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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

The single-edge-V-notched-beam (SEVNB) testing method was used to measure the crack growth resistance (R-curve) behavior of multilayered alumina–zirconia composites. Crack initiation and extension from the V-notch tip were observed via in situ optical microscopy. The resulting R-curves were compared with an R-curve measured from a monolithic composite having a similar composition and a homogeneous microstructure, where the influence of layer–layer interfaces, gradient microstructures, and the direction of crack propagation on the resulting R-curves were observed. Additionally, the stress intensity factor for crack initiation from the V-notch tip was ∼0.2 MPa·m1/2 higher than the stress intensity factor to further extend this crack.

The interfacial reactions between Cu and Al 2 O 3 which occur during the eutectic bonding process have been examined. A thermodynamic analysis of phase equilibria in the Cu–Al–O system shows that a five-phase equilibrium exists among solid copper with oxygen in solution, liquid copper with oxygen in solution, solid CaAlO 2 , Al 2 O 3 and oxygen gas at the invariant state T =1348 K, p O 2 =5.6×10 −7 atm (0.055 Pa). The existence of this invariant state has been confirmed experimentally by heating slightly oxidized copper disks placed in contact with alumina disks. The experimentally determined invariant state was found to be in good agreement with that calculated. During eutectic bonding the compound CuAlO 2 forms at the interface between copper and the alumina in specimens containing solid copper only at temperatures lower than 1348±3 K.

Previous experiments indicated that the contact angles required for spontaneous infiltration of molten metal alloys into particulate ceramic preforms are significantly less than 90°. Analysis of capillarity in pores between packed particles shows the origin of this effect to be in the non-cylindrical curvature of these pore surfaces. A simple geometrical approach for predicting critical contact angles, θ c , for spontaneous infiltration of non-cylindrical pores is presented and applied to the pore structure between closepacked spheres. Although the critical contact angle for entry of the first layer of pores varies with the direction of infiltration, complete spontaneous infiltration of the structure is limited by penetration of the tetrahedral pores, for which θ c = 50.7°.

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.

A tri-arc Czochralski apparatus and procedure used to grow MoSi2 crystals is detailed. Problems with Si evaporation and compositional banding are described. Growth orientations and other microstructural features of the crystals are discussed.

Microstructural development during the oxidation of (001)-oriented γ′-Ni3Al single crystals at 1223 K under an oxygen partial pressure of 4 × 10−19 atm has been studied by electron microscopy. After 1 min oxidation, TEM cross sections revealed a continuous 4 nm thick film of γ-Al2-O3 with equiaxed 20 nm protrusions into the metal. Pre-thinned foils oxidized for 6 min and studied in plan view in the TEM showed that the scale consisted of 20 nm γ-Al2O3 grains oriented to the metal such that (111) γ-Al2O3 (001) γ′-Ni3Al. Continued oxidation resulted in thickening of the γ-Al2O3 scale, no grain growth, and the development of a plane metal/γ-Al2O3 interface. Depletion of Al from the adjoining metal resulted in a well-defined disordered zone of NiAl solid solution between the Al2O3 scale and the γ′-Ni3Al. After 5 h oxidation large, randomly oriented α-Al2O3 grains nucleated at the metal/γ-Al2O3 interface, growing inward and transforming from the γ-Al2O3 outward. The α-Al2O3 contained intragranular and intergranular voids. The γ-Al2O3 exhibited a high density of planr defects and the interface between the γ-Al2O3 and α-Al2O3 contained many voids. Voids at the metal/oxide interface were never observed.

Subsolidus ternary phase relationships in the systems Fe Al O and Cu Al O are reviewed in order to provide a basis for thermodynamic analysis of aluminate formation at Fe/α-Al 2 O 3 and Cu/α-Al 2 O 3 interfaces. Expressions for the critical oxygen activity in the Fe-rich and Cu-rich solid solutions necessary to stabilize the equilibrium aluminate phases (FeAl 2 O 4 and CuAlO 2 , respectively) in the presence of α-Al 2 O 3 are derived using data available in the literature. As in previous work in the Ni α Al 2 O 3 system, aluminate formation by solid state reaction of Fe and Cu with α-Al 2 O 3 was calculated to require a threshold concentration of oxygen in the metal, which is of the order of 1/5 the solubility limit. The sults are presented in stability diagrams and compared with previous results on the Ni/α-Al 2 O 3 system in terms of the free energies of formation of the aluminates and the relative free energes of solution of oxygen in the metals. The results are also compared with available experimental observations on Fe/α-Al 2 O 3 and Cu/α-Al 2 O 3 interfaces.

Interface microstructural development during solid state diffusion bonding of Ni to single-crystal α-Al2O3 has been studied by electron microscopy. Nickel aluminate spinel (NiAl2O4) interphase layers ∼ 1 μm thick formed under high vacuum bonding conditions. Very high vacuum (VHV) annealing caused the spinel to disappear, indicating that its stability depends critically upon the oxygen activity. High vacuum diffusion bonding utilizing initially oxygen-free Ni and oxygen-containing Ni established that spinel formation requires a threshold oxygen activity, and furthermore, that the source of the required oxygen can be oxygen initially dissolved in the Ni. Thermodynamic calculations confirm that the threshold oxygen level necessary to stabilize the spinel increases from 0.006 at.% (60 at.ppm) at 1273 K to 0.025 at.% (250 at. ppm) at 1663 K. Further analysis indicates the spinel exhibits a maximum thickness determined by the difference between the initial and threshold oxygen concentrations and the Ni thickness. Considering the solubility limit of oxygen in solid Ni, the spinel thickness is limited to ∼0.005 times the Ni thickness. The reaction is explored further in the context of diffusion path concepts with a calculated NiAlO phase diagram.

Alumina has been liquid state bonded with pure Al and Al-4 wt% Mg and the mechanical behavior of the bonds has been characterized. It has been shown that failure never occurs by interface cracking. Instead, when the bond layer is thick, the bond strength is limited either by plastic flow or by ductile fracture in the metal. Conversely, when the bond layer is thin, failure occurs in the ceramic, limited by the strength of the ceramic. The Al alloy bond has also been shown capable of arresting cracks by plastic blunting.