Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

https://dc.engconfintl.org/cgi/viewcontent.cgi?article=1032&context=superalloys_ii

A critical review of high entropy alloys and related concepts

Microstructures and properties of high-entropy alloys

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.

Mechanical Alloying And Milling

Amorphous alloys were first developed over 40 years ago and found applications as magnetic core or reinforcement added to other materials. The scope of applications is limited due to the small thickness in the region of only tens of microns. The research effort in the past two decades, mainly pioneered by a Japanese- and a US-group of scientists, has substantially relaxed this size constrain. Some bulk metallic glasses can have tensile strength up to 3000 MPa with good corrosion resistance, reasonable toughness, low internal friction and good processability. Bulk metallic glasses are now being used in consumer electronic industries, sporting goods industries, etc. In this paper, the authors reviewed the recent development of new alloy systems of bulk metallic glasses. The properties and processing technologies relevant to the industrial applications of these alloys are also discussed here. The behaviors of bulk metallic glasses under extreme conditions such as high pressure and low temperature are especially addressed in this review. In order that the scope of applications can be broadened, the understanding of the glass-forming criteria is important for the design of new alloy systems and also the processing techniques.

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Shek-MaterSciEng04-Bulk%20Metallic%20Glasses.pdf

Bulk metallic glasses

Cyclic deformation has been carried out on a directionally solidified cobalt base superalloy at room temperature in air under the control of different total strain amplitudes. Dislocation structures of different stages in the cyclic stress response curve were studied by TEM. Observations show that a large number of stacking faults and fault intersections are formed in the initial hardening stage, and this leads to the initial hardening of the alloy. However, formation of hexagonally close packed (hcp) zones and twins is proposed to be the cause of cyclic saturation. Models for both the transition from stacking faults to a hcp layer structure and to twins are proposed.

Evolution of dislocation structure induced by cyclic deformation in a directionally solidified cobalt base superalloy

Multicomponent AlCoCrFeNiMo(x) (x values in molar ratio, x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) alloys were prepared using a well-developed copper mould casting. The effects of Mo element on the structure and properties of AlCoCrFeNi alloy were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC). It was found that Mo addition took significant effects on the structure and properties of AlCoCrFeNi alloy. Mo(0.1) alloy, similar to Mo(0) alloy, was of single BCC solid solution structure. When Mo content was more than 0.1, the alloy exhibited a typical laminar eutectic structure. The alloy strength was improved obviously, but the ductility of alloy was lowered at the same time. The maximum yield strength reached 2757 MPa when Mo content was 0.5, and the maximum compressive fracture strength reached 3208 MPa when Mo content was 0.3. The strengthening effect and mechanism of Mo addition on AlCoCrFeNi alloy were discussed from different aspects. (C) 2010 Elsevier B.V. All rights reserved.

Microstructures and compressive properties of multicomponent AlCoCrFeNiMox alloys

Age-hardening behavior of cast Al–Si base alloy

By introducing nonmetallic Si element, AlCoCrFeNiSi(x) (x values in molar ratio, x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) alloys are designed and prepared. One kind of nanoscale cellular structure forms due to the introduction of nonmetallic Si element. The alloy is composed mainly of BCC solid solution and possesses excellent room-temperature compressive mechanical properties. The excessive introduction of Si element leads to the precipitation of 8 phase at grain boundary. The improvement of mechanical properties is attributed to the solid solution of Si element and precipitation strengthening of nanoscale cellular structure. The precipitated 8 phase at grain boundary should be responsible for transition of alloy from plastic fracture to brittle fracture. Among them, Si(0.4) alloy exhibits excellent comprehensive mechanical properties, yield stress of 1481 MPa, fracture strength of 2444 MPa and plastic strain of 13.38%, respectively. (C) 2010 Elsevier B.V. All rights reserved.

Zushu Hu

Papers

Evolution of dislocation structure induced by cyclic deformation in a directionally solidified cobalt base superalloy

Microstructures and compressive properties of multicomponent AlCoCrFeNiMox alloys

Age-hardening behavior of cast Al–Si base alloy

Synthesis and properties of multiprincipal component AlCoCrFeNiSix alloys

TiZr-base Bulk Metallic Glass with over 50 mm in Diameter