High-temperature synthesis of the Ni<Subscript>3</Subscript>Al intermetallic compound under pressure

We investigate by experimental and numerical methods the high-temperature synthesis of the Ni₃Al intermetallic compound in the thermal explosion mode under the pressure of a powder mixture of nickel and aluminum of a stoichiometric composition. The calculated and experimental thermograms of self-propagating high-temperature synthesis are analyzed depending on the temperature of preliminary heating of the powder mixture and the magnitude of external pressure.     

Diamond cutting tools with a Ni<Subscript>3</Subscript>Al matrix processed by reaction pseudo-hipping

Nickel aluminide, Ni₃Al, has high hot strength, which could help overcome the high heat and the interrupted vibrations that diamond cutting tools encounter during operation. Reaction pseudo-hipping, on the other hand, require only a short dwell time at high temperatures, which are detrimental to the diamond grits. Thus, it is promising to combine the unique nickel aluminide with the unique reaction pseudo-hipping process and replace the commonly used cobalt matrix. This study reports for the first time the process and application of reaction-pseudo-hipped Ni₃Al matrix for diamond tools. In this work, mixtures of elemental nickel, aluminum, boron powder, and diamond particles are reaction-pseudo-hipped. Densities greater than 99 pct and mechanical properties comparable to those of the cobalt are attained. With high-grade diamond grits, the tools thus prepared show, under dry cutting conditions, a grinding ratio 118 pct higher than that with the cobalt matrix.     

High-temperature deformation of single-crystal Ni<Subscript>3</Subscript>Al-Based alloys

Comparative studies of the structure and strength properties of VKNA-1V and VKNA-4U 〈001〉 single-crystal alloys were performed using tensile tests at 1200 and 1250°C. Dynamic recovery is the principal relaxation mechanism. At 1250°C, the strength properties of the VKNA-4U alloy are higher than those of the VKNA-1V alloy.     

Stress Annealing Induced Diffuse Scattering from Ni<Subscript>3</Subscript> (Al,Si) Precipitates

Diffuse scattering caused by L₁2 type Ni₃ (Al, Si) precipitates after stress annealing of Ni-Al-Si alloys is studied. Peculiarities of diffuse scattering in the asymptotic region as compared to the Huang scattering region are discussed. Coupling between the stress annealing direction and the precipitate shape is demonstrated. Experimental reciprocal space maps (RSMs) are compared to theoretical ones. Oscillations of diffuse scattering due to Ni₃ (Al, Sc) precipitates are observed. The strengths of the precipitates are estimated from the analysis of the diffuse scattering oscillations.     

Influence of smelting on the structure and properties of an Ni<Subscript>3</Subscript>Al intermetallic alloy

Ni₃Al intermetallic alloys are produced by open inductive smelting with two different fluxes and subsequent centrifugal casting. The structure and phase composition of the alloys are investigated. Alloy samples undergo tensile tests at room temperature and elevated temperatures. The dependence of the structure and mechanical properties of the alloys on the smelting conditions is established.     

Ordering transformations in Ni<Subscript>75</Subscript>Mo<Subscript>15</Subscript>Mn<Subscript>10</Subscript> alloy

Effect of partial substitution of Mo in Ni₃Mo by Mn on its ordering behaviour is studied here using Transmission Electron Microscopy (TEM). The change in alloy composition does not change the nature of the short range ordered (SRO) state, which shows intensity maxima at {1½ 0} and equivalent positions. However, prolonged aging at 973 K leads to transformation of the Ni₇₅Mo₁₅Mn₁₀ alloy, studied here, almost entirely into the ordered D0₂₂ phase unlike in the case of the binary Ni-Mo alloy. Curved antiphase boundaries (APBs), with wetting of the interdomain D0₂₂ regions by the disordered phase, characterize the microstructure of the aged alloy. A small volume fraction of a sigma-like topologically close packed (TCP) phase that appears in the as quenched alloy seems to remain unaffected by ageing.     

Structure and phase composition of alloyed intermetallic compound Ni<Subscript>3</Subscript>Al after annealing and high-temperature creep

The structure and phase composition of a VKNA-25 alloy based on the Ni₃Al intermetallic compound, produced by directional solidification, and alloyed with rare-earth metals are studied in the following two states: after annealing at 1100°C and after creep at 1100°C.     

Kinetics of Ni<Subscript>3</Subscript>S<Subscript>2</Subscript> sulfide dissolution in solutions of sulfuric and hydrochloric acids

The kinetics of Ni₃S₂ sulfide (heazlewoodite) dissolution in solutions of hydrochloric and sulfuric acids is studied. The process under study in the temperature range of 30–90°C is found to occur in a kinetic regime and is controlled by the corresponding chemical reactions of the Ni₃S₂ decomposition by solutions of inorganic acids (E _a = 67–92 kJ/mol, or 16–22 kcal/mol). The only exception is the Ni₃S₂-HCl system at elevated temperatures (60–90°C). In this case, the apparent activation energy decreases sharply to 8.8 kJ/mol (2.1 kcal/mol), which is explained by the catalytic effect of gaseous chlorine formed under these conditions. The studies performed are related to the physicochemical substantiation of the hydrometallurgical processing of the copper-nickel converter mattes produced in the industrial cycle of the Norilsk Mining Company.     

Long-term oxidation of an as-cast Ni<Subscript>3</Subscript>Al alloy at 900 °C and 1100 °C

The oxidation behavior of a cast nickel aluminide alloy, IC221M, was examined after long-term aging in air for up to 16,600 hours at 900 °C and 5000 hours at 1100 °C. The oxidation products were identified using X-ray diffraction and energy-dispersive X-ray (EDX) spectroscopy with multivariate statistical analysis. At 900 °C, NiO dominates the oxidation products initially, but at longer times, NiAl₂O₄ spinel and Al₂O₃ predominate and remain stable for times up to 16,600 hours. Cross-sectional observation confirmed that a continuous surface oxide that is mostly a mixture of Al₂O₃ and NiAl₂O₄ protects the base metal. In its initial stages, the oxidation process at 1100 °C is qualitatively similar to that at 900 °C but with faster kinetics. However, as aging proceeds, NiO spalls freely from the surface, and a protective continuous oxide scale does not form. The oxidation mechanism can be qualitatively understood by the selective oxidation mechanism maps developed by Giggins and Pettit. An erratum to this article is available at .     

Study of the Ni<Subscript>41.3</Subscript>Ti<Subscript>38.7</Subscript>Nb<Subscript>20</Subscript> wide transformation hysteresis shape-memory alloy

The shape-memory characteristics in the Ni_41.3Ti_38.7Nb₂₀ alloy have been investigated by means of cryogenic tensile tests and differential scanning calorimetry measurement. The martensite start temperature M _s could be adjusted to around the liquid nitrogen temperature by controlling the cooling condition. The reverse transformation start temperature A′ _s rose to about 70 °C after the specimens were deformed to 16 pct at different temperatures, where the initial states of the specimens were pure austenite phase, martensite phase, or duplex phase. The shape-memory effect and the reverse transformation temperatures were studied on the specimens deformed at (M _s +30 °C). It was found that once the specimens deformed to 16 pct, a transformation hysteresis width around 200 °C could be attained and the shape recovery ratio could remain at about 50 pct. The Ni_41.3Ti_38.7Nb₂₀ alloy is a promising candidate for the cryogenic engineering applications around the liquid nitrogen temperature. The experimental results also indicated that the transformation temperature interval of the stress-induced martensite is smaller by about one order of magnitude than that of the thermal-induced martensite.     

Mechanically induced solid-state devitrifications of Zr<Subscript>70</Subscript>Pd<Subscript>20</Subscript>Ni<Subscript>10</Subscript> glassy alloy powders

A single glassy phase of Zr₇₀Pd₂₀Ni₁₀ alloy powder was synthesized by mechanical alloying the elemental powders for 48 hours, using a high-energy ball-milling technique. The obtained glassy phase transformed into a metastable big-cube phase upon increasing the ball-milling time (100 hours). After 150 hours of milling, a complete glass-metastable-phase transformation was achieved, and the end product was nanocrystalline big-cube powder, which has a lattice constant of 1.23 nm. As the ball-milling time was further increased the big-cube phase could no longer withstand the mechanical deformation that was generated by the milling media and transformed into a new metastable phase of nanocrystalline fcc Zr₇₀Pd₂₀Ni₁₀. The lattice constant of this metastable phase was calculated to be 0.455 nm. The reported metastable phases here are new and have never been, so far as we know, reported for the ternary Zr-Pd-Ni system, or its binary-phase relations.     

Shape memory effect in a rapidly quenched Ti<Subscript>50</Subscript>Ni<Subscript>25</Subscript>Cu<Subscript>25</Subscript> alloy

The structural and thermomechanical properties of rapidly quenched layered amorphous–crystalline Ti₅₀Ni₂₅Cu₂₅ composite materials with various ratios of amorphous and crystalline phases are studied. These layered composite materials are shown to exhibit the two-way shape memory effect accompanied by bending deformation without additional thermomechanical treatment. The ratio of amorphous and crystalline phases is found to affect the reversible change in the shape of the composite material.     

Mechanochemical preparation of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposites

The mechanochemical preparation of nickel aluminide/corundum (Ni _x Al _y /Al₂O₃) powder nanocomposites is shown to be possible during the mechanochemical aluminum reduction of nickel oxide at various weight proportions of the components.