Jerzy Latuch

Kinetics of crystallization processes in AlYNiCo studied by electrical resistivity

Abstract Al90Y5Ni1Co4 amorphous and partially crystalline alloys were investigated by means of differential scanning calorimetry, direct current four probe method and X-ray diffraction. The process of crystallization of particles of the order of 10 nm (nanocrystallization) was induced by decreasing the rate of the quenching process from 54 to 39 rev/s or by annealing amorphous samples. The resistivity versus temperature isochronal relation for both groups of alloys was interpreted assuming diffusion controlled growth and zero nucleation rate. The effect of yttrium on the decrease of the growth rate was assumed to be a transformation mechanism leading to nano-size crystalline phase formation.

Magnetically soft nanomaterials for high-temperature applications

FeCo-based soft magnetic alloys of compositions Fe/sub 45/Co/sub 43/Cu/sub 1/B/sub 3.6/Zr/sub 7.4-x/AM/sub x/, where x=3.7 at.% and 7.4 at.%, and the alloying metals (AM) are Nb and Hf and were prepared in the form of amorphous ribbons by a melt-spinning technique. A two-phase microstructure, consisting of /spl alpha/-FeCo nanocrystals and amorphous matrix, was created by partial devitrification of the amorphous alloys during annealing for 1 h at temperatures 500/spl deg/C-600/spl deg/C. The crystallization process of the amorphous alloys was studied using differential scanning calorimetry, X-ray diffractometry, and transmission electron microscopy. The quasi-static hysteresis loop was measured using an inductive method. Partial replacement of zirconium by hafnium improved thermal stability of the amorphous structure and the magnetic properties of the alloys studied. The effect of niobium is opposite. The best magnetic properties were found in the alloy Fe/sub 45/Co/sub 43/Cu/sub 1/B/sub 3.6/Zr/sub 3.7/Hf/sub 3.7/. It was found that the nanocrystallization temperature strongly influences the thermal stability of the magnetic properties of the alloys studied.

Crystallization of amorphous Al85Y10Ni5 and Al85Y5Ni10 alloys

The devitrification of melt-spun Al 85 Y 10 Ni 5 (A) and Al 85 Y 5 Ni 10 (B) amorphous alloys was studied in continuous heating and isothermal experiments. Isochronal annealing reveals a strong dependence of the number of heat effects on the heating rate. At a scan rate of 40 K min -1 , five and three peaks are observed for alloys A and B respectively. The process of phase transformation were examined by continuous heating at the rate of 40 min -1 . Many phases, mainly metastable, appear in devitrified glasses. The compositions of most of them were identified. In the equilibrium state in both alloys, the orthorhombic Al 16 YN 3 , phase exists, which until now has not been reported in the Al-Y-Ni system

The effect of Cu addition on the formation of f.c.c.-Al phase in rapidly quenched Al-Y-Ni alloys

Abstract The structure and microhardness of amorphous and nanocrystalline melt-spun Al 88 Y 3 Ni 9 − x Cu x ( x = 0, 2, 4, 6 at.%) alloys were examined. Variation of cooling rate controlled by the rotational wheel speed (15–60 s −1 ) resulted in the formation of ductile nano-composite material ( x = 2, 4) composed of nanoscale f.c.c.-Al particles embedded in an amorphous matrix. The effect of replacement of Ni by Cu on structural and mechanical properties was studied. This replacement extended the temperature region in which the Al phase precipitates, causing a decrease in particle size from 50 ( x = 0) to 10 nm ( x = 4). The volume fraction of the nanoscale particles and lattice parameter of Al phase were calculated. Due to the nanoscale Al particles, a significant increase in microhardness compared with the amorphous single phase was observed.

Structural and magnetic properties of bulk amorphous alloys Fe-Al-Ga-P-B-Si

Abstract Structural and magnetic properties of bulk amorphous alloys Fe 74 Al 4 Ga 2 P 12 B 4 Si 4 (A), Fe 76 Al 4 P 12 B 4 Si 4 (B), Fe 80 P 12 B 4 Si 4 (C) and Fe 74 Al 4 Ga 2 P 8 B 4 Si 8 (D) fabricated by a single-roller melt-spinning method were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), magnetic measurements and Mossbauer spectroscopy (MS). The supercooled liquid region up to 45 K was determined from the DSC spectra. Magnetic and MS measurements revealed strong ferromagnetic ordering in the ribbons. XRD and MS were used to recognise the phases formed during annealing of the alloys. The average magnetisation became more random after annealing of samples A and B, while for the ribbons C and D an in-plane orientation of magnetisation was found.

Electron Structure, Stability and Nanocrystallization of Al - Based Amorphous Alloys

Electron transport studies of Al-based alloys show that the strong bonds between Al-TM and Al-Y atoms arise by mixing of 3d and 4d electron states of TM and Y atoms with the 3s and 3p states from Al. Thermal stability of the Al-RE alloys is controlled by the low diffusity of heavy RE atoms. The results allow to optimize preparation conditions for nanocrystallizing Al-based alloys with enhanced mechanical properties.

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

Mechanically and thermally induced structural transformations in Fe-Pt-B alloys

Mechanically and thermally induced structural transformations in the Fe56Pt24B20 and Fe59.5Pt25.5B15 alloys are compared. Both alloys were prepared as ribbons by the melt spinning and were subsequently exposed to high-energy ball milling. Thermal behaviour of the samples was studied by differential scanning calorimetry measurements. The structure of the samples was characterised by Mossbauer spectroscopy and X-ray diffraction. The as-quenched alloys have shown disordered structures with a major contribution of the disordered cubic FePt solid solution. Ball milling of the as-quenched alloys induced a separation of the Fe-Pt and Fe-B regions. The heating of the final powders up to 993 K led to a transformation of the fcc FePt solid solution to the ordered tetragonal FePt phase, and to a formation of the Fe2B phase.

Magnetic properties of the Fe48.75Pt26.25 B25 nanostructured alloy

The Fe48.75Pt26.25B25 powder was prepared by high-energy ball milling of the crystalline melt-spun ribbon. The X-ray diffraction and transmission Mossbauer spectroscopy measurements allowed the identification of the tetragonal FePt and orthorhombic FeB phases in the as-quenched alloy. The ball milling of the ribbon led to the transformation of the ordered tetragonal FePt phase into a disordered cubic FePt solid solution with the average crystallites size of about 15 nm. Annealing of the as-milled powder recovered the nanocrystalline tetragonal FePt phase. Differences in magnetic properties between the as-milled and annealed powders were revealed by hysteresis loop and magnetization vs. temperature measurements.

The microstructure of melt-spun alloys with liquid miscibility gap

Effect of the melt ejection temperature on the microstructures of (FexCu1-x)62Si13B9Al8Ni6Y2 (x=0.48, 0.60 and 0.71) alloys was investigated. Rapid cooling of the examined alloys from the temperature range conventional to single-phase amorphous alloys brought about a non-uniform microstructure due to a liquid/liquid phase separation prior to cooling. The systems with a miscibility gap need to be heated over a critical temperature where homogeneous liquid exists. Microstructures of the ribbons melt spun from the homogeneous melt region are characterized by presence of the spherical precipitates distributed in homogeneous matrix. Both, precipitates and matrix, can constitute either the Fe-rich or the Cu-rich phases depending on the alloy composition. The studies confirmed amorphous nature of the Fe-rich phases, both matrix and precipitates whereas the Cu-rich liquid crystallized due to lower glass forming ability.