Papers by Keyword: Nickel Aluminides

Abstract: This paper presents a method for fabricating a porous Ni-Al₂O₃-Al compact using uniaxial double-action pressing, which was subsequently infiltrated with molten aluminium. Al₂O₃ ceramic particles primarily serve to create porosity within the composite compact. Due to the difficulty pressing hard metal powders, aluminium powder was introduced into the Ni+Al₂O₃ mixture to act as a plasticizer, improving the material's compressibility. Experiments indicated that the optimal infiltration temperature was 750 °C with an infiltration duration of 300 seconds. To evaluate the reaction extent among the initial components, a subset of infiltrated samples underwent annealing at 800 °C for 3 hours under an inert argon atmosphere. Both annealed and reference samples were subjected to thermal cycling. The microstructure and thermal stability of the resulting composite materials were analyzed and characterized using scanning electron microscopy with energy-dispersive spectroscopy, respectively.

Abstract: 3D simulation by the finite element method (FEM) using MSC.Marc of sclerometric test with a conical indenter of a nickel aluminide intermetallic coating has been determined. The effect of the coating thickness and composition on the strain distribution has been determined. It is shown that an increase in the thickness of the coating makes it possible to reduce the magnitude of the maximum plastic strain. NiAl and Ni₃Al coatings reduce maximum value of plastic strain and the penetration depth of indenter by 40% compared to a coating made of Ni₂Al₃.

Abstract: The paper presents the investigation on the structure, chemical and phase composition of the diffusion coating formed during the liquid-phase heat treatment in the explosion-welded Cr20Ni80 + AD1 bimetal. It is shown that the coating structure consists of NiAl₃, CrAl₇, Ni₂Al₃ intermetallic inclusions, as well as a metastable ternary compound – τ₂-phase (Al_77.5Cr_12.5Ni₁₀) of different dispersion and morphology. There are no crystallization defects in the coating structure.

Abstract: The article presents the research results on obtaining coatings on steels 1030 and AISI 420 by the method of electrospark deposition and subsequent smoothing by means of ultrasonic surface plastic deformation (USPD). Intermetallic alloys consisting mainly of NiAl and Ni₃Al phases were used as materials for obtaining coatings. It was found that the coatings consist of columnar crystallites of complex composition and have high plastic properties. To ensure the minimum parameters of the surface roughness of the obtained coatings, it is necessary to carry out 3-6 times of ultrasonic surface treatment.

Abstract: The structure, phase and chemical composition of the diffusion interaction zone, formed at the interlayer boundary of a layered composite of the alloy Cr15Ni60-aluminum AD1, are studied. The temperature-time conditions for its nucleation and growth are determined. The diffusion zone has a fine predominantly heterogeneous structure and consists of solid solutions based on aluminides Al₃Ni, Al₃Ni₂ and Al₇Cr, as well as the ternary compound Al₅FeNi. It is shown that the intensity of diffusion zone growth at the interlayer boundary of the bimetal Cr15Ni60-AD1 is determined mainly by the heating temperature, and the dependence of its thickness on the exposure time obeys a parabolic law. The presence of chemical micro-inhomogeneity in the form of a melted metal at the interlayer boundary does not have a qualitative effect on the kinetics of the process: at the first stage, the diffusion zone repeats the contour of the fusion, and then, as the service time increases, «absorbs» it.

Abstract: Both FeAl and NiAl with B2 crystal structure are envisaged for their usage in high temperature applications and hence, availability of diffusion data in these intermetallics is crucial in designing their alloys and processes as well as deciding their in-service performance. A comprehensive overview of diffusion data available in B2 FeAl and NiAl and their alloys is provided in this article. Nearest neighbor vacancy jumps in B2 intermetallic lead to a local disorder in the lattice and hence it is not necessarily the unit step of diffusion in these structures. Several mechanisms of diffusion proposed in the literature are discussed including nearest neighbor jumps, next nearest neighbor jumps, six-jump vacancy cycle, triple defect and antisite bridge. Relevance of these mechanisms in FeAl and NiAl is discussed. An overview is given on the self-and solute diffusion and interdiffusion data available in both binary FeAl and NiAl. Due to wide solubility range of both FeAl and NiAl as well as their alloying requirements for improved properties, it becomes pertinent to study the multicomponent diffusion in the alloys based on these B2 itnermetallics. Hence, in the latter part of the article, various methods used for determining multicomponent diffusion data are reviewed. A detail overview is also provided on the diffusion studies available in literature on ternary alloys based on FeAl and NiAl with an emphasis on highlighting the diffusional interactions observed in these systems.

Abstract: A critical review of interdiffusion processes in the binary β-NiAl and γ'-Ni₃Al intermetallic compounds is presented. The molar volume changes associated with interdiffusion and partial molar volumes of the reacting species, required for the determination of the diffusion parameters, are found using lattice parameter data and, in the case of NiAl, the available information about vacancy concentration within homogeneity range of the β-phase. The presented treatment is purely phenomenological, and its use is convenient since no exlicit assumption of the underlying mechanisms required. A critical analysis of diffusion data for β-NiAl and γ'-Ni₃Al ordered phases is followed by discussion of error sources encountered in the interdiffusion experiments. From Kirkendall marker experiments with incremental diffusion couples, information about relative mobilities of species in the intermetallic phases can be obtained, and tracer diffusion coefficients can be deduced using pertinent thermodynamic data on the nickel aluminides. Contribution of the vacancy wind effect to the calculated tracer diffusivities can also be estimated. The Kirkendall plane bifurcation in the Ni_41.7Al_58.3/Ni_72.24Al_27.76 reaction couple, in which a single-phased layer of β-NiAl intermatallic is formed during interdiffusion from its adjacent phases, is directly related to the growth of grains of the reaction product at a location in between interfaces with starting materials. This diffusion phenomenon can be rationallised using a corresponding Kirkendall velocity diagram. Changes in magnitude and sign of the difference in intrinsic mobilities of the components inside the homogeneity range of the β-NiAl lead to a velocity curve that makes bifurcation of the Kirkendall marker plane possible.

Abstract: Advanced modern gas-turbine engines strongly rely on high-temperature thermal barrier coatings (TBCs) for the improved efficiency and power. Interdiffusion between the bond coat and the underlying Ni-based superalloy is one key factor limiting the lifetime of TBCs. In order to assist the engineering-oriented lifetime assessment and even design new TBCs, reliable composition- and temperature-dependent interdiffusivity databanks for γ, γ′ and β phases in different types of bond coats and Ni-based superalloys are the prerequisite. This chapter starts from a very brief introduction of the state-of-art experimental techniques and calculation methods for interdiffusivity determination in ternary systems. After that, the status of the interdiffusion databanks of γ, γ′ and β phases in NiAl-based ternary systems is then summarized, with a special focus on the demonstration of interdiffusivity data measured by means of single-phase diffusion couple/multiple techniques in combination with Matano-Kirkaldy method or numerical inverse method. Several typical results for NiAl-based γ, γ′ and β phases are also given. Finally, two examples of successful applications of the available interdiffusion databanks of ternary NiAl-based γ, γ′ and β phases are presented. One lies in the Re-substitutional element searching in potential new-generation Ni-based superalloys, while the other is the phase-field modeling of interdiffusion microstructure in ternary mode NiAlCr-based TBCs without/with the effect of temperature gradient.

Abstract: The effect of isothermal annealing at 1100°C on the kinetics of phase transitions in the coatings system Ni-Al, obtained by the complex technology, is studied. The cyclic heat resistance of the coating is investigated at 1100°C.

Abstract: The transformation of the structure, phase and chemical composition of the diffusion coatings of the system Al-Ni and Al-Cr-Ni at 1100 °C is studied. It is shown that the diffusion redistribution of Al by the coating thickness during the heat treatment is slower in the system Al-Cr-Ni than in the binary system Al-Ni.