Showing papers on "Superplasticity published in 1973"

Flow stress and microstructure in superplastic 60/40 brass

Abstract: Stress-strain curves have been obtained for a superplastically deformed industrial 60/40 brass tested in tension under constant true strain-rate conditions at 600‡C. This alloy produced by extrusion shows a fibrous structure with elongated grains. It is shown that the flow stress is influenced by two microstructural factors, i.e. the change of phase shape which becomes approximately equiaxed and the variation of the phase size during superplastic deformation. These factors are of different relative importance according to the strain-rate.

Cavitation at grain and phase boundaries during superplastic flow of an aluminum bronze

Abstract: Cavities have been observed to form at grain and phase boundaries under certain strain rate conditions during superplastic tensile deformation of a Cu-9.5 pct Al-4 pct Fe aluminum-bronze. The cavities form preferentially at α-β interfaces or triple junctions involving both phases. The process of cavitation is associated with grain boundary sliding and cavity nucleation probably occurs at points of stress concentration in the sliding interfaces. The ductility is not markedly impaired by the cavities because the high strain-rate sensitivity of the material inhibits the interlinkage of cavities at high strains. A range of strains and strain rates for superplastic forming processes has been determined at which the volume fraction of cavities present was tolerable.

Models for grain rearrangement resulting from grain boundary sliding

Abstract: An analysis of grain boundary sliding (GBS) in polycrystalline solids is made using two-dimensional arrays of identically shaped grains. It is shown that GBS not requiring accommodation at grain boundary triple-points, acts in such a way as to produce a grain rearrangement in which the number of grains along the length of the sample changes. This is classified as Rachinger sliding. On the other hand, when the grains are deformed to accommodate GBS, the number of grains along the length of the sample does not necessarily change during deformation and we have only Lifshitz sliding. The implication of these models is that Rachinger's grain-shape change technique for measuring GBS is incorrect when GBS requires grain boundary triple-point accommodation. Also, these models are used to discuss some features of superplastic deformation and diffusional creep.

Steel product having improved mechanical properties

Abstract: Steel products, which have been subjected to a desired deformation, are characterized by superior strength, including markedly improved toughness or tensile properties or both, as a result of procedure whereby the steel is made temporarily superplastic at an elevated temperature and is deformed while in such state. This procedure for converting steel, notably ordinary and alloy grades of low carbon, ferritic character, to a superplastic state, e.g. affording very high ductility, and for deforming such superplastic steel in a desired manner, embraces: rapidly heating a body of steel to a temperature, advantageously in the alpha-plus-gamma phase field, where the steel is then found, over a brief interval, to experience a transitional state of severe microstructural instability and to be characterized by superplasticity; and applying stress to the body in such interval to effect the desired deformation. The new products, which are compositionally of the character required for the process, are found to have much higher strength than the original steel.

Superplasticity in a new dispersion strengthened zinc alloy

Abstract: A new dispersion strengthened zinc alloy has been developed which exhibits both high yield strengths at room temperature and superplasticity at elevated temperatures The alloy has a nominal composition of Zn-010 Ni-004 Mg A dispersion of submicron size precipitates was readily produced within this alloy by rapid solidification to form a supersaturated solid solution followed by thermal mechanical processing The precipitates suppressed superplastic deformation at room temperature and stabilized the grains at elevated temperatures, reducing the grain growth rate of zinc to 41 × 10−2 µ/h at 203°C The deformation characteristics of the alloy are investigated with special emphasis on the influence of the precipitates on the tensile properties It was found that the stress increased with a decrease in precipitate size and spacing for strain rates less than those at maximum rate sensitivity at 151°C and also for nonsuperplastic strain rates at 24°C The slope of the Hall-Petch plot was found to be sensitive to both the grain diameter and strain rate at 24°C The change of sign of the slope of the Hall-Petch plot at slow strain rates and small grain diameters was found to coincide with a rapid increase in the strain rate sensitivity An equation of the form σ =A d ψ exp(Q/RT) eηemhas been developed to describe the deformation characteristics of this alloy at elevated temperatures and presuperplastic strain rates

Superplasticity and residual tensile properties of a microduplex copper-nickel-zinc alloy

Abstract: Structural superplasticity in two phase alloys of the copper-nickel-zinc system (nominal composition in wt. pct Cu-15Ni-38 Zn-0.2 Mn) occurs over a wide range of strain rates in the temperature range 850 to 1050∮F (454 to 565°). The upper temperature limit for super-plastic behavior in this system is determined by the reversion of the fine-grained two-phase structure to a single phase structure in which extensive grain growth is possible. Residual room temperature tensile properties and microstructure of the microduplex alloy after superplastic straining have been studied as a function of test temperature and total super-plastic strain. At test temperatures sufficiently removed from the phase transformation temperature, the high tensile properties and fine microstructure of the starting material are essentially retained after superplastic strains approaching 200 pct. In the immediate vicinity of the phase transformation temperature, rapid degradation of the microduplex structure occurs during superplastic deformation with a consequent severe degradation of the residual room temperature tensile properties.

High strength microduplex Cu-Ni-Zn alloys

Abstract: High ambient temperature tensile and fatigue strengths have been obtained in two-phase α-β Cu-Ni-Zn alloys (nickel silvers) by controlled thermomechanical working. The thermomechanical working operation involves cold working of solution annealed stock, followed by annealing in the two-phase region. This results in simultaneous recrystallization and precipitation yielding a fine-grained two phase microstructure termed “microduplex”. The high mechanical properties obtained are attributed to the fine-grained two-phase microduplex microstructure. Compositional variations studied included 10 to 40 pct Ni, 35 to 40 pct Zn, balance Cu. On the basis of ease of processing and mechanical properties, a particularly attractive composition is Cu-15Ni-37.5Zn, designated IN-836. Typical room temperature properties of IN-836 in the microduplex condition include 100 ksi (690 MN/m2) yield strength with 25 pct elongation and 40 ksi (275 MN/m2) fatigue limit (107 cycles). Finally, superplastic behavior has been observed in IN-836.

Superplasticity in Extruded Zn-40wt.-%Al and Zn-50wt.-% Al Alloys

Abstract: The mechanical properties of extruded Zn-40wt.-%Al and Zn-50wt.-%Al alloys have been investigated and correlated with their microstructures as determined by transmission electron microscopy. The effect of composition on the superplastic properties is discussed and microstructural evidence has been obtained for slip deformation during superplastic flow of the Zn-40wt.-% Al alloy.

Production of homogeneous alloy articles from superplastic alloy particles

Abstract: The constitutionally complex alloys, particularly those exhibiting good high temperature strength and prone to the development of unacceptable heterogeneity in conventional casting operations, are produced by consolidation of a cold-worked particulate material which is sized to preclude the development thereon, in the time span at temperature used in consolidation, of undesirable surface phases such as carbides which inhibit particulate bonding.

Forming of superplastic alloy sheet

Abstract: A method of moulding superplastic alloy sheet material by holding a blank of sheet material, heated to a temperature at which it exhibits superplasticity, adjacent a fluid pressure duct or manifold, and applying fluid pressure to the blank sheet through the duct or manifold to cause the heated sheet to conform to the shape of a mould surface arranged on the side of the sheet remote from the duct or manifold. The fluid pressure manifold may be a heated plate having a plurality of apertures therein.

Superplastic zinc alloys - improved creep resistance

Abstract: Super plastic zinc alloys with alloying additions of 0.001 to 0.03 pref. 0.005-0.02% Mg and 1-35% Al have much improved creep characteristics, far superior to other Zn/Al alloys or Zn/Al/Cu alloys. Some or all the Mg may be replaced by Be, Cr, Fe, Si, B or Ti. Two main ranges of composition are used i.e. 3-6% Al; 20-23% Al. General compositions are 1-35% Al; 0.005-0.02% Mg; Bal Zn plus 0.5-1.2% Cu and/or other elements to replace Mg. Theses alloys have all the super plastic properties but their higher creep resistance enlarges the scope for their use in deep drawing.

Extended ductility in beryllium

Abstract: Fine grained ingot-source beryllium exhibits extensive ductility near 700°C at strain rates between 5 x 10-5/s and 5 x 10-4/s. Elongations of approximately 100 pct and strain rate sensitivities as high as 0.9 were measured in 16 μm grain size beryllium sheet under these conditions. The high ductility and high strain rate sensitivity in ingot-source beryllium involves a substantial grain boundary sliding contribution to the deformation process at high temperatures and moderately low strain rates. The deformation can probably be characterized as superplastic even though the elongation observed is low compared with that seen in other superplastic materials. Fine-grained, powder source beryllium did not show high ductility under similar conditions, presumably because of the high oxide content.

Moulding of superplastic alloy sheet

Abstract: A superplastic alloy sheet material which has been removed from a mould is held at a temperature of from 180* to 220*C to remove undesired warping or distortions from the moulded sheet.

Drawing and extrusion of superplastic metals through cone-shaped dies

Abstract: Closed-form solutions are obtained for the stress and die pressure distributions, time and flow rates for drawing and extruding superplastic cylinders through a cone-shaped die with Coulomb friction. Numerical examples are presented graphically and the possible existence of a maximum limit for area reduction in the drawing process is pointed out and discussed.

Low temperature deformation characteristics and cavitation of the eutectoid Al-Zn superplastic alloy

Abstract: The strain rate and temperature dependences of the low stress of the superplastic Al-Zn alloy were studied by conducting tensile tests between -80°C and 30°C. Microstructures before and after deformation were also examined. The principal results obtained are as follows:(1) The linear relationships of logσy-loge., logσO2-loge, logσm-loge and logσ6.0-loge were valid not only at high temperatures but at low temperatures.(2) The strain rate sensitivity exponents, m, determined from the logσ-loge curves, were 0.23, 0.17 and 0.12 at, 30°C, 0°C and -20°C, respectively. However, the m-values, obtained by the Backofen method, depended on the strain rate. It was suggested that this was due to structural changes during deformation.(3) The strain rate showed the Arrhenius type temperature dependence when deformation was beyond the maximum stress in tensile tests. The activation energy was independent of the stress and equal to 0.58eV, which was smaller than that of the bulk and grain boundary self-diffusion of Al and Zn.(4) When deformation was carried out between -20°C and 30°C, many voids and cavities developed at grain boundaries, transverse to the tensile axis, and grew as the strain increased.(5) Grain-and phase-boundary sliding was predominant at 30°C. It was still observed at 0°C. Any evidence of crystallographic slip inside grains were not detected at these temperatures.

Method of making lamp cap connections using superplastic alloy

Abstract: Electric lamps are disclosed having lead-in wires which extend out of the lamp envelopes and are connected to external electrical terminals, the terminals including hollow metal sleeves receiving the wires and the wires being joined thereto using alloys which exhibit superplastic behaviour, the alloys being heated, without melting, and caused to flow or creep superplastically into the sleeves and around the wires.

Superplasticity of steel Kh18N10T

Abstract: : The possibility of producing superplasticity in single-phase alloys through creation of fine-grain structure in them by preliminary heat treatment was investigated.

Superplastic deformation and high temperature creep of a monotectoid- composition uranium-base alloy

Abstract: The elevated-temperature creep properties of a monotectoidcompositicm uranium-base alloy have been studied as a function of microstructure. The alloy used In this investigation, U-7.5Rb-2.5Zr (vv... pet), exists as a single Y phase above 637°C and transforms to a two-phase structure (a + Y ) below 637'C. Three areas of investiga­ tion were undertaken; (1) theraojaechanical processing techniques to achieve a fine-grain equiaxed a + y microstrueture; (2) creep defor­ mation of the fine-grain equiaxed a + Y structure; (3) creep deforma­ tion of the coarse-grain y structure. Deformation behavior was studied using tension and compression teats performed in the temperature range 500 1000°C on an Instron -machine using an inert atmosphere. Deformation-enhanced spheroidization was studied as a technique to produce a fine-grain equlaxv'.d microstructure from the lamellar a + Y, structure formed by isothermal transformation. The spheroidization kinetics were slower than observed in a eutectoid-composition Fe-C allay at the sane homologous temperature and strain rate. Although incomplete spneroidization was observed after strains as large as Z * 1.9, the results were in qualitative agreement with spheroidization mechanisms proposed for steels, A fine-grain equiaxed a + y structure can be most efficiently produced by employing a quench-cold work-anneal treatment before hot working. An equiaxed structure with a 0.5 urn grain size was produced by gamma quenching, cold working to e = 0,5, annealing at 5S0*C for