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

https://www.tcd.ie/Physics/people/Graham.Cross/SF%20Poster%202011/Schuh-ActaMater07-Mechanical%20behaviour%20of%20amorphous%20alloys.pdf

Mechanical behavior of amorphous alloys

Plasticity in small-sized metallic systems: Intrinsic versus extrinsic size effect

During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.

Microstructural and mechanical characteristics of in situ metal matrix composites

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1443&context=ameslab_manuscripts

Additively manufactured hierarchical stainless steels with high strength and ductility

The effect of compression and tension on shear-band structure and nanocrystallization in amorphous Al90Fe5Gd5: a high-resolution transmission electron microscopy study

The formation of Al-Ni compounds by ball-milling of elemental powders has been investigated by means of in situ thermal analysis, x-ray diffraction, and scanning electron microscopy. The results show that AlNi forms in an explosive, exothermic reaction, driven by the large heat of compound formation. The mechanism discovered is suggested to explain the mechanical alloying of other systems.

/pdf/in-situ-thermal-observation-of-explosive-compound-formation-3bwod7v94y.pdf

In situ Thermal Observation of Explosive Compound-Formation Reaction During Mechanical Alloying

Metastable solid solutions of Fe and Cu, which are immiscible in equilibrium, have been formed using high-energy ball milling of elemental powder mixtures. Single-phase face-centered-cubic (fcc) solid solution was obtained for 0<x≤60, and body-entered-cubic (bcc) solid solution for 75≤x<100. The transition from fcc to bcc occurred near x=70, where a mixture of fcc and bcc phases was obtained. The enthalpy of transformation to equilibrium was measured using differential scanning calorimetry. The average atomic volume of the phases exhibits a positive deviation from Vegard’s law, in qualitative agreement with the large positive enthalpy of mixing in this system. The magnetic moments and Curie temperatures for the metastable solid solutions have been determined and compared with those reported for Fe-Cu alloys formed by vapor deposition. Calculations of the formation enthalpy (ΔH) and free energy (ΔG) have been performed based on calphad data, with corrections based on our magnetization measurements. The calculated ΔG results are used to explain the observed fcc-bcc transition under polymorphous constraints.

/pdf/thermodynamic-and-magnetic-properties-of-metastable-fexcu100-2mo3iwyws0.pdf

Thermodynamic and magnetic properties of metastable FexCu100−x solid solutions formed by mechanical alloying

Mechanical behavior of shear bands and the effect of their relaxation in a rolled amorphous Al-based alloy

Plastic deformation of amorphous Al90Fe5Gd5 was investigated using nanoindentation and atomic force microscopy. While serrated flow was detected only at high loading rates, shear bands were observed for all loading rates, ranging from 1 to 100 nm/s. However, the details of shear-band formation depend on the loading rate.

/pdf/rate-dependence-of-serrated-flow-in-a-metallic-glass-bkz4h9hm16.pdf

Michael Atzmon

Papers

The effect of compression and tension on shear-band structure and nanocrystallization in amorphous Al90Fe5Gd5: a high-resolution transmission electron microscopy study

In situ Thermal Observation of Explosive Compound-Formation Reaction During Mechanical Alloying

Thermodynamic and magnetic properties of metastable FexCu100−x solid solutions formed by mechanical alloying

Mechanical behavior of shear bands and the effect of their relaxation in a rolled amorphous Al-based alloy

Rate dependence of serrated flow in a metallic glass