21 Matching Results

Search Results

Advanced search parameters have been applied.

Plastic flow and strength of uranium and its alloys

Description: The mechanical behavior of uranium and its alloys is reviewed with special emphasis on plastic flow behavior of polycrystalline materials. The strength of uranium is influenced by crystal structure as well as by point, planar, and volume defects; wit these factors in mind, texture hardening, strain hardening, solute hardening, grain and subgrain size hardening, and precipitation and particle hardening are discussed. Temperature and strain rate influence the various strengthening mechanisms in different ways, and these variables are considered whenever possible. Unusual mechanical effects result from the polymorphic nature of uranium and from anisotropic properties of alpha uranium such as thermal expansion and elastic stiffness; their importance on plastic flow is considered. Uranium and its alloys can be made superplastic, and the factors which contribute to such characteristics are discussed. (101 references) (auth)
Date: January 28, 1974
Creator: Sherby, O.D.; Bly, D.L. & Wood, D.H.
Partner: UNT Libraries Government Documents Department

Ultrahigh carbon steels, Damascus steels, and superplasticity

Description: The processing properties of ultrahigh carbon steels (UHCSs) have been studied at Stanford University over the past twenty years. These studies have shown that such steels (1 to 2.1% C) can be made superplastic at elevated temperature and can have remarkable mechanical properties at room temperature. It was the investigation of these UHCSs that eventually brought us to study the myths, magic, and metallurgy of ancient Damascus steels, which in fact, were also ultrahigh carbon steels. These steels were made in India as castings, known as wootz, possibly as far back as the time of Alexander the Great. The best swords are believed to have been forged in Persia from Indian wootz. This paper centers on recent work on superplastic UHCSs and on their relation to Damascus steels. 32 refs., 6 figs.
Date: April 1, 1997
Creator: Sherby, O.D. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

History of ultrahigh carbon steels

Description: The history and development of ultrahigh carbon steels (i.e., steels containing between 1 and 2.l percent C and now known as UHCS) are described. The early use of steel compositions containing carbon contents above the eutectoid level is found in ancient weapons from around the world. For example, both Damascus and Japanese sword steels are hypereutectoid steels. Their manufacture and processing is of interest in understanding the role of carbon content in the development of modern steels. Although sporadic examples of UHCS compositions are found in steels examined in the early part of this century, it was not until the mid-1970s that the modern study began. This study had its origin in the development of superplastic behavior in steels and the recognition that increasing the carbon content was of importance in developing that property. The compositions that were optimal for superplasticity involved the development of steels that contained higher carbon contents than conventional modern steels. It was discovered, however, that the room temperature properties of these compositions were of interest in their own right. Following this discovery, a period of intense work began on understanding their manufacture, processing, and properties for both superplastic forming and room temperature applications. The development of superplastic cast irons and iron carbides, as well as those of laminated composites containing UHCS, was an important part of this history.
Date: June 20, 1997
Creator: Wadsworth, J. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Influence of Iron Oxide Particles on the Strength of Ball-Milled Iron

Description: Detailed microstructural and mechanical property studies of ball-milled iron, in the powder and consolidated states, are reviewed and assessed. The analyses cover three and one-half orders of magnitude of grain size (from 6 nm to 20 mm) and focus on the influence of oxide particles on the strength. The study includes the early work of Koch and Yang, Kimura and Takaki and continues with the more recent work of Umemoto et al and Belyakov, Sakai et al. It is shown that the major contributors to strength are the nanooxide particles. These particles are created by adiabatic shear banding during ball-milling leading to a bimodal distribution of particles. The predicted strength from particles, {sigma}{sub p}, is given by {sigma}{sub p} = B {center_dot} (D*{sub S}){sup -1/2} where D*{sub S} is the surface-to-surface interparticle spacing, and B = 395 MPa {center_dot} {micro}m{sup -1/2}. A model is proposed that accounts for the influence of the bimodal particle size distribution on strength.
Date: December 7, 2005
Creator: Lesuer, D R; Syn, C K & Sherby, O D
Partner: UNT Libraries Government Documents Department

Nano-subgrain Strengthening in Ball-milled Iron

Description: The strength and deformation behavior of ball-milled, iron-base materials containing nano-scale subgrains have been evaluated. As reported by several authors, nanosubgrains form during the early stages of ball milling as a result of severe plastic deformation inherent in the ball milling process. The strength for these nano-scale subgrains are compared with the strength of larger-scale subgrains in iron and iron-base alloys produced by traditional mechanical working. The data covers over 2 orders of magnitude in subgrain size (from 30 nm to 6 {micro}m) and shows a continuous pattern of behavior. For all materials studied, the strength varied as {lambda}{sup -1}, where {lambda} is the subgrain size. Strengthening from subgrains was found to breakdown at a much smaller subgrain size than strengthening from grains. In addition, the ball-milled materials showed significant strengthening contributions from nano-scale oxide particles. Shear bands are developed during testing of ball-milled materials containing ultra-fine subgrains. A model for shear band development in nano-scale subgrains during deformation has also been developed. The model predicts a strain state of uniaxial compression in the shear band with a strain of -1.24. Subgrains are shown to offer the opportunity for high strength and good work hardening with the absence of yield point behavior.
Date: March 23, 2006
Creator: Lesuer, D R; Syn, C K & Sherby, O D
Partner: UNT Libraries Government Documents Department

MICROSTRUCTURE IN ADIABATIC SHEAR BANDS IN A PEARLITIC ULTRAHIGH CARBON STEEL

Description: Adiabatic shear bands, obtained in compression deformation at a strain rate of 4000 s{sup -1}, in a pearlitic 1.3%C steel, were investigated. Shear-bands initiated at 55% compression deformation with the width of the band equal to 14 {micro}m. Nano-indentor hardness of the shear band was 11.5 GPa in contrast to the initial matrix hardness of 3.5 GPa. The high strength of the shear band is attributed to its creation from two sequential events. First, large strain deformation, at a high strain rate, accompanied by adiabatic heating, led to phase transformation to austenite. Second, retransformation upon rapid cooling occurred by a divorced eutectoid transformation. The result is a predicted microstructure consisting of nano-size carbide particles within a matrix of fine ferrite grains. It is proposed that the divorced eutectoid transformation occurs in iron-carbon steels during high rate deformation in ball milling, ball drop tests and in commercial wire drawing.
Date: September 22, 2003
Creator: Syn, C K; Lesuer, D R & Sherby, O D
Partner: UNT Libraries Government Documents Department

Thermo-Mechanical Processing and Properties of a Ductile Iron

Description: Thermo-mechanical processing of ductile irons is a potential method for enhancing their mechanical properties. A ductile cast iron containing 3.6% C, 2.6% Si and 0.045% Mg was continuously hot-and-warm rolled or one-step press-forged from a temperature in the austenite range (900{degrees}C-1100{degrees}C) to a temperature below the A, temperature. Various amounts of reduction were used (from 60% to more than 90%) followed by a short heat ent at 600`C. The heat ent lead to a structure of fine graphite in a matrix of ferrite and carbides. The hot-and- warm worked materials developed a pearlitic microstructure while the press-forged material developed a spheroidite-like carbide microstructure in the matrix. Cementite-denuded ferrite zones were developed around graphite stringers in the hot-and-warm worked materials, but such zones were absent in the press-forged material. Tensile properties including tensile strength and total elongation were measured along the direction parallel and transverse to the rolling direction and along the direction transverse to the press-forging direction. The tensile ductility and strength both increased with a decrease in the amount of hot-and-warm working. The press- forged materials showed higher strength (645 MPa) than the hot-and-warrn worked materials (575 MPa) when compared at the same ductility level (22% elongation).
Date: July 14, 1997
Creator: Syn, C.K.; Lesuer, R.R. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Ultrahigh carbon steel for automotive applications

Description: Ultrahigh carbon steels (UHCSs), which contain 1--2.1% carbon, have remarkable structural properties for automotive application when processed to achieve fine ferrite grains with fine spheroidized carbides. When processed for high room temperature ductility, UHCS can have good tensile ductility but significantly higher strength than current automotive high strength steels. The material can also be made superplastic at intermediate temperatures and exhibits excellent die fill capability. Furthermore, they can be made hard with high compression ductility. In wire form it is projected that UHCS can exhibit extremely high strengths (5,000 MPa) for tire cord applications. Examples of structural components that have been formed from fine-grained spheroidized UHCSs are illustrated.
Date: December 4, 1995
Creator: Lesuer, D.R.; Syn, C.K. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Processing and mechanical behavior of hypereutectoid steel wires

Description: Hypereutectoid steels have the potential for dramatically increasing the strength of wire used in tire cord and in other high strength wire applications. The basis for this possible breakthrough is the elimination of a brittle proeutectoid network that can form along grain boundaries if appropriate processing procedures and alloy additions are used. A review is made of work done by Japanese and other researchers on eutectoid and mildly hypereutectoid wires. A linear extrapolation of the tensile strength of fine wires predicts higher strengths at higher carbon contents. The influence of processing, alloy additions and carbon content in optimizing the strength, ductility and fracture behavior of hypereutectoid steels is presented. It is proposed that the tensile strength of pearlitic wires is dictated by the fracture strength of the carbide lamella at grain boundary locations in the carbide. Methods to improve the strength of carbide grain boundaries and to decrease the carbide plate thickness will contribute to enhancing the ultrahigh strength obtainable in hypereutectoid steel wires. 23 refs., 13 figs., 1 tab.
Date: June 25, 1996
Creator: Lesuer, D.R.; Syn, C.K.; Sherby, O.D. & Kim, D.K.
Partner: UNT Libraries Government Documents Department

Laminated metals composites fracture and ballistic impact behavior

Description: Recent advances in the fracture and ballistic impact response of laminated metal composites (LMCs) are reviewed. The laminate structure can provide significant improvements to these properties relative to the component materials. Typical fracture and ballistic impact properties in LMCs are illustrated for systems containing Al alloys and Al matrix composites. The unique mechanisms operating in a layered structure that contribute to fracture or ballistic impact resistance are discussed. The influence of laminate architecture, component material properties and interface strength on mechanisms and properties are briefly reviewed for these Al-based LMCs.
Date: January 20, 1998
Creator: Lesuer, D. R.; Syn, C. K.; Sherby, O. D. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

Ancient Blacksmiths, The Iron Age, Damascus Steels, and Modern Metallurgy

Description: The history of iron and Damascus steels is described through the eyes of ancient blacksmiths. For example, evidence is presented that questions why the Iron Age could not have begun at about the same time as the early Bronze Age (i.e. approximately 7000 B.C.). It is also clear that ancient blacksmiths had enough information from their forging work, together with their observation of color changes during heating and their estimate of hardness by scratch tests, to have determined some key parts of the present-day iron-carbon phase diagram. The blacksmiths' greatest artistic accomplishments were the Damascus and Japanese steel swords. The Damascus sword was famous not only for its exceptional cutting edge and toughness, but also for its beautiful surface markings. Damascus steels are ultrahigh carbon steels (UHCSs) that contain from 1.0 to 2.1%. carbon. The modern metallurgical understanding of UHCSs has revealed that remarkable properties can be obtained in these hypereutectoid steels. The results achieved in UHCSs are attributed to the ability to place the carbon, in excess of the eutectoid composition, to do useful work that enhances the high temperature processing of carbon steels and that improves the low and intermediate temperature mechanical properties.
Date: September 11, 2000
Creator: Sherby, O.D. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

Enhancing tensile ductility of a particulate-reinforced aluminum MMC by lamination with Mg-9% Li alloy

Description: A laminated metal composite has been made by press bonding alternating layers of a particulate-reinforced aluminum MMC, 6090/SiC/25p, and a Mg-9%Li alloy. The mechanical properties including tensile ductility were evaluated. The tensile ductility of the Al MMC was found to increase from 3.5% to 11.5%. In contrast to other laminates based on ultrahigh carbon, steel, the laminate of this study and other Al MMC laminates exhibited tensile yield strengths that did not follow the rule of averages. This is attributed to interlayer reaction products developed during processing of the Al MMC laminates.
Date: May 1995
Creator: Syn, C. K.; Lesuer, D. R. & Sherby, O. D.
Partner: UNT Libraries Government Documents Department

Influence of volume fraction of component materials and interlayer bond strength on fracture toughness of multi-layer Al 6090-25 vol % SiCp and Al 5182 laminates

Description: Multilayer laminates of Al 6090/SiC/25p MMC and Al 5182 were prepared by hot pressing alternating layers of the component materials at 450{degree}C in an argon gas atmosphere. Tensile properties, interlayer normal and shear bond strengths, and fracture toughness were measured in the T6-treated and untreated conditions. Fracture toughness was also measured as a function of the volume fraction of the MMC component. Yield and tensile strengths increased substantially by the T6 treatment while the total-elongation and interlayer bond strengths decreased even more substantially. Fracture toughness, on the other hand, did not change appreciably by the T6 treatment. The fracture toughness increased perceptibly with an increase in the volume percent of the MMC component.
Date: November 1, 1993
Creator: Syn, C. K.; Stoner, S.; Lesuer, D. R. & Sherby, O. D.
Partner: UNT Libraries Government Documents Department

Mechanical and Thermal Properties of Ultra-High Carbon Steel Containing Aluminum

Description: The properties of ultrahigh carbon steels (UHCS) are strongly influenced by aluminum additions. Hardness studies of quenched UHCS-Al alloys reveal that the temperature for the start of transformation increases with increases in aluminum content. It is shown that this change is a function of the atomic percent of solute and of the valence state when comparisons are made with UHCSs containing silicon and tin as solutes. The thermal expansion of UHCSs with dilute aluminum additions shows no discontinuity in the vicinity of the ferrite-austenite transformation temperature. This is the result of a three phase region of ferrite, carbides and austenite. The slope of the expansion curve is higher in the austenite range than in the ferrite range as a result of the dissolution of carbon in austenite with temperature. Processing to achieve a fine grain size in UHCS-Al alloys was principally by hot and warm working (HWW) followed by isothermal warm working (IWW). The high temperature mechanical properties of a UHCS-10Al-1.5C material show nearly Newtonian-viscous behavior at 900 to 1000 C. Tensile elongations of 1200% without failure were achieved in the 1.5%C material. The high oxidation corrosion resistance of the UHCS-10Al materials is described.
Date: January 31, 2006
Creator: Syn, C K; Lesuer, D R; Goldberg, A; Tsai, H & Sherby, O D
Partner: UNT Libraries Government Documents Department

Mechanical and Thermal Properties of Ultra-High Carbon Steel Containing Aluminum

Description: The properties of ultrahigh carbon steels (UHCS) are strongly influenced by aluminum additions. Hardness studies of quenched UHCS-Al alloys reveal that the temperature for the start of transformation increases with increases in aluminum content. It is shown that this change is a function of the atomic percent of solute and of the valence state when comparisons are made with UHCSs containing silicon and tin as solutes. The thermal expansion of UHCSs with dilute aluminum additions shows no discontinuity in the vicinity of the ferrite-austenite transformation temperature. This is the result of a three phase region of ferrite, carbides and austenite. The slope of the expansion curve is higher in the austenite range than in the ferrite range as a result of the dissolution of carbon in austenite with temperature. Processing to achieve a fine grain size in UHCS-Al alloys was principally by hot and warm working (HWW) followed by isothermal warm working (IWW). The high temperature mechanical properties of a UHCS-10Al-1.5C material show nearly Newtonian-viscous behavior at 900 to 1000 C. Tensile elongations of 1200% without failure were achieved in the 1.5%C material. The high oxidation corrosion resistance of the UHCS-10Al materials is described.
Date: October 3, 2005
Creator: Syn, C K; Lesuer, D R; Goldberg, A; Tsai, H C & Sherby, O D
Partner: UNT Libraries Government Documents Department

An Evaluation of Power Law Breakdown in Metals, Alloys, Dispersion Hardened Materials and Compounds

Description: Creep at high stresses often produces strain rates that exceed those that would be predicted by a power law relationship. In this paper, we examine available high stress creep data for pure metals, solid solution alloys, dispersion strengthened powder metallurgy materials and compounds for power law breakdown (PLB). The results show that, if PLB is observed, then the onset of PLB is generally observed at about {epsilon}/D{sub eff} = 10{sup 13} m{sup -2}, where D{sub eff} is the effective diffusion coefficient incorporating lattice and dislocation pipe diffusion. The common origins of PLB for the various systems studied can be found in the production of excess vacancies by plastic deformation. Anomalous behavior in two pure metals (nickel and tungsten) and a solid solution alloy (Fe-25Cr and Fe-26Cr-1Mo) has been analyzed and provides insight into this excess vacancy mechanism. In metal systems, the onset of PLB is related to a change in the nature of the subgrain structure developed. In the PLB region, subgrains become imperfect containing dislocation tangles adjacent to the sub-boundary, and dislocation cells are evident. The dislocation tangles and cells are the source of excess vacancies and increase the creep rate above that predicted from power law creep. If subgrains do not form then PLB is not observed. In solid solution alloys, in which the dominant deformation resistance results from the interaction of solute atoms with moving dislocations, excess vacancies influence the diffusion of these solute atoms. PLB is not observed in many systems. This is attributed either to the presence of a high equilibrium vacancy concentration (because of a low activation energy for vacancy formation) or to the inability to form subgrains.
Date: October 20, 1999
Creator: Lesuer, D.R.; Syn, C.K. & Sherby, O.D.
Partner: UNT Libraries Government Documents Department

Deformation mechanisms in crystalline solids and Newtonian viscous behavior

Description: The three principal mechanisms of plastic flow in crystalline solids at elevated temperature are crystal slip, grain boundary sliding, and diffusional flow. All three mechanisms involve the diffusion of atoms as the rate-controlling process, either in the lattice or in the grain boundary. Under the correct conditions of microstructure, temperature, and stress, each mechanism can lead to Newtonian-viscous behavior. That is, the strain rate increases linearly with the applied stress. In the case of crystal slip, Newtonian-viscous behavior is observed at very � low stresses and, in pure metals, is known as Harper-Dom (H-D) creep. This Newtonian behavior can also be observed in anisotropic crystalline solids that are deformed under thermal cycling conditions. The dislocation density and the stacking fault energy are important structural factors that contribute to crystal slip-controlled Newtonian flow. In the case of grain boundary sliding, Newtonian-viscous behavior is observed in fine-grained, solid solution alloys under conditions where grain-boundary sliding is accommodated by dislocation glide controlled by the diffusion of solute atoms. In the case of diffusional creep, which is rigorously described by the Nabarro-Herring (N-H) theory, the creep rate is controlled by grain size and by the rate of atom diffusion in the lattice and in the grain boundary. Deformation mechanism maps describe the conditions of dislocation density, grain size, stress, and temperature under which each deformation process can be expected to be rate-controlling.
Date: November 4, 1999
Creator: Ruano, O A; Sherby, O D & Wadsworth, J
Partner: UNT Libraries Government Documents Department

Deformation by grain boundary sliding and slip creep versus diffusional creep

Description: A review is presented of the debates between the present authors and other investigators regarding the possible role of diffusional creep in the plastic flow of polycrystalline metals at low stresses. These debates are recorded in eleven papers over the past seventeen years. ln these papers it has been shown that the creep rates of materials in the so-called �diffusional creep region� are almost always higher than those predicted by the diffusional creep theory. Additionally, the predictions of grain size effects and stress exponents from diffusional creep theory are often not found in the experimental data. Finally, denuded zones have been universally considered to be direct evidence for diffusional creep; but, those reported in the literature are shown to be found only under conditions where a high stress exponent is observed. Also, the locations of the denuded zones do not match those predicted. Alternative mechanisms are described in which diffusion-controlled dislocation creep and/or grain boundary sliding are the dominant deformation processes in low-stress creep. It is proposed that denuded zones are formed by stress-directed grain boundary migration with the precipitates dissolving in the moving grain boundaries. The above observations have led us to the conclusion that grain boundary sliding and slip creep are in fact the principal mechanisms for observations of plastic flow in the so-called �diffusional creep regions. �
Date: November 4, 1998
Creator: Ruano, O. A.; Sherby, O. D. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department

Influence of severe plastic deformation on the structure and properties of ultrahigh carbon steel wire

Description: Ultrahigh-carbon steel wire can achieve very high strength after severe plastic deformation, because of the fine, stable substructures produce. Tensile strengths approaching 6000 MPa are predicted for UHCS containing 1.8%C. This paper discusses the microstructural evolution during drawing of UHCS wire, the resulting strength produced and the factors influencing fracture. Drawing produces considerable alignment of the pearlite plates. Dislocation cells develop within the ferrite plates and, with increasing strain, the size normal to the axis ({lambda}) decreases. These dislocation cells resist dynamic recovery during wire drawing and thus extremely fine substructures can be developed ({lambda} < 10 nm). Increasing the carbon content reduces the mean free ferrite path in the as-patented wire and the cell size developed during drawing. For UHCS, the strength varies as {lambda}{sup {minus}5}. Fracture of these steels was found to be a function of carbide size and composition. The influence of processing and composition on achieving high strength in these wires during severe plastic deformation is discussed.
Date: July 1, 1999
Creator: Leseur, D R; Sherby, O D & Syn, C K
Partner: UNT Libraries Government Documents Department

Laminated metal composites of ultrahigh carbon steel/brass and Al/Al-SiC: Processing and properties

Description: We have fabricated laminated metal composites of (i) ultrahigh carbon steel (1.8%C) and brass (70Cu-30Zn), and (ii) aluminum 5182 and aluminum 6061 with 25 vol.% SiC{sub p}. The laminates were prepared by hot pressing alternating layers of the component materials in an argon gas atmosphere. The steel was thermo-mechanically processed to produce a fine grained microstructure that exhibited superplasticity. The brass and aluminum materials were obtained from commercial sources and used in the as-received condition. Laminates with different numbers of layers and layer thickness were made. The compressive stress and strain rate were measured during hot pressing, and material flow behavior in the UHCS-brass laminate was found to be rate-controlled by the stronger component rather than by the softer one (brass). Material flow behavior was more complicated in the Al-laminate. Tensile and behavior were determined by tensile tests and by chevron notched fracture toughness tests. Details of processing, microstructure and initial results of mechanical property tests of these laminates are discussed.
Date: October 1, 1991
Creator: Syn, C. K.; Lesuer, D. R.; Cadwell, K. L.; Sherby, O. D. & Brown, K. R.
Partner: UNT Libraries Government Documents Department

Overview on superplasticity research on small-grained materials

Description: Superplasticity is generally associated with fine grains, grain boundary sliding, and high tensile ductility at elevated temperature. This paper reviews some of the recent important findings in fine-grained superplasticity, including the areas of superplastic ceramics and bf-high-strain-rate superplasticity (HSRS). Deformation mechanism maps are shown to be powerful tools for predicting the conditions where HSRS can be expected. Ultrafine grained materials, processed economically, remain an important objective in achieving HSRS. Threshold stresses, observed in fine-grained superplastic materials, are shown to be functions of temperature and grain size but their origin, however, remains obscure. Quasi-superplastic materials, with a strain-rate-sensitivity exponent of m = 0.33, are shown to have high elongations, and have considerable promise for netshape isothermal forming of sheet and bulk components.
Date: July 1, 1994
Creator: Sherby, O. D.; Nieh, T. G. & Wadsworth, J.
Partner: UNT Libraries Government Documents Department