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Mechanical alloying and milling - Suryanarayana

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Moagem de alta energia e formação de ligas.
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  Mechanical alloying and milling C. Suryanarayana Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden,CO 80401-1887, USA Abstract Mechanical alloying (MA) is a solid-state powder processng technique involving repeatedwelding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originallydeveloped to produce oxide-dispersion strengthened (ODS) nickel- and iron-basesuperalloys for applications in the aerospace industry, MA has now been shown to becapable of synthesizing a variety of equilibrium and non-equilibrium alloy phases startingfrom blended elemental or prealloyed powders. The non-equilibrium phases synthesizedinclude supersaturated solid solutions, metastable crystalline and quasicrystalline phases,nanostructures, and amorphous alloys. Recent advances in these areas and also ondisordering of ordered intermetallics and mechanochemical synthesis of materials have beencritically reviewed after discussing the process and process variables involved in MA. Theoften vexing problem of powder contamination has been analyzed and methods have beensuggested to avoid/minimize it. The present understanding of the modeling of the MAprocess has also been discussed. The present and potential applications of MA aredescribed. Wherever possible, comparisons have been made on the product phases obtainedby MA with those of rapid solidi®cation processing, another non-equilibrium processingtechnique. 7 2001 Elsevier Science Ltd. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32. Historical perspective. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 0079-6425/01/$ - see front matter 7 2001 Elsevier Science Ltd. All rights reserved.PII: S0079-6425(99)00010-9Progress in Materials Science 46 (2001) 1±184www.elsevier.com/locate/pmatsci E-mail address: schallap@mines.edu (C. Suryanarayana).  3. Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94. The process of mechanical alloying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.1. Raw materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114.2. Types of mills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134.2.1. SPEX shaker mills. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134.2.2. Planetary ball mills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.2.3. Attritor mills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154.2.4. Commercial mills . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.2.5. New designs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184.3. Process variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.3.1. Type of mill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.3.2. Milling container. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.3.3. Milling speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224.3.4. Milling time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.3.5. Grinding medium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234.3.6. Ball-to-powder weight ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244.3.7. Extent of ®lling the vial. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.3.8. Milling atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.3.9. Process control agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.3.10. Temperature of milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295. Mechanism of alloying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325.1. Ductile±ductile components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355.2. Ductile±brittle components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375.3. Brittle±brittle components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386. Characterization of powders. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397. Temperature rise during milling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438. Solid solubility extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458.1. Diculties in solid solubility determination . . . . . . . . . . . . . . . . . . . . . . . 468.2. Mechanisms of solid solubility extension . . . . . . . . . . . . . . . . . . . . . . . . . 568.3. Comparison between mechanical alloying and rapid solidi®cation . . . . . . . 609. Synthesis of intermetallics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 629.1. Quasicrystalline phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 649.2. Crystalline intermetallic phases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 659.2.1. Metastable crystalline phases . . . . . . . . . . . . . . . . . . . . . . . . . . . 659.2.2. High-pressure phases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699.2.3. Equilibrium crystalline phases . . . . . . . . . . . . . . . . . . . . . . . . . . 759.3. Refractory compounds. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8210. Disordering of intermetallics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8611. Solid-state amorphization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9511.1. Thermodynamics and kinetics of amorphous phase formation. . . . . . . . . . 112 C. Suryanarayana/Progress in Materials Science 46 (2001) 1±184 2  11.2. Mechanism of amorphization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11411.3. Theoretical predictions of amorphous-phase-forming range. . . . . . . . . . . . 11611.4. Comparison between mechanical alloying and rapid solidi®cation . . . . . . . 11912. Nanostructured materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12213. Mechanochemical synthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12513.1. Process parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12913.1.1. Milling temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12913.1.2. Ball-to-powder weight ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13013.1.3. Process control agent. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13013.1.4. Relative proportion of the reactants . . . . . . . . . . . . . . . . . . . . . . 13113.1.5. Grinding ball diameter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13113.2. Phase formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13213.3. Combustion reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13413.4. Mechanosynthesis of compounds and composites. . . . . . . . . . . . . . . . . . . 13414. Powder contamination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13615. Modeling studies and milling maps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14415.1. Modeling studies. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14515.2. Milling maps. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14616. Applications of mechanical alloying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15016.1. Nickel-base alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15216.2. Iron-base alloys. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15516.3. Aluminum-base alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15716.4. Magnesium-base alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15816.5. Other applications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15817. Safety hazards. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15918. Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162 1. Introduction Scienti®c investigations by materials scientists have been continuously directedtowards improving the properties and performance of materials. Signi®cantimprovements in mechanical, chemical, and physical properties have been achievedthrough chemistry modi®cations and conventional thermal, mechanical, andthermomechanical processing methods. However, the ever-increasing demands for``hotter, stronger, stier, and lighter'' than traditional materials have led to the C. Suryanarayana/Progress in Materials Science 46 (2001) 1±184 3  design and development of advanced materials. The high-technology industrieshave given an added stimulus to these eorts.Advanced materials may be de®ned as those where ®rst consideration is givento the systematic synthesis and control of the structure of the materials in order toprovide a precisely tailored set of properties for demanding applications [1]. It isnow well recognized that the structure and constitution of advanced materials canbe better controlled by processing them under non-equilibrium (or far-from-equilibrium) conditions [2]. Amongst many such processes, which are incommercial use, rapid solidi®cation from the liquid state [3,4], mechanical alloying[5±9], plasma processing [2,10], and vapor deposition [2,11] have been receivingserious attention from researchers. The central underlying theme in all thesetechniques is to synthesize materials in a non-equilibrium state by ``energizing andquenching'' (Fig. 1). The energization involves bringing the material into a highlynon-equilibrium (metastable) state by some external dynamical forcing, e.g.,through melting, evaporation, irradiation, application of pressure, or storing of mechanical energy by plastic deformation [12]. Such materials are referred to as``driven materials'' by Martin and Bellon [13]. The energization may also usuallyinvolve a possible change of state from the solid to liquid or gas. The material isthen ``quenched'' into a con®gurationally frozen state, which can then be used asa precursor to obtain the desired chemical constitution and/or microstructure bysubsequent heat treatment/processing. It has been shown that materials processedthis way possess improved physical and mechanical characteristics in comparisonwith conventional ingot (solidi®cation) processed materials.The ability of the dierent processing techniques to synthesize metastablestructures can be conveniently evaluated by measuring or estimating the departurefrom equilibrium, i.e., the maximum energy that can be stored in excess of that of  Fig. 1. The basic concept of ``energize and quench'' to synthesize non-equilibrium materials. C. Suryanarayana/Progress in Materials Science 46 (2001) 1±184 4
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