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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.

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.

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.

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 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.