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Shear-based deformation processing by hybrid cutting-extrusion and free machining are used to make continuous strip, of thickness up to 1 mm, from low-workability AA6013-T6 in a single deformation step. The intense shear can impose effective strains as large as 2 in the strip without pre-heating of the workpiece. The creation of strip in a single step is facilitated by three factors inherent to the cutting deformation zone: highly confined shear deformation, in situ plastic deformation-induced heating, and high hydrostatic pressure. The hybrid cutting-extrusion, which employs a second die located across from the primary cutting tool to constrain the chip geometry, is found to produce strip with smooth surfaces (Sa < 0.4 μm) that is similar to cold-rolled strip. The strips show an elongated grain microstructure that is inclined to the strip surfaces—a shear texture—that is quite different from rolled sheet. This shear texture (inclination) angle is determined by the deformation path. Through control of the deformation parameters such as strain and temperature, a range of microstructures and strengths could be achieved in the strip. When the cutting-based deformation was done at room temperature, without workpiece preheating, the starting T6 material was further strengthened by as much as 30% in a single step. In elevated-temperature cutting-extrusion, dynamic recrystallization was observed, resulting in a refined grain size in the strip. Implications for deformation processing of age-hardenable Al alloys into sheet form, and microstructure control therein, are discussed.

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.

The proliferation of single‐use plastics has stimulated interest in sustainable material substitutes with sufficient ductility and structural integrity. Herein, the mechanical behavior and high formability of the leaf sheath from a representative palm species—Areca catechu—and its immense potential for manufacturing of eco‐friendly food packaging are reported on. Using microstructural analyses, such as X‐ray micro‐computed tomography (μCT), electron microscopy, and optical profilometry, under different loading conditions, it is shown that this leaf can accommodate forming strains as large as 200%, similar to ductile metals. The sheath deformation response is highly sensitive to hydration, with up to 400% increase in forming strain. The embodied energy for leaf products is four to five orders smaller than for plastic or paper products. The results establish the microstructure basis for the high formability and the contours of a forming limit diagram that delineates product shapes that can be formed in a single step from this plant material.

Commercial electrical conductor wires are currently produced from aluminum alloys by multi-step deformation processing involving rolling and drawing. These processes typically require 10 to 20 steps of deformation, since the plastic strain or reduction that can be imposed in a single step is limited by material workability and process mechanics. Here, we demonstrate a fundamentally different, single-step approach to produce flat wire aluminum products using machining-based deformation that also ensures adequate material workability in the formed product. Two process routes are proposed: (1) chip formation by free-machining (FM), with a post-machining, light drawing reduction (56% IACS). The wire microstructure, which can also be varied via the large-strain deformation parameters, is correlated with mechanical and electrical properties. Implications for commercial manufacture of flat wire products are discussed.

Shear banding, a type of inhomogeneous plastic flow involving very large local strains, occurs in a variety of material systems. We study dynamics of evolution of single shear bands at strain rates of up to 10(6) per second in three different polycrystalline metal systems, using a special shear deformation framework and a micro-marker technique calibrated to track localised deformation fields at micrometer resolution. Once a band is nucleated as a weak interface, localised plastic flow occurs via Bingham-type viscous sliding between material segments on either side of the interface. As a result, the evolution and magnitude of strains and material displacements in the band vicinity are well-described by a model based on momentum diffusion. The viscosity at the band interface is very small, only a few mPasec, and is comparable to those of liquid metals at their melting point. Based on analysis of various contributions to band viscosity at the microscopic level, a plausible explanation based on phonon drag on dislocation motion is presented for the small viscosity. The accuracy of predictions made by the momentum diffusion model for different materials and deformation rates suggests that once nucleated, a shear band evolves by a common mechanism that is relatively insensitive to microstructure details.

Enhanced workability, as characterized by the magnitude and heterogeneity of accommodated plastic strains during sheet processing, is demonstrated in high Si content Fe-Si alloys containing 4 and 6.5 wt% Si using two single-step, simple-shear deformation techniques – peeling and large strain extrusion machining (LSEM). The model Fe-Si material system was selected for its intrinsically poor material workability, and well-known applications potential in next-generation electric machines. In a comparative study of the deformation characteristics of the shear processes with conventional rolling, two distinct manifestations of workability are observed. For rolling, the relatively diffuse and unconfined deformation zone geometry leads to cracking at low strains, with sheet structures characterized by extensive deformation twinning and banding. Workpiece pre-heating is required to improve the workability in rolling. In contrast, peeling and LSEM produce continuous sheet at large plastic strains without cracking, the result of more confined deformation geometries that enhances the workability. Peeling, however, results in heterogeneous, shear-banded microstructures, pointing to a second type of workability issue – flow localization – that limits sheet processing. This shear banding is to a large extent facilitated by unrestricted flow at the sheet surface, unavoidable in peeling. With additional confinement of this free surface deformation and appropriately designed deformation zone geometry, LSEM is shown to suppress shear banding, resulting in continuous sheet with homogeneous microstructure. Thus LSEM is shown to produce the greatest enhancement in process workability for producing sheet. These workability findings are explained and discussed based on differences in process mechanics and deformation zone geometry.

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.

Modulation-Assisted Machining (MAM) is an emerging method of metal particulate production where the tool feed rate in a metal cutting process is modulated to form chip particles directly from a solid workpiece. During the cutting process, a periodic disengagement occurs between the tool and the workpiece forming discrete corresponding particles of uniform shape and size. As a result of the large plastic strains that occur during metal cutting, the final particle morphology (size and shape) produced by MAM is determined by the deformation conditions. Average strains in MAM are in the range of ~2–4 depending on the modulation and cutting conditions. Numerical simulation and finite element analysis have shown that the strain imparted in MAM can vary significantly even during the formation of an individual chip. The variation of deformation is a result of the transient nature of cutting and commonly observed in periodic deformation processes. In the present paper, the particle shape, strain and hardness were studied using Al6061-T6 as a model material. Particles of short fiber-like morphology were produced. The cross-sectional shape of the fibers was dictated by the amount and distribution of strain during the cutting process. Hardness measured by nano-indentation at different points on the fiber cross-section varied between 1.7–2 GPa consistent with the variations in strain reported in individual MAM particles. Consequently, the cross-sectional shape of fibers differs from the one simulated using only process kinematics and assuming steady-state conditions.

Fe-3Si-3Al and Fe-4Si-4Cr (wt%) experimental alloys were processed to assess the electrical resistivity and workability effects of substituting Al and Cr for Si in high-Si electrical steel alloys. The experimental alloys were made by arc melting, and processed by hot rolling and cold rolling to produce strips. Samples were characterized by means of metallography, hardness, workability and resistivity. Results showed that the two alloys could be rolled down to 200 µm thickness (90% hot-rolled reduction and 80% cold rolled reduction) without crack formation in the strips. Hardness in the annealed condition and electrical resistivity were 228 HV/74 µΩ cm and 243 HV/85 µΩ cm, respectively, for the Fe-3Si-3Al and for Fe-4Si-4Cr alloys. The resistivity measured for Fe-4Si-4Cr was higher than the resistivity reported for the benchmark high-Si alloy, Fe-6.5Si. Both experimental alloys showed improvement on the workability compared to Fe-6.5Si since there was no edge cracking on the cold-rolled strips up to 80% reduction, and the hardness was approximately 35% lower.

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.

Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has a detection limit of sub-parts-per-trillion (ppt) level. However, it was found the detection limit increased to ~10 ppb for the analysis of impurities in ultra-pure Ga of 7 N (99.99999%) and 8 N (99.999999%) by ICP-MS due to matrix-induced interference. By extracting Ga during sample preparation, matrix-induced interference can be reduced and a lower detection limit can be achieved in the ICP-MS measurement. The dextran-based resin Sephadex G-25 can chemically separate the impurity Ge from Ga. The hydroxide complexes of Ga and Ge are adsorbed on Sephadex G-25 and desorbed into acid depending on pH. Viability of Ge separation from Ga by pH change was evaluated by thermodynamic calculation of the hydrolysis reaction of Ga and Ge. The distributions of Ga-hydroxide species and Ge-hydroxide species in 0.64 M HNO3 were derived by numerical calculation for thermodynamic equilibrium. The effect of presence of medium and ionic strength in aqueous solutions on hydrolysis reaction was evaluated. From the derived speciation diagram for Ga and Ge hydrolysis reactions, the optimal pH range to separate impurity Ge from Ga for ICP-MS sample preparation was investigated.

Large strain plastic flow in cutting of metals is studied at multiple length scales using high-speed imaging and marker techniques, complemented by particle image velocimetry and electron microscopy. Quantitative analysis of streak-lines, strain fields and microstructure, shows the flow to be often unsteady. Instabilities such as segmentation driven by ductile fracture, vortex-like flow in ductile metals, and shear banding in low-thermal diffusivity systems are elucidated using direct observations. A constrained-cutting process is demonstrated for suppressing the instabilities and unsteady flow.

Prior studies of cast AA7050 mechanical property are sparse, and only include the as-cast condition. In order to generate data for simulation of stress development in direct chill (DC) casting, compression tests were performed on AA7050 specimens in both as-cast and homogenized conditions in the temperature range of 20–500 °C at strain rates from 10−4 to 10−2 s−1 to a strain of 0.5. Results from test specimens having round and square cross-sections were compared to each other and to published tensile data. The round specimens are preferred due to less cornering effect. The flow stress-strain data is fit to the Ludwik equation to generate constitutive relations for the flow stress as a function of strain, strain rate and temperature. The microstructural changes from as-cast to homogenized structures lowers the flow stress of AA7050 with the removal of harder eutectic microconstituent. This effect is most significant at an intermediate temperature (200 °C) and decreases with increasing temperature.

High mobility GaAs/AlGaAs heterostructure have been achieved at Purdue University through in-situ distillation of the source Ga prior to growth. A significant amount of Ga is lost during distillation and growth. To evaluate the Ga behavior during MBE operation, the evaporation rate from a planar source of liquid Ga in a crucible is analyzed, correcting for transmission probability according to Clausing theory. The transmission probability which depends on the diameter and receding depth of the liquid surface in the crucible, explains condensation of Ga particles by collision for the vertically standing crucible. The good agreement furthermore suggests that the usual tilt of the cell has little effect on the flux.

This work features a characterization of AA7050 strip produced for the first time in a single deformation step via large strain extrusion machining (LSEM), which has emerged as an alternative method to produce AA7050 strip. The resultant LSEM plate or sheet microstructure is promising for applications where SCC and exfoliation cracking resistance are important. LSEM has been shown to produce grains with a lower aspect ratio than conventional hot rolling, which has been linked to SCC resistance. In addition, LSEM grains have a different orientation relative to the strip direction, which may result in an improvement in exfoliation cracking resistance as compared to hot-rolled strip.

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.

A microstructural investigation of Type-II hot corrosion was carried out on a single crystal Ni-based superalloy (CMSX-4) pre-coated with Na2SO4 at 700 °C in a flowing O2–SO2–SO3 atmosphere. Corrosion occurred by rapid dissolution of the alloy by molten sulfate eutectics, forming an outer layer rich in Co and Ni and an inner layer rich in Cr and Al. The outer layer transformed into mixed oxides of Co and Ni, with concurrent evolution of the continuous S-rich inner layer. A multicomponent analysis provides insight into diffusional interactions among Co, Ni, and S. Crystal orientation and microstructure effects were also studied.

Constrained chip (sheet) formation by large strain extrusion machining is used to impose effective strains of ∼1 in Mg alloy AZ31B sheet in a single step of deformation. High-speed image analysis shows the deformation underlying sheet formation to be simple shear that is confined to a narrow zone. This confinement of the deformation limits the need for pre-heating of the workpiece to realize continuous sheet forms. Tilted-basal textures, wherein the basal poles are inclined from the sheet surface normal, are achieved by this processing. These textures are quite different from those prevalent in rolled sheet. By controlling the strain path, the basal pole inclination could be varied in the range 32–53°. The primary texture component is the B-fiber, indicating basal slip to be the main deformation mode over the temperature range 165–400 °C. An additional C2-fiber component appears above 250 °C due to the activation of pyramidal 〈 c + a 〉 slip. In conjunction with these textures, microstructures ranging from ultrafine-grained (∼200 nm) to fine-grained (∼2 μm) could be obtained by controlling the deformation temperature. Implications of the results for production of Mg sheet are discussed.

The role of grain orientation and grain boundary misorientation on the formation of subcritical grain boundary cracks in creep of a conventionally cast nickel-based superalloy has been studied. The crystallographic orientations of the grains adjacent to grain boundaries normal to the tensile axis were measured using electron backscattered diffraction. The difference in the Schmid factor for the {111} ⟨112⟩ slip system between the grains was compared to the occurrence of grain boundary cracking. In addition, the difference in the amount of potential primary creep was calculated. The cracked grain boundaries were found to have a larger difference in Schmid factor, as well as a larger difference in potential primary creep, compared with uncracked grain boundaries.

Extrusion machining combines cutting with simultaneous extrusion using an additional constraining tool to induce very large and well-characterized strains. Unlike conventional extrusion, accurate analytical models exist for extrusion machining to calculate values of effective strain, strain rate, and temperature rise as a function of processing parameters. Additionally, the size, shape, and microstructural effects of a secondary shear zone that forms due to friction during extrusion machining have been characterized. This secondary shear zone can be manipulated by varying processing parameters, and can produce a severely inhomogeneous microstructure. This microstructure is also seen during conventional extrusion, as the material on the outside of the extrudate is strained more than the inside material, potentially causing an incomplete recrystallization across the face of the product. The secondary shear effect in the extrusion machining process is utilized to reproduce the inhomogeneous microstructure seen in conventional extrusion in order to better understand the recrystallization behavior during AA7050 extrusion.

A constrained chip formation technique, large strain extrusion machining (LSEM), was used to produce bulk magnesium alloy (AZ31B) strips with fine grain size (2–6 μm) and non-basal textures. These characteristics are known to enhance the final formability. The deformation temperature during extrusion-machining was varied by preheating the workpiece to a range of temperatures (50°C to 375°C). Microstructural refinement and texture evolution were studied as function of deformation temperature. It was possible to refine the grain size down to ∼2 µm by restricting the dynamic grain growth at low to moderate deformation temperatures (below 320°C). LSEM was shown to be capable of resulting in non-basal textures at low deformation temperatures (below 220°C) as well as at elevated deformation temperatures (above 420°C). The influence of active deformation mechanisms and dynamic recrystallization on the texture development is also addressed.

When attempting to cast sharp corners, the wetting behavior of liquid metal in a mold will greatly affect the extent to which the corner will be filled. The contact angle, mold material, surface roughness, and applied pressure can alter the wetting behavior of the liquid metal. An analytical model was developed to predict the filling of sharp corners by a non-wetting liquid as a function of contact angle, corner angle, head height, and surface roughness. The effects of applied pressure on the final shape of the metal in the corners of various feature sizes and angles was investigated. The results from these predictions will help improve the casting of sharp corners, allowing more intricate turbine component designs.

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.

An analysis of the mechanics of large strain extrusion machining (LSEM), a constrained chip formation process, is presented for deformation processing of bulk alloys. The deformation field is shown to be narrowly confined and controllable, with attributes ranging from conventional deformation processing to severe plastic deformation. Controllable deformation parameters include strain/strain rate, hydrostatic pressure, temperature and deformation path. These attributes are highlighted in deformation processing of Mg AZ31B, an alloy of commercial significance but noted for its poor workability, into sheet and foil forms. Noteworthy features of the processing are suppression of segmentation, realization of a range of strains and deformation rates, engineering of microstructures ranging from conventional to ultrafine grained, and creation of sheet/foil from the bulk in a single step of deformation without pre-heating. Guidelines for realizing specific sheet attributes, and scalability of LSEM for production are analyzed and discussed.

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.

Mechanical properties and microstructure characterization of a series of graded commercial rigid polyurethane foams commonly used to mimic trabecular bone in testing orthopaedic devices is reported. Compressive testing conducted according to ASTM standard F1839-08, which requires large specimens (50.8 mm x 50.8 mm x 25.4 mm blocks) gave elastic modulus and compressive strength values ranging from 115 to 794 MPa and 4.7 to 24.7 MPa, respectively, for foams having densities of 0.240-0.641 g/cm(3). All these results were within the requirements of the specification for the corresponding grades. Compression testing using smaller specimens (7.5 mm diameter x 15 mm) typical of testing bone, gave results in good agreement with those obtained in the standard tests. Microstructural measurements showed the average pore size ranged from 125 to 234 microm for densities ranging from 0.641 to 0.159 g/cm(3), respectively. The relative modulus as a function of relative density of the foams fit well to the model of Gibson and Ashby. Cyclic testing revealed hysteresis in the lower density foams with a loading modulus statistically equivalent to that measured in monotonic testing. Shore DO durometry (hardness) measurements show good correlations to elastic modulus and compressive strength. The results suggest additional parameters to consider for the evaluation of polyurethane foams for bone analog applications.

The deformation field in machining was controlled to access a range of deformation parameters—strains of 1–15, strain rates of 10–100,000 s −1 and temperatures of up to 0.4 T m —in the severe plastic deformation (SPD) of copper. This range is far wider than has been accessed to date in conventional SPD methods, enabling a study of the interactive effects of the parameters on microstructure and strength properties. Nano-twinning was demonstrated at strain rates as small as 1000 s −1 at −196 °C and at strain rates of ⩾10,000 s −1 even when the deformation temperature was well above room temperature. Bi-modal grain structures were produced in a single stage of deformation through in situ partial dynamic recrystallization. The SPD conditions for engineering specific microstructures by deformation rate control are presented in the form of maps, both in deformation parameter space and in terms of the Zener–Hollomon parameter.

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.

In DC casting of aluminum alloys, thermal strains can cause cracks during and after solidification and rejection of the ingot. Previous numerical models have simulated strain and stress in rounds, but less attention has been paid to slabs. To study residual stresses as a function of rectangular ingot aspect ratio and absolute ingot size, a 3D finite element model is used with simplified dynamic thermal boundary conditions. In industrial practice, a wiper is sometimes placed below the mold to isolate the lower part of ingot from cooling water, and that effect is also simulated. Stresses throughout the process start-up are predicted; the surface is first under tension, and later in compression, while the center has the opposite history. Results indicate decreasing stress magnitudes with the addition of a wiper. Also, placing the wiper closer to the mold will further reduce the residual tension in ingot center, but, if the wiper is too close, the ingot surface temperature will rebound and the surface may begin to remelt. A height limit of wiper position is determined to prevent the surface remelting. Larger ingots and slabs with larger aspect ratios are found out to have a higher overall tension level.

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.

A technique for producing ceramic preforms with graded porosity via colloidal infiltration of molded polymer sponges has been developed. Polymer sponges have been compression molded into various shapes with continuous and/or stepwise gradients in porosity. Infiltration of the graded sponge with ceramic slurry, followed by pyrolysis of the sponge and sintering of the ceramic, produces a ceramic component with graded porosity. A relationship between compressive strain and the volume fraction of porosity in the sponge has been derived and compared to measured values. The applicability of this technique to the manufacture of planar and axisymmetric composite shapes is demonstrated.

In-situ crack-propagation experiments, in conjunction with thermochemical experiments, have been used to examine the role of discontinuous interphases on the fracture behavior of solid-state diffusion-bonded Cu/α-Al2O3 couples. Clean, interphase-free interfaces exhibit crack extension by brittle decohesion at the crack tip at an initiation fracture energy of 125 J/m2. Crack propagation is characterized by an increase in the fracture energy with increases in the crack length (R-curve behavior). When interfacial chemical reaction products are present, the crack growth is altered, depending on the characteristics of the interphase. The presence of Cu2O needles results in preferential debonding along the Cu2O/Al2O3 interface. On the other hand, finer CuAlo2 needles visibly impede crack propagation and result in a higher interface initiation fracture energy (}190 J/m2) than that of the interphase-free interface. The effects of the Cu2O and CuAlo2 phases on the fracture energy are discussed.