Showing papers on "Equiaxed crystals published in 1983"

Processing-microstructure relationships for Ti-6Al-2Sn-4Zr-2Mo-0.1Si

Abstract: The detailed relationships between thermal-mechanical processing parameters and resulting microstructures for Ti-6Al-2Sn-4Zr-2Mo-01 Si (Ti-6242) have been established through compression testing and heat treatment Beginning with either an equiaxed alpha or Widmanstatten alpha preform microstructure, isothermal compression tests were run at strain rates typical of isothermal forging (10−3 to 10−1 s−1) and conventional forging (1 to 100 s−1) Metallographic investigation of these test specimens in as-deformed and heat treated conditions was used to characterize deformation-induced microstructures and transformations For the equiaxed alpha microstructure, it was shown that deformation, as well as post-deformation heat treatment, were more effective in promoting microstructures close to the expected equilibrium ones than heat treatment alone, a finding similar to that for other alloy systems For the metastable Widmanstatten alpha microstructure, the deformation and heat treatment parameters that promote the development of an equilibrium, equiaxed alpha microstructure have been determined For this microstructure, two separate temperature-strain rate regimes have been identified, and the resulting microstructures correlated with the measured flow stress behavior For the low temperature regime, deformation is highly nonuniform, and the microstructural features are shown to be similar to those in pearlitic steels and other lamellar alloys In the higher temperature regime, on the other hand, deformation is much more uniform The results presented can be applied to select hot forging parameters for the control of final microstructure and properties in Ti-6242 and similarα/β titanium alloys

Ferritic steel having ultra-fine grains and a method for producing the same

Abstract: A novel hot-rolled ferritic steel composed of 70% or more of equiaxed ferrite grains having an ultra-fine grain size of 4 μm or less. This steel is produced by a hot working at approximately the Ar 3 point and by one or more passes of the hot working having a total reduction ratio of at least 75%. When a plurality of passes is carried out, the time between passes is less than one second. Due to hot working, dynamic transformation of austenite and/or dynamic recrystallization of ferrite takes place. The total reduction ratio may be at least 35% for a high purity steel.

Structural and compositional variations in aluminium alloys rapidly quenched from the melt

Abstract: Rapid quenching of aluminium alloys by meltspinning results in ribbons showing a heterogeneous solidification structure [1, 2] . This structural heterogeneity is expected to result from local differences in cooling rate. Thus, compositional variations due to differences in solidification conditions may be expected. Therefore, the relation between the local concentration of the alloying element and the microstructure has been investigated. Ribbons of A1Si and A1Mg alloys were prepared by applying a melt-spinning technique ([3]; in the present investigation the circumferential velocity was 31 .4msec-1) . The hypo-eutectic alloys used were prepared from 99.994 wt% A1, 99.99 wt % Si and 99.99 wt % Mg. The thickness of the ribbons obtained varied between 40 and 80 /an . Cross-sections were obtained by preparation of the ribbons along their longitudinal axis. After mechanical polishing and etching in Keller and Wilcox's reagent the cross-sections were examined with a Neophot 2 (Carl Zeiss Jena) optical microscope. X-ray microanalysis was performed with an ARL electron microprobe. The content of alloying element was determined near the wheel side, near the upper side and in the centre as an average value obtained from tracks with a length of about 45/am parallel to the outer surfaces. Cross-sections of melt-spun ribbons are shown in Fig. 1. Three regions can be distinguished. 1. A very finely grained (sometimes "featureless") zone at the wheel (chill) side. 2. A zone of columnar grains. 3. A zone of equiaxed grains at the upper side. The results of the X-ray microanalysis are gathered in Table I. It is concluded that the concentration o f alloying element is highest in the centre and lowest near the upper side, whereas the concentration near the wheel side takes an intermediate value. The results obtained suggest a close relation

Behavior of Pores in the Sintering of Acicular Fe2O3 Powder

Abstract: The sintering of acicular Fe2O3 powder was studied by isothermal dilatometry, hysteresis Hg porosimetry, and SEM of powder compacts using a resin-impregnating technique, and compared with an ordinary equiaxed powder. It is shown that the pores in the acicular powder compacts remain connected until a later stage of sintering than those in the spherical powder, and that the observed rapid initial densification, along with preferential shrinkage in the parallel-to-pressing direction, can be interpreted in terms of particle rearrangement.

Effect of electromagnetic forces on aluminium cast structure

Abstract: Molten commercial aluminium was oast in sand mould in the presence of high electric current. Grain refinement was enhanced as the current was increased. In case of alternating external magnetic field, however, there was no proportionality between the refinement and magnetic field strength. The ingot acquired fine equiaxed grains when the magnetic field was about 0.3 kilo gauss. At all other values, ingots showed mixed structure of equiaxed and columnar areas to varying proportions. The ingot cast in this experiment was about 100g.The behaviour of the 4-kg ingot cast in an experimental semi-continuous casting machine was almost the same. The number of grains/cm2 in both experiments was about 700.

Low cycle fatigue of Ti-Mn alloys: Microstructural aspects of fatigue crack growth

Abstract: Fatigue crack path behavior of a series of Ti-Mn alloys heat treated to produce volume fractions of the alpha phase ranging from 0 to 97.5 pct was investigated. Both Widmanstatten and equiaxed morphologies of the α phase were used in this study. Interior and surface crack paths are discussed in terms of slip behavior and microstructural details.

PHASE AND MORPHOLOGY OF PbNb2O6 OBTAINED BY MOLTEN SALT SYNTHESIS

Abstract: : The morphological development of lead metaniobate powder particles in KCl is examined with special emphases on the heating conditions and starting compositions. Potassium ions are substituted in the Pb-site resulting in Pb;-xK2Nb2O6(PKN) with the orthorhombic modification. The morophology particles changed during PKN formation and particle growth. During the formation process of PKN, equiaxed and rod-shaped particles were obtained both above and below the melting temperature of KCl. The rod-shaped particles have a columnar structure but decrease in number with increasing potassium content in the starting mixtures. During the growth process, equiaxed particles grew to simple rod-shaped particles without a coulmnar structure. Potassium in the starting oxide was found to promote the formation of simple rod-shaped particles is obtainable. Originator-supplied keywords include: Molden Salt Synthesis, Lead Niobates, Potassium Chloride, Ceramics.

Superconducting properties of a liquid‐infiltration Nb‐Nb3Sn composite formed during a low‐temperature reaction

Abstract: A powder metallurgy based ‘‘liquid‐infiltration’’ method was used to produce multifilamentary Nb‐Sn composite wires. New heat treatments combining relatively low‐temperature aging (≤800 °C) and long reaction time (≥ one day) were used to form superconducting A15 Nb3Sn. This heat treatment can be used for large conductors and practical magnets. Transmission electron microscopy studies revealed that the A15 Nb3Sn was formed in fine filaments which were embedded in the ductile Nb matrix. Small, equiaxed A15 grains extended across the reacted filament. A Tc onset of 17.9 K with a 0.4‐K transition width was obtained. Excellent high‐field critical currents, overall Jc’s ≥104 A/cm2 in a field of 18 T at 4.2 K, were achieved.

Multifilamentary Nb-Nb 3 Sn composite by liquid infiltration method: Superconducting, metallurgical, and mechanical properties

Abstract: A rapid solid-liquid reaction mechanism has been used to form A15 Nb 3 Sn in the liquid-infiltration processed Nb-Sn wire. Small, equiaxed A15 grains across the fine reacted filaments of 0.2-1.0 μm thickness were revealed with the transmission electron microscopy studies. A uniform Sn concentration near the stoichiometry was found in the A15 region. High inductive T c 's of 17.9K with sharp transition widths ( c 's of 104A/cm2at 19T and 4.2K were achieved. Mechanical properties of the reacted wire are no worse than those of typical commercial bronze-process Nb 3 Sn conductors, and e irrev is slightly higher.

Influence of microstructure on the properties of bronze-processed multifilamentary wire

Abstract: The A15 layer of a commercial Airco wire containing 2869 Nb filaments was analyzed as a function of heat treatment. Its microstructure is composed of three morphologically concentric shells. The central shell consists of fine equiaxed grains and has a nearly stoichiometric Sn concentration. High resolution electron microscopic analysis suggests that the fine grains are formed through the polygonization of dislocations. The homogeneous composition through the fine-grained layer is a probable consequence of the small grain size, which permits relatively rapid chemical redistributions through grain boundary diffusion. In contrast, the chemical gradient in the large-grained inner and outer sheels is steep. The microstructure is established by the reaction heat treatment, and determines the critical current. The best combination of grain size, composition, and volume of the fine-grained shell is obtained with an intermediate reaction temperature (700 to 730/sup 0/C); this temperature range also yields the best values of J/sub c/. Various two-step heat treatments were studied and compared to isothermal aging. The best microstructure and, hence, the best critical current characteristic was obtained by aging the specimen at 700/sup 0/C for 4 days followed by 730/sup 0/ for 2 days.

Microstructure of Rapidly Solidified Cu-Fe Alloys

Abstract: Rapidly solidified ribbons of Cu-Fe alloys with iron contents up to 20 at.-% have been prepared by melt-spinning. Optical and electron microscopy as well as x-ray and electron diffraction techniques were used to characterize quantitatively the microstructure, i.e., grain size and shape, solubility of iron, lattice parameter, volume fraction and distribution of precipitated iron-particles, etc. Whereas the free surfaces of melt-spun Cu-Fe ribbons have been found to be very smooth, the contact surfaces usually consist of isolated areas of good thermal contact with small equiaxed grains separated by bands without contact during casting and therefore poor heat transfer. The cross sections of the ribbons generally exhibit a strong anisotropy in their microstructure: very fine crystals adjacent to the contact surface develop into narrow columnar grains, generally significantly elongated and extending across the whole section. The average columnar width of the grains has been found to decrease significantly with increasing iron content. Precipitation of iron not only depends on the iron content but also on the distance from the contact surface.