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

The precipitation sequence in Al–Mg–Si alloys

Recovery, recrystallization, grain growth and phase stability of a family of FCC-structured multi-component equiatomic solid solution alloys

In this paper, recent progress in magnesium matrix composite technologies is reviewed. The conventional and new processes for the fabrication of magnesium matrix composites are summarized. The composite microstructure is subsequently discussed with respect to grain refinement, reinforcement distribution, and interfacial characteristics. The mechanical properties of the magnesium matrix composites are also reported.

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Review of recent studies in magnesium matrix composites

Intumescence: Tradition versus novelty. A comprehensive review

Novel phosphorous–nitrogen intumescent flame retardant system. Its effects on flame retardancy and thermal properties of polypropylene

Kinetics of natural aging and precipitation hardening (T4 and T6 tempers) were compared in 6061 aluminium alloy (AA) and 6061 AA−14vol.%SiC particle composite. Aging processes have been studied by hardness measurements and differential scanning calorimetry (DSC). The latter technique is used as a screening tool to follow the aging sequence; in fact, the DSC thermogram depicts characteristic features of different heat treatments undergone by samples. DSC curves for both 6061 AA and 6061AA-SiCp, after solution treatment, display the same aging path; on the contrary, the two materials differ in solution temperature, which is about 30 °C higher in the case of the composite. The precipitation hardening (at 180°C) occurs faster in the composite than in 6061 alloy. The latter presents a broad hardness peak ranging between 4 and 10 h of aging while the composite shows a sharp peak after about 4 h. Probably this behaviour is due to the high dislocation density close to the metal matrix-SiC particle interface. In these strongly deformed zones nucleation processes are accelerated. The aging kinetics at room temperature for the composite is slower than for the 6061 AA. In fact the two materials show the same aging rate when solution treatment in the case of the composite is complete. On the contrary, the composite ages more slowly than 6061 AA. Hence the high dislocation density at the interface, between composite constituents, does not affect T4 treatment.

6061 aluminium alloy-SiC particulate composite: a comparison between aging behavior in T4 and T6 treatments

Differential scanning calorimetry (DSC) is used in order to investigate the aging behaviour of AlCuMg alloys with different Cu:Mg ratios. Mechanism and kinetics of aging for these materials are compared with those of an (AlCuMg)-SiC composite. DSC results are in fairly good agreement with metastable AlCu and AlCuMg phase diagrams. The SiC reinforcement does not affect the precipitation path; furthermore, the activation energy for θ″ precipitation, calculated by Ozawa's method, is not appreciably different, taking into account the experimental error, for unreinforced alloy and composite. However, all the transformations involved in the aging sequence are shifted towards lower temperatures during the DSC scans of the composite material.

calorimetric study on precipitation path in 2024 alloy and its SiC composite

The present manuscript has been focused on the extraction of cellulose from rice husk through a multi-step process. Three consecutive steps have been performed in order to separate impurities, hemicellulose, lignin and silica and thus to obtain pure cellulose. The crystallinity and morphology of the extracted cellulose have been investigated by using X-ray diffraction and scanning electron microscopy. Subsequently, poly(lactic acid) (PLA) bio-composites with different filler contents (namely, 5, 10, 20 and 30 wt%) have been prepared by melt-blending. The thermal and mechanical properties of the resulting bio-composites have been investigated and correlated with the observed morphologies. In spite of a broad micrometric distribution of the cellulose particle size, the mechanical properties turned out to be strongly improved as well as the oxygen permeability properties have proven to be reduced. These data have been compared with those of analogous compounds containing a commercial cellulose; the collected results have shown that similar mechanical properties have been found using both celluloses. Finally, this work has also demonstrated that an industrial waste as rice husk can be recycled for conferring enhanced final properties to PLA.

Francesco Marino

Papers

Novel phosphorous–nitrogen intumescent flame retardant system. Its effects on flame retardancy and thermal properties of polypropylene

6061 aluminium alloy-SiC particulate composite: a comparison between aging behavior in T4 and T6 treatments

calorimetric study on precipitation path in 2024 alloy and its SiC composite

Cellulose extracted from rice husk as filler for poly(lactic acid): preparation and characterization

Electrical resistivity and structural relaxation in Fe75TM5B20 amorphous alloys (TM = Ti, V, Cr, Mn, Co, Ni)