Mechanical alloying of Fe100−−Nb B (x= 5, 10; y= 10, 15): From pure powder mixture to amorphous phase

Abstract

The mechanical alloying process of Fe 75 Intermetallics. Vol. 16. Núm. 9. 2008. Pag. 1073-1082 http://dx.doi.org/10.1016/j.intermet.2008 2 1 Introduction Nanocrystalline materials are defined by a crystal size below 100 nm. As a limit, amorphous materials are solid systems where the structural long range order is lost.These materials have received much attention due to their physical properties (mechanical and magnetic), which are clearly different from those exhibited by conventional microstructures and, in some cases, improve their technological applicability [1,2,3]. One way to obtain nanocrystalline materials is by partial devitrification of a precursor amorphous alloy during controlled thermal annealing. This technique controls the microstructure of materials and thus optimizes the properties of the final product. Another possibility is mechanical alloying, which has become a very versatile technique to directly produce metastable microstructures (amorphous, nanocrystallines, supersaturate solid solution, etc) [1] from elemental powders or alloys.During this milling process the material is submitted to fracture and cold welding phenomena, as well as intensive plastic deformation, which define the powder morphology, microstruture and properties. The continuous storing of defects in the crystalline phase during milling process unstabilizes it, leading to nanocrystalline and/or amorphous structures [1].Nanocrystalline Fe-M-B type alloys (M= Zr, Nb, etc), so-called Nanoperm [4], are attractive due to their soft magnetic properties after optimum thermal treatment and are used in commercial applications such as telecommunications, micro devices and power electronics [5,6]. Although these systems are generally obtained by rapid quenching and subsequent annealing, nanocrystalline alloys of these compositions can be directly obtained by mechanical alloying of elemental powders. As soft magnetic properties depend on the structure of the material [7,8,9], its structural characterization Intermetallics. Vol. 16. Núm. 9. 2008. Pag. 1073-1082 http://dx.doi.org/10.1016/j.intermet.2008 3 is a very important task to understand the system behavior and to predict its possible technological capabilities.In this study, two Fe 100-x-y Nb x B y (x=5, y=10 and x=10, y=15) alloys were produced by mechanical alloying from a mixture of pure elements and their morphological, compositional and microstructural evolution, as well as their thermal stability, were studied as a function of milling time. The amorphization of the ternary FeNbB system by rapid quenching methods has been studied previously [10]. Whereas compositions similar to Nb10 can be obtained in amorphous structure, those similar to Nb5 can not be obtained as amorphous. ExperimentalFe 100-x-y Nb x B y (x=5, y=10 and x=10, y=15) compositions were prepared by ball milling in a planetary mill Fritsch Pulverisette 4 Vario from elemental powders ( 99 % purity), with particle size d <200 m for Fe and Nb and d <1 mm for B. For simplicity, the studied alloys will be ...

Structure and magnetic properties of Fe–Nb–B amorphous/nanocrystalline alloys produced by compaction of mechanically alloyed powders

“…Fe 75 Nb 10 B 15 and Fe 85 Nb 5 B 10 compositions were prepared by ball milling in a shaker mill ͑Spex 8000D͒ from pure crystalline powders of Fe, Nb, and B ͑Ͼ99% purity͒. For simplicity, the studied alloys will be named in the following by their Nb content: Nb10 for Fe 75 Nb 10 B 15 and Nb5 for Fe 85 Nb 5 B 10 .…”

“…For simplicity, the studied alloys will be named in the following by their Nb content: Nb10 for Fe 75 Nb 10 B 15 and Nb5 for Fe 85 Nb 5 B 10 . The initial powder mass was 10 g and the ball to powder ratio was 12:1.…”

“…In this work, mechanical alloying of Fe 75 Nb 10 B 15 and Fe 85 Nb 5 B 10 powders have been performed, and their morphology, composition, microstructure, and magnetic properties studied as a function of milling time. At the end of the studied milling time, partially amorphous and nanocrystalline powders were compacted at different temperatures.…”

“…From DSC scans, a crystallization temperature of ϳ850 K was measured for the amorphous phase developed during milling of Nb10 composition in a planetary mill, 15 which could explain the weak evolution of X C after compaction at 823 K ͑below crystallization temperature͒. Moreover, both onset temperatures and activation energies of crystalli- zation processes increase as the pressure increases in some nanocrystalline systems compacted in similar conditions, 16 which could explain that, even after compaction at 973 K ͑above the crystallization temperature at room pressure͒, the bulk sample still presents amorphous phase.…”

“…Figure 12 shows DSC scans of samples at different compaction temperatures as well as that of as-milled powders for both alloys. It can be observed that the broad exothermic peak, typical of powder samples, 15 reduces its enthalpy from 320Ϯ 5 to 130Ϯ 5 J/ g and from 230Ϯ 5 to 64Ϯ 5 J/ g, for Nb10 and Nb5, respectively, after compaction at 823 K with respect to as-milled samples. As this temperature does not produce microstructural changes, this enthalpy change should be ascribed to relaxation processes of the powder samples during hot compaction.…”