Type Of Initial Structure Research Articles

Comparative Analysis of Nanostructure and Phase omposition of Amorphous and Polycrystalline Al85Ni7Fe4La4 Alloys after Complex Impacts of Deformation and Flash Lamp Annealing

The structure and phase composition of an aluminum-based alloy Al-Ni-Fe-La with two types of initial structure (polycrystalline and amorphous) after complex action of plastic deformation and pulsed photonic processing were studied by metallography, X-ray diffraction analysis, and differential scanning calorimetry. It was found that in alloys of both types, after intensive plastic deformation (IPD), a multiphase nanostructural state is formed. In a polycrystalline alloy, IPD develops the dispersion of all phase components present in the alloy after quenching. In an amorphous alloy, IPD causes the development of partial multiphase crystallization, which is not completed in the entire range of the studied deformation parameters. The retained amorphous phase and high dispersion of all phase components in the amorphous alloy provide increased values of hardness in comparison with the hardness of a polycrystalline alloy under all investigated deformation modes. It is shown that preliminary deformation increases the stability of the amorphous alloy to temperature. Complex processing, including IPD and FLA, leads to additional hardening of alloys. The optimal mode of complex action on the structure, which ensures their maximum strength characteristics, has been determined. The hardness of the alloy with the initial amorphous structure remains higher in the entire investigated range of complex processing parameters.

Theoretical predictions of a bucky-diamond SiC cluster

A study of structural relaxations of SinCm clusters corresponding to different compositions, different relative arrangements of Si/C atoms, and different types of initial structure, reveals that the SinCm bucky-diamond structure can be obtained for an initial network structure constructed from a truncated bulk 3C-SiC for a magic composition corresponding to n = 68 and m = 79. This study was performed using a semi-empirical Hamiltonian (SCED–LCAO) since it allowed an extensive search of different types of initial structures. However, the bucky-diamond structure predicted by this method was also confirmed by a more accurate density functional theory (DFT) based method. The bucky-diamond structure exhibited by a SiC-based system represents an interesting paradigm where a Si atom can form three-coordinated as well as four-coordinated networks with carbon atoms and vice versa and with both types of network co-existing in the same structure. Specifically, the bucky-diamond structure of the Si68C79 cluster consists of a 35-atom diamond-like inner core (four-atom coordinations) suspended inside a 112-atom fullerene-like shell (three-atom coordinations).

Recovery of Young's Modulus During Annealing of Submicrocrystalline Cu and Cu : ZrO2 Composite

Young's modulus of pure Cu (99.98%) and precipitate hardened Cu:ZrO 2 polycrystals with an ultrafinegrained (UFG) structure has been investigated at temperatures 20-600°C. Nanoparticles of ZrO 2 with a size of about 10nm have been formed by an internal oxidation of Cu-Zr solid solution. The polycrystals have been produced by a heavy plastic deformation using the equichannel angular pressing technique, which yields an average size of grains d of about 200nm. Young's modulus E has been measured as a function of temperature T and of the annealing temperature T a . The dependence E(Ta) in Cu-ZrO 2 demonstrates a recovery stage near 200-250°C (4-6% increase in E). Structural investigations show that d practically does not change during 2 hours annealing up to 500°C. Such a structural stability was observed only in the composite material. Pure copper with the same type of initial structure (d=200nm) shows approximately the same recovery in E at T near 200-250°C, however, this recovery corresponds to a steep (an order of magnitude) increase in d. This fact is a direct experimental proof that the softening of the Young's modulus in UFG materials is due to not only the smallness of grains but also the structure of grain boundaries and, in particularly, the mobility of grain boundary dislocations.

Molecular packing analysis. Part 3. The prediction of m-nitroaniline crystal structure

Molecular packing analysis of m-nitroaniline was carried out in order to study whether it is possible to predict the crystal structure of systems that include hydrogen bonds. Off-ridge eigenvector minimization with annealing (OREMWA) was carried out with Biosym's potential parameters and potential-derived charges obtained from an ab initio Hartree-Fock calculation using the 6-31++G ∗∗ basis set. Two types of initial structure were prepared for the OREMWA calculations (ten structures were created for each type of initial structure). The first-type initial structures were created by deforming the observed crystal structure up to 1 Å in the unit cell lengths and molecular translations, and up to 10 ° in the unit cell angles and molecular rotations. The second-type initial structures were created by four molecules satisfying space symmetry relationships of the observed space group Pbc2 1 in a 12 A ̊ × 12 A ̊ × 12 A ̊ cubic unit cell. In the second-type initial structures, the orientation of a reference molecule was determined randomly. Molecular translation variables of three molecules, molecular rotation valuables of all four molecules, and six unit cell parameters were varied in the OREMWA calculations starting from the first-type initial structures. Molecular translation variables and molecular rotation variables of a reference molecule, and cell lengths only, were varied in the OREMWA calculations starting from the second-type initial structures in order to retain the observed space group symmetry, because the Pbc2 1 space group is orthorhombic with 90 ° cell angles. This space group is also polar in the c-axis direction, so that one molecular origin in this direction is fixed. The observed crystal structure of m-nitroaniline was reproduced as the most stable crystal structure starting from both types of initial structure.

Experimental study of the austenitization process of hypereutectoid steel alloyed with small amounts of silicon, manganese and chromium, and with an initial structure of globular cementite in a ferrite matrix

The austenitization process was examined in steel containing 0.80 wt.% C, 2.02 wt.% Si, 2.06 wt.% Mn and 1.05 wt.% Cr by structure observations in the scanning electron microscope, and microanalytical measurements of structural phases. The initial structure of the material, consisting of globular cementite in a ferrite matrix, was obtained in two different ways, resulting in two types of initial structure. The kinetics of the α → γ transformation in this steel is very slow. The kinetics and the morphology of the structure are significantly influenced by the type of initial structure, and in particular by the morphology of the ferrite grains. The origin of these effects is regarded as being the result of the specific influence of silicon on carbon activity in austenite, and of the redistribution of silicon and manganese at the α- γ phase boundary during the α → γ transformation.