A. S. Aronin

Nanocrystallization of bulk ZrCuTi metallic glass

The phase transformations during heating of Zr 30 Cu 60 Ti 10 bulk metallic glass were studied by differential scanning calorimetry, dilatom-etry, X-ray diffraction, transmission and high resolution electron microscopy. The crystallization of bulk metallic glass was found to occur in several stages. According to X-ray diffraction studies the structure was closely similar to amorphous structure when the sample was heated to the end of the first DSC sub-peak (781 K). However, the volume effect of the first stage of transformation is 1.6%; it forms about 80% of total volume effect of the crystallization (2%). A change of the shape of the diffraction maxima has been analyzed for the cases of structure relaxation and nanocrystalline structure formation. The nanocrystalline structure with very fine grain size was found to form during first stage of crystallization. The grain size of the nanocrystals was 1-5 nm.

Nanocrystalline Cu2O prepared under high pressures

The effect of high pressure on the structure of Cu2O is investigated. Polycrystalline samples are treated during different periods of time at different temperatures and pressures in the vicinity of the kinetic curve of the decomposition Cu2O → Cu+CuO. The structure of the samples subjected to thermobaric treatment is characterized by x-ray diffraction, electron diffraction structural analysis, and electron microscopy at atmospheric pressure. It is found that, upon treatment of Cu2O at temperatures and pressures close to the decomposition region, the microstructure undergoes a transformation into the nanocrystalline state.

Nanocrystallization of an amorphous Fe80B20 alloy during severe plastic deformation

The structural evolution of an amorphous Fe80B20 alloy subjected to severe plastic deformation at room temperature or at 200°C was studied. Deformation leads to the formation of α-Fe nanocrystals in an amorphous phase. After room-temperature deformation, nanocrystals are localized in shear bands. After deformation at 200°C, the nanocrystal distribution over the alloy is more uniform. Possible causes of the crystallization of the amorphous phase during severe plastic deformation are discussed.

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

The fine structure of FCC nanocrystals in Al-and Ni-based alloys

The structural perfection of nanocrystals in alloys of different chemical composition is studied by x-ray diffraction and high-resolution electron microscopy. In all the alloys studied, crystallization of the amorphous phase produces a nanocrystalline structure. The nanocrystal size depends on the chemical composition of the alloy and varies in aluminum-based alloys from 5 nm in Al89Ni5Y6 to 12 nm in Al82Ni11Ce3Si4. Nanocrystals in nickel-based alloys vary in size from 15 to 25 nm. Al nanocrystals are predominantly defect-free, with microtwins observed only in some nanocrystals. The halfwidth of the diffraction lines is proportional to sec θ, which implies the small grain size provides the major contribution to the broadening. Nanocrystals in nickel alloys contain numerous twins, stacking faults, and dislocations.

Structural transformations in the Al85Ni6.1Co2Gd6Si0.9 amorphous alloy during multiple rolling

The effect of multiple rolling at room temperature on the structure and crystallization of the Al85Ni6.1Co2Gd6Si0.9 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.

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.

Magnetic structure and magnetization process of the glass-coated Fe-based amorphous microwire

Magnetic structure of amorphous Fe73,9B13,2Si10,9C2 microwires was studied. The magnetic structure of the as-prepared microwire was found to consist of a magnetic core and a ring-shaped surface magnetic layer made up by radially magnetized small ring domains. The geometric characteristics of microwire magnetic structure were first experimentally determined. The width of the surface ring domains is about 5 μm, and the thickness of the surface magnetic layer is 2 μm. The magnetic core of the as-prepared microwire has been shown to consist of extensive domains, no less than 500 μm in size, and their spontaneous magnetization vector deviating from the microwire axis. The effect of magnetostriction on magnetic structure and its changes induced by magnetization has been established. The magnetic structure model for microwires with positive magnetostriction constant is proposed.

Influence of deformation on the structural transformation of the Pd40Ni40P20 amorphous phase

The influence of plastic deformation on the structure of the Pd40Ni40P20 amorphous alloy has been investigated using X-ray diffraction and measurements of the velocity of sound. It has been revealed that the rolling of the sample leads to a change in the structure of the amorphous phase (distortion of the first coordination sphere) and that the structural transformations are more pronounced in the near-surface region of the sample. The rolling also results in a decrease in the transverse velocity of sound. The observed effects decrease with time. It has been demonstrated that the revealed effects are associated with the inelastic deformation of the amorphous alloy.

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.