Showing papers on "Equiaxed crystals published in 1985"
TL;DR: In this article, the authors investigated the role of vacancy coalescence in the growth of spherical porosity in nickel-base superalloys, and found that vacancy formation is the operative mechanism of pore growth.
54 citations
TL;DR: In this article, the authors analyzed the solute distribution of a directionally solidified Al-4 wt pct Cu-0.2 wlt pct Ti alloy ingots with equiaxed structures.
Abstract: Directionally solidified Al-4 wt pct Cu-0.2 wt pct Ti alloy ingots with equiaxed structures were analyzed for solute distribution. Inverse segregation was found to exist, and the extent of segregation in the first 50 pct of the ingot solidified agreed well with that calculated from inverse segregation theory based on the flowback of enriched liquid. However, at higher points in the ingot, the solute distribution deviated from the theoretical one. Also, more and bigger shrinkage pores existed in the equiaxed grained ingot than in a columnar grained ingot. It is suggested that the formation of randomly distributed, equiaxed grains restricts the flowback of enriched interdendritic liquid much more than the formation of columnar grains where interdendritic channels exist. In an equiaxed grained ingot solidified vertically from the bottom upward, the hydrostatic pressure becomes insufficient to cause complete flowback of enriched liquid in the latter stages of solidification. This effect causes porosity in the ingot and a solute distribution which deviates from that predicted by the theory of inverse segregation.
39 citations
TL;DR: In this article, magnetron sputtering was carried out on electrolytically thinned steel substrates for transmission electron microscopy examination, and as-deposited films showed fine equiaxed grains of TiN on the substrate that was not sputter etched.
36 citations
TL;DR: In this article, the Czochralski method was used to grow single crystals of BaLaGa3O7 with a distinct dependence of the chemical composition on the growth plane orientation.
29 citations
TL;DR: In this paper, the authors show that the response to multiaxial stress is also strongly influenced by the anisotropy of the diffusion distances of vacancies between their sources and sinks.
Abstract: The rate of Nabarro-Herring creep is known to depend strongly on grain size and shape since it involves the diffusion distances of vacancies between their sources and sinks. The anisotropy of creep rate by this mechanism is thus apparent in materials in which grains are not equiaxed. An analysis is presented which shows that the response to multiaxial stress is also strongly influenced by such anisotropy. From the analysis, formulae are derived which permit the creep rate along three axes parallel to the three principal stresses to be calculated for orthorhombic grains of different shapes.
28 citations
TL;DR: In this paper, the morphology, grain size and composition of A15 diffusion layers produced on heat-treating Nb-bronze and (Nb, Ta)-Bronze multifilamentary composites over the temperature range 650 to 800 ˚ C have been investigated and compared using transmission electron microscopy with energy dispersive spectroscopy.
Abstract: The morphology, grain size and composition of A15 diffusion layers produced on heat-treating Nb-bronze and (Nb, Ta)-bronze multifilamentary composites over the temperature range 650 to 800‡ C have been investigated and compared using transmission electron microscopy with energy dispersive spectroscopy. A characteristic two-fold layer structure of columnar and equiaxed grains has been confirmed in both cases at all temperatures while tantulum was shown to be incorporated into the A15 phase and to retard grain growth. A model for evolution of the microstructure is proposed and discussed.
17 citations
TL;DR: In this article, the authors used electron microscopy to characterize the microstructure of commercial binary and ternary Al5 multifilamentary composites and found that columnar structure develops into an equiaxed grain structure; the mean grain size depends on the core composition.
Abstract: Electron microscopy has been used to characterize the microstructure of commercial binary and ternary Al5 multifilamentary composites. TEM sections have been prepared using ion beam milling from samples reacted for various times at temperatures in the range 650- 800°C. Layer growth kinetics have also been investigated using a combination of SEM and low temperature inductive measurements. The presence of a band of columnar grains adjacent to the refractory core is confirmed in all cases and is particularly marked at the lower temperatures. As layer growth proceeds, the columnar structure develops into an equiaxed grain structure; the mean grain size depends on the core composition. On the basis of this microstructural investigation and precise measurements of filament volume and length changes during reaction, it is proposed that the mechanism for microstructure modification is stress driven grain boundary sliding. A model describing this process is summarised.
14 citations
TL;DR: In this article, the authors describe the structural changes occurring during hot deformation by compression or by rolling under comparable conditions, and the structures formed during rolling at ϵ g3′ > 1 s −1 correspond to the unsteady stage of hot deforming.
13 citations
TL;DR: In this article, transmission electron microscopy studies have been carried out on the structures of chips formed during the high-speed machining of steel, showing that the chip bodies, which reached temperatures of ~300°C during machining, had very fine, elongated, parallel-sided ferrite cells.
Abstract: Transmission electron microscopy studies have been carried out on the structures of chips formed during the high-speed machining of steel. The chip bodies, which reached temperatures of ~300°C during machining, had a pearlitic-ferritic structure with very fine, elongated, parallel-sided ferrite cells. The structure of the flow zone, which attained a maximum temperature of ~900°C, consisted, in all cases, of equiaxed ferritic cells, 0·5–1·5 μm dia., with dislocation tangles in many cell boundaries, but few internal dislocations. No pearlite was observed in the flow zone, but initially pearlitic areas showed cementite networks at cell boundaries and very small cementite particles. Coarse cementite particles in spheroidized steel remained largely intact in the flow zone. Textures developed in the flow zone and in the chip body were ferrite shear textures. The flow zone is a thermoplastic instability, and this work suggests that the observed fine, equiaxed cell structures have the characteristic of pe...
9 citations
TL;DR: In this paper, three basic requirements for superplastic deformation are listed: the material must be tested at a temperature of at least 0.5 Tm, where Tm is the absolute melting point of the matrix.
7 citations
TL;DR: Fusion zone microstructures in an electron beam welded powder metallurgy Al-8Fe-1.7Ni alloy have been examined using optical and electron microscopy techniques as mentioned in this paper.
TL;DR: In this article, it is shown that the equilibrium dihedral angles in deformed polycrystals will give rise to curved interfaces, which will force migration of boundaries in such a direction that the equiaxed grain structure of the polycrystal is restored.
TL;DR: In this article, the properties of melt-spun Cu-Ni and Cu-Fe alloys are investigated and three regions can be distinguished: a narrow zone of equiaxed chill crystals at the contact side, a zone with columnar grains and a layer of equilibrium crystals near the free surface.
Abstract: Copper-based alloys with up to 30 at.% Fe, Ni and Zr which are selected because of their different solubility in Cu have been prepared by melt-spinning. Whereas rapid solidification of Cu-Fe alloys results in supersaturated solid solutions with Fe contents up to about 20 at.%, no significant increase of zirconium solubility, but the formation of a number of intermetallic compounds as well as glassy structures have been observed. In cross or longitudinal sections of melt-spun Cu-Ni as well as Cu-Fe alloys three regions can be distinguished: a narrow zone of equiaxed chill crystals at the contact side, a zone with columnar grains and a layer of equiaxed crystals near the free surface. Analyzing these microstructures the micromechanisms responsible can be derived. Changing the wheel speed or the melt temperature has been found to result in an extension of one or the other of these regions at the others cost, thus influencing other properties, e.g. fracture strength or microhardness.
TL;DR: In this article, the transition from columnar to equiaxed solidification is controlled by the extent of the constitutionally undercooled zone, and it is shown that the transition is controlled through the effects of fluid flow, heat flow and solute mass transport during meltspinning of aluminium alloys.
Abstract: By application of a mathematical model including the effects of fluid flow, heat flow and solute mass transport during meltspinning of aluminium alloys in combination with experimentally obtained data, it was found that the transition from columnar to equiaxed solidification is controlled by the extent of the constitutionally undercooled zone.
01 Jan 1985
TL;DR: The heat treatments examined produced alternate microstructures to the lamellar structure and some approached the totally transformed acicular alpha structure, which has been shown to exhibit the best fatigue properties for Ti-6A1-4V alloy in the notched condition.
Abstract: Previous studies have shown that the application of a porous Ti-6A1-4V alloy coating results in a substantial decrease in the substrate material fatigue properties. This phenomenon is due to both a microstructural change from the equiaxed alpha-beta microstructure to a lamellar structure and a notch effect created by the porous coating. The lamellar microstructure has been shown to exhibit the worst fatigue properties of the most common structures obtained in Ti-6A1-4V alloy. This study examined various post-sintering heat treatments which would alter the material microstructure and possibly result in improved fatigue performance. The heat treatments examined produced alternate microstructures to the lamellar structure and some approached the totally transformed acicular alpha structure. The acicular alpha structure has been shown to exhibit the best fatigue properties for Ti-6A1-4V alloy in the notched condition.
01 Dec 1985
TL;DR: In this paper, the effect of a bimodal grain size distribution on the compressive strength of equiaxed randomly oriented polycrystalline ice Ih was examined and two possible candidates of a significant grain size were examined, one derived from the use of Hall-Petch relation and the second being the average of the two grain sizes.
Abstract: : Previous studies have shown that grain size directly affects the strength of fresh-water equiaxed polycrystalline ice Ih, where strength decreases as grain size increases. This has been shown both in tension and compression at constant strain rates over a range of temperatures (-5 C, -1o C, -20C). The mechanical behavior of the ice is well described by the Hall-Petch relation. This thesis presents the results of a study to examine the effect of a bimodal grain size distribution on the compressive strength of equiaxed randomly oriented polycrystalline ice Ih. Laboratory prepared specimens of right circular ice consisting of different amounts of large (5.5 mm) and small(2.0 mm) grains by volume (75%/25L%, 50%/50%, 25%75%) were tested at -10 C in uniaxial unconfined compression. Tests were conducted at two strain rates, 0.00001/S and 0.001/s. Building on the results of Cannon (1985), this work establishes the law of mixtures for the compressive strength of a specimen composed of a bimodal mix of grains. First hypotheisized by Lee(1985), the law of mixtures states that the strength of a bimodal specimen is linearly dependent on the volume fraction of large and small grains. A single significant grain size may be used to charcterize the mechanical behavior of the specimen. Two possible candidates of a significant grain size are examined, one derived from the use of the Hall-Petch relation and the second being the average of the two grain sizes. Results show the use of the average is more expedient with little loss in accuracy.
Patent•
07 Aug 1985
TL;DR: In this article, an equiaxed, passivated iron or iron alloy particles for magnetic recording purposes are produced by casting a melt comprising a base metal, e.g. copper or gold, and iron and iron alloy into strip form, optionally rolling the strip, and then electrolytically dissolving the base metal from the strip to recover the iron particles formed in the strip during the casting step.
Abstract: Equiaxed, passivated iron or iron alloy particles for magnetic recording purposes are produced by casting a melt comprising a base metal, e.g. copper or gold and iron or iron alloy into strip form, optionally rolling the strip, and then electrolytically dissolving the base metal from the strip to recover the iron particles formed in the strip during the casting step. Apparatus for collecting ferromagnetic particles distributed in metallic material comprises a tank 60, support surface means 31 for supporting dissolving metallic material and collecting undissolved particles and magnetic field forming means 70 for adhering undissolved particles to the support surface means. Cast, equiaxed, iron or iron alloy particles having a size in the range 0.05 to 0.5 microns are claimed per se. The particles may include up to 10% (preferably 2-7%) Ni, CO or Mn.
TL;DR: In this paper, a microscope optique de la solidification d'etain pur a 99,9% and d'alliages contenant en poids: 0,5, 10,0, 30,0; 38,1, 50,0 and 70,0% de Pb, sous 2 gradients de temperature differents, to determiner l'influence du gradient de temperature and de la composition sur la formation of cristaux equiaxes.
Abstract: Observation directe au microscope optique de la solidification d'etain pur a 99,9% et d'alliages contenant en poids: 0,5; 10,0; 30,0; 38,1; 50,0 et 70,0% de Pb, sous 2 gradients de temperature differents, afin de determiner l'influence du gradient de temperature et de la composition sur la formation de cristaux equiaxes
01 Jan 1985
TL;DR: In this paper, the effect of grain anisotropy on the creep resistance of the Al alloy, Type 7075, was studied and it was found that stressing parallel to the longitudinal axis of heavily deformed grains produces the best creep resistance.
Abstract: The effect has been studied of grain anisotropy on the creep resistance of the Al alloy, Type 7075. It is found that the effect of stressing parallel to the longitudinal axis of heavily deformed grains produces the best creep resistance. Comparative tests on equiaxed material reveal this to have relatively poor creep properties. These results are interpreted in terms of the influence of grain boundaries.
TL;DR: In this article, the concurrent effects of temperature and deformation on microstructure and mechanical properties of a 1.85 pct Sb lead alloy were examined by extrusion over the temperature range 0.7T m to 0.9T m, at deformation rates between 0.65 and 12 s-1.
Abstract: The concurrent effects of temperature and deformation on microstructure and mechanical properties of a 1.85 pct Sb lead alloy were examined by extrusion over the temperature range 0.7T
m to 0.9T
m, at deformation rates between 0.65 and 12 s-1. Alloys deformed in the solid-solution regime or at the solvus temperature exhibited microstructures consisting of a mixture of elongated deformed grains and equiaxed recrystallized grains; some discontinuous precipitation was also evident. In the two-phase regime the structure was mainly fibrous; in this, the high resistance to recrystallization and the suppression of the discontinuous precipitation reaction could be attributed to the presence of fine precipitates in the dynamically formed substructure. A regime for providing optimum strength and stability was defined in the strain rate-temperature field investigated.
TL;DR: In this article, two typical macrostructures were observed: one with an equiaxed zone and the other without, and it was shown that the formation of the equiaXed zone is caused by an excessive gap between the rollers.
Abstract: High-silicon steel was rapidly solidified to thin strips by the double roller method. Two typical macrostructures were observed: one with an equiaxed zone and the other without. The formation of the equiaxed zone is caused by an excessive gap between the rollers. Heat transfer calculations and dendrite arm syacing measurements both suggested that the cooling rate is about 10 3 to 10 4 K/sec.
TL;DR: Titanium alloys containing alpha matrices with various rare earth compound dispersions were prepared by melt extraction as discussed by the authors, and the melt extracted material was HIPped, extruded, and thermally exposed to yield various microstructures including transformed beta and equiaxed alpha.
Abstract: Titanium alloys containing alpha matrices with various rare earth compound dispersions were prepared by melt extraction. The melt extracted material was HIPped, extruded, and thermally exposed to yield various microstructures including transformed beta and equiaxed alpha. Tensile and creep tests were conducted on material in the different microstructural conditions. Trends in mechanical behavior as a function of alloy chemistry and process history are discussed. The alloys with a transformed beta microstructure had superior creep resistance. Alloys containing dispersoids had better tensile ductilities compared with those which did not contain a dispersoid. Portions of this work were carried out under Air Force Contract F33615-83-C-5034.
TL;DR: In this paper, the microstructures of ordered Ti3Al-1Zr (alpha2+Zr) and Ti-Al-Nb alloys produced by ingot metallurgy (IM) and by rapid solidification (RS) are compared.
Abstract: The microstructures of ordered Ti3Al-1Zr (alpha2+Zr) and Ti-Al-Nb alloys produced by ingot metallurgy (IM) and by rapid solidification (RS) are compared. The RS Ti3Al-1Zr (alpha2 structure) alloy displayed small antiphase domains (APD) of 10–20 nm in the as-produced condition, but large grain size. The latter observation is rationalized in terms of the cooling history used to produce the material. The RS Ti-Al-Nb alloy exhibited an equiaxed microstructure. The IM Ti-Al-Nb material displays a complete change in microstructure between 1010°C and 1035°C, indicating a narrow alpha+beta phase field.
TL;DR: In this paper, the effects of controlled rolling on transformation behavior of two powder forged (P/F) microalloyed vanadium steels and a cast micro-alloying vanadium steel were investigated.
Abstract: The effects of controlled rolling on transformation behavior of two powder forged (P/F) microalloyed vanadium steels and a cast microalloyed vanadium steel were investigated. Rolling was carried out in the austenitic range below the recrystallization temperature. Equiaxed grain structures were produced in specimens subjected to different reductions and different cooling rates. The ferrite grain size decreased with increasing deformation and cooling rate. Ferrite nucleated on second phase particles, deformation bands, and on elongated prior austenite grain boundaries; consequently a high fractional ferrite refinement was achieved. Deformation raised the ferrite transformation start temperature while the time to transformation from the roll finish temperature decreased. Cooling rates in the cast steel were higher than in P/F steels for all four cooling media used, and the transformation start temperatures of cast steels were lower than that of P/F steel. Intragranular ferrite nucleation, which played a vital role in grain refinement, increased with cooling rate. Fully bainitic microstructures were formed at higher cooling rates in the cast steel. In the P/F steels inclusions and incompletely closed pores served as sites for ferrite nucleation, often forming a ‘secondary’ ferrite. The rolling schedule reduced the size of large pores and particle surface inclusions and removed interconnected porosity in the P/F steels.