Compound NiAl Research Articles

Grain Size and Strength of the Ni<sub>3</sub>Al Intermetallic Compound Synthesized under Pressure

This paper presents the results of the investigation of the grain structure formation in the intermetallic compound Ni3Al under conditions of its high-temperature synthesis under pressure in a powder mixture of nickel and aluminum of stoichiometric composition and the effect of grain size on the strength properties of the synthesized intermetallic compound. The grain structure was investigated by optical metallography, transmission electron microscopy, and EBSD analysis; the ultimate tensile strength of the intermetallic compound was investigated under the tension of the samples in the temperature range from 20 to 1000 °C. It was found that with a decrease in the grain size, not only does the tensile strength of the intermetallic compound multiply increases but also on the anomalous temperature dependence of the intermetallic compound strength there is a significant shift in the maximum strength value to the region of higher temperatures.

ВЛИЯНИЕ РЕЖИМА ОТЖИГА НА ИЗНОСОСТОЙКОСТЬ ГАЗОТЕРМИЧЕСКИХ ПОКРЫТИЙ ИЗ Ni-Cr-Al-ПСЕВДОСПЛАВА

The structural-phase state and tribotechnical properties of gas-thermal coatings made of Ni-Cr-Al pseudoalloy are investigated in the initial state and after annealing in the temperature range of 550-650 °С with holding time of 20–60 min. It is shown that in coatings sprayed by the method of high-speed metallization of wires made of Х20Н80 (Kh20N80) and aluminum АД-1 (AD-1), the phase composition includes γ-(Ni, Cr, Fe), Al and Al2O3. It is found that high-temperature annealing of Ni-Cr-Al coatings leads to the precipitation of intermetallic compounds Al3Ni, Ni2Al3, Ni3Al, and NiAl in them, as well as to an increase in the porosity of the coatings up to ≈15–20 vol.%, which is associated with the implementation of the Frenkel and Kirkendall effects. Tribotechnical tests of coatings are carried out according to the scheme of the reciprocating movement of the sample along the plate counterbody in the dry friction mode at a load of 1.5 MPa. It is shown that as a result of the annealing of the coatings, an increase in their wear resistance under dry friction conditions is registered up to 24 times in comparison with the initial state. In particular, the intensity of mass wear of the Ni-Cr-Al coating in the initial state is 28.7 × 10–3 mg/m, and those subjected to annealing at 600 °C for 60 min — 1.2 × 10–3 mg/m. Based on the carried out multifactorial experiment, it is found that the maximum wear resistance of Ni-Cr-Al-pseudo-alloy coatings under dry friction conditions is achieved as a result of their annealing at temperatures of 630–640 °С and a holding time of 40–50 min, which is associated with the release of large number of dispersed intermetallic phases Ni3Al and NiAl with a relatively insignificant increase in the porosity of the coatings.

Internal friction of Ni-Al intermetallic compound formation in sintering process

The Ni-Al intermetallic compounds, as important high-temperature structural materials, have clear target requirements in a number of fields. Powder metallurgy is an important candidate for preparing the Ni-Al intermetallic compounds. Clarifying the formation and transformation process of Ni-Al intermetallic compounds in sintering process and determining the solid diffusion reaction temperature and types of intermetallic compounds are greatly important for tailoring sintering process and optimizing product quality. In this paper, the internal friction behaviors of Ni-Al powder mixture compacts in the sintering process are systematically investigated by the internal friction technique. A typical internal friction peak is observed in the internal friction-temperature spectrum. The peak height decreases with the measuring frequency increasing, but the peak temperature is independent of frequency. Moreover, the internal friction peak shifts toward higher temperature and the peak height increases as the heating rate increases. It is reasonable that the internal friction peak belongs to the typical phase transformation internal friction peak which is associated with the formation of intermetallic compounds NiAl<sub>3</sub> and Ni<sub>2</sub>Al<sub>3</sub> in the heating process. Furthermore, the microstructure of the Ni-Al powder mixture can be tailored by mechanical ball-milling. The internal friction peak shifts toward lower temperature and the peak height decreases with the ball-milling time increasing, which indicates that the solid diffusion reaction can be activated at lower temperature with a slower reaction rate. This decrease is related to the refinement of powder particles, the lamellar formation of powder mixture, the enhancement of solid solution degree and surface energy, and the shortened atomic diffusion distance due to the mechanical ball-milling. It is also indicated that the mechanical ball-milling can effectively reduce the initial temperature of solid diffusion reaction, thus lowering sintering temperature.

Development of nanocrystalline Ni-Al coatings and its thermal stability

In this paper, Ni-Al compound coatings were electrodeposited from a nickel sulphate electrolyte containing metallic Al particles (1-3um). The deposition conditions adopted were: compound content 50 g/l, pH 4.0, and present density 1.6A/dm'. At electrode position, the particles were held in suspension by magnetic stirring. The deposition was carried out on a stainless steel substratum and the coating was mechanically Segregated out of the substratum as an electroform after completion of the deposition. The thermal sustainability of the Ni-Al coatings was observed by annealing electroforms at temperatures of 200°, 400°, 600°, and 800 °C for 6hrs in an electric furnace under normal conditions. To further enhance the thermal stability of Ni-Al coatings, the cobalt element has been code posited with the addition of cobalt sulphamate in Ni electrolytic bath to obtain Ni-Co alloy matrix containing Al particles. The electrodeposited coatings were characterized for their shape and the phases formed during annealing using the X-ray diffraction technique (XRD). The Al particle distribution was studied using optical microscopy (OM) and field emission scanning electron microscopy (FESEM). The Ni-Aland Ni-Co-Al coatings were also characterized by their cross-sectional micro hardness. As these Ni-Al coatings tend to form Al2O3; upon exposure to high temperatures, a comparative study of the structure, microhardness, thermal stability has also been made between Ni-Al. Ni-Co-Al and Ni-Al2O3; coatings. The Ni-Al2O3; (um) composite coating was obtained under the same conditions as that of the Ni-Al coating. The properties of the three coatings were compared and discussed.

Study on microstructure and oxidation behavior of Fe–xMn–14Al–8Ni–C alloy prepared by vacuum arc melting

In this study, Fe–xMn–14Al–8Ni–C alloy (x = 10, 15, 20, 25 wt.%) was prepared by vacuum arc melting method. The microstructure of this series of alloys and the oxidation behavior at 600 °C were studied. The conclusions are as follows: Fe–xMn–14Al–8Ni–C alloy mainly contains austenite phase, NiAl intermetallic compound phase and k-carbide phase. As the content of Mn increases, the amount of austenite increases while the amount of NiAl compound decreases. At the same time, the content of k-carbide phase precipitated at the interface between austenite and NiAl compound and inside austenite increases. The oxidation resistance results show that as the Mn content increases, the oxidation resistance of the alloy is improved. After oxidation, due to the difference in thermal stress and thermal expansion coefficient, the oxide film is mainly divided into two layers (when the Mn content is 10% and 15%, respectively), the outer oxides are Fe2O3 and a small amount of Mn2O3, the inner oxides are mainly the mixture of Al2O3, Mn2O3 and NiO. When the Mn content increases to 20%, the oxide film is a three-layer, and a uniform dense oxide film mainly composed of Al2O3 appears at the junction with the substrate, which better prevents the further diffusion of oxygen in the air to the inside and protects the substrate. The surface oxide film is dense and stable, so it can prevent further oxidation. Therefore, the alloy with 25% Mn content exhibits the most excellent oxidation resistance.

DFT-CEF Approach for the Thermodynamic Properties and Volume of Stable and Metastable Al–Ni Compounds

The Al–Ni system has been intensively studied both experimentally and theoretically. Previous first-principles calculations based on density-functional theory (DFT) typically investigate the stable phases of this system in their experimental stoichiometry. In this work, we present DFT calculations for the Al–Ni system that cover stable and metastable phases across the whole composition range for each phase. The considered metastable phases are relevant for applications as they are observed in engineering alloys based on Al–Ni. To model the Gibbs energies of solid phases of the Al–Ni system, we combine our DFT calculations with the compound energy formalism (CEF) that takes the Bragg–Williams–Gorsky approximation for the configurational entropy. Our results indicate that the majority of the investigated configurations have negative energy of formation with respect to Al fcc and Ni fcc. The calculated molar volumes for all investigated phases show negative deviations from Zen’s law. The thermodynamic properties at finite temperatures of individual phases allow one to predict the configurational contributions to the Gibbs energy. By applying a fully predictive approach without excess parameters, an acceptable topology of the DFT-based equilibrium phase diagram is obtained at low and intermediate temperatures. Further contributions can be added to improve the predictability of the method, such as phonons or going beyond the Bragg–Williams–Gorsky approximation that overestimates the stability range of the ordered phases. This is clearly demonstrated in the fcc order/disorder predicted metastable phase diagram.

Investigation the Effect of Titanium on Adhesive Wear and Hardness of NiAl-Y2O3 Composite Material

In the present study, the nickel aluminide NiAl-based composite, reinforced with yttrium oxide Y2O3 with addition of titanium, was prepared by sintering at 1350 °C for one and a half hours under argon gas atmosphere. Brinell hardness test was carried out according to (ASTM E140 – 12b). Titanium addition leads to an increase in hardness of (NiAl-Y2O3) composite. The increase in hardness is mainly due to increased NiAl-Y2O3 mechanical resistance when titanium is added by the solid-state solution strengthening, as well as by the high density (5.7514 g/cm3) and very low porosity (1.93%) of the final samples. The addition of 2 wt % Ti to the NiAl compound increases the hardness of the compound material (90NiAl-10Y2O3) to 295 HB and then increases to 330 HB by adding 2.5 wt. % Ti and continues to increase to 378 HB by adding (3 wt. % Ti). Wear test is carried out to find the wear characteristics of the composites developed by powder metallurgy route. The results revealed that the addition of titanium leads to a decrease in the wear-rate of NiAl-Y2O3. Addition of 2 wt. % Ti to (70NiAl-30Y2O3) leads to a reduction in adhesion-wear rate from (7.611 * 10−6 g/cm) to (5.81* 10−6 g/cm) and to (5.47*10−6 g/cm) by adding 2.5 wt. % Ti. The adhesion-wear ratio continues to decrease to 4.77 * 10−6 g/cm by adding 3 wt. % Ti.

MODELING OF STRUCTURE FORMATION PROCESS IN INTERMETALLIC NiAl ALLOYS DURING THERMOCHEMICAL PRESSING

Mathematical model aimed at obtaining NiAl alloys with a given structure and properties is proposed and implemented, based on the use of data on the features of the physical modeling of the thermochemical pressing process. For a mathematical description of the process of extrusion of a high-temperature synthesis product, it is necessary to determine a system of equations that takes into account the distribution of the thermo-kinetic and rheological properties of the synthesis product in a mold and caliber. High-temperature synthesis of intermetallic compound NiAl in a powder mixture of pure elements in the conditions of thermochemical pressing allows to obtain an intermetallic alloy with an average grain size of ~ 40—50 microns.

Microstructure and mechanical properties of Ni-Al intermetallic thin coatings produced by magnetron sputtering

In the present study the thin NiAl intermetallic foils formed on different types of substrates by magnetron sputtering technique were investigated. To provide the deposition of intermetallic NiAl compound in one step without additional heat treatment the composite targets assembled from parts of Al and Al plates were used. The structure of formed thin NiAl coatings was studied using scanning electron microscopy and X-ray diffraction analysis. Mechanical properties were assessed by nanohardness indentation and wear testing of deposited coatings. During sputtering the distance from the target to the substrates varied from 60 to 100 mm to estimate the effect of this parameter on structure and properties of the coatings. The results revealed that thin coatings sputtered at the closer distance from the target to the substrates had the higher hardness about 11 GPa and exhibited the high level of wear properties.

The role of Si on solidification behaviour of the NiAl intermetallic cladding produced by the GTAW process

ABSTRACT In this research, the role of Si on the solidification behaviour of NiAl cladding produced by the GTAW process was studied. NiAl and Ni2AlSi compounds were synthesised by mechanical alloying. The produced powders were cladded on the surface of CK45 steel using the GTAW process. Phase evolutions, microstructural changes and fractography of the produced powders as well as the cladded layers were characterised by X-ray diffraction, optical microscopy and scanning electron microscopy methods. After cladding of Ni2AlSi powder mixture, in the first pass of this coating, only NiAl phase and in the second pass, only (Ni,Si)Al intermetallic compounds were formed. For ternary coating, a narrow area including cellular solidification mode was seen at fusion boundary which transformed to equiaxed dendritic solidification mode. Fractography analysis of the claddings revealed that by the addition of Si into NiAl lattice, brittle fracture changed to more ductile fracture with ‘eggcrate-type’ appearance, indicating solidification cracking.

Phase transformations in nickel- and titanium-based alloys during chemical heat treatment

The structure of surface areas and cores of Ni-40Cr-4Al and Ti-6Al-5V alloys in the process of thermal and chemical heat treatment - nitriding, oxidation and carburizing was studied by X-ray diffractometry, optical microscopy and hardness measurement. Ni-40Cr-4Al alloy after quenching contains two supersaturated solid solutions based on fcc-Ni and bcc-Cr and a small amount of compound Ni3Al; subsequent aging leads to decrease in the degree of supersaturation of fcc-Ni and increase in the amount of bcc-Cr and Ni3Al. Nitriding leads to the formation of continuous CrN layer 3-4 µm thick on the surface, decomposition of Ni3Al and formation of AlN in underlying layer 100-140 µm thick. After nitriding high microhardness value of CrN (up to 1060 HV) and a slight decrease from 740 to 650 HV in the subsurface layers due to the transformation of Ni3Al to AlN were found. The surface layer of Ti-6Al-5V alloy is oxidized by erosion cutting in water, but the oxides formed during this process do not influence on subsequent diffusion saturation. During nitriding, oxidation, carburizing of Ti-6Al-5V alloy, diffusion layers are formed. They are characterized by the increased amount of α-solid Ti solution and formation of the surface intermediate phases. The thickness of the hardened layers is 8-20 μm. The hardness of these layers is 1000 HV for oxidation, 1000 HV for nitriding, 570 HV for carburizing.

Microstructure and mechanical properties in the solid-state diffusion bonding joints of Ni3Al based superalloy

Directional solidification (DS) of intermetallic compounds Ni3Al based superalloys were joined by solid-state diffusion bonding (SSDB) with the joining interface perpendicular to the solidified direction. The joining process was conducted with a 4 μm pure Ni interlayer at 1100 °C under 15 MPa for 2–7 h. The results showed that the microstructure characteristics of the SSDB joints, microvoids, tiny carbides, a higher volume fraction of γ′ phase and high angle grain boundaries (HAGB) formed in the interlayer region, were significantly different from that of the base metal (BM). The joint of the best mechanical property, strength of 926 MPa and elongation of 7.2%, was produced by the bonding time of 7 h owing to the decrease of the microvoids and the large carbides with the bonding time increasing. However, the relative (ratio between the joint and the BM) tensile strength of the joint was merely 90% due to the existence of high angle grain boundaries (HAGB) generated after the recrystallization of the interlayer. Moreover, because microvoids were not vanished completely and the strain mismatch caused by the structure of the interlayer region, the hard center region (higher volume fraction of γ′ phase) and soft interface region (lower volume fraction of γ′ phase), so the stress concentration were produced between the joint and the BM under the tensile load. Therefore, the relative elongation of the SSDB joint was only 57%.

Regularities of the influence of temperature and pressure on the grain size in the synthesized intermetallic compound Ni3Al

The intermetallic compound Ni3AI (γ′-phase, ordered solid solution) is the main strengthening phase of nickel superalloys is, the content of which in modern superalloys reaches up to 0.89. The efficiency of the intermetallic phase as a heat-resistant component in large part limited by low ductility and by strength in a wide temperature range accordingly. An increase in strength limit of the intermetallic component is possible with a decrease in grain size less than a critical value, less than 10 microns. Application of the known methods of plastic deformation for refining an intermetallic grain is almost impossible, but it is physically justified in the period of the grain structure nucleation under non-equilibrium conditions of the exothermic reaction of an intermetallic compound formation in a powder mixture of nickel and aluminum. The retention of low-dimensional grain structure in the synthesized intermetallic compound is possible with combining the processes of crystallization and compaction of the high-temperature synthesis product. This paper presents the results of investigation of the influence of high-temperature synthesis product deformation on the formation of a grain structure in a Ni3Al intermetallic compound synthesized under pressure.

Influence of the Thermal-force Effect on the Process of High-temperature Synthesis of the Ni3Al Intermetallic Compound

In this work, the intermetallic compound Ni3Al was obtained by high-temperature synthesis under pressure at various values of the preliminary pressure on the initial powder mixture (3Ni+Al). The study of pressure-time and displacement-time diagrams gave a coherent picture of the synthesis passage over time. It was found that an increase of preliminary pressure leads to a decreasing of the powder compacts porosity. In this regard, the smallest displacement of the press plunger after initiating the synthesis reaction in the powder compact was observed at the highest value of the preliminary pressure on the compact. The role of preliminary pressure on the initial powder mixture in the process of the grain structure formation of the Ni3Al intermetallic compound synthesized under pressure was determined.

Peculiarities of a NiAl/Mo Transition Zone Formed during Self-Propagating High-Temperature Synthesis

Abstract—This work has demonstrated the possibility of joining (“welding”) a coating of intermetallic compound NiAl to an Mo substrate using the self-propagating high-temperature synthesis (SHS) method, without melting the Mo substrate. It has been revealed that an intermediate layer is formed between the Mo substrate and the welded NiAl coating. The main component of this layer is a cellular rod-like pseudobinary NiAl–Mo eutectic consisting of branched Mo threads 200 nm thick and of a NiAl matrix. It has been found that the microhardness of the Mo/NiAl transition layer is higher (2860 MPa) than that of the welded NiAl coating (2360 MPa) and of the Mo substrate (1830–1990 MPa). This indicates the occurrence of a strengthening of the NiAl intermetallic compound owing to the dissolution of Mo in it and to the formation of a pseudobinary NiAl–Mo eutectic and of Mo nanoprecipitates in the NiAl dendrites. Upon mechanical fracture of the sample, the Mo threads in the eutectic cells undergo significant plastic deformation. Using the selective chemical etching method in a mixture of HCl + H2O2, Mo-based structural components in the form of branched bundles of threads with a thickness of about 200 nm and a length of up to 300 μm have been separated.

The assessment of growth kinetics in the intermetallic layers of Al-AlxNiy-Ni laminate composites

Ni aluminides have technologically attracted much attention as oxidation protective layers on Ni-superalloys for high-temperature and harsh environments applications as well as for reinforcements in metal-matrix composites. Among the Ni aluminides, the AlNi compound exhibits the best combination of oxidation-protective characteristics and hardness; thus there is a progressive demand to produce it particularly through convenient in-situ fabrication processes. Therefore, the evaluation of growth kinetics in AlxNiy layers is of crucial importance in determining an optimum compound formation process. To this purpose, Al-Ni intermetallic laminate composites were produced through cold roll bonding and subsequent annealing of aluminum and nickel sheets. The microstructure of the intermetallic layers was investigated in order to specify the controlling mechanisms and subsequently the growth model of the different phases. The Al3Ni layer was kinetically the first to appear but started to decompose at the expense of the AlNi compound when the direct source of Al disappeared for the reactive diffusion couples. The Al3Ni layer growth was initially controlled by bulk diffusion, but then at T≥525°C was modified as a function of competition between formation and consumption, whereas the AlNi growth was governed strongly by the interfacial reaction. The time dependence of the growth rate revealed different behaviors of linear and parabolic kinetics. The overall assessment revealed a bulk diffusion-controlled growth for all of the intermetallic layers. Arrhenius parameters could be derived for the Al3Ni layer, while it was impossible for the AlNi phase because the formation of this layer was caused by a mixture of diffusion mechanism.

Structural, electronic, elastic and thermodynamic properties of Al1-xZxNi (Z=Cr, V and x= 0, 0.125, 0.25) alloys: First-principle calculations

The AlNi intermetallic compound is one of the most promising engineering materials for high temperature applications. Unfortunately, this compound has low tensile ductility at high temperature which limit its functional applications. We show that alloying the AlNi compound with the Cr or V will improve its tensile ductility and therefore its industrial applications. In this paper, the structural, electronic, elastic and thermodynamic properties of Al1-xZxNi (Z = Cr, V and x = 0, 0.125, 0.25) alloys have been studied by the first principles calculations in the framework of density functional theory. The calculated formation energy and cohesive energy of the alloys show that, all alloys have stable structures. The valence charge density distribution study reveals that, chemical bonds between the Z and Ni atoms in the alloys have the nature of covalent, which improve the brittleness of the AlNi alloys. The calculated Pugh’s ratio (or the Poisson’s ratio), shear and bulk modules show that, the increasing of hardness by increasing the x. Moreover, the ductility of the alloys decreased when the value of x is nonzero. The calculation results show that the Pugh’s (Poisson’s) ratio is higher than 1.75 (0.26), indicating a ductile nature of these alloys. Furthermore, thermodynamic properties of the alloys including Grüneisen parameter, thermal expansion coefficient, bulk modulus, Debye temperature and constant volume heat capacity have been investigated and discussed under different pressures and temperatures.

Demonstration of low-temperature toluene degradation mechanism on hydrotalcite-derived oxides with ultrasonic intervention

A series of transition binary metal oxides were derived from Mg-Al, Ni-Al and Co-Al hydrotalcite-like compounds (HTLCs) with the intervention of ultrasound during the crystallization process, and the toluene removal rate of the hydrotalcite-derived oxides (HTOs) was investigated. The results of the toluene oxidation test showed that the conversion efficiency of ultrasonic intervened samples was higher than those of untreated samples. Focus solely on the elements difference, the conversion efficiency of CoAl-HTO is the highest among all samples, followed by NiAl-HTO, and MgAl-HTO is the lowest for both ultrasonic-treated and untreated samples. However, the conversion efficiency of ultrasonic treated NiAl-HTO (T90 = 275 °C) is higher than that of untreated CoAl-HTO (T90 = 300 °C) but still lower than that of treated CoAl-HTO (T90 = 270 °C), inferred the positive influence of the ultrasonic intervention to the HTOs on toluene degradation. The properties of those samples were characterized by XRD, XPS, SEM, H2-TPR and physisorption equipment. The characterization results showed that the better toluene degradation ability might be attributed to the more reactive Co2+ and abundant oxygen vacancies exposed on the sample’s surface which revealed by the ultrasonic intervention, as well as the large surface area and the high Oads/Olatt. This work provided novel evidence for the influence of ultrasonic intervention on the material surface modification and toluene degradation which corresponding to the Mars-van Krevelen mechanism.

The Influence of Vacancy Concentration of Low-Stability Pre-Transitional Structural-Phase States and Energy Characteristics of NiAl Intermetallide

Using the Monte Carlo method, the influence of vacancy concentration on the structural-phase states and energy characteristics is investigated by the example of an intermetallic compound NiAl in the course of its heating and cooling. According to the analysis, the availability and concentration of vacancies are important factors in the pre-transitional low-stability structural-phase states prior to transformation. On the one hand, neither the vacancies nor their concentration affect the temperature ranges of structural-phase transformations, on the other hand, they essentially influence both the pre-transitional low-stability structural-phase states and the rate of diffusion processes. The temperature behavior of the short-range order parameter suggests that the higher the vacancy concentration (i.e., system’s defectiveness), the higher the temperatures at which the tendencies for increasing atomic ordering would be manifested due to intensified diffusion. This, in turn, evidences of a higher starting structural transformation temperature with an increase in the number of defects in the alloy during cooling. An analysis of the temperature curves of the long-range order parameter of the NiAl intermetallide allows making a conclusion that an increased vacancy concentration (i.e., the alloy’s defectiveness) gives rise to a logical result – decreased long-range ordering in the system in the region of low-stability pre-transitional states and increased starting transformation temperature.

Structural-Phase Features of Low-Stability Pre-Transitional States of BCC-Alloys with Complexes of Planar Defects (Antiphase Boundaries)

Using the Monte Carlo method, the influence of the complexes of antiphase boundaries (APBs) (a pair of shear APBs and a pair of thermal APBs) on the low-stability, pre-transitional states of BCC-alloys is considered by the example of a conventional copper alloy CuZn and an intermetallic compound NiAl. It is shown that in the region of low-stability structural-phase states the energy of formation of a complex of thermal APBs is higher than that of shear APBs. The contribution of APBs into disordering is appreciable up to the structural-phase transition temperature. The most significant factor in terms of the long-range order is the formation of the defect itself; the differences in the APB type or the plane of their occurrence do not so much affect the longrange order behavior with the temperature variation. The type of APBs however appreciably affects the structural-energy characteristics of the system at the temperatures below the phase transformation temperature. Logically, a system with structural defects is less ordered than a defect-free system. The presence of a defect favors the onset of disordering at lower temperatures: it starts at lower temperatures in the case of thermal APBs (TAPBs) compared to shear APBs (TAPBs). In a BCC-system with a complex of TAPBs the first signs of disordering invariably appear near the phase boundary in the neighborhood of large atoms (Zn–Zn in the CuZn alloy or Al–Al in the NiAl intermetallide). In the alloy with a complex of shear APBs the distortion of ordering at low temperatures is observed in the regions where the boundaries cross. The presence of antiphase boundaries affects the alloy stability under heating. It is shown that disordering is accompanied by smearing of the boundaries and their faceting. It follows from a comparative analysis of the peculiarities of disordering in the BCC-system under study (classical alloy CuZn and intermetallide NiAl) under conditions of higher temperatures in the region of low-stability, pre-transitional states that the order – disorder phase transition in the CuZn alloy takes place as a result of disordering of the system, while in the intermetallide NiAl the change of long-range order results from the structural-phase transition.