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Most methods used to synthesize and prepare NiAl intermetallics and their alloys have the disadvantages of complexity and high cost. In this paper, the NiAl alloy was prepared by a Combustion Synthesis and Hot Pressing (CSHP) technique under rapid solidification. The grain size of the NiAl alloy is significantly refined to 60–80 μm, which reduces the stress concentration during deformation and improves the fracture strength and fracture hardness. Moreover, the large internal stress and greater amount of dislocations in the as-cast microstructure are produced by their formation under pressure due to the fast cooling rate in the solidification process. The high dislocation density strengthens the NiAl alloy, giving it higher strength, hardness, and work-hardening ability. The high compression properties are also present in the NiAl intermetallics at room temperature, in which the fracture strength is around 1005 MPa and the fracture strain reaches 21.6%. The compressive fracture strength at room temperature is higher than that of the pure NiAl alloy prepared by the Hot-Pressing-Aided Exothermic Synthesis (HPES, about 632 MPa), while it is slightly lower than that of pure NiAl alloy treated by HPES and Hot Isostatic Pressing (HIP, 1050 MPa). The fracture strain is significantly higher than that of the NiAl alloy prepared by other methods. This study can provide guidance for the successful preparation of the NiAl alloy with high strength and toughness. [ABSTRACT FROM AUTHOR]

Abstract—Fractional gas analysis is used to study the oxide nonmetallic inclusions (NIs) in a nickel alloy based on the NiAl intermetallic compound. Aluminum, lanthanum, and calcium oxides are shown to be the main NIs; the oxygen content in the alloy, which corresponds to them, is 11.6 ± 1.7 ppm. The NI compositions, which are determined with a scanning electron microscope by local energy-dispersion analysis, confirm the fractional gas analysis data for the NiAl-based nickel alloy. [ABSTRACT FROM AUTHOR]

Experimental studies have been carried out with theoretical calculations of wave synthesis in the Ni–Al–Cu system using a mathematical model. Approximate analytical formulas are obtained for synthesis performance evaluation. The inverse problem method was used to get kinetic constants that determine process dynamics based on the experimental data and analytical relationships. It is shown that the combustion front propagation velocity increases monotonically with an increase in the reaction sample relative density in the range of relative density values of 0.4 to 0.6. The depth of copper-melt penetration from the center of the sample into the nickel–aluminum matrix depends on the relative density of the sample and diameter of the copper wire: higher densities and larger diameters lead to an increase in the liquid-phase impregnation area. The rate of nickel and aluminum powder frame wetting with copper melt is limited by the synthesis wave speed. Based on the experimental data and analytical ratios, we estimate the effective kinetic constants describing the high-temperature synthesis of the Ni + Al reaction mixture in the presence of copper additives. The thermal effect of the NiAl intermetallic formation reaction and the preexponential factor in the chemical transformation equation are calculated, the exponent value in the ratio for the mixture thermal conductivity is established, and a constant determining the process of nickel–aluminum matrix impregnation with copper melt is found. The macroscopic approach used to analyze the NiAl intermetallic synthesis makes it possible to determine all the desired physicochemical characteristics and model parameters. The mathematical model is suitable for predictive estimates and experimental data analysis in the macroscopic approximation. Approximate analytical formulas are obtained for calculating the NiAl intermetallic synthesis characteristics. They allow for calculating the through channel characteristics and can be used in the design of NiAl products. [ABSTRACT FROM AUTHOR]

The article presents a study of the effect of various modes of annealing and process heatings on microstructure and properties of single-crystalline blanks of VKNA-1 intermetallic alloy on the basis of NiAl with crystallographic orientations of 〈001〉 and 〈111〉, obtained by the method of directional crystallization, and billets with polycrystalline structure from the VKNA-1VR alloy, made by the precision investment casting method. [ABSTRACT FROM AUTHOR]

A possibility of determining the corrosion current density in the case that cathodic reaction proceeds under the conditions of mixed kinetics is analyzed using the equation proposed by Nagy and Thomas and the method of fitting. By the examples of model and real corrosion systems, it is shown that, under certain conditions, this approach enables one to estimate the corrosion current density and the cathodic diffusion limiting current density with regard for the contributions of cathodic and anodic reactions to the corrosion current on the stationary electrode, in particular, in the absence of Tafel region in the cathodic polarization curve. [ABSTRACT FROM AUTHOR]

A series of iron-doped NiAl ternary alloys is investigated by resistivity measurements and differential thermal analysis. Temperatures of phase transformations and disordering onset are determined. A hysteresis phenomenon is observed in the liquid state in polytherms of resistivity upon heating the alloy under study to the critical temperature. [ABSTRACT FROM AUTHOR]

The well-known concept of γ surfaces originally suggested by Prof. Vitek is extended to the case of a shift of one part of a crystal with respect to the other part in two adjacent {111} planes of a stacking fault. The proposed approach is used to construct the effective γ surfaces in the {111} plane in fcc Ni and L1 NiAl of intermetallic compound. It is shown that NiAl can have five metastable stacking faults in this plane, namely, an intrinsic superlattice stacking fault, an extrinsic superlattice stacking fault, a complex stacking fault, an antiphase boundary, and a complex extrinsic stacking fault. The existence of the latter in the {111} plane in the L1 NiAl intermetallic compound has not been reported previously. The shift of the crystal in two close-packed planes in fcc Ni makes it possible to avoid the formation of a high-energy stacking fault which arises when constructing an ordinary γ-surface, as well as to self-consistently include the extrinsic stacking fault into consideration. [ABSTRACT FROM AUTHOR]

The corrosion behavior of NiAl containing small additions of Ti, Zr, and B in combustion gases both with and without NaSO−NaCl deposits at 600-800°C has been studied for times up to four days. The corrosion of the saltfree NiAl leads to the formation of very thin alumina scales at 600°C but of mixed NiO−AlO scales containing also some sulfur compounds at higher temperatures, while the rate increases with temperature up to 800°C. The presence of the salt deposits considerably accelerates the corrosion rate, especially at 600 and 800°C. The duplex scales formed at 600°C are composed mostly of a mixture of NiO and unreacted salt in the outer layer and of alumina and aluminum sulfide with some nickel compounds in the inner layer. The scales grown at 700°C contain only one layer of complex composition, while those grown at 800°C are similar but have an additional outer layer containing similar amounts of nickel and aluminum. At 600 and 700°C NiSO can be detected also in the salt layer. The samples corroded at 700°C and 800°C also show an Al-depleted zone containing titanium sulfide precipitates at the surface of the alloy. The hot corrosion of NiAl involves a combination of various mechanisms, including fluxing of the oxide scale as well as mixed oxidation-sulfidation attack. At all temperatures NiAl shows poor resistance to hotcorrosion attack as a result of the formation of large amounts of Ni compounds in the scales. [ABSTRACT FROM AUTHOR]