RevAdvMaterSci 182008 203211 RECENT DEVELOPMENTS IN MECHANICAL ALLOYING ID: 235854
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203Recent developments in mechanical alloying Rev.Adv.Mater.Sci. 18(2008) 203-211 RECENT DEVELOPMENTS IN MECHANICAL ALLOYING !"# $%& 'and rewelding. The transfer of mechanical energycations and other defects which act as fast diffu-sion paths. Additionally, refinement of particle anddistances are reduced. Further, a slight rise in pow-effects lead to alloying of the blended elementalthese effects have been well documented in theare available dealing with the different aspects [1,2].As has been pointed out frequently, the tech-, the tech-during the last 40 years or so can be divided intothree major periods. The first period, covering from1966 to 1985, was mostly concerned with the de-velopment and production of oxide dispersionthe aerospace industry. Several alloys, with im-military during the Gulf war and subsequently. The 204C. Suryanarayana Schematic showing the different periods of development in mechanical alloying (MA) since its SEM micrograph of Al-50 vol.% Al (50 in SEM micrograph of Al-10 vol.% Al (50 (50have been frequently made between MA and othernon-equilibrium processing techniques, notablyrapid solidification processing (RSP). It was shownthat the metastable effects achieved by these twonon-equilibrium processing techniques are similar.opment schematically. 2. PAST DEVELOPMENTSin the turbine industry. After several trials, high-acceptance in the industry. At the moment, a large. At the moment, a large7]. Apart from these major industrial applications,the MA products were also finding use, on a smallerscale, in meals, ready-to-eat (MRE) heaters, pig-ment and paint industry, as super-corroding alloysduring the late 1980s and the 1990s was in tryingtal powders and formation of different types often lamellar if the constituent elements are suffi-ciently ductile) of the components is formed afterperature was found to promote diffusion and con-sequently alloy formation. Accordingly, it was shownest free energy, under the continuous deformationpositive heats of mixing that are difficult to alloyrules, so widely used to rationalize equilibrium sub-rules, so widely used to rationalize equilibrium sub-the range of solubilities. Powders with fine grainsizes, and consequently a large grain boundaryarea, were shown to have a higher solid solubilitylevel than the coarse-grained powders. Reasonsfor the formation of intermetallic phases (equilib-rium and metastable crystalline as well asquasicrystalline) were also provided. An importantquasicrystalline) were also provided. An importantin this case was that if the glassy powders couldbe consolidated to full density without crystalliza-tion, then it would be possible to overcome the limi-tation of section thickness imposed by the solidifi-cation route. A number of investigations were alsoundertaken to develop aluminides based on Ti, Ni,i, Ni,encouraging since the MA-processednanostructured aluminide alloys did not show anyimproved ductility at room temperature. However,of Ti and 40 vol.% of -TiAl alloy showed sig-and exhibited even superplastic behavior at 950°C and at a strain rate of 4·10 [16]. [16].of energy available in different types of mills [18,19]mation. However, based on the available experi-, based on the available experi-that we have still a long way to go before we canreliably predict the nature of phases that form un-der the given conditions of milling.3. CURRENT ACTIVITIESAs mentioned earlier, in recent years, there has AlYieldCompressive Elastic Elastic ModulusParticle sizeVolume Strength Strength Modulus calculated by thefraction (MPa) (MPa) (GPa) (GPa) 50 nm 5% 488 605 78 83 50 nm 10% 515 628 90 95 150 nm 5% 409 544 75 83 150 nm 10% 461 600 77 95 = represent the elastic modulus and volume fraction, respectively and the represent the composite, matrix, and reinforcement, respectively.Table 1. nanocomposites obtained by milling and subsequent consoli- tively pursued in our research group now. Thesecal properties of composites. Further, the mechani-size of the reinforcement. Traditionally, a reason-was large (on a micrometer scale). But, if the rein-stricted to about 2 to 4%. However, if we are able composites with the reinforcement varying in size from 50 nm to particles, up to a volume frac-confirmed through the X-ray elemental mappingconfirmed through the X-ray elemental mappingThese composite powders were very hard andstrong and consequently it was not possible to con-solidate them to full density by any of the presentlyavailable different techniques. Therefore, to deter-mine the effect of reinforcement particle size andsolidated to full density. Even at these small vol-termined. Table 1 lists the mechanical propertiesbehave closer to the iso-strain condition, while com- -TiAl and Ti phase, with 60nm. Tensile testing of these composite specimenswas conducted at different temperatures and strainat temperatures as low as 950 °C and a strain rateof 4·10relatively low, it is interesting that superplasticity, it is interesting that superplasticityabout 0.5 Tm, where Tm is the melting point of thehavior only at temperatures about 300-400 °CCmens before and after tensile testing.3.2. Glass formationMetallic glasses have been produced in severalalloy systems by many different techniques. Oneof the most commonly used techniques is rapidsolidification processing (RSP). As is well known,the critical cooling rate for glass formation needsto be exceeded for the glass to form. However, (a) Stress-strain curve of -TiAl+60 vol.% Ti composites showing that superplastic deformationwas achieved at 950 °C and a strain rate of 4·10 and 1000 °C and a strain rate of 4·10(and is also difficult to measure), several other cri- where is the glass tran- is the liquidus tempera-ture of the alloy, (b) presence of deep eutectics inbetween the constituent elements, and for bulkdius dif�ference of 12% between the elements, andsome others [25]. We could also determine if other alloythe X-ray diffraction patterns were recorded as afunction of milling time. All the diffraction peaks(110) peak of Fe at 50 h of milling time. This is onlying the glassy alloy powder for 1 h at 700 °C, al- 208C. Suryanarayana (a) Comparison of the XRD patterns of blended elemental powdersphous powder annealed for 1 h at 700 °C showing Time required for formation of the glassyphase in mechanically alloyed Fe Ignition time, and burning time, as afunction of particle size for two different alloy com-ferent alloy com-ders without allowing crystallization to occur, onenot in other systems (Table 2). From an analysis of addition of an alloying element that has a positiveheat of mixing with one of the constituent elementspromotes glass formation and also the plasticity ofthe glassy alloys. We had also noted that additionthan Zr. All these seem to increase the glass form-ability of the alloys [30]. However, this effect seemsfect seemscan be easily combusted, but it has a low heat con-tent (14.9 MJ/kg). On the other hand, Al has ahigher heat content (32.9 MJ/Kg), but is more diffi-cult to combust. Therefore, it was decided to see iftively easily. Accordingly, a series of Al-Mg powderblends of different compositions were mechanicallym, 44-53 Meeker burner, at a temperature of approximatelydigital photography. Knowing the rotational speed and the ignition time, could be determined. Fig. 7 shows the plot of and with particle size for two dif-90 at.% Mg) [32]. It is clear from this plot that bothMA is very efficient in synthesizing a variety of equi-librium and non-equilibrium materials. Some of thether, large-scale applications require materials thathas been the three Cs Cost, Consolidation, andbe high. However, in some cases, e.g., hydrogen Element X Milling time for glass formation (h) Number of intermetallics between X andZrFe Al10 8 5 Co No glass formation 5 Ge10 5 5 Mn No glass formation 1 Ni20 7 1 Sn No glass formation 3 2Table 2. Time required for glass formation in Fe alloys and the number of intermetallics in the metastable effects. Newer and improved methodsfects. Newer and improved methodsthat contamination of the MA powder has been aserious issue in many cases [2]. Some solutionshave also been suggested to minimize/avoid con-tamination completely. These include enclosing thelysts, pigments, solder, hydrogen storage materi-may not be relevant. Further, even if a bulk com-knowledges useful discussions with Dr. EugeneIvanov of Tosoh SMD, Grove City, OH and Profes-sity, Hamburg, Germany. Finally, he acknowledges Pushkar Katiyar, Balaji Prabhu, Satyajeet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