Papers by Keyword: Nickel Aluminide

Abstract: The structure and mechanical properties of materials fabricated by spark plasma sintering of mechanically activated mixture of nickel and aluminum nanopowders were investigated. On account of the elemental powders ratio formation of Ni₃Al compound was expected. Relative density of sintered samples was equal to ~ 95 %, microhardness of materials was 6540 MPa. Ultimate tensile strength of samples tested according to three-point bending scheme exceed 1100 MPa.

Abstract: In this paper structure and mechanical properties of Ni₃Al intermetallic compound was studied. The materials was fabricated according to different schemes, which combined mechanical alloying of Ni and Al powders, self-propagating high temperature synthesis (SHS) and spark plasma sintering (SPS). Relative density of all sintered samples was ~ 97 %. Microhardness of the sintered materials ranged from 6100 to 6300 MPa. SPS of 86.71 % wt. Ni and 13.29 % wt. Ni powder at 1100 °C led to formation of material with the highest level of tensile strength equal to 400 MPa.

Abstract: Nickel alloys have been widely used for high temperature applications such as gas turbine engine, turbine blade and many high temperature resistance components. Aluminizing is one of effective to increase oxidation resistant of nickel alloys by forming nickel aluminide compounds on nickel surface. Nickel aluminide is formed by the diffusion mechanism. This research aims to study the diffusion behavior of nickel in Ni₂Al₃ compound. The diffusion coefficient is determined using Ni/Al diffusion couple forming Ni₂Al₃ and NiAl₃ phases. The temperatures under study are 873, 973, and 1073 K, which are at above and below melting point of aluminum. Determination of diffusion coefficient of Ni in Ni₂Al₃ is from mass balance concept: flux difference at interphase causes accumulation of atoms in compound layer, which as be derived as: dx_αβ/dt = [1/(n^β-n^α)] * [D_α *(dn^α/dx) - D_β *(dn^β/dx)] From this equation, diffusion coefficient of Ni in Ni₂Al₃ at 873 and 1073 K are calculated as 6.243×10^-11 and 6.82×10^-9 m²/s, respectively. From Arrhenius equation of diffusivity, D = D_oexp (-Q/RT), the activation energy for diffusion of nickel in Ni₂Al₃ is found to be 183 kJ/mol. The result obtained in this research is of great use in controlling aluminizing process.

Abstract: Most traditional aluminium casting alloys are based on the aluminium-silicon eutectic system because of its excellent casting characteristics. However, the solidus in this system does not exceed 577 °C and the major alloying elements used with silicon in these alloys have high diffusivity in aluminium. Therefore, while these elements enhance the room temperature strength of the alloy, they are not useful at elevated temperatures. Considering nickel-base superalloys, whose mechanical properties are retained up to temperatures that approach 75% of their melting point, it is conceivable that castable aluminium alloys can be developed on the same basis so that they are useful at temperatures approaching 300 °C. In this publication, we present the thought process behind developing a new castable aluminum alloy that is designed specifically for such high temperature applications and we present the alloy’s measured castability characteristics and its elevated temperature tensile properties.

Abstract: A Ni aluminide layer containing Zr or Hf was formed on a Ni specimen by the simultaneous electrodeposition of Al and Zr or Al and Hf using a molten-salt bath. When the simultaneous electrodeposition of Al and Zr was carried out using molten NaCl-KCl containing 3.5 mol%AlF₃ and 0.05 mol%ZrF₄, the electrodeposited layers were formed in the order of Ni₂Al₃, NiAl₃ and Al from the Ni substrate side. The ZrAl₃ particles were uniformly formed in the surface region of the NiAl₃ and Al layers. On the other hand, when the simultaneous electrodeposition of Al and Hf was carried out using molten NaCl-KCl containing 3.5 mol%AlF₃ and 0.05 mol%HfF₄, the electrodeposited layer consisted of Ni₂Al₃ as the inner layer and NiAl₃ as the outer layer were formed with HfAl₃ particles uniformly formed in the surface region of the NiAl₃ layer. For the sample treated with the simultaneous electrodeposition of Al and Zr, no significant change in the mass gain was observed during the cyclic-oxidation test at 1423 K, suggesting that the sample had a high cyclic-oxidation resistance. Similarly, the sample treated by the simultaneous electrodeposition of Al and Hf had a high cyclic-oxidation resistance. An adhesive scale, having localized inward penetrations consisting of Al₂O₃ containing ZrO₂ or HfO₂, was formed on the samples having the high cyclic-oxidation resistance.

Abstract: Nickel(Ni) layer was applied to the surface of pure aluminum(Al) by electrodeposition for 15 minutes using a direct current (DC) condition at 0.13 Acm-2. Heat treatment was employed subsequently for 1, 2.25 and 4 hours at the temperatures of 600 and 650oC, which are below and above the eutectic temperature of Al-NiAl3, respectively. All samples were characterized by OM, SEM, EDS and GIXD. DTA was also performed to study heat release in the reactions. After heat treatment at 600oC, the specimens exhibit the non-uniform formation of Ni2Al3 and NiAl3, even after 4 hours of heat treatment where local melting possibly occurs due to the exothermic heat of formation. In contrast, owing to fast interdiffusion of Al and Ni as assisted by a liquid phase formation, multi-layer of Ni2Al3 and NiAl3 was uniformly formed along the interface of the specimens heat treated at 650oC.

Abstract: Discovery of new high temperature alloys is a multidimensional problem which encompasses the intrinsic thermodynamic stability and their thermo-chemical and thermo-mechanical response to the combustion environment. Even when considering only the transition metals in combination with stable oxide formers, the number of ternary combinations exceeds 104. Hence, the traditional Edisonian process is not a practical approach to develop new alloy systems. Using formation enthalpy as a guide to compound stability, we propose a hierarchical scheme for identifying potential alloy systems which involves sifting through large regions of phase space with increasingly more accurate analysis. The coarsest sieve is a semi-empirical method based on the Miedema model extended to ternary systems. The next stage is ab initio simulations for a more accurate assessment and the basis for selecting system to investigate experimentally. We describe the implementation of this approach through the discovering of ternary additions that improve the oxidation stability -NiAl alloy.

Abstract: The diffusion couples for experimental study were prepared by HVOF spraying of nickel and nickel with 20 wt.% of chromium powders onto an aluminium sheet surface. The interfaces with sharp gradients of chemical concentration of these elements were prepared. Annealing at temperatures of 600°C and 630°C, close to the Al + Al3Ni eutectic melting point (639.9°C), with different dwell times were used. During annealing, the reactants diffuse and form layers of Al3Ni2 and Al3Ni intermediate phase compositions. Moreover, nickel without the assistance of chromium diffuses preferably along the grain boundaries into aluminium substrate and produces the strengthening of the substrate by stable Al3Ni and metastable Al9Ni2 particles. The microstructures were obtained by scanning electron microscopy. Layer thickness measurements were realized by means of image analyses. Chemical composition was estimated by energy dispersive microanalysis measurements. According to the results of the analyses performed the average chemical interdiffusion coefficients and Wagner’s integral interdiffusion coefficients were calculated.

Abstract: Interdiffusion coefficients of Al replacing elements in Ni-Al-X (X=Ti, V and Nb) were estimated by a series of experiments using diffusion couples of Al rich pseudo-binary systems at three different temperatures of 1423, 1473 and 1523K. In order to obtain interdiffusion coefficients of the pseudo-binary systems, the experimental data was analyzed by the Sauer and Freise method, and also impurity diffusion coefficients of Ti, V and Nb in Ni3Al were estimated by applying the Darken-Manning equation. The magnitude of interdiffusion coefficient decreased in order of V, Ti and Nb at all three temperatures. Impurity diffusion coefficients were described by the expressions: , , . The activation enthalpies obtained from the experimental data confirmed the retardation of Ti, V and Nb diffusion in Ni3Al by the anti-site diffusion mechanism. These results are consistent with our previous work on diffusion of Re and Ru in Ni3Al .

Abstract: Two different methods were utilized to synthesize intermetallic nickel aluminide alloy. The first method was combination of powder metallurgy and reaction synthesis (IMC_RS) and the second method was plasma melting to form homogenous plasma melted samples (IMC_PM). XRD patterns for both samples showed complete formation of single phase Ni3Al. Saturation magnetization value for IMC_RS was 0.445 emu/g and IMC_PM was 0.157 emu/g. This was comparable with Ms value of commercial Ni3Al from Alfa Aeser (0.398 emu/g). The reduced elastic modulus, Er value of IMC_PM and IMC_RS were 441.09 MPa. 408.2 MPa respectively. Both samples were exposed to 1%SO2/air gas mixture at 1000oC for 24-hour duration. The isothermal kinetic results for both samples were parabolic indicating rate limiting step. The oxide scales consisted of NiO, NiAl2O4 and Al2O3.