J.T. Guo

Bio: J.T. Guo is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Nial & Microstructure. The author has an hindex of 25, co-authored 102 publications receiving 1725 citations. Previous affiliations of J.T. Guo include Lanzhou University of Technology.

Investigation on NiAl–TiC–Al2O3 composite prepared by self-propagation high temperature synthesis with hot extrusion

Abstract: The NiAl-TiC-Al2O3 in situ composite was fabricated by self-propagation high temperature synthesis and hot extrusion (SHS/HE) technique using element powders. Its microstructure and mechanical properties were investigated by OM, SEM, TEM and compression test. The results revealed that the NiAl-TiC-Al2O3 composite was densified by the SHS/HE process and had fine microstructure. In the composite, TiC particles along NiAl grain boundary agglomerated and grew, but the TiC particles in NiAl grain were fine. The TiC and Al2O3 particles exhibited an obvious trend to distribute along extrusion direction. Moreover, stacking fault and microtwins in TiC particles and thin amorphous layer along NiAl/TiC phase interface were also observed. In addition, Ti2AlC particle with intergrowth TiC plate inside formed along the NiAl grain boundary. Generally the SHS/HE synthesized NiAl-TiC-Al2O3 composite possessed better mechanical properties, especially at room temperature, which should be ascribed to the fine microstructure and predeformation caused by hot extrusion. (c) 2012 Elsevier Ltd. All rights reserved.

Mechanical Alloying And Milling

Abstract: Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

A Promising New Class of High-Temperature Alloys: Eutectic High-Entropy Alloys

Abstract: High-entropy alloys (HEAs) can have either high strength or high ductility, and a simultaneous achievement of both still constitutes a tough challenge. The inferior castability and compositional segregation of HEAs are also obstacles for their technological applications. To tackle these problems, here we proposed a novel strategy to design HEAs using the eutectic alloy concept, i.e. to achieve a microstructure composed of alternating soft fcc and hard bcc phases. As a manifestation of this concept, an AlCoCrFeNi 2.1 (atomic portion) eutectic high-entropy alloy (EHEA) was designed. The as-cast EHEA possessed a fine lamellar fcc/B2 microstructure, and showed an unprecedented combination of high tensile ductility and high fracture strength at room temperature. The excellent mechanical properties could be kept up to 700°C. This new alloy design strategy can be readily adapted to large-scale industrial production of HEAs with simultaneous high fracture strength and high ductility.