Henryk Matyja

Crystallization characteristics of amorphous Fe-Si-B alloys

Crystallization of soft magnetic Fe-Si-B glasses was investigated by transmission electron microscopy and X-ray diffraction. Electron micrographs of the successive crystallization stages of some Fe-Si-B glasses were obtained and the morphology variations for different alloy compositions were determined. The compositional dependence of the crystallization mode exhibited by the Fe-Si-B glasses was analysed, and on this basis some suggestions about crystallization rules in these glasses are proposed. Two kinds of iron—silicon phases occurred, depending on the Fe-Si-B alloy composition: bcc Fe(Si) solid solution and an ordered solid solution on the structural basis of Fe3Si iron suicide. It is suggested that the metastable Fe3B phase (observed during crystallization of only few glasses) was not a simple consequence of boron content. Crystallization of the Fe3B phase was related to the formation of the iron—silicon phase which was produced during the first crystallization stage.

Flash annealing nanocrystallization of FeSiB-based glasses

Abstract The possibility of reducing the role of alloy composition in the creation of nanocrystalline structure in FeSiB-based amorphous alloys (with copper, niobium and tantalum additions) by application of flash annealing was studied. Crystallization products were studied using X-ray diffractometry and transmission electron microscopy. It was found that flash annealing remarkably decreases the influence of composition on alloy microstructure after crystallization of the glasses studied. Ultrafine structure with an average grain diameter of less than 25 nm was created in all the iron-based glasses studied in this work. Flash annealing appeared to be a very suitable method for the creation of nanocrystalline materials from metallic glasses. It was revealed that the crystallization product of the first stage of crystallization of Fe 73.5 Cu 1 Ta 3 Si 13.5 B 9 glass depends on the heat treatment method. Primary crystals of α-Fe(Si) and Fe 3 B were observed after conventional and flash annealing respectively.

Structural defects and thermal stability of Ti(Al) solid solution obtained by mechanical alloying

Abstract The structure of a metastable Ti(Al) hexagonal close packed (h.c.p.) solid solution obtained by mechanical alloying of the Al50Ti50 powder, was investigated using X-ray diffractometry (XRD). An analysis of the profiles shows physical broadening of (100), (002) and (101) diffraction lines. The probability of stacking faults on the basal (0001) and prismatic {1010} planes was determined from the differences between the physical broadening of the (100) and (101) lines which are influenced by the stacking faults and the (002) line which is not affected by the stacking faults. The total concentration of stacking faults is comparable to the values obtained earlier for Al–Ti solid solutions deformed by filing. Thermo-desorption and mass-spectrometery showed that, during mechanical alloying, about 1 at.% of hydrogen is dissolved in the alloy. A significant amount of this hydrogen contributes to the formation of stacking faults on the basal and prismatic planes. The temperature range within which the metastable h.c.p. structure is transformed into the equilibrium AlTi (L10) structure was determined by DSC calorimetry. The transition of the Ti(Al) solid solution into the AlTi intermetallic proceeds through an intermediate stage of the metastable f.c.c. phase with a lattice parameter a=0.4012 nm.

Solid state reactions in Ni–Al–Ti–C system by mechanical alloying

Abstract Several Ni–Al–Ti–C compositions from different areas of the Ni–Al phase diagram containing various amounts of Ti and C were prepared by mechanical alloying. Synthesized samples were investigated by X-ray diffraction and differential scanning calorimetry methods. Solid state reactions in Ni–Al–Ti–C powder mixtures with an equiatomic Ni/Al ratio lead to the formation of NiAl and TiC equilibrium phases. Metastable solid solution of Ni(Al,Ti,C) and non-stoichiometric TiC x are formed in the mixtures with C Ni /C Al ratio of 1.7–3. The grain size of metastable intermetallic phases is less than 5 nm, if Ni and Al content in the mixtures corresponds to the dual-phase and Ni 3 Al-areas of the Ni–Al phase diagram.

Explosive consolidation of mechanically alloyed Ti-Al alloys

Abstract Ti-Al intermetallics are of great interest because of their attractive mechanical properties, but they require advanced processing methods, due to their low ductility at room temperature. In this work, the following processes were employed in order to obtain bulk TiAl and Ti 3 Al intermetallics: (1) mechanical alloying: ball milling of elemental Ti and Al powders caused formation of supersaturated solid solutions; (2) explosive consolidation: in this operation no phase transitions were observed and sample densities after consolidation reached over 90% of theoretical values; (3) annealing: resulted in additional increase of material density and caused phase transitions leading to formation of TiAl and Ti 3 Al compounds.

Studies of structural relaxation of some chalcogenide binary glasses using D.S.C. measurements

Abstract The phenomena accompanying the temperature-induced structural changes in splat-quenched glassy alloys TeSn, TePb and TeBi of eutectic composition are discussed. Differential scanning calorimeter studies are reported and it is suggested that devitrification proceeds through several states of different granulation until the layer structure of chalcogenide glasses completely disappears.

Phase transformations in Co-B-Si alloys induced by high-energy ball milling

X-ray diffraction analysis, differential scanning calorimetry and magnetization measurements were used to determine the structural changes of the Co 78 B 11 Si 11 alloys prepared by a ball milling of amorphous, crystallized ribbons and a mixture of elemental crystalline powders in vibratory mill. For all starting materials the high-energy ball milling of Co 78 B 11 Si 11 alloy produces a crystalline structure with nanometer sized crystals. The average crystallite size is about 5 nm. Three series of Co 78 B 11 Si 11 alloys are the ferromagnetic materials. Milling of amorphous alloys causes an increase of the room temperature magnetic moment from 0.90 to 1.08 μ B . A similar tendency is observed for alloys produced by milling of the initially crystallized ribbons for which the magnetic moment increases from 0.73 μ B at t = 0 to 1.17 μB after 250 h. Somewhat different dependence is found for alloys milled from powders since magnetization of the alloy subjected to longer milling is reduced by 10% due to structural disorder introduced during a formation of the crystalline Co(Si,B) phase with nanometer sized crystals.

Studies on crystallization and domain structure of a ferromagnetic amorphous alloy Co90Zr10

The paper presents the first results of studies on crystallization and domain structure of a new ferromagnetic amorphous alloy Co90Zr10. Amorphous Co-Zr alloys were obtained by the ″piston and anvil″ method with 20 to 45 at% of Co and 90 at% of Co. Crystallization of Co90Zr10 was studied by X-ray diffraction and differential calorimetry, as well as by transmission electron microscopy (TEM) with simultaneous heating of the material. Domain structure in the amorphous phase was investigated by the method of Lorentz. The types of structures occurring were described, domain wall widths were calculated, and the direction of changes in the parameters of the magnetic structure — caused by annealing and phase transformation — was suggested.

Effect of flash annealing on the grain size and morphology of crystallization products of Co-Si-B glasses

Influence of flash annealing (rapid heating followed by rapid cooling) on the grain size and morphology of crystallization products of primarily and polymorphously crystallizing Co 78 Si 11 B 11 and Co 70.5 Si 14.75 B 14.75 glasses. It is showed that this method is suitable for tha creation of a nanocrystalline structure in metallic glasses

Structural investigations of the Al50Fe25Ti25 powder mixture mechanically alloyed under various conditions

Abstract The aim of this work was to study the structural and phase transformations that take place during mechanical alloying of the ternary Al50Fe25Ti25 alloy in a high-energy planetary ball mill. Two experiments were performed: one with addition of ethanol and the other without any additional agent. The structural changes and the formation of new phases occurring in the material during mechanical alloying at various milling times were examined using X-ray diffractometry (XRD), differential scanning calorimetry, conventional transmission electron microscopy and high-resolution electron microscopy. The XRD patterns show that a b.c.c. Fe(Al) solid solution and an fcc phase with the lattice parameter a 0 =4.295 A isomorphous with TiC are the final products of the process performed with addition of ethanol. Electron microscopy observations reveal that after the longest milling time, the structure of the powder particles becomes nanocrystalline. No phase changes were found in the XRD pattern of the final product of ethanol-added milling, annealed at 720°C for 2 h. The milling process performed without addition of ethanol leads to an amorphous phase. Heating of this phase in a calorimeter causes crystallisation of the ternary τ 2 phase (Al 2 FeTi) and an Fe(Al,Ti) solid solution.