A precipitation-hardened high-entropy alloy with outstanding tensile properties

A review on fundamental of high entropy alloys with promising high–temperature properties

Bulk nanostructured (ns)/ultrafine-grained (UFG) metallic materials possess very high strength, making them attractive for high strength, lightweight and energy efficient applications. The most effective approach to produce bulk ns/UFG metallic materials is severe plastic deformation (SPD). In the last 30 years, significant research efforts have been made to explore SPD processing of materials, SPD-induced microstructural evolutions, and the resulting mechanical properties. There have been a few comprehensive reviews focusing mainly on SPD processing and the mechanical properties of the resulting materials. Yet no such a review on SPD-induced microstructural evolutions is available. This paper aims to provide a comprehensive review on important microstructural evolutions and major microstructural features induced by SPD processing in single-phase metallic materials with face-centered cubic structures, body-centered cubic structures, and hexagonal close-packed structures, as well as in multi-phase alloys. The corresponding deformation mechanisms and structural evolutions during SPD processing are discussed, including dislocation slip, deformation twinning, phase transformation, grain refinement, grain growth, and the evolution of dislocation density. A brief review on the mechanical properties of SPD-processed materials is also provided to correlate the structure with mechanical properties of SPD-processed materials, which is important for guiding structural design for optimum mechanical properties of materials.

Structural evolutions of metallic materials processed by severe plastic deformation

Microstructure and strengthening mechanisms in an FCC structured single-phase nanocrystalline Co25Ni25Fe25Al7.5Cu17.5 high-entropy alloy

http://nucapt.northwestern.edu/refbase/files/IsheimCuPPTActaMat2005.pdf

Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale

Mechanical Behavior and Strengthening Mechanisms in Ultrafine Grain Precipitation-Strengthened Aluminum Alloy

Heterophase interfaces are characterized with respect to atomic-scale local compositions in two α-Fe-based alloy systems by three-dimensional atom probe microscopy The proximity histogram method is utilized for determining the compositions of the precipitates, the matrix phase and the Gibbsian interfacial excess of solute Suitable methods to measure segregation in multicomponent systems at heterophase interfaces independent of the position of the dividing interface are discussed Very little Sb segregates to the heterophase interface between coherent plate-shaped moybdenum nitride precipitates, which are <1 nm thick, and the α-Fe matrix: the relative interfacial excess of Sb is only 012 ± 01 nm−2 This is in sharp contrast to the interfacial excess of 7 ± 3 nm−2 for molybdenum nitride plates that have grown to 2–10 nm thick (or 20–30 nm in diameter for spheroidal precipitates) with a semicoherent interface with misfit dislocations, as reported earlier Small coherent Cu-rich precipitates with a metastable bcc structure in an α-Fe matrix exhibit interfacial segregation of Ni and Mn at their interfaces with excesses of 147 ± 043 and 095 ± 031 nm−2, respectively Copyright © 2004 John Wiley & Sons, Ltd

Nanoscale studies of segregation at coherent heterophase interfaces in α-Fe based systems

The precipitation of Heusler phase (L21: Ni2TiAl) from a supersaturated B2 (TiNi-based) matrix at 600°C and 800°C is studied using transmission electron microscopy (TEM), analytical electron microscopy (AEM), and three-dimensional atom-probe (3DAP) microscopy in Ni-Ti-Al and Ni-Ti-Al-X (X=Hf and Zr) alloys. The B2/L21 two-phase system, with ordered structures based on the bcc lattice, is chosen for its microstructural analogy to the classical γ/γ′ system with an fcc lattice. Knowledge of the temperature-dependent partitioning of alloying elements and their atomic volumes in the B2-TiNi and L21 phases is desired to support design of high-performance shape-memory alloys (SMAs) with controlled misfit strain and transformation temperatures. After aging at 600°C for up to 2000 hours, the L21 precipitates remain fully coherent at a particle diameter of ∼20 nm. The observed effects of a misfit strain of −1.9 pct on the microstructure of the B2/L21 system are similar to those theoretically predicted and experimentally observed for the γ/γ′ system. The similarities are demonstrated in terms of the precipitate shape, spatial distribution, and minimum distance of separation between L21 precipitates. However, all these effects disappear after aging the alloys at 800°C for 1000 hours, when the L21 precipitates become semicoherent at particle diameters above ∼400 nm. A simple analysis of the size evolution of L21 precipitates after an isochronal aging (1000 hours) experiment suggests that they follow coarsening kinetics at 600°C and growth kinetics at 800°C, consistent with the Langer-Schwartz theory of precipitation kinetics, which predicts that a high supersaturation suppresses the growth regime. Microanalysis using AEM and 3DAP microscopy define the TiNi-Ni2TiAl phase boundaries at 800°C and 600°C. At 800°C, Hf and Zr partition to the B2-TiNi, while at 600°C, they partition slightly to the L21 phase, reducing the lattice misfit to −1.7 and −0.011 pct, respectively, and partition strongly to the metastable phase Ti2Ni3. To describe the composition dependence of the lattice parameter of multicomponent B2 and L21 phases, the atomic volumes of Al, Hf, Ni, Ti, and Zr in the B2-TiNi and L21 phases are determined. A simple model is proposed to predict the lattice parameters of these phases in multicomponent systems.

Precipitation of heusler phase (Ni2TiAl) from B2-TiNi in Ni-Ti-Al and Ni-Ti-Al-X (X=Hf, Zr) alloys

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

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Combining Atom-Probe Tomography and Focused-Ion Beam Microscopy to Study Individual Presolar Meteoritic Nanodiamond Particles

http://www.arc.nucapt.northwestern.edu/refbase/files/UM_89_1-3_195.pdf

Dieter Isheim

Papers

Mechanical Behavior and Strengthening Mechanisms in Ultrafine Grain Precipitation-Strengthened Aluminum Alloy

Nanoscale studies of segregation at coherent heterophase interfaces in α-Fe based systems

Precipitation of heusler phase (Ni2TiAl) from B2-TiNi in Ni-Ti-Al and Ni-Ti-Al-X (X=Hf, Zr) alloys

Combining Atom-Probe Tomography and Focused-Ion Beam Microscopy to Study Individual Presolar Meteoritic Nanodiamond Particles

Nanometer-scale solute segregation at heterophase interfaces and microstructural evolution of molybdenum nitride precipitates.