Formation and structure of nanocrystals in bulk Zr<Subscript>50</Subscript>Ti<Subscript>16</Subscript>Cu<Subscript>15</Subscript>Ni<Subscript>19</Subscript> metallic glass

The possible formation of a nanocrystalline structure in controlled crystallization of a bulk Zr₅₀Ti₁₆Cu₁₅Ni₁₉ amorphous alloy has been studied using differential scanning calorimetry, transmission and high-resolution electron microscopy, and x-ray diffraction. It was established that crystallization of the alloy at temperatures above the glass formation point occurs in two stages and brings about the formation of a nanocrystalline structure consisting of three phases. Local spectral x-ray analysis identified the composition and structure of the phases formed.     

Magnetic structure and properties of a bulk Fe72Al5P10Ga2C6B4Si1 alloy in the amorphous and nanocrystalline states

The structure forming under controlled crystallization of a bulk Fe₇₂Al₅P₁₀Ga₂C₆B₄Si₁ amorphous alloy has been studied using differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. Crystallization of the alloy was established to result in the formation of a nanocrystalline structure consisting of three phases. The domain structure and magnetic properties of amorphous and nanocrystalline samples were investigated using the magnetooptic indicating film technique (MOIF) and a vibrating-sample magnetometer. The coercive force and the saturation magnetization of the amorphous samples were found to be 1 Oe and 130 emu/g, respectively. It was shown that the formation of the nanocrystalline structure entails a dramatic decrease in domain size (down to 1–4 μm) as compared to an amorphous sample (∼1 mm). Simultaneously, a decrease in the saturation magnetization and a strong increase in the coercive force of the samples were observed. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 5, 2004, pp. 858–863. Original Russian Text Copyright ? 2004 by Abrosimova, Aronin, Kabanov, Matveev, Molokanov.     

Phase separation and nanocrystallization in Al92Sm8 metallic glass

Crystallization of Al₉₂Sm₈ metallic glass was investigated in situ using combined small-angle and wide-angle X-ray scattering (SAXS/WAXS) techniques during isothermal annealing at temperatures close to crystallization point. A continuously growing interference maximum shifting progressively towards lower angles was found to develop in SAXS regime. Simultaneously taken WAXS spectra reveal formation of fcc-Al nanocrystalline phase. The analysis of the SAXS/WAXS data indicate that amorphous phase separation is responsible for the nanocrystalline microstructure formation. The primary fcc-Al crystals nucleate inside the Al-rich amorphous regions formed during alloy decomposition and their growth is constrained by the region size.     

Influence of hydrogenation on the microstructure and crystallization of Zr-Cu-Ni-Al-Y metallic glass

Zr-Cu-Ni-Al-Y metallic glass was electrochemically charged with hydrogen. The hydrogen content in the hydrogenated specimen was derived from the shift of scattering maxima of the X-ray diffraction (XRD) spectra. The microstructures of the untreated Zr-Cu-Ni-Al-Y metallic glass and the hydrogenated specimen have been studied using conventional transmission electron microscopy, high-resolution transmission electron microscopy and energy-dispersive X-ray spectrometry as well as XRD. The untreated Zr-Cu-Ni-Al-Y specimen was found to be almost totally amorphous with a trace amount of yttrium oxide. The addition of the rare-earth element yttrium is beneficial for decreasing the oxygen content in the matrix. Some nanosized precipitates have been found in the hydrogenated specimens. The crystallization of the precipitates was found to consist of two stages. The Zr(Cu, Ni, Al, Y) precipitates segregate in the first stage, while the formation of crystalline ZrH₂ dominates the second stage. The size, amount and distribution of the nanocrystals are mainly related to the charging current and time.     

Effect of thermal treatment on the microstructure and magnetic properties of a bulk amorphous Fe72Al5P10Ga2C6B4Si1 alloy

The structure and chemical composition of the phases that form in the controlled crystallization of a bulk amorphous Fe₇₂Al₅P₁₀Ga₂C₆B₄Si₁ alloy are studied by differential scanning calorimetry, transmission electron microscopy, and x-ray diffraction. It was established that, when the alloy is annealed at a temperature above the glass transition point, a nanocrystalline structure consisting of three phases arises. The magnetic properties of amorphous and nanocrystalline samples were studied with a vibrating-sample magnetometer. The coercive force and saturation magnetization of amorphous samples were found to be 1 Oe and 130 emu/g, respectively. The structure and chemical composition of the forming phases and their correlation with the magnetic properties of the samples were determined. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 12, 2004, pp. 2158–2163. Original Russian Text Copyright ? 2004 by Abrosimova, Aronin, Kabanov, Matveev, Molokanov, Rybchenko.     

Phase segregation and crystallization in the amorphous alloy Ni70Mo10P20

Structural evolution of the amorphous alloy Ni₇₀Mo₁₀P₂₀ has been studied by x-ray diffraction, and by following transmission and high-resolution electron microscopy annealing both above and below the glass-transition temperature. When annealed above this temperature, the amorphous phase undergoes segregation into regions about 100 nm in size having different chemical composition. Diffraction from such samples produces diffuse rings, and the scattering vector corresponding to the maximum intensity varies from point to point within the interval of 4.88 to 4.78 nm⁻¹. When occurring between the glass-transition and crystallization temperatures, crystallization produces groups of nanocrystals, 20–30 nm in size, which are in direct contact with one another and form a polymorphic mechanism. The crystallization mechanism changes when the annealing temperature is brought below the glass-transition point. At these temperatures the amorphous matrix crystallizes entectically with formation of eutectic colonies. Fiz. Tverd. Tela (St. Petersburg) 40, 1577–1580 (September 1998)     

Formation and structure of nanocrystals in an Al86Ni11Yb3 alloy

The formation and structure of the nanocrystalline phase in the Al₈₆Ni₁₁Yb₃ alloy are investigated using differential scanning calorimetry (DSC), transmission electron and high-resolution electron microscopy, and x-ray diffraction. The nanocrystalline phase is formed upon controlled crystallization of the amorphous alloy prepared by quenching of the melt on a rapidly moving substrate. It is revealed that the nanocrystalline alloy consists of aluminum nanocrystals (5–12 nm in size) randomly distributed in the amorphous matrix. The maximum fraction of the nanocrystalline phase does not exceed 25%. The nanocrystal size substantially increases at the initial stage of isothermal treatment (at 473 K) and then changes insignificantly. It is found that nanocrystals are usually free of defects. However, some nanocrystals have a more complex microstructure with twins and dislocations. The size distributions of nanocrystals are determined at several durations of isothermal treatment. It is demonstrated that the nucleation of nanocrystals predominantly occurs through the heterogeneous mechanism. The experimental distributions are compared with those obtained from a computer simulation. The activation energy of crystallization, the time-lag, and the coefficient of ytterbium diffusion in the alloy are estimated     

Investigating the structure of electrolytically deposited alloys of the CoP-CoNiP system under thermal action

The problems of structural relaxation and crystallization of electrolytically deposited amorphous metal alloys of the CoP-CoNiP system are investigated. The onset of the structural relaxation and crystallization is found to occur through the nucleation of nanocrystalline particles of an unrecognized Co _x Ni _y P_1−x−y phase. An increase in the concentration of Ni is shown to yield a substantial thickening of the amorphous structure and to increase the temperature of the onset of structural relaxation and crystallization by 50–70°C.     

超导金属玻璃Zr78Co22的结晶化动力学研究

综合利用x射线小角散射、广角衍射、场离子显微镜等测量,并结合超导临界温度和显微硬度的观测,研究了金属玻璃Zr₇₈Co₂₂的结构及其结构弛豫和结晶化过程.结果表明,淬态金属玻璃Zr₇₈Co₂₂中存在明显的相分离,其中一个相的组分似乎趋向于纯Zr,另一相的组分则与ZO₄Co接近.在结构弛豫过程中,主要是拓扑短程序发生了变化,它受成核长大机理支配.当核的数量足够多时,两相均匀一致地长大. 关键词：     

Influence of surface on the nanocrystalline structure formation

In contrast to the common Fe-B-base amorphous alloys, Mössbauer transmission and CEMS studies of the early stages of the nanocrystalline structure formation in the new magnetically soft FeCuNbSiB alloys produced via the amorphous way, revealed that the primary crystallization of the Fe₃Si-like phase is inhibited by the surface. This result supports the role of copper as nucleation agent in the amorphous structure.     

Internal friction and change in Young’s modulus in the alloy Mg-Ni-Y due to a transition from an amorphous to a nanocrystalline state

The effect on the internal friction and Young’s modulus of the evolution of the structure of the amorphous alloy Mg₈₄Ni_12.5Y_3.5 (relaxation of internal stresses, devitrification, nucleation and decay of nanocrystalline phases) was investigated as it was heated. The measurements were performed on ribbon samples by flexural oscillations. Irreversible peaks of the internal friction and anomalies in the behavior of Young’s modulus as a function of temperature were observed. The position of the anomalies correlates with the characteristic temperatures of restructurings observed by differential thermal and x-ray diffraction. Possible internal-friction mechanisms associated with various types of structural relaxation and nanocrystallization processes in the alloy are discussed. Fiz. Tverd. Tela (St. Petersburg) 41, 561–566 (April 1999)     

Oxidation of Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass in the glassy state and the supercooled liquid state

The oxidation behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass in air in the glassy state and the supercooled liquid state was studied using a thermogravimetric analyzer, X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. It was found that the isothermal oxidation kinetics of the glass in both states follows a two-step parabolic law. The oxidation process is governed by the inward diffusion of oxygen and the outward diffusion of Cu, with the first being dominant. The faster diffusion of atoms in the supercooled liquid state led to a network precipitation of crystalline Cu, and the crystallization that occurred in this state in the later stage of oxidation caused a reduction in the rate of oxidation. Two types of Zr oxides, i.e. t-ZrO₂ and m-ZrO₂, were formed in the oxidation process in both the glassy and supercooled liquid states. t-ZrO₂ mainly formed in the outer layer of the oxide scale, while m-ZrO₂ tended to form in the inner layer. The formation of m-ZrO₂ is possibly activated by the crystallization of the glass near the interface of the oxide scale and the substrate alloy. In addition, oxidation also has a substantial effect on the formation of crystallized phases. The formation of a Cu-rich phase of Cu₁₀Zr₇ occurred in the oxidizing atmosphere. However, the formation of a Zr-rich phase of Zr₂(Ni, Cu) mainly took place in a vacuum environment. PACS 81.05.Kf; 81.65.Mq; 64.60.-i     

Surface properties of Fe76Mo8Cu1B15 alloy after annealing

NANOPERM-type alloy Fe₇₆Mo₈Cu₁B₁₅ is investigated in amorphous and in partially crystallized state. Samples were prepared by 1 h isothermal annealing in vacuum at temperatures ranging from 330°C up to 700°C. Bulk and surface microstructural characteristics were studied using transmission and conversion electron Mössbauer effect techniques, respectively. Surface features were checked by the help of atomic force microscopy. Presence of nanocrystalline bcc-Fe phase was detected during the first crystallization stage. The crystallization process starts at 450°C and it is more pronounced in surface regions than in the bulk. With progressing crystallization, hyperfine parameters especially of the amorphous residual phase are altered. Distinctions in surface morphology are revealed between wheel and air side of the ribbon-shaped samples.     

Effect of nanocrystallization on the mechanical and magnetic properties of finemet-type alloy (Fe<Subscript>78.5</Subscript>Si<Subscript>13.5</Subscript>B<Subscript>9</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript>)

The kinetics of primary crystallization and the effect of structural parameters of the precipitating nanocrystalline α-phase Fe-Si on changes in microhardness, coercive force, and saturation magnetization in an amorphous Finemet-type 5BDSR alloy (Fe_78.5Si_13.5B₉Nb₃Cu₁) obtained by melt quenching are studied. It is found that both an increase in bulk density and an increase in the average nanoparticle size contribute to the hardening of the amorphous/nanocrystalline alloy.     

Magnetic Behavior of Nanocrystalline FeNbCrBCu Alloys at Elevated Temperatures

The magnetic behavior of nanocrystalline Fe_73.5Nb_4.5Cr₅B₁₆Cu₁ alloys is investigated in a series of specimens with different volume fractions of crystalline phase. It is shown that the Curie temperature of amorphous phase firstly decreases after structural relaxation in amorphous state and then rapidly increases during the first stages of crystallization. The strikingly different behavior of coercivity at elevated temperatures is observed for the samples with low and high volume fractions of nanocrystalline particles.     

Features of the doping effect on YAlO3 phase sequences during synthesis from an amorphous precursor state

Using X-ray diffraction methods, it has been shown that small lanthanum (La) dopants during solid-phase synthesis of YAlO₃ from an amorphous precursor state initiate the formation of the high-temperature hexagonal modification of yttrium aluminate in the first crystallization stages, whereas the equilibrium perovskite phase has an orthorhombic cell. At the same time, during YAlO₃ synthesis without dopants, yttrium-aluminum garnet Y₃Al₅O₁₂ is formed in the first crystallization stages, rather than the perovskite modification, as it follows from the precursor stoichiometry. The effect of lanthanum dopants on YAlO₃ phase sequences during synthesis from the amorphous precursor state is qualitatively explained.     

Chemical reduction of hematite by sodium borohydride

Well-crystallized hematite was suspended in water and treated at room-temperature (RT) with sodium borohydride. The product of the reaction is a highly magnetic black powder, which is stable at RT. The NaBH₄ treatment converts about half of the hematite to an amorphous Fe–B alloy and to a small fraction of sub-micron sized, amorphous metallic-Fe nodules. Heating at 400°C of this composite has resulted in the crystallization and/or oxidation of more than half of the amorphous Fe–B phase to α-Fe and Fe₃O₄ and B₂O₃, respectively. After treatment at 800°C, the metallic Fe and the amorphous Fe–B have completely vanished, and the resulting product consists of hematite and FeBO₃ embedded in the matrix of α-Fe₂O₃.     

Effect of the concentration of a rare-earth component on the parameters of the nanocrystalline structure in aluminum-based alloys

The effect of the concentration of a rare-earth component on the parameters of the nanocrystalline structure formed during crystallization of an amorphous phase in the Al₈₈Ni₆Y₆ and Al₈₈Ni₁₀Y₂ alloys is studied using X-ray diffraction and transmission electron microscopy. It is shown that, as the yttrium concentration increases, the nanocrystal size increases and the content of the nanocrystalline component of the structure decreases. The precipitation of nanocrystals is accompanied by separation of the amorphous matrix into regions with different radii of the first coordination spheres due to the enrichment or depletion with the rare-earth element. The parameters of the nanocrystalline structure support the assumption of the heterogeneous nucleation of the nanocrystals.     

Pr基大块纳米晶合金及其特性研究

研究了Pr₆₀Al₁₀Ni₁₀Cu₂₀ 大块金属玻璃 的结构和磁性随Fe含量 的变化关系，结果表明Pr基合金逐步从玻璃状态，转变为非晶与纳米晶的复合状态，最后成 为纳米晶合金，Pr基合金的磁性也相应地发生变化.提出了一种通过对大块稀土基金属玻璃 进行Fe掺杂，制备出微观结构和性能具有可调控性的大块纳米晶合金的方法, 并讨论了纳米 晶结构和性能的关系. 关键词： 金属玻璃 大块纳米晶 掺杂     

Structural transformations in the Al<Subscript>85</Subscript>Ni<Subscript>6.1</Subscript>Co<Subscript>2</Subscript>Gd<Subscript>6</Subscript>Si<Subscript>0.9</Subscript> amorphous alloy during multiple rolling

The effect of multiple rolling at room temperature on the structure and crystallization of the Al₈₅Ni_6.1Co₂Gd₆Si_0.9 amorphous alloy has been studied using transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction. The total plastic strain is 33%. It has been shown that the deformation results in the formation of aluminum nanocrystals with the average size that does not exceed 10–15 nm. The nanocrystals are formed in regions of localization of plastic deformation. The deformation decreases the thermal effect of nanocrystallization (∼15%) as compared to the heat release at the first stage of crystallization of the unstrained sample. The morphology, structure, and distribution of precipitates have been investigated. Possible mechanisms of the formation of nanocrystals during the deformation have been discussed.