₃ (C₂F). The C₂F phase then reacts with hematite to produce CaO·Fe₂O₃ (CF). The breakdown temperature of C₂F to produce the higher-Fe₂O₃ CF ferrite increases proportionately with the amount of alumina in the bulk sample. Quartz does not react with CaO and hematite, remaining essentially inert until SFCA and SFCA-I began to form at around T=1050 °C. In contrast to previous studies of SFCA formation, the current results show that both SFCA types form initially via a low-temperature solid-state reaction mechanism. The presence of alumina increases the stability range of both SFCA phase types, lowering the temperature at which they begin to form. Crystallization proceeds more rapidly after the calcium ferrites have melted at temperatures close to T=1200 °C and is also faster in the higher-alumina-containing systems.     

Effect of microstructure on the corrosion and deformation behavior of a newly developed 6Mn-5Cr-1.5Cu corrosion-resistant white iron

An experimental study has been made of the effect of heat treatment on the transformation behavior of a 4.8 pct Cr white iron, alloyed with 6 pct Mn and 1.5 pct Cu, by employing optical metallography, X-ray diffractometry, and differential thermal analysis (DTA) techniques, with a view to assess the suitability of the different microstructures in resisting aqueous corrosion. The matrix microstructure in the as-cast condition, comprising pearlite + bainite/martensite, transformed to austenite on heat-treating at all the temperatures between 900 °C and 1050 °C. Increasing the soaking period at each of the heat-treating temperatures led to an increase in the volume fraction and stability of austenite. M₃C was the dominant carbide present in the as-cast condition. On heat-treating, different carbides formed: M₂₃C₆ carbide was present on heat-treating at 900 °C and 950 °C; on heat-treating at 1000 °C, M₇C₃ formed and persisted even on heattreating at 1050 °C. The possible formation of M₅C₂ carbide in the as-cast and heat-treated conditions (900 °C and 950 °C) is also indicated. Dispersed carbides (DC), present in austenite up to 950 °C, mostly comprised M₃C and M₅C₂. On stress relieving of the heat-treated samples, M₇C₃-type DC also formed. The hardness changes were found to be consistent with the micro-structural changes occurring on heat-treating. The as-cast state was characterized by a reasonable resistance to corrosion in 5 pct NaCl solution. On heat-treating, the corrosion resistance improved over that in the as-cast state. After 4 hours soaking, increasing the temperature from 900 °C to 1050 °C led to an improvement in corrosion resistance. However, after 10 hours soaking, corrosion resistance decreased on increasing the temperature from 900 °C to 950 °C and improved thereafter on increasing the heat-treating temperature. Deformation behavior responded to the microstructure on similar lines as the corrosion behavior. Although in an early stage of development, the composition thus developed betters the performance of 22 pct Ni containing Ni-Resist irons as far as strength and freedom from pitting and graphitic corrosion are concerned; however, the corrosion resistance is somewhat lower. In conclusion, the usefulness of the different microstructures in attaining a useful combination of corrosion resistance and deformation behavior has been assessed. The data thus generated provide definite clues to developing new materials with improved performance for resisting aqueous corrosion in marine environments. Formerly Postdoctoral Candidate, University of Roorkee     

The neodymium-gold phase diagram

The Nd-Au phase diagram was studied in the 0 to 100 at. pct Au composition range by differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy (LOM), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Six intermetallic phases were identified, the crystallographic structures were determined or confirmed, and the melting behavior was determined, as follows: Nd₂Au, orthorhombic oP12-Co₂Si type, peritectic decomposition at 810 °C; NdAu, R.T. form, orthorhombic oP8-FeB type, H.T. forms, orthorhombic oC8-CrB type and, at a higher temperature, cubic cP2-CsCl type, melting point 1470 °C; Nd₃Au₄, trigonal hR42-Pu₃Pd₄ type, peritectic decomposition at 1250 °C; Nd₁₇Au₃₆, tetragonal tP106-Nd₁₇Au₃₆ type, melting point 1170 °C; Nd₁₄Au₅₁, hexagonal hP65-Gd₁₄Ag₅₁ type, melting point 1210 °C; and NdAu₆, monoclinic mC28-PrAu₆ type, peritectic decomposition at 875 °C. Four eutectic reactions were found, respectively, at 19.0 at. pct Au and 655 °C, at 63.0 at. pct Au and 1080 °C, at 72.0 at. pct Au and 1050 °C, and, finally, at 91.0 at. pct Au and 795 °C. A catatectic decomposition of the (βNd) phase, at 825 °C and ≈1 at. pct Au, was also found. The results are briefly discussed and compared to those for the other rare earth-gold (R-Au) systems. A short discussion of the general alloying behavior of the “coinage metals” (Cu, Ag, and Au) with the rare-earth metals is finally presented.     

The eutectoid region of the Zr−Ga system

The zirconium-rich portion of the Zr?Ga phase diagram was determined by the optical examination of microstructures of isothermally annealed and quenched alloys. A deviation from binary equilibrium, was observed even though careful selection of materials and techniques held impurities to a minimum and produced alloys with a purity of at least 99.9 pct. The slopes of the α-β boundaries are depressed and the range of solubility of the solid solution phases is restricted when compared to the phase diagrams of other Group IIIB elements, apparently as a result of the large difference in atomic size between zirconium and gallium. Thea ₀ andc ₀ lattice constants of cph zirconium are contracted and the axial ratio is expanded by the addition of gallium. The change inc/a at 1 at. pct was very close to the change observed in Zr-In alloys, in agreement with general dependence of these properties in zirconium alloys upon electron to atom ratio. A eutectoid reaction occurs at 860°C with β solid solution (1.8 at. pct Ga) decomposing into α solid solution (0.8 at. pct Ga) and Zr₃Ga. Cast microstructures suggest a eutectic reaction in which liquid (21.0 at. pct Ga) decomposes into β (8.0 at. pct Ga) and Zr₅Ga₃. It is proposed that intermediate phases are formed at 25.0 at. pct Ga (Zr₃Ga), 37.5 at. pct Ga (Zr₅Ga₃), and 50.0 at. pct Ga (ZrGa) although the exact composition was not determined.     

A microstructural investigation of the bcc to A15 phase transition in sputter-deposited Nb3Al superconductors

The bcc to A15 phase transition in sputter-deposited Nb₃Al (Cb₃Al) superconductors was studied using transmission electron microscopy. Four distinct microstructures were observed for the sputter-deposited and isochronally heat treated samples. Heat treatments were for 24 h at temperatures between 500 and 700°C. Deposition at 10°C produced the bcc phase with a small grain size of 1000Å. The bcc grains contained a high density of dislocations and fine precipitates. Coarse precipitates were found in the bcc grains and at the grain boundaries after heat treatment between 500 and 600°C. At 650°C, the A15 phase was detected in the presence of the bcc phase; the nucleation of the A15 phase originated at the grain boundary. Finally, a homogeneous microstructure of A15 phase resulted from heat treatment at 700°C. The A15 phase had a small, but defect free grain of 2500A. It is believed that such microstructures of A15 phase could have enhanced superconducting critical current (J_c) and critical temperature (T_c).     

The diffusivity of sulfur in wüstite and its solubility in wüstite and γ iron in equilibrium with each other and a liquid oxysulfide

The solubility of sulfur in wüstite in equilibrium with γ iron and liquid oxysulfide was found to be 0.011 wt pct at 1050°C. The sulfur solubility in γ iron in equilibrium with wüstite and liquid oxysulfide was also determined at 1050°, 1150°, and 1250°C and found to be 135, 165, and 160 ppm respectively. These values are considerably lower than the sulfur-solubility in y iron in the binary Fe-S system saturated with pyrrhotite. The diffusivity of sulfur in wüstite was determined by oxidizing Fe-S alloys in mixtures of CO and CO₂, and analyzing the entire sample for sulfur afterwards. From the amount of sulfur diffused through the growing wüstite layer into the gas phase, the diffusivity of sulfur in wüstite was evaluated, and found to be 4.1 × 10⁻⁸ and 9.6 × 10⁻⁷ cm²/s at 1050° and 1250°C respectively. These values are of the same order as the self-diffusivity of iron in wüstite in equilibrium with iron at the same temperatures.