NiAl Alloys Research Articles

Study Effect Treatment Thermal for Cermet Composite Prepared by Flame Thermal Spray Method.

Flame thermal spraying technology was used in the production of 25% zirconia composite material with 25% alumina particle with binder material of 50% Al-Ni alloy base on 316L alloy steel base, after preparation the base surface with a method of roughing the granular. Spraying was carried out using a spray distance (12,14,16,18,20) cm. Hardness tests were carried out on the composite material to study the effect of changing spray distance on the properties of the resulting layer. The thermal treatment was performed on the samples at (850,950,1050,1150) for an hour. The results of the tests confirmed that the best spraying distance (16 cm) and the thermal treatment (1050 ) have a significant effect on improving the hardness of the layers of the composite material.

Investigation of surface characteristics and effect of electrodeposition parameters on nickel-based composite coating

In this work, metallic deposition with the help of electrochemical energy is performed with the in-house fabricated experimental set-up. Controlled deposition of nickel and graphite was carried out while varying electrodeposition process parameters namely, bath temperature, deposition time, current density, etc. to achieve optimum condition. The effects of graphite particles on surface morphologies, compositions, coating thickness were investigated by optical microscopy, SEM, EDS, and XRD. Results of XRD and SEM images show that graphite particles have been dispersed uniformly throughout the substrate. Optical microscopy images show the uniform average thickness with excellent surface finish which can be achieved at optimized process parameters such as; 10-minute deposition time, 4.0 pH value of the solution, 8–10 A dm−2 current density, and 40° C bath temperature under specific stirring condition. Further, thermal conductivity and tensile strength of electrodeposited sample have been evaluated. Thermal conductivity of the developed coated substrate is found to be greater than that of the platinum, Al-Ni alloys and silicon nitrides and hence it can be envisioned as potential substrate as micro heaters used in MEMS based applications.

Nanoporous Ni-Al alloy by De-alloying for Electrocatalytic hydrogen Evolution Reaction

As the main method to solve the current problem about energy shortage and environment pollution, hydrogen production via overall water splitting exhibits great prospects. The Pt-based metals were acknowledged as the optimal electrocatalysts for hydrogen evolution reaction (HER) but cannot be used commercially due to the exorbitant price. In this work, nano-porous Ni was successfully obtained through one-pot de-alloying with different atomic ratio of Ni-Al precursor (Ni25Al75, Ni15Al85, Ni10Al90). The electrochemistry testing results show that the Ni10Al90 provide a lowest onset overpotential with -1.44 V for HER. Besides, the potential decrease non-significantly after 1000 cycles of cyclic voltammetry demonstrates a considerable durability.

Application of two-step diffusion couple technique in high-throughput screening of optimal composition and aging temperatures for alloys design: A demonstration in binary Ni-Al system

In this paper, four binary Ni-13.4 at.% Al/Ni-17.7 at.% Al diffusion couples were first prepared and subjected to homogenization at 1573 K for 10,800 s, from which a continuous concentration profile formed. The three diffusion couples were then cooled down for aging at respective temperatures, i.e., 1173, 1123, and 1073 K, for 14400 s. The effect of composition and aging temperature on the aging microstructure was studied in detail by means of different experimental techniques and statistical analysis. The volume fraction, grain size, and shape factor of ?? precipitates in the three diffusion couples were plotted as a function of alloy composition and annealing temperatures. Together with the previously proposed evaluation function in which the phase fraction, grain size, and shape factor of ?? precipitates were chosen as the evaluation indicators, the optimal alloy composition and aging temperature for binary Ni-Al alloys with the best mechanical properties were evaluated, and finally validated by the measured hardness values. The successful demonstration of alloy design in the present binary Ni-Al alloys indicated that the two-step diffusion couple, together with the evaluation function for mechanic properties, should be of generality for high-throughput screening of optimal alloy composition and heat treatment process in different alloys.

Post-annealing effects on structural and magnetic properties of pulsed laser deposition grown Co–Ni–Al ferromagnetic shape memory alloys thin films

Co–Ni–Al is considered as a suitable ferromagnetic shape-memory alloy and has significant control over structural transformation temperature, magnetic parameters, and ductility. In this paper, the fabrication of Co–Ni–Al alloy thin films on Si (1 0 0) substrate was achieved via pulsed laser deposition (PLD) technique. The developed films annealing was done at 573, 673, and 773 K temperatures and inveterate their crystalline structure, phase analysis, and magnetic nature of the annealed Co38Ni35Al27 films. X-ray diffraction analysis at 773 K annealing temperature reveals that, the Co38Ni35Al27 film shows high crystallinity, and all annealed films have a body-centered cubic phase structure. The crystallite size estimated from Scherrer rule is noticed to increase from 10 to 22 nm when the annealing temperature raised to 773 K. From the SEM images, we infer that there is an increase in grain size when the annealing temperature increases and the grains shape looks spherical. The magnetic study of the samples shows that the film possesses highest magnetic saturation and lowest coercivity at 773 K annealing temperature. Also, the film annealed at 773 K exhibits a wide range of transformation temperatures and has a curie temperature of 180 K.

Cuboidal γ' phase coherent precipitation-strengthened Cu–Ni–Al alloys with high softening temperature

Coherent precipitation of cuboidal γ' phase is an efficient strategy to improve high temperature properties in nickel-based alloys. The present work aims to introduce this strengthening mechanism into copper alloys to solve the issue of deficient heat resistance. The results shown that a series of cuboidal γ' coherent precipitation-strengthened Cu100-y(Ni3/4Al1/4)y alloys were obtained in the (Ni+Al) content range of 20 at. % to 50 at. %. These alloys are shown to exhibit excellent comprehensive mechanical properties, high melting point, and a softening temperature of 1273K or more than 1273K. Their hardness and yield strength increased with the rise of temperature, ascribing to splitting of γ′ phase. AFM surface current mode and three-dimensional reconstruction of microstructure was performed to determine that γ phases remain conductive body in Cu100-y(Ni3/4Al1/4)y alloys, and meanwhile temperature-dependent resistivity was characterized and discussed, which showed the improvement of resistivity thermal stability attributing to coherent precipitation of γ' phase. Comparing to other Cu commercial alloys, cuboidal γ' phase coherent precipitation-strengthened alloys possess a great potential under high-temperature loads and service environments. In further researches, continued efforts will be required in the multi-component design of Cu100-y(Ni3/4Al1/4)y alloys to improve the comprehensive performance.

Laser powder bed fusion of eutectic Al–Ni alloys: Experimental and phase-field studies

Eutectic alloys offer great promises for additive manufacturing owing to an enhancement of mechanical properties due to ultra-fine eutectic microstructures. We study experimentally and numerically through phase-field simulations the Laser Powder-Bed Fusion processing of several near-eutectic Al–Ni alloys. The large variations of cooling rate within the melt pool allow us to investigate the dependence of the selected microstructure on the concentration of the alloy and the solidification velocity. We find that the coupled zone, i.e. the temperature-dependent concentration interval within which the two-phase eutectic coupled growth takes place, drifts towards higher concentrations when the solidification velocity increases. The phase-field simulations essentially support the experimental observations.

ОБРАБОТКА ЭЛЕКТРОИСКРОВЫХ ПОКРЫТИЙ МЕТОДОМ УЛЬТРАЗВУКОВОГО ПЛАСТИЧЕСКОГО ДЕФОРМИРОВАНИЯ

In the paper there are shown results on roughness parameter decrease on the electrospark coatings of 20H13 and 30 steel surfaces by means of smoothing with the use of the plant for non-abrasive ultrasonic finishing (NUF). 
 For the coating formation there were used Ni, Cu and an intermetallic alloy based on Ni3Al phase. At the NUF increase of coatings formed with the use of Cu there is a roughness growth caused with material “pickup” upon an indenter. It is determined that for smoothing the surfaces with electrospark coating with the assurance of roughness considerable decrease a six-fold NUF processing is required. A microstructure of the coating obtained with the use of anode material based on the Ni3Al alloy consists of columnar crystal grains the cross-section dimensions of which change from some mkm to several tens of nm. Crystal grains are directed mainly normally regarding a cathode surface. By means of micro-X-ray spectrum analysis there is defined an elementary composition of columnar crystal grains corresponding to the alloy of the Nix-Aly-Fez system which is alloyed with Cr and contains admixtures of Si and Mn. By means of the microstructure investigation of the coating smoothed surface in a number of areas there are revealed crystal grains with the signs of plastic deformation.

Microstructure and mechanical properties of Cu-12 Al-6 Ni with Ti addition prepared by powder metallurgy

Abstract Owing to its excellent wear resistance and good mechanical properties, the sintered Cu–Al–Ni alloy is an ideal material for preparing sliding bearings and self-lubricating sleeves. Adding trace elements into the Cu–Al–Ni alloy is expected to further enhance these properties. Hence, in this work, the microstructure and properties of sintered Cu-12 Al-6 Ni alloys with varying contents of added Ti are studied. Results indicated that the NiAl, γ2, and α phases were distinctly refined when the Ti addition was 0.2 wt%, and a small amount of the granular X phase ((Cu, Ni)2AlTi) appeared in the alloy. The X phase increased and coarsened with increasing Ti addition. When the Ti addition was 0.7 wt%, pores appeared in the center of the large granular X phase. With increasing Ti addition, the sintered density of the alloys gradually decreased, while the hardness and tensile strength increased first and then decreased. When the Ti addition was 0.7 wt%, the hardness reached the maximum (160 HB), while when the Ti addition was 0.2 wt%, the tensile strength reached the maximum (412.2 MPa). Moreover, the friction coefficient and wear loss of the alloy were the lowest when the Ti addition was 0.2 wt%. These findings can provide some theoretical guidance for fabricating high-performance Cu–Al–Ni powder alloys.

Effect of Nd addition on the microstructure, mechanical properties, shape memory effect and corrosion behaviour of Cu–Al–Ni high-temperature shape memory alloys

The effects of rare earth element Nd on the microstructure, mechanical, shape memory properties and corrosion behaviour of Cu-13.0Al-4.0Ni-xNd (wt.%) high-temperature shape memory alloys were investigated in this paper. It was observed that the grains in Cu-13.0Al-4.0Ni-xNd alloys can be refined by adding Nd, and the grain size decreased from the millimeter scale to several hundred microns. The matrix of the Cu-13.0Al-4.0Ni-xNd alloys, composed of 18R and 2H martensite, was not changed by Nd doping. However, the hexagonal (Al,Ni)Cu4Nd phase was formed as the Nd content increased. The grain refinement led to an improvement in the mechanical properties of the Cu-13.0Al-4.0Ni-xNd alloys. When x = 0.5, the compressive fracture stress and strain increased from 580 MPa to 10.5% to 940 MPa and 18.3%, respectively. The Nd addition also enhanced the shape memory effect of the Cu-13.0Al-4.0Ni-xNd alloys, and a reversible strain of 6.8% was obtained for x = 0.2 under a prestrain of 10% after heating. In addition, the results of electrochemical impedance measurement and polarization measurement showed that the corrosion resistance of Cu–Al–Ni alloy were slightly reduced by Nd addition, and the corrosion behaviour of Cu–Al–Ni alloy was mainly controlled by Cu element.

The Microstructure Evolution and Mass Transfer in Mushy Zone during High-Pressure Solidifying Hypoeutectic Al-Ni Alloy

The mushy zone of hypoeutectic Al-1.5 wt% Ni alloy during high-pressure synthesis was obtained by changing the structure of the graphite heater. Meanwhile, the evolution of the microstructure was investigated. The results demonstrated that three distinguished zones were successfully generated along with the direction of the temperature gradient, including the fully melted area consisting of the columnar dendrite. The mushy zone is composed of an α-Al phase, bulk β-Al3Ni phase, and a eutectic microstructure as well as a non-melted, solid region. In addition, the mass transfer velocity and the time required for the liquid pool to migrate through the mushy zone during thermal-stable treatment under different high pressures were also analyzed. The results showed that the mass transfer was greatly inhibited, and the minimum time required for a liquid droplet to go through the whole mushy zone at 1 GPa and 3 GPa was 746 h and 5523 h, respectively.

Surface Properties of Liquid Al-Ni Alloys: Experiments Vs Theory

The present study is an overview of the surface properties of liquid Al-Ni alloys, which are of great importance for the design and development of new Al-Ni and Ni-based industrial alloys, widely used as functional and structural materials. The solidification and thus, the microstructural evolution are directly dependent on the interface/surface properties of metallic melts. Therefore, numerical simulation of microstructure evolution requires reliable property data as input to such models. Taking into account the experimental difficulties related to a high reactivity of liquid Al-Ni alloys and the effects of impurities on their surface properties, the surface tension over the whole concentration range has been determined in the frameworks of three international research projects. Namely, the surface tension measurements have been carried out by both traditional container-based and as an alternative, containerless methods within the ESA-MAP ThermoProp and ESA-MAP Thermolab Projects and also under the EU FP6-IMPRESS Project. The obtained datasets were analysed and subsequently compared with the model predicted values as well as with the literature data. A strong exothermic mixing characterises the Al-Ni system and the presence of a few intermetallic compounds in the solid state leads to the formation of short range ordered elements or complexes in the liquid phase, at least near the melting temperature, which significantly affects the surface properties of alloy melts. Aiming to estimate the effects of short range ordering on these properties, the Compound Formation Model (CFM) and the Quasi Chemical Approximation (QCA) for regular solution were applied.

Deformation and fracture behavior of the novel NiAl alloy sheet with bimodal laminated structure by in-situ reaction synthesis

Due to the intrinsic brittleness of NiAl alloy, its sheets are difficult to fabricate with traditional casting and rolling methods. To solve this problem, a novel NiAl alloy sheet with a special bimodal laminated structure was successfully designed and fabricated via the in-situ solid-state reaction synthesis using pure Ni and Al foils. The mechanical properties of the bimodal laminated NiAl alloy sheet were tested by hot tensile tests at temperatures ranging from 850 °C to 1000 °C and strain rates ranging from 0.01/s to 0.0005/s. To clarify the deformation mechanism, the deformation microstructure was characterized by scanning electron microscopy and electron backscatter diffraction technology. The fracture behavior was characterized by a three dimensional X-ray microscope. It was found that the sheet with the bimodal laminated structure composed of overlapped coarse-grained layers (CGLs) and fine-grained layers (FGLs) exhibits a significant deformation incompatibility between CGLs and FGLs, leading to a special deformation and fracture behavior. During hot deformation, dislocations mainly accommodate in FGLs at the beginning, and the coarse grains then begin to play a major role in replacing the privilege of FGLs and vital in storing dislocations during further deformation. The bimodal laminated grains are broken up into many fragments and the average grain sizes are refined after deformation due to the transformation of low angle boundaries into high angle boundaries. The nucleation of dynamic recrystallization grains preferentially takes place in FGLs, and DRX will occur in CGLs when sufficient strain and storage energy are accumulated. The fracture surface demonstrates a jagged fracture pattern parallel to the loading direction, which results from the special laminated grain structure. The fracture morphology along the thickness direction experiences dramatic changes related to the non-uniform strain distribution, which presented as the density and size distribution of voids in 3D space. The study is vital to guiding the high temperature forming and service performance of NiAl alloy.

Correction to: Trans-interface-diffusion-controlled coarsening of γ′ particles in Ni–Al alloys: commentaries and analyses of recent data

Two empirical equations in the original article are incorrect.

Structural and Energy Characteristics of NiAl Alloys with Deviations from Stoichiometric Composition. Part 2

The analysis of the atomic and phase structure confirmed the difference between the structural-phase states at the heating and cooling stages. Based on the analysis of the influence of the deviation of the atomic composition from the stoichiometric condition of the intermetallic compound during cooling, it is established that the deviation is a significant factor in the area of low-stability pre-transitional structural-phase states before the transformation. The behavior of the long-range parameter temperature dependence curves during the cooling of alloys of non-stoichiometric compositions differs significantly from the behavior of the corresponding alloy curve of a stoichiometric composition alloy. It is shown that in the case of cooling of alloys of non-stoichiometric compositions, a significant supercooling is required to establish a long-range order, and the appearance of ordered phases occurs at significantly lower temperatures. It is found that the temperature dependence curve of the long-range parameter of the Ni45Al55 alloy is significantly lower than the corresponding curve of the Ni55Al45 alloy. This indicates different mechanisms for establishing the long-range order of alloys with non-stoichiometric compositions. It is noted that the deviation of the system composition from the stoichiometric one causes a significant reduction of ordered and disordered regions. This article is a continuation of the work published earlier in the journal Izvestiya AltGU. 2020. №1 (111).

Effect of Alloying Element Segregations on the Grain Boundary Sliding in Al–Mg and Al–Ni Alloy Bicrystals: Atomistic Modeling

Segregation and grain boundary sliding were studied using atomistic modeling methods for special Σ5{013}〈100〉 and Σ5{012}〈100〉 grain boundaries in Al–3 at % Mg and Al–3 at % Ni alloys bicrystals. To reveal the mechanisms controlling the sliding processes, the energy of generalized grain boundary stacking faults (GB-SF) was determined in the plane of grain boundaries, the crystallography of grain boundary shears was analyzed, and the preferable directions and energy barrier of grain boundary sliding were established. It was shown that alloying with Mg and Ni essentially modified the GB-SF energy, increasing the resistance to sliding.

Structure and Energy Profile of the Skeletal Nickel Surface According to the Small-Angle X-Ray Diffraction and Adsorption Calorimetry Data

A systematic study of the surface of Raney nickel-based pyrophoric catalysts by small-angle X-ray diffraction analysis was carried out for the first time. The parameters of the crystallites constituting the active catalyst surface were determined. A correlation between the surface structure and the activity of skeletal nickel for the liquid-phase hydrogenation reactions was demonstrated. The effect of treatment of Ni–Al alloy with sodium hydroxide and hydrogen peroxide on the catalyst particle size and on the course of the hydrogenation reaction was revealed and substantiated. The X-ray diffraction data on the catalyst surface structure and the adsorption calorimetry data were correlated with the skeletal nickel activity parameters.

Hydrodechlorination of Different Chloroaromatic Compounds at Room Temperature and Ambient Pressure—Differences in Reactivity of Cu- and Ni-Based Al Alloys in an Alkaline Aqueous Solution

It is well known that the hydrodechlorination (HDC) of chlorinated aromatic contaminants in aqueous effluents enables a significant increase in biodegradability. HDC consumes a low quantity of reactants producing corresponding non-chlorinated and much more biodegradable organic compounds. Two commonly used precious metals free Al alloys (Raney Al-Ni and Devarda’s Al-Cu-Zn) were compared in reductive action in an alkaline aqueous solution. Raney Al-Ni alloy was examined as a universal and extremely effective HDC agent in a diluted aqueous NaOH solution. The robustness of Raney Al-Ni activity is illustrated in the case of HDC of polychlorinated aromatic compounds mixture in actual waste water. In contrast, Devarda’s Al-Cu-Zn alloy was approved as much less active for HDC of the tested chlorinated aromatic compounds, but with a surprisingly high selectivity on cleavage of C-Cl bonds in the meta and sometimes the ortho position in chlorinated aniline and sometimes chlorinated phenol structures. The reaction of both tested alloys with chlorinated aromatic compounds in the aqueous NaOH solution is accompanied by dissolution of aluminum. Dissolved Al in the alkaline HDC reaction mixture is very useful for subsequent treatment of HDC products by coagulation and flocculation of Al(OH)3 caused by simple neutralization of the alkaline aqueous phase after the HDC reaction.

Effect of water vapor on high-temperature oxidation of NiAl alloy

The high-temperature oxidation of NiAl is studied with dry oxygen and water vapor. The oxidation in H2O results in a thicker Al2O3 oxide scale than that in O2. The oxide scale formed initially is a single layer of γ-Al2O3 that subsequently transforms into a α-Al2O3/γ-Al2O3 bilayer structure, in which the inner α-Al2O3 layer formed in H2O has a higher porosity than that in O2. Further density functional theory calculations show that H protons derived from H2O molecules penetrate into the oxide lattice and boost the formation of lattice vacancies in both α-Al2O3 and γ-Al2O3, thus enhancing the oxide scale growth.

Oxidation behaviour of NiAl intermetallics with embedded Cr and Mo

The isothermal oxidation of directionally solidified NiAl-34Cr and NiAl alloys with embedded Cr bar and Mo wire were studied in a thermobalance at 800 °C, 1200 °C and 1300 °C for 50 h (Ar/ 13 vol.% O2). NiAl-Cr showed formation of a continuous Al2O3-Cr2O3 solid solution in the vicinity of the interface of NiAl and Cr in which the composition changed from almost pure Al2O3 near the metal matrix to almost pure Cr2O3 near the gas surface. DS NiAl-34Cr showed more spallation compared to NiAl-Cr. In case of NiAl-Mo, a weight loss was observed due to formation of volatile oxides.