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Showing papers on "Equiaxed crystals published in 1971"


Patent
06 Jul 1971
TL;DR: A mechanically alloyed composite powder wherein individual particles include an aluminum matrix having equiaxed aluminum oxide dispersoid particles having a size of about 100A to 2,000A uniformly distributed therethrough at particle spacings of about 500 to 3,000 A as mentioned in this paper.
Abstract: A mechanically alloyed composite powder wherein individual particles include an aluminum matrix having equiaxed aluminum oxide dispersoid particles having a size of about 100A to 2,000A uniformly distributed therethrough at particle spacings of about 500 to 3,000A. Products made by consolidating the mechanically alloyed powder exhibit improved strength properties at relatively low dispersoid contents.

114 citations


Journal ArticleDOI
01 Sep 1971
TL;DR: In this paper, the grain structure of catalytically clean Ni−Cu alloys is examined as a function of the degree of supercooling below the equilibrium liquidus, and it is concluded that solute elements can promote grain formation in certain castings at supercoolings insufficient to cause heterogeneous nucleation.
Abstract: Two related experimental programs on the solidification structure of alloy castings are reported. In the first, the grain structure of catalytically clean Ni−Cu alloys is examined as a function of the degree of supercooling below the equilibrium liquidus. For supercoolings greater than 85°C, the Ni−Cu alloys exhibit a structure which is in accord with previous observations in pure nickel,i. e., the structure is found to be coarse and dendritic in the range 85° to 150°C supercooling, but fine and equiaxed for supercoolings greater than 150°C. However, in the lower range of supercooling (<85°C) the structure is fine and equiaxed. It is concluded that solute elements can promote grain formation in certain castings at supercoolings insufficient to cause heterogeneous nucleation. To study the effect of solute elements on the structure of a solidifying material, castings of pure nickel and aluminum are compared with binary alloys of these base materials. Over the composition ranges studied in both alloy systems, the structure is observed to be related to a parameter which includes the slope of the liquidus, the bulk solute concentration, and the solute distribution coefficient. It is shown or is argued that heterogeneous nucleants are not involved and therefore another mechanism must be operating in determining the structure. In any event, these latter experiments suggest that an effective means of controlling the structure of castings is by appropriate selection of alloying additions on the basis of the alloy variables contained in such a parameter.

87 citations


Journal ArticleDOI
01 Jan 1971
TL;DR: Fracture toughness of an α-Β titanium alloy heat treated to a constant yield strength has been found to depend upon the morphology of α produced or remaining after the initial solution treatment.
Abstract: Fracture toughness of anα-Β titanium alloy heat treated to a constant yield strength has been found to depend upon the morphology of α produced or remaining after the initial solution treatment. In equiaxed α structures, fracture toughness depends linearly upon the grain boundary area per unit volume,Sv, and is independent of equiaxed α particle size or spacing. In a grain boundary α structure fracture toughness depends both onSv and, within limits, linearly on the thickness of the α. Explanations are offered for the observed propagation of cracks at α-@#@ Β interfaces and for the observation that high fracture toughness can accompany low tensile ductility.

68 citations



Patent
21 Sep 1971
TL;DR: In this article, a martensitic or bainitic alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenitic crystals thoughout the material.
Abstract: Ferrous alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to form a martensitic or bainitic structure. The material is then worked to an extent sufficient to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenite crystals thoughout the material. Exceptionally fine equiaxed grains in the micron and submicron range are achieved, thereby providing unique combinations of both increased strength along with increased ductility and increased notch toughness.

10 citations


Journal ArticleDOI
TL;DR: In this paper, the growth kinetics of Niobium and niobium alloys have been studied and the structures of the coatings (equiaxed-, columnar- or needle grains) vary according to the structural state of the niibium, either recrystallized or cold-worked, (or with the microhardness value of the alloy).
Abstract: Niobium and niobium alloys have been coated by pack-cementation. The compound NbAl3 was the main constituent of the coatings. The structures of the coatings (equiaxed-, columnar- or “needle grains”) vary according to the structural state of the niobium, either recrystallized or cold-worked, (or with the microhardness value of the alloy), the temperature of the heating cycle and the composition of the pack. The mechanical properties of the metal are found to have a strong influence on the structures. If the deformation of the substrate allows the growth stresses arising in the coating to be relaxed, columnar or needle grains are formed, otherwise the structure consists of equiaxed grains. The growth kinetics of the coatings were also studied.

8 citations


Journal ArticleDOI
TL;DR: In this paper, a double cantilever beam specimen was used to study the intergranular fracture of an Al-15 wt pct Zn alloy tested in air, distilled H2O, and 0.5M NaCl with two different types of specimens: polycrystals with large equiaxed grains and bicrystals.
Abstract: Crack propagation rates for the intergranular fracture of an Al-15 wt pct Zn alloy tested in air, distilled H2O, and 0.5M NaCl have been studied using a double cantilever beam specimen. This technique has been applied to two different types of specimens: polycrystals with large equiaxed grains and bicrystals. The susceptibility to intergranular fracture in air and 0.5M NaCl increases as the volume fraction of G.P. zones in the matrix increases. The microstructure which is most susceptible to fracture exhibits intense planar slip traces while the more resistant microstructures have a more diffuse surface slip pattern. The dependence of cracking rates on the microstructure is explained in terms of the blocking of inhomogeneous plastic flow in the matrix by grain boundaries, resulting in locally severe stress concentrations at the boundaries. Bicrystal tests substantiate these results and show that orientations favoring partial continuity of slip bands across grain boundaries are less susceptible to stress corrosion cracking than arbitrarily oriented boundaries with no slip continuity.

7 citations



20 Oct 1971
TL;DR: In this paper, the authors investigated the fatigue crack growth behavior of Ti-6Al-6V-2Sn for five different microstructures, using contoured double-cantilever beam specimens.
Abstract: : The fatigue crack growth behavior of Ti-6Al-6V-2Sn was investigated for five different microstructures, using contoured double-cantilever beam specimens The fatigue crack growth behavior was compared with the mechanical strength, toughness, and ductility properties for each microstructure The fatigue fracture suffaces were examined with a scanning electron microscope Annealed structures consisting of equiaxed primary alpha have the lowest crack growth resistance, while the acicular alpha microstructure resulting from beta annealing has a growth resistance four times greater in the intermediate growth regime No simple model of crack growth rate using gross mechanical properties describes the relative magnitude nor the ralative order of crack resistance among the different microstructures (Author)

6 citations



Journal ArticleDOI
TL;DR: In this article, the authors investigated the changes and the construction mechanism of solidification structure for the weld metal which had been welded with a moving arc heat source and found that the nominal growth rate in the welding metal increases generally as the inward growth proceeds, while the temperature gradient decreases.
Abstract: The changes and the construction mechanism of solidification structure were investigated for the weld metal which had been welded with a moving arc heat source. The materials used were aluminum sheets with different chemical compositions. The conclusions obtained are as follows:(1) The nominal growth rate in the weld metal increases generally as the inward growth proceeds, while the temperature gradient decreases.(2) When the welding is performed in a condition that the bead width is almost the same, the values of the temperature gradient decrease as the welding speed increases. Accordingly the extent of the constitutional supercooling zone in the weld metal increases as the inward growth proceeds and besides the welding speed increases.(3) The columnar crystals develop in the weld metal and under certain circumstances the equiaxed dendrites develop near the center of the weld metal.(4) In the 99.96%- and 99.93%-aluminum sheets, the planar growth is observed near the fusion boundary and afterwards the cellular subgrain is observed. In this case the equiaxed dendrites do not develop.(5) In the commercially pure aluminum sheets, the solidification structure changes from planar to cellular subgrain and cellular dendrite as the inward growth proceeds. The equiaxed dendrites develop near the center of the weld metal when the welding is performed in a high speed.(6) In aluminum alloy sheets, the cellular dendrite is observed even near the fusion boundary and afterwards a lot of equiaxed dendrites develop.(7) The changes of the solidification structure shown in (4), (5) and (6) can be accounted for in terms of the phenomenon of the constitutional supercooling.(8) When the welding is performed in a condition that the bead width is almost the same, it becomes easy for the equiaxed dendrites to develop in the weld metal as the welding speed increases. This phe-nomenon will be accounted for in terms of the extent of the constitutional supercooling zone.

01 Nov 1971
TL;DR: In this paper, the tensile properties and fracture toughness levels found in forged and heat treated pancake forgings of the high strength titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, were analyzed as to their relationship to microstructural features.
Abstract: : The tensile properties and fracture toughness levels found in forged and heat treated pancake forgings of the high strength titanium alloy, Ti-6Al-2Sn-4Zr-6Mo, were analyzed as to their relationship to microstructural features. The desired microstructure for the alloy, resulting in an optimum combination of both fracture toughness and tensile ductility at yield strengths of 170-180 ksi, is described as containing about 10 volume percent equiaxed globular alpha (primary alpha) along with a matrix containing relatively coarse acicular alpha (secondary alpha) and aged beta. (Author)

Journal ArticleDOI
01 Oct 1971-JOM
TL;DR: In this paper, metal flow is shown to have an influence in determining whether equiaxed, columnar, or twin columnar grains form in continuously cast aluminum alloys.
Abstract: Metal flow is shown to have an influence in determining whether equiaxed, columnar, or twin columnar grains form in continuously cast aluminum alloys.

Journal ArticleDOI
TL;DR: In this article, the authors obtained 2-3mm in diameter α-SiC crystals with high pure silicon as a solvent at 2200°C for 5 hours or less.
Abstract: Platy α-SiC crystals, 2-3mm in diameter were obtained by the method. Growth experiments were performed using purified dense graphite crucible (bulk density>1.80) and high pure silicon as a solvent at 2200°C for 5 hours or less.These crystals were consisted of mainly 6 H type. The probability to form wurtzite type twinning, the angle between basal plane being ca. 70°30′ in these crystals is less than that in these obtained by sublimation method.Though some of the crystals include very thin silicon layer, generally these inclusions show a tendency to localize in a part of a crystal. Fine and dispersed inclusion such as carbon particle in the crystals by sublimation method is not observed in these crystals. The relation between the polality of the basal surfaces and their growth rate is studied by chemical etching, and it is suggested that there is reverse relation between crystals grown from silicon solution and sublimation.

01 Mar 1971
TL;DR: In this article, the relationship between fracture toughness and microstructure of both equiaxed alpha and Widmanstatten plus grain boundary in aged beta matrix morphologies was investigated.
Abstract: : The investigation to relate fracture toughness, void formation and growth and ductility to microstructural features in an alpha-beta alloy, Ti-5.25Al-5.5V-0.9Fe-0.5Cu continued. New data confirm the earlier reported relationships between fracture toughness and microstructure of both equiaxed alpha and Widmanstatten plus grain boundary in aged beta matrix morphologies. In equiaxed alpha structures, fracture toughness depends linearly upon the grain boundary area per unit volume, S sub V, and is independent of equiaxed alpha particle size or spacing. In a grain boundary alpha structure, fracture toughness depends both on S sub V and, within limits, linearly on the thickness of the grain boundary alpha. Equations relating tensile void growth rates to microstructure for both morphologies have been derived. Tensile fracture is shown to be intergranular in nature and occurs when a critical crack length-stress relationship s satisfied. The amount of ductility achievable in a specimen depends upon the rate of void growth. If the growth rate is rapid, the crack reaches a critical size for fracture at a lower applied stress and strain and hence the ductility is less. A mechanism for void growth at alpha-beta interfaces is presented which accounts for the higher frequency of voids at 30-70 degrees to the tensile axis. An explanation is offered to the apparently contradictory behavior in which grain boundary alpha improved fracture toughness but lowers tensile ductility. (Author)