The niobium (columbium)-palladium constitution diagram

The Nb-Pd 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 ∼36 at. pct Pd at. 1520°C and ∼20 at. pct Pd at 800°C; α-Pd dissolves ∼31 at. pct Nb at 1610°C and ∼18 at. pct Nb at temperatures below 1500°C. The presence of three intermediate phases NbPd₂ (MoPt₂-type), α-NbPd₃ (TiAl₃-type), and β-NbPd₃ (β-NbPd₃-type) was confirmed; NbPd₂ melts at 1610°C and one of the NbPd₃ phases transforms at the same temperature into α-Pd solid solution which melts at 1625°C. In addition, an approximately equiatomic high-temperature phase α-NbPd with a homogeneity range of ∼11 at. pct was found which melts at 1520 to 1565°C and probably is an extension of and isomorphous with the α-Pd solid solution. Five three-phase reactions are described, and crystal chemical relationships are discussed. D. P. PARKER formerly with MIT . R. C. MANUSZEWSKI formerly with the ADAHF Research Unit at NBS.     

The resistive critical field of niobium (columbium) wire

The transverse and longitudinal resistive critical fields of niobium (columbium) wires with drawing strains up to eleven were measured. The magnitude and anisotropy of the resistive critical field can both be much greater than the bulk Ginzburg-Landau parameters indicate, even if “internal surface” nucleation of superconductivity is assumed. It is suggested that these effects are due to superconductivity in the dislocation cell walls created by drawing or swaging. A simple model for this effect is offered, and various experiments which test this model are discussed. J. R. PEARSON formerly Graduate Student, Department of metallurgy and Materials Science, M.I.T., Cambridge, Mass.     

The vanadium-platinum constitution diagram

The system V-Pt was investigated over the entire composition range by metallography, X-ray diffraction and electron microprobe studies. There are at least four equilibrium intermediate phases in this system and they are stable to progressively higher temperatures with increasing vanadium concentration. The phases which have been observed are: γ^′, cubic, Cu₃Au type; θ, tetragonal, TiAl₃ type; δ, orthorhombic, MoPt₂ type; ζ, orthorhombic, AuCd type; and β, cubic, Cr₃Si type (A15). The gg^′ phase is possibly metastable. A very stable ribbon-like growth of ζ phase in the fcc platinum terminal solid solution has been observed in alloys containing about 43 at. pct V. The platinum terminal solid solution forms a congruent melting maximum at about 1805°C. A eutectic reaction occurs at 1720° ± 10°C and a peritectic reaction is indicated at 1800° ± 10°C. Vanadium is soluble in the fcc platinum terminal solid solution up to about 57 at. pct at 1720°C. Platinum dissolves only to the extent of about 12 at. pct at 1800°C in bcc α-V.     

The tantalum-palladium constitution diagram

The Ta-Pd system was investigated over the entire composition range by metallography, X-ray diffraction and electron microprobe analysis. The solubility limits of terminal and intermediate phases and solidus temperatures were determined. α-Ta dissolved ∼20 at. pct Pd at 2550°C and ∼10 at. pct Pd at 1000°C; α-Pd dissolves ∼22 at. pct Ta at 1730°C and ∼18 at. pct Ta at 1000°C. The presence of four intermediate phases a, (β-U type), α-TaPd (TiCu type), TaPd₂ (MoPt₂ type), and TaPd₃ (TiAl₃ type) was confirmed; they melt or decompose (α-TaPd) at about 2550, 1410; 1800, and 1770°C, respectively. In addition, an equiatomic high temperature phase, β-TaPd was found which melts at ∼1720°C and may be an extension of and isomorphous with the α-Pd solution. Seven three-phase reactions are described. Formerly with Massachusetts Institute of Technology     

The chromium-platinum constitution diagram

The system Cr?Pt has been investigated over the entire composition range by metallography, X-ray diffraction, and electron microprobe studies. There is only one intermediate phase and it has a Cr₃Si(A15)-type crystal structure. The fcc platinum terminal solid solution extends to 71 at. pct Cr at 1530°C and forms a congruent melting maximum at about 1790°C. Atomic ordering within this solid solution range begins at about 17 at. pct Cr and there is a continuous change from the Cu₃Au-type structure to the CuAu-type structure with increasing chromium content. Two eutectic reactions at 1530°C±10°C and at 1500°C ±10°C were indicated and there is evidence of a syntectic reaction at 1580°C±10°C. Platinum is soluble in the bcc chromium terminal solid solution up to about 10 at pct Pt at 1500°C but the solubility decreases rapidly at lower temperatures.     

The effects of composition and annealing conditions on the stability of columbium (niobium)-treated low-carbon steels

The effects of composition and annealing conditions on the yielding behavior of vacuum melted, columbium(niobium) -treated, low-carbon steels were investigated. Additions of columbium were found to result in stabilization,i.e. freedom from inhomogeneous yielding or Lüder’s strain in the as-recrystallized condition. Stabilization is accounted for by considering the role of columbium as a carbide former, thereby reducing the carbon content in solution to a very low level. The nitrogen present is preferentially removed from solid solution by the formation of A1N. The results were used to estimate the solubility product of columbium carbide in ferrite. The amount of columbium required to provide stability is a function of total carbon content and annealing temperature.     

The activation energy for creep of columbium (Niobium)

The activation energy for creep of nominally pure columbium (niobium) was determined in the temperature range 0.4 to 0.757T_M by measuring strain rate changes induced by temperature shifts at constant stress. A peak in the activation energy vs temperature curve was found with a maximum value of 160 kcal/mole (672 kJ/mole). A pretest heat treatment of 3000F (1922 K) for 30 min (1800 s) resulted in even higher values of activation energy (>600 kcal/mole, 2520 kJ/mole) in this temperature range. The activation energy for the heat-treated columbium (Nb) could not be determined near 0.5T_M because of unusual creep curves involving negligible steady-state creep rates and failure at < 5 pct creep strain. It is suggested that the anomalous activation energy values and the unusual creep behavior in this temperature range are caused by dynamic strain aging involving substitutional atom impurities and that this type of strain aging may be in part responsible for the scatter in previously reported values of activation energy for creep of columbium (Nb) near 0.5TM.     

Texture in deep drawing columbium (Nb)-treated interstitial-free steels

The development of the crystallographic texture in hot-rolled, cold-rolled, and recrystallized Cb-treated interstitial-free steels was investigated using the crystallite orientation distribution analysis as well as X-ray pole figures. The influence of chemical composition of the steel and processing variables on texture and on normal and planar anisotropy of the γ-value of cold-rolled and annealed sheet are discussed and compared with those of aluminum-killed deep drawing steels. While, in terms of ideal orientation components, the re-crystallization texture of aluminum-killed steels can be described as having significant amounts of {lll}〈110〉 and {lll}〈112〉 components, Cb-treated steels show these components and in addition even stronger {554}〈225〉 and {322}〈296〉 components. Distinctions in the hot-rolled texture, the cold-rolled texture, and the recrystallization texture are described. Cb-treated steels have an entirely different planar distribution of γ values or plastic strain ratios compared with aluminum-killed steels. The resulting average γ value, γ_m, is significantly higher for Cb-treated steels and results in superior deep drawing characteristics. A. ELIAS is deceased.     

Texture in deep drawing columbium (Nb)-treated interstitial-free steels

Metallurgical and Materials Transactions A - The development of the crystallographic texture in hot-rolled, cold-rolled, and recrystallized Cb-treated interstitial-free steels was investigated...     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Effect of solute interactions in columbium (Nb) on Creep Strength

The creep strength of 17 ternary columbium (Nb)-base alloys was determined using an abbreviated measuring technique, and the results were analyzed to identify the contributions of solute interactions to creep strength. Isostrength creep diagrams and an interaction strengthening parameter, S_T, were used to present and analyze data. It was shown that the isostrength creep diagram can be used to estimate the creep strength of untested alloys and to identify compositions with the most economical use of alloy elements. Positive values of S_T were found for most alloys, showing that interaction strengthening makes an important contribution to the creep strength of these ternary alloys.     

Recrystallization of deep drawing columbium (Nb)-treated interstitial-free sheet steels

The softening response after isochronal annealing of cold-rolled, Cb-treated, vacuum decarburized-deoxidized, interstitial-free steels was investigated by hardness measurements, tension tests, and optical and transmission electron microscopy. Softening after annealing, following cold reduction, occurs by recovery-recrystallization and a reduction in precipitation hardening due to the coarsening of CbC precipitates. The recrystallization start temperature increases markedly with increasing amounts of Cb in solid solution in ferrite. Fine CbC precipitates retard recrystallization to a much lesser degree, and their effects can be eliminated by coarsening prior to cold reduction. Recrystallization initiates at free surfaces. Partially recrystallized structures consist of two layers of recrystallized matrix separated by an unrecrystallized zone. The recrystallized layers thicken with increasing temperature or time. This phenomenon is an inherent characteristic of these steels and not a result of external influences.     

Effect of solutes in binary columbium (Nb) alloys on creep strength

The effect of seven different solutes in binary columbium (Nb) alloys on creep strength was determined from 1400 to 3400°F (760 to 1871°C) for solute concentrations to 20 at. pct using a new method of creep strength measurement. The technique permits rapid determination of approximate creep strength over a large temperature span. All of the elements were found to increase the creep strength of columbium except tantalum. This element did not strengthen columbium until the concentration exceeded 10 at. pct. Hafnium, zirconium, and vanadium strengthed columbium most at low temperatures and concentrations, whereas tungsten, molybdenum, and rhenium contributed more to creep strength at high temperatures and concentrations.     

The role of nickel,copper, and columbium (Niobium) in strengthening a low-carbon ferritic steel

The contributions of the alloying elements nickel, copper, and columbium are evaluated in a low-carbon precipitation hardenable ferritic steel. The influences of nickel, copper, and columbium as individual and dual elemental additions on microstructure and mechanical properties are described. These elements each contribute to the as-rolled strength by grain refinement and solid solution strengthening. Copper provides an additional strength increment of about 15,000 psi as a precipitation hardener upon 1050°F aging.     

Open aluminothermic reduction of columbium (Nb) pentoxide and purification of the reduced metal

This investigation is concerned with the extraction of columbium metal by aluminothermic reduction of its pentoxide in a refractory-lined open reactor. Reduction with 15 pct of aluminum in excess of stoichiometric and priming at the center are found to be optimum parameters. Trials with 3 kg batches of columbium oxide have resulted in high yields of consolidate columbium. Aluminum-reduced columbium has been further processed by electron-beam melting-after prior pyro-vacuum treatment for removal of aluminum, and also directly—and in either case it has been possible to produce pure and ductile columbium. The investigation proceeds to evaluate fused salt electrorefining of the reduced columbium employing NaCl-KCl-K₂CbF₇ bath. Conditions for operating the cell at 90 pct or more current efficiency have been established. Electrorefining has been found to be effective in lowering of most of the impurities in the anode feed. Electrolytic columbium on consolidation by electron-beam melting is found to have a hardness value of 50 Dph. This paper is based upon a thesis to be submitted by G. R. KAMAT in partial fulfillment of the requirements of the degree of Master of Science (Tech.) at the University of Bombay.     

Surface distortions in twinned niobium (Columbium) crystals

The surface distortions resulting from the formation of mechanical twins in niobium single crystals are more complex than the simple tilts predicted from the twinning shear. Tilt angles observed vary from zero to well in excess of the conventionally predicted values. In addition, the shear offset is not limited to the twinned lamella, but is generally also observed in the adjacent matrix. These observations suggest that macroscopic shear need not be necessary in the initial twin formation. It is suggested that such shear offset, when present, is associated with the simultaneous occurrence of slip, and that the shear probably takes place after the initial twin formation, during the subsequent transverse twin growth. Observed slip markings, and the energy associated with the initial twin formation, are also briefly discussed.