Solid State Phenomena Vols. 101-102

Abstract: Three kinds of bulk nanocrystalline Fe-24at%Al-Xat%C (X=1,2,4) alloy were produced from Fe and Al powders with addition of methanol by MA with subsequent SPS at 1273K under 64MPa. Their microstructure and mechanical properties were investigated. The compacts have the relative densities of 99.97% (1at%C) to 99.6% (4at%C). The structure of compacts with 1at%C is composed of Fe3Al grains of 1.5µm in diameter and nano k-carbides (Fe3AlC0.5) precipitates, while those of compacts with 2 and 4at%C are composed of nanocrystalline Fe3Al of about 80nm in diameter, nano k-carbides and a-grains of about 1µm in diameter. These structures have the good thermal stability, maintaining the nanostructure even at 973K. The mechanical properties of these compacts were measured by compression tests at R.T. to 973K. The compacts with 1at%C and 2at%C of this work perform the superior mechanical properties (e.g. yield strength of 2.15GPa and rupture strain of 0.14 for compact with 2at%C at R.T.) when compared with the ordinary Fe3Al casting (e.g. 380MPa and 0.12). They also exhibit no environmental embrittlement, which is one of fatal problems for the ordinary Fe3Al mateials.

Abstract: In this paper both electric discharge assisted milling [1, 2] and conventional mechanosynthesis techniques were applied to investigate the effects of milling conditions on the fracture and agglomeration of amorphous CoSiB ribbons produced by planar flow casting. The effect of spark energy on particle shape and size produced by discharge milling was studied. Conventional milling in inert atmosphere for extended periods generally leads to the formation of porous powder particle aggregates, each particle comprised of small amorphous or, after extended milling times, nanocrystalline elements. The mechanism of agglomeration was believed to originate from repeated fracture, deformation and cold welding of individual ribbon elements. In contrast to conventional milling, spark discharge milling was found to induce the formation of predominantly sub-micron single particles of amorphous powder. The morphology of individual particles varied from sub-micron irregular shaped particles to remelted particles, depending on selection of vibrational amplitude during discharge. For high vibrational amplitudes and high energy input a wider range of particles as produced. These included sub-micron particles, remelted particles and welded agglomerates, and nano-sized particles produced as a fume and collected during discharge milling under flowing argon. These results combined with observations that most re-melted particles produced by discharge milling were also amorphous confirmed that extremely high heating and cooling rates are associated with discharge milling of metals. They also confirm the potential of electrical discharge milling as a new route for the synthesis of ultrafine and nanosized powder particles from amorphous ribbon, for possible processing into 3-D shapes.