Papers by Keyword: Ni₃Al

Abstract: Directional or single crystal technique was applied to enhance the ductility, and two phases of γ (Ni) phase or β (NiAl) phase in γ‘(Ni3Al) matrix were also considered to increase the strength and ductility. In this study, directionally solidified rods were prepared at the solidification rate of 50µm/s in 23-27 at.% Al-Ni alloys, and tensile strengths of these rods were analyzed at room temperature. Directionally solidified samples showed the γ dendrite fibers formed in the Ni3Al matrix in the hypo eutectic composition of 23 at.% Al, the γ‘ single phase in the eutectic composition of 24.5 at. % Al, and the β dendrite fibers in the γ‘ matrix in the hyper eutectic compositions of 25, 26, 27 at.% Al. The hypoeutectic alloy including γ dendrites with γ‘ matrix exhibited a large elongation of over 70% with ductile transgranular fracture at room temperature. With increasing Al contents, the γ dendritic microstructure changed to the β dendrite in the γ‘ matrix, which resulted in decreasing the elongation by increasing the volume fraction of the brittle β dendrites in the ductile γ’ matrix.

Abstract: Anisotropic deformation behavior of single crystalline Ni3Al-base intermetallic compounds, including Ni3Al single-phase and Ni/Ni3Al two-phase alloys, was systematically studied by the plane strain compression tests. Plastic flow behavior of single phase Ni3Al is strongly dependent on the initial crystal orientation and the flow stress becomes higher with increasing the numbers of the operative slip planes. In the case of the Ni/Ni3Al two phase alloys, the flow behavior is found to be divided into two stages. Such flow behavior is considered to be closely related to the difference in the deformation behavior between Ni solid solution and Ni3Al precipitates.

Abstract: Texture and microstructure evolution during cold rolling of binary Ni3Al single crystals were studied as a function of the initial crystal orientations. Cold rolling behavior of the single crystals is strongly dependent on the initial crystal orientations, especially on the initial rolling direction (RD). Macroscopic texture evolutions for binary Ni3Al single crystals with the initial RD close to <001> are characterized as development of dual {110}<¯112> texture above 90% cold reduction and the banded structure formation. Microstructure observations reveal the extensive formation and accumulation of the planar defects including the stacking faults and the planes where the localized shear deformations occurs, which must be responsible for the observed anisotropic cold rolling behavior of Ni3Al single crystals.

Abstract: Ni3Al has been considerable research area due to its high temperature behavior increasing strength with increasing temperature. A series of directional solidification studies showed that the eutectic occurred between g’/b and the metastable eutectic of g/b forms under slightly different conditions, however, it is not well established whether the eutectic is composed of g/g‘, g’/b, or g/b . In order to understand solidification behavior of the eutectic structure, directional solidification experiments have been carried out with solidification rate near the Ni3Al composition in this study. The effects of the solidification rate and composition on formation of the equilibrium and metastable eutectics have been discussed. The (g’+g) coupled phase was also shown to form with the eutectic at the solid/liquid interface.

Abstract: The point defect properties of L12 Ni3Al are determined by MD with a simple modified analytic EAM model with the basic physical properties of pure constituents Ni and Al. On the basis of the calculated lattice constants, the formation energies of vacancy and antisite are calculated and the defect types are also discussed. The energies of alloying element Re replacing Ni site and Al site in Ni3Al are estimated. The occupational site of Re is found in Al site. The present calculations are in agreement with the experimental value and the theoretical results obtained from other authors.

Abstract: Ni3Al has attractive high temperature properties, such as high strength and good oxidation/corrosion resistance, and is possible to be used for high temperature chemical processing and manufacture. Until now, the catalytic properties of Ni3Al were rarely investigated since the leaching of aluminum from Ni3Al is difficult to obtain a porous Raney-Ni compared to NiAl3 and Ni2Al3. In the present work, the catalytic properties of Ni3Al were examined for hydrogen production reactions from methanol. It was found that alkali-leached Ni3Al showed high activity for methanol decomposition (CH3OH→ 2H2+CO). Furthermore, Ni3Al catalysts suppress the formation of methane, i.e. they show higher selectivity for the methanol decomposition reaction than Ni catalyst. These results indicate a possibility for Ni3Al used as a catalyst for hydrogen production reaction.

Abstract: We have studied the texture and microstructure evolution during cold rolling of Ni3Al single crystals as a function of the initial crystal orientations and revealed that the cold rolling behavior of the single crystals are strongly dependent on the initial crystal orientations, especially on the initial rolling direction (RD). An optimum condition for thin foil fabrication is determined that the initial RD is close to <001>. According to the conditions we have successfully fabricated the wide and thin foils of binary Ni3Al by cold rolling the single crystalline ingots. The thinnest foils obtained so far are about 20µm in thickness and 50mm in width. This document reviews the current status of our research on the thin foils of intermetallic compound Ni3Al.