Ni3Al-based Alloy Research Articles

Influences of solution cooling rate on microstructural evolution of a multiphase Ni3Al-based intermetallic alloy

In present work, a multiphase Ni3Al-based intermetallic alloy with complex components of γ'+γ dendrite comprising extremely high volume fraction (81 vol %) of γ′ phase and interdendritic β phase is investigated, the microstructure evolution and phase transformation behavior tailored by different solution cooling rates are studied by applying different cooling methods of water cooling (WC, 138 °C/s), air cooling (AC, 72 °C/s), and furnace cooling (FC, 0.05 °C/s) after solution treatment at 1200 °C for 10 h. Results show that the cubic degree, size and volume fraction of cuboidal primary γ′ as well as size of spherical secondary γ′ particles in the γ'+γ dendrite are improved by decreasing cooling rates, and the average sizes of the primary and secondary γ′ particles are found to meet logarithmic relationships with cooling rates. There are three kinds of precipitates in the interdendritic β phase resulted from different cooling methods, i.e., the rod-like Cr3C2 carbides, the semi-spherical α-Cr particles, and the long acicular γ′ precipitates. The lower cooling rate decreases the number of rod-like Cr3C2 carbides, increases the number and size of the semi-spherical α-Cr particles, and promotes the formation of long acicular γ′ precipitates in the interdendritic β-matrix. The semi-spherical α-Cr particles play the role of pinning dislocations in the β-matrix and have the orientation relationship of [‾110]α-Cr//[‾110]β-matrix. In addition, the precipitation of semi-spherical α-Cr particles in β-matrix is observed to accomplish in two sequential stages and grow in an onion-like ordered way. Stacking faults existed in partial of α-Cr particles due to the nanotwins in β-matrix. Microtwins are observed in the interdendritic β-matrix after water cooling, which have a bimodal configuration of nanotwins at the microtwinning boundaries and interior stacking faults. Besides, γ′-envelope formed between the γ'+γ dendrite and interdendritic β phase dependent on the solution cooling processes.

Thermal Stability of Ni3Al-Based Composite with Honeycomb Structure

By powder metallurgy, materials in the form of a single-phase alloy based on Ni3Al and the corresponding composite Ni3Al + W with honeycomb structure are produced. The structural unit of the composite is a round granule (mean size 25 μm) of nickel alloy surrounded by a continuous tungsten coating (thickness ~0.4 μm) applied by chemical gas-phase deposition. Compressive tests at room temperature show that the yield point of the composite Ni3Al + W at 20–1000°C exceeds that of the single-phase Ni3Al-based alloy (by a factor of as much as 1.7). However, at higher temperatures, the yield points of the alloy and composite are comparable. The unit yield point (standardized at a density of 7.8 g/cm3 for the alloy and 9.5 g/cm3 for the composite) behaves analogously. At 1300°C, the single-phase Ni3Al-based alloy exhibits solid–liquid behavior in compression. Creep tests with compression in vacuum at 1000–1200°C are conducted. By pair and parametric analysis of the creep processes according to Hollomon, regression equations for the creep rate, stress, and test temperature are obtained. The creep limit is calculated from the tolerances on the steady creep rate and its inverse. At all the test temperatures, the composite is characterized by lower creep rate (by a factor of seven) and higher creep limit (by a factor of 2.5) than for the nickel alloy on which it is based. The activation energy of creep is determined for the alloy and composite on the basis of an exponential relationship between the experimental quantities. The activation energy of creep for the nickel alloy is close to the activation energy of nickel self-diffusion in Ni3Al and materials based on it (230–310 kJ/mol). For the composite, it is close to the activation energy of tungsten self-diffusion (503 kJ/mol).

Dynamic deformations tests of Ni3Al based intermetallic alloy by using the split Hopkinson pressure bar technique

In this work, the Ni3Al-based intermetallic alloy was subjected to room temperature dynamic plastic deformation tests by using a split Hopkinson pressure bar technique. The dynamic compression processes were carried out at strain rates in the range of =(1.9x102 / 1x104 s-1). A strong impact of applied deformation conditions on microstructure and mechanical properties evolution in the examined Ni3Al intermetallic, was documented. Generally, very high maximum compressive stress values were obtained, reaching 5500 MPa for the sample deformed at the highest strain rate (i.e. ??=1x104 s-1). The results of performed SEM/EBSD evaluation point towards an occurrence of dynamic recovery and recrystallization phenomena in Ni3Al samples deformed at high strain rates.

Structural and Phase Characteristics of the Ni3Al-Based Intermetallic Alloy Fabricated by High-Gradient Directional Solidification and Selective Laser Melting

The microstructure and the phase composition of an experimental Ni3Al-based intermetallic alloy containing (wt %) 7.8 Al, 14.5 Ta, 0.9 Mo, 0.5 W, 0.5 Re, 0.15 C, and Ni for balance, which was prepared by slow (6 mm/h) high-gradient (15°C/mm) directional solidification and selective laser melting, are studied, and the lattice parameters of phases and solidus and liquidus temperatures are determined. The phase compositions of the intermetallic alloy samples prepared by these technologies are found to be identical and consist of a γ'-phase matrix and TaC carbide particles.

Solid-phase joining of the cast intermetallic Ni3Al-based alloys and wrought nickel-based superalloys via using superplastic deformation

The paper summarizes the results of solid-phase joining experiments performed for intermetallic single-crystal Ni3Al-based alloys (known as Russian VKNA-alloys) and wrought fine grained nickel-based superalloys using superplastic deformation of the wrought superalloys. For this, two single-crystal VKNA-alloys, VKNA and VKNA-25 and two Russian nickel-based superalloys, EK61 and EP975, were taken. It was shown that the formation of an ultrafine grained structure (d<1 µm) in the EK61 superalloy made it possible to obtain the solid-phase joint of EK61/VKNA under pressure welding at T = 800 °C using superplastic deformation of the nickel-based superalloy. Another nickel-based superalloy, EP975, was taken in a fine grained condition (d = 8 µm). High-quality solid-phase joints of EP975/VKNA and EP975/VKNA-25 were obtained under pressure welding at T = 1125 °C using the superplastic deformation of the EP975 superalloy. The obtained solid-state joints EP975/VKNA and EP975/VKNA-25 were subjected to heat treatment, which led to the formation of coarse γ grains in the EP975 superalloy. This also led to an increase in thickness of the γ phase interlayers up to 500 nm in both VKNA-alloys near the solid-phase joints

Diffusion induced recrystallization of Ni3Al-based alloy

The paper represents the study of the kinetics of diffusion-induced recrystallization (DIR) and its effect on the disordering and creep resistance of an alloy based on Ni3Al doped nickel aluminide. Recrystallization was observed in the Ni3Al-based alloy hardened by the particles of chromium carbides at a temperature of 1573 K due to dissolution of carbides and diffusion of chromium in the volume of grains. Recrystallization leads to a sharp decrease in the creep resistance of the alloy due to the formation of an unordered γ phase. The alloy can be used as a heat-resistant material at a temperature of not more than 1500 K.

Structure and Properties of the Solid-Phase Joints of a Wrought EP975 Nickel Alloy and a Single-Crystal Intermetallic VKNA-25 Alloy Formed by Pressure Welding at a Strain of 24% under the Superplasticity of the EP975 Alloy

Experiments on solid-phase pressure welding (PW) of a wrought EP975 nickel superalloy with a Ni3Al-based VKNA-25mono intermetallic alloy in a single-crystal state are performed under the superplasticity of the EP975 alloy, where its deformation was 24%. The structure and the phase composition of the interaction zone that forms between the materials to be joined after PW and PW followed by heat treatment are studied. The mechanical properties of the welded samples with a solid-phase joint are investigated. The ultimate tensile strength of the welded samples is shown to be 0.76 of the strength of the VKNA-25 alloy.

Tribological performance of Ni3Al matrix self-lubricating composites containing Ag prepared by laser melting deposition

For improving tribological properties of Ni3Al-based alloy, Ni3Al matrix self-lubricating composites with 10 wt% Ag are successfully fabricated by spark plasma sintering (SPS) and laser melting deposition (LMD), which are abbreviated as NAS and NAL, respectively. Tribological behavior of NAS and NAL against Si3N4 ball under constant load (12 N) and variable speeds (from 0.2 to 1.1 m s−1, 0.3 m s−1 in tolerance) are systematically investigated. The results showed that NAL exhibited lower friction coefficients (0.28–0.36) and considerable wear resistance (4.6–5.9 × 10−5 mm3 N−1 m−1) as compared to NAS. It should be noticed that the tribological performance of NAL is excellent at 1.1 m s−1, while the tribological behavior of NAS is deteriorated significantly. LMD, as a process of layer by layer deposition, results in that each layer is comprised of the freshly deposited materials and the previously solidified materials. The characteristic of LMD is particularly significant for obtaining the stable bonding between layer, leading to the improvement of good interface bonding capability between tribolayer and substrate during the sliding wear process. Furthermore, the stability of the tribolayer is favorable for the reduction of friction coefficient and wear rate. For NAS, the local exfoliation of lubricant layer and the occurrence of naked substrate at the sliding speed of 1.1 m s−1 is explainable for the poor tribological performance.

Coarsening behavior of γ′ precipitates in the γ'+γ area of a Ni3Al-based alloy

Abstract The morphological evolution and coarsening kinetics of γ′ precipitates in the γ'+γ area of a Ni3Al-based alloy during isothermal aging at temperature range of 800 °C to 1000 °C have been investigated. For the aging temperature above 900 °C, the average size of γ′ precipitates increases and the morphology of γ′ precipitates gradually changes from cuboidal to strip-like and L-shaped with increasing aging time up to 50 h. The temporal evolution of the average size of γ′ precipitates is evaluated by the experimentally measured data and it suggests that the cube rate law fits better for experimental data at the early stage coarsening, while the square rate law fits better for the later stage coarsening. Moreover, using these determined values of coarsening rate constants which determined by using a coarsening rate equation based on the LSEM model, the activation energy of the early stage and later stage coarsening have been calculated as 174.2 kJ/mol and 186.3 kJ/mol, respectively.

Microstructure and thermomechanical behavior of Heusler phase Ni2AlHf-strengthened NiAl-Cr(Co) alloy produced by HIP of plasma-spheroidized powder

This study demonstrates that homogeneous high-purity micropowders with grain size of 10–45 µm from refractory NiAl-Cr(Co)-Hf alloy can be produced by combustion elemental synthesis and further treated in a thermal plasma flow. The optimal parameters of plasma spheroidization of the synthesized powders are shown at which the resulting spherical alloy particles are characterized by high sphericity (~ 98%) and the absence of satellites or internal porosity. The spherical powders were consolidated by HIP. The alloy structure was investigated by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The fine structure and features of segregation of hardening nanoparticles of Ni2AlHf (the Heusler phase) and hafnium solid solution (ssHf) in the NiAl matrix were thoroughly studied. Furthermore, in situ examination of structural phase transformations occurring in the as-HIP NiAl-based alloy was carried out upon heating in the temperature range of 25–850 °C. The α-Cr phase nanoparticles are formed inside the NiAl grains via two different mechanisms: (1) spinodal decomposition of solid solution at 250–450 °C resulting in segregation of the Guinier-Preston zone rich in Cr and its subsequent transformation into α-Cr precipitates 25–170 nm in size; (2) heterogeneous nucleation and growth of α-Cr nanocrystallites 7–40 nm long on prismatic dislocation loops at 750–850 °C.The thermomechanical properties of the alloy were studied in the temperature range of 596–1100 °C on a Gleeble System 3800 testing system. The correlation between the thermal load and the high-temperature creep rate, as well as the temperature dependences of the Young's modulus (E), the offset yield strength (σ0.2), and the rate sensitivity coefficient (m), were ascertained. The Young's modulus (E), the ultimate tensile strength, the offset yield strength σ0.2, and the proportional limit of the alloy being examined during uniaxial compression test of a cylindrical sample at 750 °C and at true strain rate of ~ 0.01 s−1 were as high as 137.8 GPa, 682, 455 and 358 MPa, respectively.

Microstructure evolution behavior of Ni3Al (γ′) phase in eutectic γ-γ′ of Ni3Al-based alloy

Based on its excellent high-temperature performances, polycrystalline Ni3Al-based alloys have attracted more and more attention. In this work, different thermal cycle aging treatments (TCAT) were applied to investigate microstructure evolution behavior of Ni3Al (γ′) phase in eutectic γ-γ′ area of JG4246A alloy. SEM equipped with energy dispersive X-ray spectrometer (EDS) and high-resolution transmission electron microscopy (HRTEM) were used for microstructure observation and mechanism analysis. The results showed that plate-like Ni3Al (γ′) phase and twinning Ni3Al (γ′) formed in eutectic γ-γ′ area due to its initial state of the alloy and thermal cyclic aging treatment conditions. Meanwhile, blocky Ni3Al (γ′) phase precipitated along eutectic γ-γ′ area and dual phase (γ+γ′) area ((γ-γ′)/(γ+γ′)) interfaces. Vacancies and dislocations generated during short-term TCAT were responsible for the formation of plate-like Ni3Al (γ′) phases in eutectic γ-γ′ area of as-cast alloy. While, for the solution-treated alloy, dislocations and internal stress generated during long-term TCAT led to the formation of twinning Ni3Al (γ′) in eutectic γ-γ′ area and blocky Ni3Al (γ′) phase along (γ-γ′)/(γ+γ′) interface.

Formation of Gradient Structures in the Zone of Joining a Deformable Nickel Alloy and a Single-Crystal Intermetallic Alloy during Thermodiffusion Pressure Welding and Subsequent Heat Treatment

The possibility of formation of a high-quality solid-phase joint of an Ni3Al-based single-crystal intermetallic VKNA-25 blade alloy with a high-temperature deformable EP975 disk alloy by pressure welding is studied to create high-performance one-piece blisk unit for the next-generation aviation gas turbine engines and to decrease the unit mass. The influence of the conditions of thermodiffusion pressure welding under the hightemperature superplasticity of the disk alloy and the influence of heat treatment of welded joints on the gradient structures in the welded joint zone and the structure at the periphery of the welded samples are investigated.

Tribological Performance of Ni3Al Matrix Self-Lubricating Composites Containing Multilayer Graphene Prepared by Additive Manufacturing

In order to improve tribological performance of Ni3Al-based alloy, Ni3Al matrix composites containing 1.5 wt.% multilayer graphene (MLG) are prepared through additive manufacturing (AM) and spark plasma sintering (SPS), which are denoted as NMAM and NMSPS, respectively. Tribological behaviors of NMAM and NMSPS against Si3N4 balls are researched under constant speed (0.2 m/s) and varied loads (from 4 to 16 N) for evaluating the tribological properties of NMAM and NMSPS. The results present that NMAM exhibits the excellent tribological properties [low friction coefficients (0.26-0.40) and considerable wear resistance (2.8-4.6 × 10−5 mm3 N−1 m−1)] as compared to NMSPS, which attributes to the uniform enrichment of MLG with properties of high tensile strength and being easily sheared off on the worn surfaces. Owing to the use of spherical prealloyed powder containing multilayer graphene and the characteristics of layer by layer depositing in the AM process, NMAM has a more compact and uniform substrate, which persistently provides a source of the formation of continuous and stable frictional layer. Due to the characteristics of AM rapid solidification, NMAM has the small grain size and well-compacted microstructure, which can effectively reduce the probability of spalling wear and lead to the increase in wear resistance of materials. The research can offer the reference for self-lubricating materials prepared by AM technology.

First-principles modeling of superlattice intrinsic stacking fault energies in Ni3Al based alloys

High-throughput quantum mechanics based simulations have been carried out to establish the change in lattice parameter and superlattice intrinsic stacking fault (SISF) formation energies in Ni3Al-based alloys using the axial Ising model. We had direct access to the variation in SISF energies due to finite compositional change of the added ternary transition metal (TM) element through constructing large supercells, which was equally necessary to account for chemical disorder. We find that most added TM ternaries induce an important quasi-linear increase in the SISF energy as a function of alloying composition x. The most pronounced increase corresponds to Fe addition, while Co addition decreases the SISF energy monotonically. Our results shed light on the role played by TM elements on strengthening L12 Ni3Al precipitates against stacking fault shear. The data are of high importance for designing new Ni-based superalloys based on computational approaches.

Increase of the Durability of the Ni3Al-based alloy Piercing Plug on Account of Reinforcing Particles

В данной работе слитки изготавливались методом выплавки электродов в открытой индукционной электрической печи СЭЛТ-20С/20 с последующим их электрошлаковым переплавом как с добавлением армирующих частиц молибдена в кристаллизатор методом равномерной подсыпки во время переплава, так и без добавления. Для выплавки использовались чистые шихтовые материалы без добавления отходов. Армирующие частицы молибдена были получены измельчением заготовок молибдена марки МШ-1 (ТУ 48-19-73-86) в планетарной мельнице. В результате проведения работы методом открытой индукционной выплавки было получено четыре электрода сплава на основе Ni3Al. Первые два электрода (№ 1 и 2) были подвергнуты стандартному электрошлаковому переплаву (ЭШП), а вторые два электрода (№ 3 и 4) были подвергнуты ЭШП с добавлением в кристаллизатор во время переплава порошка молибдена. Из всех полученных слитков были изготовлены прошивные оправки, которые испытывались при прошивке прутков коррозионно-стойкой стали марки 08Х18Н10Т-Ш. При помощи оправок, изготовленных из слитков № 1 и 2, было прошито 7 и 6 прутков соответственно, а при помощи оправок из слитков № 3 и 4 было прошито 11 и 12 прутков соответственно. Полученные результаты показали, что возможно повысить стойкость оправок из сплава на основе интерметаллида Ni3Al при прошивке прутков из стали марки 08Х18Н10Т-Ш на 76 % за счет повышения жаропрочных характеристик сплава армирующими частицами из порошка молибдена, вводимыми в процессе проведения ЭШП.

The effect of long term high temperature annealing on twinning and detwinning of the wrought Ni3Al-based alloy

The effect of annealing at 1180°C from 10 to 40h on a wrought Ni3Al-based alloy was investigated using EBSD, SEM and TEM. We characterized the grain boundary character distribution (GBCD) of the annealed alloy and found that the frequency of Σ3 twin boundaries (TBs) decreased with the long term exposure. Both twinning and detwinning proceeded in the post-recrystallized microstructure during the thermal hold. The 10-hour annealing resulted in the highest frequencies of Σ3 TBs and the high order TBs. Σ3 TBs evolved into twin junctions via meeting of bulging corner twins and colliding of the nonparallel twins. With prolonged annealing, detwinning prevailed, shown by the decreasing frequency of Σ3 TBs, with simultaneous increase of fraction of substructured grains and subgrain boundaries (SGBs). Detwinning occurred via disintegration of primary twins, and dissociation of secondary microtwins/nanotwins that leads to partial formation of SGBs.

Precipitation and growth behavior of mushroom-like Ni3Al

Precipitation and growth behavior of mushroom-like Ni3Al phase along the dual phase (γ+γ′) and eutectic γ−γ′ area interfaces of as-cast JG4246A Ni3Al-based alloy were investigated by using short time cyclic heat treatment. Results showed that vacancies, small angle grain boundaries and dislocations formed along the dual phase (γ+γ′) and eutectic γ−γ′ area interfaces during the cyclic heat treatment, which promoted the precipitation of Ni3Al phase along this location. In addition, concentration gradient of Al elements between the eutectic γ−γ′ area and dual phase (γ+γ′) areas and the more rapid pipe diffusion provided by dislocations contributed to growth of directional mushroom-like Ni3Al phase.

Tribological Performance of Ni3Al Matrix Self-Lubricating Composites Containing Multilayer Graphene and Ti3SiC2 at Elevated Temperatures

The application of Ni3Al-based alloy (NA) in the field of aerospace was limited by its poor tribological properties. For improving the tribological performance of NA, multilayer graphene (MLG) and Ti3SiC2 were added in Ni3Al matrix composites. Tribological behavior of Ni3Al matrix composites containing 1.5 wt.% MLG and 10 wt.% Ti3SiC2 (NMT) against Si3N4 ball at 12 N-0.2 m/s from 25 to 750 °C was investigated. The results showed that NMT exhibited the excellent tribological behavior [lower friction coefficients (0.26-0.57) and less wear resistance (3.1-6.5 × 10−6 mm3 N−1 m−1)] due to synergetic effect of MLG and Ti3SiC2 over a wide temperature range from 25 to 750 °C. At 25-350 °C, part of MLG enriched on worn surface could play a role in reducing friction and improving wear resistance. At 350-550 °C, although MLG gradually lost the lubricating properties, the partial decomposition of Ti3SiC2 could continually improve the tribological properties of NMT. At 550-750 °C, Ti3SiC2 on worn surface was oxidized to form lubricating film, while Ti3SiC2 in the subsurface played an important role in supporting the film, resulting in the excellent high-temperature tribological performance. The research had good guiding significance for the preparation of wide temperature range self-lubricating material and the study of synergetic effect of complex solid lubricants.

Effects of frictional heat on the tribological properties of Ni3Al matrix self-lubricating composite containing graphene nanoplatelets under different loads

In order to analyze the effects of frictional heat on the tribological performance of Ni3Al matrix self-lubricating composite containing 6.2 vol.% graphene nanoplatelets (NB), the dry sliding friction tests of Ni3Al-based alloy and NB against GCr15 steel ball are undertaken under different loads from 3 to 18 N. The effects of different amount of frictional heat on the friction and wear mechanism of NB are also studied. The results show that tribological performance of NB is better than that of Ni3Al-based alloy under same working conditions. The addition of graphene nanoplatelets promotes the formation of stable glaze layer on worn surface. In addition, graphene nanoplatelets enhance the thermal conductivity of NB, which makes the surface temperature of wear scar of NB in a proper range (about 413 ℃) at 13 N and avoids the serious friction and wear caused by the accumulation of frictional heat. At 13 N, NB shows the lower friction coefficient (0.32) and wear rate (3.6 × 10−5 mm3·N−1·m−1). It is attributed to the appropriate local temperature (about 413 ℃) of worn surface, resulting in the formation of stable glaze layer with good friction reducing and wear resistance on worn surface. This study was meaningful for optimizing applied loads to realize the appropriate frictional heat and good tribological behavior of NB.

Microstructure and mechanical properties of Ni3Al intermetallics prepared by directional solidification electromagnetic cold crucible technique

The present work focused on the Ni3Al-based alloy with a high melting point. The aim of the research is to study the effect of withdrawal rate on the microstructures and mechanical properties of directionally solidified Ni-25Al alloy. Ni3Al intermetallics were prepared at different withdrawal rates by directional solidification (DS) in an electromagnetic cold crucible directional solidification furnace. The DS samples contain Ni3Al and NiAl phases. The primary dendritic spacing (λ) decreases with the increasing of withdrawal rate (V), and the volume fraction of NiAl phase increases as the withdrawal rate increases. Results of tensile tests show that ductility of DS samples is enhanced with a decrease in the withdrawal rate.