H. Dimitrov

Nanostructured Al-Mm-Ni-(Fe,Co) Alloys Produced by Devitrification

Amorphous and nanocrystalline structures can easily be obtained in quate rnary systems, containing Al, lanthanide metal (Ln) and two late trans i io metals. Replacement of Ln by Mischmetal (Mm) reduces the cost of the materials st udied, as Mm is several times cheaper that pure lanthanide elements. Fully amorphous ribbons of Al-Mm -Ni-(Fe,Co) alloys, containing 4 and 5 at.% of Mm, were produced by the melt-spi nning technique. Structures, consisting of nanoparticles, embedded in amorphous matrix we re obtained by additional isothermal annealing of the initially fully amorphous al loys. X-ray diffractometry, transmission electron microscopy and differential scanning calorim etry were used for characterisation of the crystallization process and its products. It was found that the replacement of Al by Mm increases the thermal stability of the alloys. Isothermal annealing was found to be an effective method for producing a new group of nanocry stalline Al-based alloys. Introduction Amorphous and nanostructured Al-based alloys are interesting, mainly for their excellent mechanical properties. Amorphous Al-based alloys exhibit tensile st rength about twice that of the highest values for commercial crystalline Al-based alloy s [1]. Structures consisting of a mixture of fcc-Al nanoparticles and an amorphous matrix further improve tensile strength and microhardness, combined with good bending ductility [2]. To date such str uctures have been obtained in ternary and quaternary systems, containing lanthanide met al (Ln) and transition metals (TM), by isothermal annealing of initially fully amorphous ribbons [3,4]. Re placing Ln by Mm (Ce-50.3 at.%, La-43.5 at.%, Pr-5.9 at.% and Nd-0.3 at.%) reduces t he cost of the materials studied, as Mm is several times cheaper than pure la nthanide elements. Mixed structures of fcc-Al nanoparticles embedded in amorphous matrix wer e obtained by devitrification of amorphous Al-Mm-Ni-Cu alloys [5]. The objective of the current work was to investigate the effect of annealing temperature and chemical c omposition on the volume fraction of fcc-Al nanoparticles produced. Experimental Ingots of quaternary Al 88Mm5Ni5(Fe,Co)2, Al88Mm4Ni5(Fe,Co)3 and Al87Mm5Ni5(Fe,Co)3 alloys were prepared from pure elements by arc melting in an argon atmosphere. During melt spinning, the melt is ejected from the crucible onto a rotating coppe r wh el at peripheral speeds of 30 40 m s . By this technique, it is possible to quench the melt at a rate of 10-10 K s. The resulting ribbons were typically 2-3 mm wide and 30-40 m thick. Nanostructures were obtained by isothermal annealing of initially fully amorphous ribbons. The microstructures of the ribbons were studied by X-ray diffraction (XRD) using CuKα radiation and by transmission electron microscopy (TEM). Crystallization emperatures and heat of crystallization were determined by differential scanning calor imetry (DSC). The volume Solid State Phenomena Online: 2003-06-20 ISSN: 1662-9779, Vol. 94, pp 71-74 doi:10.4028/www.scientific.net/SSP.94.71

Bulk Amorphous Samples from Al-Mm-Ni System

Recent studies have shown that bulk amorphous alloys from Al-based ternary systems, containing lanthanide metal and late transition metal can be fabricated. Such materials are characterized by good mechanical properties. The most common production method of these alloys is melt spinning, giving a ribbon as a final product. In order to reduce the cost of material it is possible to replace lanthanide metal by mischmetal (Mm), which is one order of magnitude cheaper than pure lanthanides. The mischmetal used in this study contains [in at.%]: Ce-50.3, La-43.5, Pr-5.9, Nd-0.3. This study had two main objectives. First — to check the possibility of replacement of yttrium in the Al-Y-Ni system alloys by mischmetal, without losing the structure and mechanical properties. The other goal was to produce the bulk amorphous material. Five alloys from Al-Mm-Ni system were investigated. The as-quenched ribbons were milled to powder and then semi-isostatically compacted at elevated temperature to bulk material. After every step of the investigation, the XRD and DSC measurements were performed to detect possible changes of structure occurring during each step of the process: ribbon production, milling, compaction. Mechanical properties were characterized by Vickers microhardness. The results of the studies show the possibility to produce bulk amorphous alloys of the above mentioned system in three-step production cycle. The microhardness is good or even better compared to Al-RE-Ni alloys. The microhardness depends not only on the chemical composition of the alloy but also on the temperature of the compaction process.

Bulk Nanostructured Al-Mm-Ni-(Fe,Co) Alloys Produced by High-Pressure Hot Compaction

Amorphous and nanocrystalline alloys can easily be obtained in ribbon form for quaternary systems, containing Al, lanthanide metal (Ln) and two late transition metals. Replacement of Ln by Mischmetal (Mm) reduces the cost of investigated materials, as Mm is several times cheaper than pure lanthanide elements. Bulk nanostructured Al-Mm-Ni-(Fe,Co) alloys were produced by grinding of amorphous ribbons followed by high-pressure (7.7 GPa) hot compaction. Amorphous ribbons of Al88Mm5Ni5(Fe,Co)2, Al88Mm4Ni5(Fe,Co)3 and Al87Mm5Ni5(Fe,Co)3 alloys were produced by melt-spinning technique. Nanocrystallization tooks places during grinding. Short-time heating at temperatures close to the onset crystallisation temperature during pressing does not change the microstructure. X-ray diffractometry and differential scanning calorimetry were used for characterisation of the crystallization process and its products. Mechanical properties of nanostructured compacted samples, represented by their microhardness, were better than those of amorphous ribbons.