Ni3Al-based Alloy Research Articles

Deformation behavior and processing maps of Ni3Al-based superalloy during isothermal hot compression

To study the hot deformation behavior of Ni3Al-based alloy, hot compression tests were conducted in the temperature range of 1050–1250 °C with the strain rates from 0.01 to 10 s−1. With the increase in deformation temperature and the decrease in strain rate, flow stress of the Ni3Al-based alloy would be decreased. Based on the obtained constitutive equation, the calculated values of peak flow stress are in good agreement with the experimental ones, and the activation deformation energy is determined as 802.71 kJ/mol. Moreover, by dynamic material model (DMM), processing maps of the hot-deformed Ni3Al-based alloys are established. It is indicated that the optimum processing parameters for the studied alloy correspond to deformation temperature of 1250 °C and strain rates from 0.01 to 0.1 s−1. Specimens deformed under the optimum processing conditions exhibit fine and uniform grains, which is a typical dynamic recrystallization (DRX) microstructure. The DRX degree could be effectively enhanced with the increase of deformation temperature and the decrease of strain rate.

Cyclic oxidation behavior of Ni3Al-based single crystal alloy IC21

In this study, the cyclic oxidation tests of the Ni3Al-based single-crystal superalloy IC21 were carried out at 800, 900, 950, 1000, 1050 and 1100 °C in air. The present study shows that the complex oxide scale on the surface of the alloy is made up of an outer columnar NiO layer, an intermediate mixture of NiO and NiAl2O4 layer with a small amount of Mo oxides and an inner continuous layer of α-Al2O3. The cyclic oxidation kinetics curves show that oxidation resistance at 800, 900, 950, 1000 and 1050 °C seems to follow a similar law and is better than that at 1100 °C. The overall weight changes at 1100 °C follows a parabolic law. Spallation and severe rumpling of the oxide scale are observed on the surface of the alloy at 1100 °C, revealing the occurrence of disastrous oxidation.

Tribological performance of NiAl alloy containing graphene nanoplatelets under different velocities

In this study, the friction and wear behavior of NiAl alloy containing graphene nanoplatelets (NG) under different sliding velocities were investigated. NG shows the better tribological performance, if compared to NiAl-based alloy without graphene nanoplatelets (NA). In the range of sliding velocities varying from 0.2 to 1.2 m/s, the formation of glaze layer in NG could be easily distinguished. The beneficial effect of graphene nanoplatelets (GNPs) for the formation of glaze layer of NG is obvious, if compared to NA, resulting in the reduction of friction and improvement of wear resistance of NG. Moreover, a suitable higher sliding velocity will be better for the formation of glaze layer, but the wear rate will gradually increase with the increase of sliding velocity. It can be concluded that GNPs hold great application prospect as an effective solid lubricant to improve the tribological performance of NiAl alloys.

Modeling of θ → α alumina lateral phase transformation with applications to oxidation kinetics of NiAl-based alloys

In the present work, a physical model has been developed to predict the growth of Al2O3 scale, which involves the thickening of metastable transient θ-Al2O3 phase and finally thermodynamically stable α-Al2O3 phase, accompanied by the concurrent θ→α-Al2O3 phase transformation. Based on nucleation and growth theory, the phase transition kinetics and alumina growth were modeled for both isothermal and continuous heating paths. Using this model, the phase transformation kinetics, evolution of grain size and Al2O3 scale thickness can be predicted for a given thermal path. A new scaling parameter has been proposed that quantitatively reveals the relative significance of nucleation and grain growth to the overall phase transformation kinetics. Predictions based on the model are in good agreement with the experimental observations. Limitations of the model are also presented and discussed.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ТЕРМИЧЕСКОЙ ОБРАБОТКИ НА МИКРОСТРУКТУРУ, ПАРАМЕТРЫ ДЕНДРИТНОЙ ЛИКВАЦИИ И ВРЕМЯ ДО РАЗРУШЕНИЯ ИНТЕРМЕТАЛЛИДНОГО РЕНИЙСОДЕРЖАЩЕГО СПЛАВА НА ОСНОВЕ Ni3Al

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ТЕРМИЧЕСКОЙ ОБРАБОТКИ НА МИКРОСТРУКТУРУ, ПАРАМЕТРЫ ДЕНДРИТНОЙ ЛИКВАЦИИ И ВРЕМЯ ДО РАЗРУШЕНИЯ ИНТЕРМЕТАЛЛИДНОГО РЕНИЙСОДЕРЖАЩЕГО СПЛАВА НА ОСНОВЕ Ni3Al

The hot deformation behavior and processing map of powder metallurgy NiAl-based alloy

Abstract

Experimental Investigation and CALPHAD Assessment of the Eutectic Trough in the System NiAl-Cr-Mo

NiAl-based alloys are promising candidates for high-temperature structural applications but their use is restricted by the limited mechanical properties. However, an improved performance can be achieved by strengthening the NiAl matrix with embedded fibers of refractory metals, such as Cr and Mo. Such composites can be manufactured in-situ by directional solidification of alloys with eutectic composition. For these processes the location of the eutectic trough in the NiAl-Cr-Mo system has to be known. The determination of the respective compositions was achieved by combining experimental investigations with computational thermodynamics. Thus, a series of melts in the NiAl-Cr-Mo system were prepared and their microstructures were investigated after solidification. The information on the primary phases was used to model the liquidus surface of the system NiAl-Cr-Mo using the CALPHAD approach. For this purpose, the thermodynamic datasets of the respective sub-systems from the literature have been combined into a quaternary database. The database will be used in the development of NiAl-based alloys for directional solidification. The dataset allows the calculation of the eutectic temperatures, the phase fractions and further thermodynamic properties along the eutectic trough. The present dataset will provide a reliable description for the NiAl-Cr-Mo system, but other regions of the Al-Cr-Mo-Ni system have an inferior representation.

Fabrication of the Ni3Al-based alloy formed by spark plasma sintering of VKNA powders

The material based on Ni3Al intermetallic has been obtained from the industrial powder of a VKNA type by the method of spark plasma sintering. Materials sintering was conducted at the temperature of 1100 °C, compacting pressure of 20 MPa, and during soaking time equal to 5 minutes. The heating rate of samples amounted to 50 and 200 °C/min. It has been established that the material obtained by sintering at the rate of 50 °C/min possesses a maximum value of density (5.93 g/cm3) and a maximum level of bending strength (~ 400 MPa).

Experimental investigation and thermodynamic re-assessment of the Al–Mo–Ni system

NiAl-based alloys have been investigated, because they are promising alternative materials for high temperature structural applications. Recent advancements in directional solidification offer the opportunity to manufacture metal-matrix composites of NiAl strengthened by embedded fibers of refractory metals such as Mo. The mechanical properties of these composites can be considerably improved, compared to NiAl, at least in fiber direction. The Al–Mo–Ni system has been thermodynamically assessed by several authors. However, none of them can reproduce a satisfactory description along the section NiAl–Mo. In the present work, liquidus and solidus temperatures of the NiAl–Mo system were measured by a laser heating-fast pyrometry apparatus. The results agree well with literature data. The thermodynamic descriptions of the Al–Ni and Al–Mo systems from the literature were refined and a new thermodynamic dataset of the Al–Mo–Ni system was established. The ordered B2 phase and its disordered A2 (bcc) parent phase were described by a single Gibbs energy function. Very good agreement between the calculated phase diagram and the experimental data is obtained. The description of the section NiAl–Mo is considerably improved and we conclude that this section does not represent a quasi-binary phase diagram.

Investigation into the influence of the remelting temperature on the structural heredity of alloys fabricated by centrifugal SHS metallurgy

The influence of the remelting temperature on the structural heredity of the alloy fabricated by centrifugal SHS metallurgy is investigated. It is shown by the example of the highly boron-alloyed NiAl-based alloy that overheating the alloy by more than 100°C (above Tm) during vacuum-induction remelting leads to substantial coarsening of the components of the SHS alloy and liquation appearance. All the samples of the alloy under study had a compositional structure consisting of the matrix of the NiAl-based substitutional solid solution, network inclusions of τ-boride (Ni20Al3B6), and dispersion inclusions of (Mo, Cr)B complex boride.

SHS Metallurgy of NiAl-Based Alloy

Highly caloric mixtures of metal oxides with reducing agents used in SHS metallurgy can burn at combustion temperatures well above the melting point of final products, which ensures formation of cast products. The data of basic research in the field allowed us to suggest methods for manufacturing new cast nickel aluminides based alloy.

Nanocrystalline Ni3Al-based alloys obtained by recycling of aluminium scraps via mechanical alloying and consolidation

Bulk nanocrystalline Ni3Al-based alloys were produced by ball milling of powdered aluminium scrap alloys (two silumines with chemical compositions: Al87.5Si7.8Cu2.1Fe0.7Zn1.4Mn0.4Mg0.1 (R1 scrap) and Al88.4Si5,7Cu3,9Fe0,9Zn0,6Mn0.5 (R2 scrap)) with addition of Ni powder and subsequent hot-pressing consolidation. The final products of mechanical alloying were consolidated at 1000°C for 180s under the pressure of 7.7GPa. The powders and the compacted samples were examined by XRD method. The results obtained show that during the milling supersaturated solid solutions Ni(Al,Si…) are formed and during the consolidation the disordered solid solutions transform into ordered nanocrystalline Ni3Al intermetallic based phases with a mean crystallite size of ∼30nm. The microhardness of the produced Ni3Al-based alloys is 955 for R1 process and 928 HV0.1 for R2 process respectively. The density of the pellets is nearly 100% of theoretical value for the Ni3Al intermetallic phase and the open porosity of the compacts is negligibly small.

МИКРОСТРУКТУРНЫЕ И ФАЗОВЫЕ ПРЕВРАЩЕНИЯ В ИНТЕРМЕТАЛЛИДНОМ СПЛАВЕ НА ОСНОВЕ Ni3Al ПОСЛЕ ВОЗДЕЙСТВИЯ ТЕРМИЧЕСКОЙ ОБРАБОТКИ И ГОРЯЧЕГО ИЗОСТАТИЧЕСКОГО ПРЕССОВАНИЯ

МИКРОСТРУКТУРНЫЕ И ФАЗОВЫЕ ПРЕВРАЩЕНИЯ В ИНТЕРМЕТАЛЛИДНОМ СПЛАВЕ НА ОСНОВЕ Ni3Al ПОСЛЕ ВОЗДЕЙСТВИЯ ТЕРМИЧЕСКОЙ ОБРАБОТКИ И ГОРЯЧЕГО ИЗОСТАТИЧЕСКОГО ПРЕССОВАНИЯ

ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ СПЛАВА НА ОСНОВЕ ИНТЕРМЕТАЛЛИДА Ni3Al ТИПА ВКНА-4УР В АДДИТИВНЫХ ТЕХНОЛОГИЯХ

ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ СПЛАВА НА ОСНОВЕ ИНТЕРМЕТАЛЛИДА Ni3Al ТИПА ВКНА-4УР В АДДИТИВНЫХ ТЕХНОЛОГИЯХ

Structural heredity of alloys produced by centrifugal SHS: Influence of remelting temperature

NiAl-based high alloy doped with boron was produced by centrifugal SHS and then subjected to remelting at several remelting temperatures (Trm) above its melting point (Tm = 1640°C) in order to elucidate the influence of Trm on structural heredity of the synthesized alloy. Induction remelting in vacuum at Trm > Tm + 100°C was found to markedly enlarge the size of structural constituents and lead to liquation. The remelting at 1740°C did not result in formation of new phases; it gave rise only to some redistribution of structural constituents The synthesized allow comprised a matrix of NiAl-based solid substitutional solution with embedded reticular inclusions of Ni20Al3B6 and lamellar (Mo,Cr)B precipitate.

Differential speed rolling of Ni3Al based intermetallic alloy – Effect of applied processing on structure and mechanical properties anisotropy

Results of the first principles study on the effect of differential speed rolling (DSR) and a post-deformation annealing on a microstructure and microtexture evolution as well related mechanical properties anisotropy and formability of Ni3Al-based intermetallic alloy, have been shown in the present paper. Results of the EBSD structure analysis and mechanical properties evaluation indicate that the application of the proposed DSR process leads to a higher stored energy of deformation (and thus a higher strain hardening) than in the case of the conventional rolling process. Consequently, a subsequent post-deformation annealing results with a greater extend of the structure restoration processes than in the case of the normal cold rolling. The formability of the investigated intermetallic was evaluated by both a calculation of Lankford parameter (the r values) and Erichsen cupping tests. It is found that the susceptibility to deep drawing of the investigated Ni3Al intermetallic alloy is much lower than that of conventional deep drawn materials (e.g. aluminum alloys or low carbon steels). Nonetheless, the Ni3Al alloy exhibited a very low planar anisotropy and the yield strength anisotropy (and thus, a low tendency to strain localization upon drawing) independently on its structure state. This behavior should be mainly attributed to its simple phase composition (the lack of “a second phase” precipitation).

Dendrite segregation in Ni3Al-based intermetallic single crystals alloyed with Cr, Mo, W, Ti, Co, and Re

The character of dendrite segregation in Ni3Al-based intermetallic VKNA-type alloy single crystals with a dendritic–cellular structure is studied. Distribution coefficient kd of an alloying element (AE) in the alloy during solidification kd = cd.a.I/c0 (c0 is the AE content in the alloy (liquid phase composition), cd.a.I is the AE content in primary dendrite arms of the alloy (in the solid phase)) and segregation coefficient ks = cd.a.I/ci.d (ci.d is the AE content in the interdendritic space) have been found. A comparative study of the dendrite segregation parameters in VKNA-nype Ni3Al-based intermetallic alloys and the well-known ZhS36-type nickel superalloy shows that the intermetallic alloys satisfy to the rule deduced for two- and three-component nickel-based superalloys: if an introduced AE increases the melting temperature of the basic metal, we have kd > 1 (Co, W, Re); if it decreases the melting temperature, we have kd < 1 (Al, Ti, Cr, Mo). Dendrite segregation coefficients ks are dependent on the proportion of the AE contents in the alloys. In nickel superalloys, the dendrite segregation of aluminum, tungsten, and rhenium is higher than that in the intermetallic alloys. The dendrite segregation coefficients of tungsten and rhenium is higher by a factor of 1.5–2 than that in the VKNA-type intermetallic alloys with a low content of refractory metals. This can be due to the retardation of diffusion of refractory metals in the solid phase of a nickel superalloy highly alloyed with these elements.

Effect of environmental sulfur on the structure of alumina scales formed on Ni-base alloys

Short-term oxidation exposures of an alumina-scale forming γ′-Ni3Al-based model alloy in air and O2+0.1%SO2 at 900°C revealed that the presence of sulfur can affect the kinetic competition between the θ and α structural isomorphs of Al2O3. After 2h exposure, metastable θ-Al2O3 growth predominated in air alone; whereas, a much larger percentage of stable α-Al2O3 formed during oxidation in O2+0.1%SO2. This promotion of α-Al2O3 establishment was due to sulfur enrichment on the alloy surface, which occurred even when samples were exposed to O2+0.1%SO2 in a low-temperature, pre-test position (∼150°C), i.e., prior to insertion into the hot zone. It was determined from XPS measurements that the sulfur was mainly in the S6+ valence state and, correspondingly, in the form of NiSO4. Cross-sectional scanning transmission electron microscopy (STEM) using energy-dispersive X-ray spectroscopy (EDS) corroborated the XPS results by detecting that a ∼20nm zone of sulfur enrichment within the surface region of a ∼90nm oxygen-rich layer formed during the pre-test exposure. A systematic explanation for this intriguing observation of sulfur promoting α-Al2O3 establishment is provided from the perspective of kinetics competition between θ and α. This explanation was supported by kinetic calculations and complementary tests in a low pO2 atmosphere.

Development and application of an apparatus for high-temperature measurement of magnetic susceptibility.

An apparatus for high-temperature measurement of magnetic susceptibility using the modified Gouy method was developed. It can be used at temperatures of up to 1200 °C. The apparatus consists of the heating system, weighing system, and temperature-programming controller. The sample should be placed at a position of relatively constant B(dB/dz) in a gradient magnetic field. Each crucible is used only once for a single measurement to reduce the error. The reliable accuracy and good repeatability of the apparatus are demonstrated by measuring the magnetic susceptibilities of a DD483 superalloy, Ni-based solid solution alloy, and Ni3Al-based solid solution alloy at various temperatures. The results also successfully explain the change in the γ' precipitation in DD483 superalloys. Therefore, the apparatus provides a convenient and powerful tool for investigating high-temperature phase transitions in the presence of a magnetic field.

Effect of Temperature on Tribological Properties and Wear Mechanisms of NiAl Matrix Self-Lubricating Composites Containing Graphene Nanoplatelets

Studies have been carried out to explore the friction and wear behaviors of NiAl matrix self-lubricating composites containing graphene nanoplatelets (NG) against an Si3N4 ball from 100 to 600°C with a normal load of 10 N and a constant speed of 0.2 m/s. The results show that NG exhibits excellent tribological performance from 100 to 400°C compared to NiAl-based alloys. A possible explanation for this is that graphene nanoplatelets (GNPs) contribute to the formation of a friction layer, which could be beneficial to the low friction coefficient and lower wear rate of NG. As the temperature increases up to 500°C, the beneficial effect of GNPs on the tribological performance of NG becomes invalid due to the oxidation of GNPs, resulting in severe adhesive wear and degradation of the friction layer on the worn surface of NG. GNPs could hold great potential applications as an effective solid lubricant to promote the formation of a friction layer and prevent severe sliding wear below 400°C.