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A laboratory-scale hot extrusion setup was designed to investigate recrystallization and grain growth behavior of an AA7050 alloy during extrusion and subsequent heat treatments. Compared with industrial extrusion, the laboratory-scale process enabled rapid water quenching of extrudate with less delay so that the dynamic grain structure development was captured. After extrusion, static microstructure evolution in the extrudates was studied using salt bath annealing for 5 and 15 s at 490 °C and solutionization treatment for 1 h at 490 °C. The salt bath annealing was a simulation of the delay of press quenching in typical industrial extrusion practices. In the as-quenched extrudates, the peripheral region mainly exhibited continuous dynamic recrystallization and geometric dynamic recrystallization, whereas in the core region discontinuous dynamic recrystallization dominated. A and double fiber texture was identified in extrudates, and recrystallization behavior was found to be orientation dependent. The oriented grains contained more sub-grain boundaries and better-defined sub-grains and had a higher tendency to fragment via continuous recrystallization, while the oriented grains produced less sub-grain boundaries and did not recrystallize. Subsequent heat treatments resulted in static recrystallization and abnormal growth of the continuously recrystallized grains. Additionally, the effects of extrusion temperature (440, 480 and 520 °C) and punch speed (0.7, 1.4 and 2.1 mm/s) on grain structure were discussed. A revised grain structure evolution mechanism based on the observation of 7050 extrusion was proposed.

A full 3D transient model of direct chill casting is developed to predict the thermal stress during the startup phase for AA5182. Simulations show that tensile stress starts to develop at ingot surface and gradually migrates to ingot center. By varying the position of wiper below the mold, the maximum residual stress in the ingot center is reduced by up to 35% compared to that without the use of a wiper. The closer the wiper is inserted below the mold, the larger is the stress reduction effect, but at a greater risk of remelting surfaces below the wiper. In order to prevent this, forced-convection air cooling is recommended on ingot surface below the wiper. The current study recommends application of a moving wiper, from a lower to the bottom of the sump, to combine the benefit of reducing thermal stress and centerline segregation without surface bleeding-out.

Microstructures, mechanical properties and corrosion rates (CR) of powder metallurgy derived Fe–Mn alloys have been investigated with respect to the particle size of the iron (Fe) powder and the extent of manganese (Mn) diffusion and alloying during sintering. By applying different heat treatments on Fe–30wt%Mn alloy, a phase transformation (γ → e) for this composition and its influence on mechanical and corrosion properties have been studied. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) have been conducted to characterize the transformation and identify the austenite (γ) and epsilon martensite (e) phases in the system. Microstructures and tensile fracture surfaces were examined by Scanning Electron Microscope (SEM). The results show that the Fe particle size affects the overall Mn alloying significantly, i.e., coarse Fe particles (30–200 µm) result in Fe–Mn alloys with σy = 48.2 MPa, σu = 73.6 MPa, fracture strain of 2.42% and CR = 1.36 mmpy, while ultrafine particle size (

A high purity Al-Zn-Cu-Mg alloy based on AA7050 was cast with varying Zr concentrations by directional solidification (DS) and static casting (SC). Specimens were homogenized, hot rolled and solutionized to study the recrystallization behavior. In the DS ingot a gradient of Zr concentration existed along the growth direction, but across the transverse direction the distribution of Zr was uniform, while in SC ingots a dendritically cored Zr concentration gradient was found. The variations in solidification method and Zr concentration resulted in difference in size, number and spatial distribution of Al 3 Zr-type dispersoids, and thus different degrees of recrystallization after solutionization. Recrystallization was delayed both in the SC specimen with 0.11 wt% Zr and in the specimen from the top of the DS ingot with 0.03 wt% Zr, whereas full recrystallization and grain growth were found in the SC specimen free of Zr and the DS bottom specimen with 0.11 wt% Zr. The inconsistency between the recrystallization behavior of the DS bottom specimen and its relatively high Zr concentration is likely related to the precipitation and coarsening of the dispersoids during slow DS cooling.

Simple shear deformation via hybrid cutting-extrusion is used to produce continuous electrical steel sheet from a commercial high-silicon (nominal 4 wt%) iron alloy of poor workability in a single deformation step, a fundamentally different route from the multi-step processing of rolling and annealing currently in use. The shear texture created in the sheet is found to be quite different from that produced by rolling. The magnetic properties of the shear-textured Fe–Si sheet are measured using closed-circuit permeametry and compared with those from sheet produced by rolling of the same alloy and a commercial non-grain-oriented sheet of similar composition. Properties compared include maximum relative permeability, induction, coercivity, and hysteresis loss. The results are interpreted in terms of microstructure, texture, and composition. A unit cell representation of the shear texture components is introduced that relates the expected orientation of easy magnetization directions with the sheet axes.

An analytical model was developed to predict the infiltration of a non-wetting liquid into a sharp-cornered channel with rough walls. The distance from the liquid meniscus to the corner and the liquid radius of curvature predicted by the model are a function of contact angle, corner angle, head height and surface roughness. Measurements of these lengths were made in a model experiment as a function of liquid head height. The results of the experiments suggest that the analytical model accurately predicts the wetting limit of corner sharpness.

Understanding transitions from homogeneous to localized flow, and mechanisms underlying flow localization, is of paramount importance for deformation processing of magnesium. In this study, a shear-based deformation method is utilized for imposing large strains ( ∼ 1 ), under controllable strain rates (10–10 5 /s) and temperatures (80–300 °C), in order to examine flow patterns in a magnesium alloy. Based on microstructure characterization, deformation twinning is suggested to contribute to the localized flow at temperatures below 200 °C and at low strain rates. The transition from the localized to homogeneous flow with increasing temperature is due to reduction in twinning activity, and enhanced strain-rate sensitivity. At constant temperature, an increase in the strain rate decreases the propensity for flow localization. A model is presented for characterizing the maximum uniform strain as a function of temperature and deformation state (simple shear, plane-strain compression). The model incorporates temperature-sensitive microstructural changes and flow properties of magnesium into a classical framework to capture the flow localization phenomena at low temperatures and strain rates.

Sheet processing of high Si-Fe alloys (up to 6.5 wt pct Si) is demonstrated by application of highly confined shear deformation in cutting-extrusion. This alloy system, of major interest to electromagnetic applications, is characterized by poor workability. By a suitable interactive combination of simple shear, high strain rates, near-adiabatic heating, and large hydrostatic pressure in the deformation zone, flow localization, and cracking inherent to this alloy system are suppressed. This enables creation of sheet and foil forms from bulk ingots, cast or wrought, in a single deformation step, unlike rolling. The sheet is characterized by strong shear textures, described by partial {110} and 〈111〉 fibers, and fine-grained microstructures (~20 µm grain size). The orientation (inclination) of these fibers, with respect to the sheet surface, can be varied over a range of 35 deg through selection of the deformation path. In contrast to rolling textures, the current shear deformation textures are negligibly influenced by recrystallization annealing. A recovery-based continuous recrystallization mechanism is proposed to explain the texture retention. Some general implications for shear-based processing of alloys of limited workability are discussed.

The flow stress and ultimate tensile stress of the solid–liquid mushy zone of AA7050 were measured at solid fractions greater than 0.9 using a tensile testing procedure modified to capture the non-equilibrium microstructural conditions in castings. Tensile testing was conducted by reheating as-cast AA7050 tensile bars above the equilibrium solidus to produce an interdendritic liquid region. The samples were then cooled to the solidus temperature calculated by either the lever rule or Scheil analysis. The samples were strained at different temperatures during the cooling stage. This method produced much lower stress values than heating the specimen directly to the desired test temperature. Microstructures and fracture surfaces after testing using the modified procedure were compared to those of the original as-cast microstructure, confirming the presence of an interdendritic liquid film during testing.

Microstructure development in the casting of copper-manganese alloys based on the congruent point at 34.6 wt pct Mn and 1146 K (873 °C) has been studied. The alloys were prepared by induction melting of electrolytic Cu and Mn in clay-graphite crucibles in open air. Under conventional casting conditions, the alloys exhibit fine cellular (non-dendritic) solidification morphology with a distinct absence of solidification shrinkage microporosity, and they maintain these attributes over a composition range of approximately 3 wt pct Mn about the congruent point. The high Mn concentration in the alloy admits carbon into solution in the melt, resulting in formation of manganese carbide Mn7C3 particles having two different forms (globular and angular) in the cast microstructure. The Mn carbide was eliminated or controlled to low levels by melting in an alumina or a silicon carbide crucible, or in a clay-graphite crucible at lower temperatures. Microstructure development in casting the alloy was analyzed in terms of the available phase diagrams and thermochemical data. Hardness and tensile testing indicated a potent solid solution strengthening effect of Mn and high ductility in the as-cast condition, with additional hardness (strength) when the alloy contains the Mn carbide phase.

Tantalum powders containing different oxygen concentrations have been vacuum hot-pressed in graphite dies to study the dissolution and precipitation of oxygen and carbon in powder metallurgy (PM) tantalum. Various types of oxide and carbide precipitates were observed using microscopy and analyzed by X-ray microdiffraction. An in situ contact gettering method using zirconium has been coupled with hot-pressing to control oxygen. This method is effective at removing oxygen from the solid solution, while the precipitation behavior is not significantly altered. Hardness profiles with distance from Zr contact agree well with those expected from oxygen concentration profiles predicted by analysis assuming a diffusion-limited rate of gettering. Corresponding lattice parameter measurements by microdiffraction indicate that oxygen prefers to stay in supersaturated solid solution, even under slow cooling, where it is much more effective in hardening than in the form of precipitates.

Deformation microstructure and texture in Mg-AZ31B bulk strips processed through extrusion-machining were studied as a function of deformation temperature. At warm deformation temperatures (~200°C), cold-worked type microstructures with predominant tilted basal texture were observed. With increase in temperature, grain structure sharply transformed into equiaxed type with predominant in-plane basal texture. This sharp transition was found to be consistent with change in temperature dependent dynamic recrystallization mechanism from continuous to discontinuous type.

A general approach for manufacturing of micro-scale components from high-strength, nanostructured materials is presented. The approach utilizes severe plastic deformation by large-strain extrusion machining to create the nanostructured material in a high-strength alloy system, and conventional micro-machining to produce the components. Manufacture of small-scale gears from nickel-based superalloy Inconel 718 is illustrated.

The temperature and strain rate fields in severe plastic deformation (SPD) are measured using infra-red thermography and Particle Image Velocimetry (PIV), respectively. Plane strain machining is used as the method of SPD to impose controlled strains and strain rates. For metals such as titanium, the temperature rise is small at small strain rates and SPD occurs at near-ambient temperature. The possibility of exploring dynamic recovery/recrystallization phenomena using the Zener-Hollomon parameter in this SPD framework is briefly discussed.

Continuous production of Al 6061-T6 particulate using modulation-assisted machining (MAM) is demonstrated. Superimposition of a controlled, low-frequency modulation in conventional machining causes chips to form as discrete particles. By adjusting the conditions, equiaxed, platelet and fiber-shaped particles having narrow size distributions can be produced. Large-strain deformation leads to microstructure refinement and enhanced hardness. The process is applicable to a wide range of alloys and appears to be intrinsically scalable for large-volume production.

Plane-strain machining can be used to impart large plastic strains in alloys that are difficult to deform by other severe plastic deformation (SPD) processes. By cutting at low speeds, the heating caused by friction with the tool can be reduced to insignificant levels. The utility of this approach for characterizing microstructure development in SPD is demonstrated using a variety of commercial alloys that exhibit different deformation behaviors and strengthening mechanisms, including CP-titanium, aluminum alloy 6061-T6, nickel-base superalloy IN-718, and pearlitic plain-carbon steel.

Large plastic strains between 1 and 15 can be imposed in chips formed by plane-strain (2-D) machining of metals and alloys. This approach has been used to examine microstructure changes induced by large strain deformation in model systems—copper and its alloys, precipitation-hardenable aluminum alloys, high-strength materials such as titanium, Inconel 718 and 52100 steel, and an amorphous alloy. It is shown that materials with average grain sizes in the range of 60 nm–1 μm can be created by varying the parameters of machining, which in turn affects the deformation processes. Furthermore, a switch-over from an elongated subgrain microstructure to an equi-axed nanocrystalline microstructure, with a preponderance of large-angle grain boundaries, has been demonstrated at the higher levels of strain in several of these materials. This switch-over can be readily controlled by varying the deformation conditions. Dynamic recrystallization has been demonstrated in select material systems under particular conditions of strain and temperature. This study may be seen as providing an important bridge between furthering the understanding of microstructural refinement by large strain deformation and the practical utilization of nanostructured materials in structural and mechanical applications. Conventional plane-strain machining has been shown to be a viable SPD method for examining the underlying processes of very large strain deformation.

The crack growth resistance ( R -curve) behavior of multilayered alumina–zirconia composites was measured using a single-edge-V-notched-beam (SEVNB) testing method in which crack initiation and extension were observed via in situ optical microscopy. The influence of the relative layer orientation with respect to the crack-tip front through the composite on the resulting R -curves were measured and was found to have a pronounced influence on the measured crack growth resistance behavior. By increasing the layer offset, the specific influence of a given feature within the layered structure on the measured R -curve behavior was found to diminish.

Characteristics of the deformation fields associated with chip formation in plane strain machining are described. The ability to impose very large strain deformation in a controlled manner is highlighted. The creation of nano- and ultra-fine grained structures by machining is demonstrated in a variety of metals and alloys. These results indicate that machining not only offers a simple method for large scale manufacturing of nanostructured materials, but also provides a unique experimental configuration for studying large strain deformation phenomena.

A potential method for producing selectively reinforced, single-crystal superalloy castings was investigated. Porous particulate alumina preforms were infiltrated with the liquid Ni-based superalloy CMSX-4 under a gas pressure of about 1 atm, and then the alloy was solidified directionally through the preform at different rates. Optical microscopy and Laue X-ray diffraction showed that the orientation of the metallic grains was unaffected by the preform and that no stray grains were nucleated there. In the particular experimental configuration, single grain orientations (i.e., single crystals) were achieved at cooling rates ≤15 °C/min. Furthermore, the microsegregation pattern in the composite region showed that the alloy solidified from the center of the interstices toward the alumina particles, further indicating that nucleation did not occur on the preform. Microsegregation in the composite region is lower than in the unreinforced regions due to geometric confinement of solidification in the narrow spaces between the ceramic particles.

Melt infiltration of preforms prepared by sequential centrifugal casting and by tape casting and lamination has been accomplished using a short-time infiltration process that significantly suppresses reaction product formation. For layered materials produced via infiltration of laminated ceramic tapes, of particular interest is the effect that a large change in microstructure has on infiltration, phase formation and mechanical properties.

In spite of their interesting properties, nanostructured materials have found limited uses because of the cost of preparation and the limited range of materials that can be synthesized. It has been shown that most of these limitations can be overcome by subjecting a material to large-scale deformation, as occurs during common machining operations. The chips produced during lathe machining of a variety of pure metals, steels, and other alloys are shown to be nanostructured with grain (crystal) sizes between 100 and 800 nm. The hardness of the chips is found to be significantly greater than that of the bulk material.

The single-edge-V-notched-beam testing geometry was used to measure the crack growth resistance (R-curve) behavior of multilayer graded alumina–zirconia composites for crack extensions parallel to the graded direction. Fracture mechanics weight function analysis was applied to explain the R-curve behavior of a compositional and grain-size graded microstructure. The results were then used to differentiate the influence of residual stress from other closure stresses, attributed to crack bridging, on the measured R-curve behavior.

This work investigates the effect of continuous CuAlO2 interfacial reaction product layers on the strength of eutectic bonded copper–alumina interfaces. The fracture resistance was characterized for interfaces produced by eutectic bonding with and without continuous CuAlO2 interlayers. Results show that continuous CuAlO2 layers can weaken the overall Cu/Al2O3 bond.

An alumina/epoxy suspension was used as a model system to investigate the macro-layer geometry within multilayered composites produced by centrifugation. Layer curvature and tilt are inherent features of the centrifugation process that have not been discussed or evaluated in previous centrifugal consolidation studies. Experimental results for the origin of layer curvature are presented.

The chemical and microstructural evolution of particulate (Bi,Pb)2223 in contact with pure bulk silver at 830 to 905 °C under flowing air and Ar−5% O2 atmospheres has been studied. Specimens annealed under PO2 and temperature conditions for which the (Bi,Pb)2223 phase itself is stable, based on a critical assessment of the literature, revealed a silver/(Bi,Pb)2223 interface-limited reaction, producing both solid and liquid decomposition phases. The (Bi,Pb)2223 not in direct contact with silver exhibited no reaction under the same conditions. Solid silver dissolves into the (Bi,Pb)2223 incongruent liquid, facilitating the incongruent melting reaction. On cooling, equiaxed metallic silver particles precipitated uniformly throughout bulk specimens partially melted on a silver substrate.

The chemical precipitation of silver particles is an effective method for tailoring the particle size and morphology. This article investigates a chemical precipitation method for producing silver colloids, and how processing parameters affected particle size, morphology and adherence. Decreasing the silver nitrate concentration during precipitation with sodium borohydride decreased the colloidal silver particle size. Decreasing the addition rate of the reducing agent produced faceted particles. Reversing the reactant addition order also changed the particle size and the morphology. Precipitated colloids demonstrated a difference between the growth-dominated and the equilibrium structures. Co-dispersing Bi-based superconducting platelets during precipitation allowed Ag colloids to preferentially nucleate on the platelets and to remain adhered even after the additional processing.

Laminate metal composites are often made through cold roll bonding two or more independent sheets to establish a strong, metallic bond between the metal layers without the incorporation of any liquid phase during subsequent annealing. During the bonding process, it is important to understand the nature of the bond formation within the roll bite, which additionally requires an in-depth understanding of the distribution of stresses and strains within the materials and their resulting deformation behavior. Until this understanding is developed, the design of roll bonding processes will continue to be trial and error and will remain problematic. In this paper, three recent roll bonding models are evaluated and recommendations are made for improving the validity and accuracy of the models, particularly the necessity for the incorporation of bonding criteria along with the mechanics of roll bonding.

Due to the highly anisotropic properties of BSCCO superconductors, the bulk properties of these materials can be greatly affected by preferential orientation. Substantial c-axis orientation normal to the desired direction of current flow has been demonstrated by centrifugally slip casting lead-doped BSCCO-2223. The strong preferred orientation developed in the centrifugally slip-cast material demonstrates high critical current potential.