Ni3Al-based Alloy Research Articles

Rotating bending fatigue behaviour of a Ni3Al-based single crystal alloy IC6SX at 760°C

The high cycle fatigue behaviour at 760°C of a Ni3Al-based single crystal alloy IC6SX has been studied in the present investigation. The specimens for the fatigue tests were prepared by screw selection crystal method in a directional solidification furnace. The rotating bending fatigue tests of the specimens was carried out at the temperature of 760°C in air, the stress ratio of R (σmax/σmin) was − 1, and the rotating speed of the fatigue tests was 6500 r min− 1 (108 Hz). The stress–fatigue life cycle (S − Nf) curve was obtained based on the fatigue tests, and the fracture surfaces were examined using scanning electron microscopy (SEM). The results showed that the fatigue cracks initiated from the surface defects of the specimens and the cracks propagated along the (111) crystal plane. The fatigue fracture was composed of three different characteristic regions corresponding to the three fatigue stages, including fatigue crack initiation stage, steady-state propagation stage and the fast propagation stage. The research results also showed that the rotating bending fatigue performance of alloy IC6SX is superior to that of the second-generation single crystal nickel-based superalloys containing 3 wt-% Re.

Phase-field study on the pre-precipitated phase of ordered intermetallic compounds in binary and ternary Ni–Al base alloys

The pre-precipitation processes of ordered intermetallic compound L12 (Ni3Al) in binary Ni–14.0at.%Al alloy, L12 (Ni3Al) and DO22 (Ni3V) in ternary Ni–Al–V alloy were studied using the microscopic phase-filed dynamic model. It is found that prior to the formation of L12 or DO22 ordered phase, a pre-precipitated phase appears first. For the binary alloy, Ni atoms aggregate on (002) plane and deplete on (001) plane, Al atoms aggregate on (001) plane and deplete in (002) plane, the pre-precipitated phase is L10 phase. For the ternary alloy, if the DO22 ordered phase appears first, Ni atoms aggregate on (002) plane and deplete on (001) plane, the aggregation and ordering of V atoms on (001) plane are faster than those of Al atoms, the pre-precipitated phase is L10 (M=1) phase; if the L12 ordered phase appears first, Ni atoms aggregate on (002) plane and deplete on (001) plane, the aggregation and ordering of Al atoms on (001) plane are faster than those of V atoms, the pre-precipitated phase is L10 phase.

Synergetic Lubricating Effect of WS2 and Ti3SiC2 on Tribological Properties of Ni3Al Matrix Composites at Elevated Temperatures

The tribological behaviors of the Ni3Al-WS2-Ti3SiC2 composites and synergistic effect of composite solid lubricants are investigated from room temperature to 800°C. The results show that the Ni3Al matrix composites (NASC) exhibit excellent tribological properties throughout the test temperatures compared to Ni3Al-based alloy. The excellent tribological properties of NASC are attributed to the synergistic lubricating effect of WS2 and Ti3SiC2. A lubricating film could be formed below 400°C, and an oxidation protection film is formed above 400°C on the worn surface of NASC during the sliding process, leading to low coefficients of friction (0.18–0.39) and wear rates (1.5–3.7 × 10−5 mm3N−1m−1).

Effect of directional solidification on the structure and properties of Ni3Al-based alloy single crystals alloyed with Cr, Mo, W, Ti, Co, Re, and REM

Effect of directional solidification on the structure and properties of Ni3Al-based alloy single crystals alloyed with Cr, Mo, W, Ti, Co, Re, and REM

Thermal conductivity of Ni3V–Ni3Al pseudo-binary alloys

The effect of changes in the composition and microstructure of the Ni3V–Ni3Al pseudo-binary alloys on their thermal conductivity has been investigated. For Ni3V and Ni3Al-based single-phase alloys, the thermal conductivity shows a maximum value at the stoichiometric compositions, and it decreases as the V (or Al) content of the Ni3Al (or Ni3V) alloy increases, following the Nordheim rule. For Ni3V–Ni3Al two-phase alloys, the thermal conductivity of the constituent Ni3Al phase exhibits a smaller value than that of the Ni3V phase. Eventually, the thermal conductivity of the two-phase alloys decreases as the Al content increases because of the increase in the volume fraction of the Ni3Al phase with low conductivity. As the temperature increases from 293 K to 1073 K, the conductivity increases for all of the alloys but not for stoichiometric Ni3V. However, the dependence of the thermal conductivity on the alloy composition between 293 K and 1073 K is similar. Hence, it is confirmed that the thermal conductivity of the Ni3V–Ni3Al pseudo-binary alloys is controlled by the composition and volume fraction of the constituent phase.

Analysis of the Effect of the Wearing Type on Surface Structural Changes of Ni<sub>3</sub>Al-Based Intermetallic Alloy

Results of an analysis of effect of wearing type on surface structural changes of a Ni3Al intermetallic alloy, are shown in the present paper. A microstructure evaluation was carried out by Quanta 3D FEG field emission gun scanning electron microscope (FEG SEM) equipped with an integrated EDS/WDS/EBSD system. The Ni3Al-based intermetallic alloy with an addition of boron, zirconium and chromium was examined. The investigated material had γ’ single-phase, ordered solid solution structure with 20 μm grain size. An electron backscatter diffraction (EBSD) method was applied to visualize surface structural changes upon an abrasive, a cavitational and a tribological wearing of the material.An observation of surface layer after the abrasive wear was carried out on samples examined in loose abradant by T-07 tester and according to GOST 23.2008-79 norm. An analysis of cavitational wear on changes in the near surface area of Ni3Al-based alloy was performed on an impact-jet stand. Observed structural changes were described based on results of the SEM/EBSD complex structural examination and hardness measurements. It was found, that the EBSD is an effective and sensitive method that allows estimating surface strain introduced during analyzed wearing types.

Differential speed rolling of Ni3Al based intermetallic alloy—Analysis of the deformation process

Results of the first principles study on applying of a differential speed rolling (DSR) to a processing of the Ni3Al-based intermetallic alloy have been shown in the present paper. Obtained samples were free of cracks and shape defects, what indicates that selected parameters of the DSR method are suitable for the processing of Ni3Al intermetallics. It was also found that, the differentiation of rolling speed results with a prominent reduction and stabilization of the rolling force value during a rolling pass, and causes an increase of the imposed strain and a linear rise of the strain rate. Additionally, the DSR processed samples were characterized by a higher mechanical strength than the material deformed with an equal speed of both rolls.

Study of the properties and the choice of alloys for bladed disks (blisks) and a method for their joining

The choice of materials for the bladed disks (blisks) that are intended for next-generation aviation gas turbine engines is grounded. As blade materials, single crystals of light heterophase γ′ + γ VKNA-type alloys based on the γ′(Ni3Al) intermetallic compound with an ordered structure are proposed. The choice of novel deformable EP975-type nickel superalloys, which are intended for operation at 800–850°C, as the disk material is grounded. It is shown that the most effective method for forming one-piece joints of an Ni3Al-based alloy and a high-alloy EP975-type nickel superalloy is the new process of solid-phase pressure welding under conditions of high-temperature superplasticity. Solid-phase joints are formed for heterophase Ni3Al-based alloy single crystals and deformable EK61 and EP975 nickel alloys. The gradient structures in the zone of the solid-phase joints that form under the conditions of low- and high-temperature superplasticity at homologous temperatures of ∼0.6T m and 0.9T m are studied. The character and direction of the diffusion processes at the joint of an intermetallic alloy single crystal and a deformable polycrystalline alloy are determined.

Effect of directional solidification on the structure and properties of Ni3Al-based alloy single crystals alloyed with W, Mo, Cr, and REM

The effect of the solidification rate (R = 2, 5, 10, 20 mm/min) at the same solidification gradient (G = 150°C/cm) on the structural parameters of single-crystal blade workpieces made of an alloy based on the γ′(Ni3Al) intermetallic compound and alloyed with cobalt and rhenium apart from chromium, molybdenum, titanium, and rare-earth metal microadditions is studied. The single crystals have a dendritic-cellular structure. Primary γ′-phase precipitates are observed in the interdendritic space of heterophase γ′ + γ dendrites. An increase in the solidification rate from 2 to 20 mm/min at a solidification gradient of 150°C/min leads to refinement of all structural constituents by a factor of 1.5–2, with the morphology and the mutual position of the structural constituents being independent of the solidification rate. In experiments with moderate additional alloying with cobalt and rhenium, the yield strength increases by 10–20% and the long-term strength increases by at least 20–25% at a temperature of 900 and 1100°C upon holding for 100 and 500 h. The VKNA-25 alloy single crystals have moderate plasticity (δ = 6–20%) over the entire temperature range (20–1200°C) and have no sharp increase in the plasticity characteristic of a VKNA-1V alloy without cobalt and rhenium. During long-term tests, local raft structure regions misoriented with respect to the tension direction form in γ′ + γ dendrites. γ′-Phase nanoparticles precipitate in the γ layers. During tests, refractorymetal-rich nanoparticles of a predominantly acicular-lamellar shape precipitate in dendrite arms.

Effect of the method of producing Ni3Al-based alloy single crystals on the macro- and microhomogeneity of component distribution, structure, and properties

The mechanisms of hardening heterophase Ni3Al-based cast alloys, which are thermally stable natural eutectic composites, are studied in the operating temperature range. The distribution of basic and alloying elements and impurities in macrovolumes along the height of a charge billet prepared in a vacuum induction furnace is analyzed. The effect of the deviation of the axis of intermetallic alloy single crystals from the 〈111〉 orientation on their mechanical properties is considered. It is shown that the deviation from this orientation within 2.5°–5.4° does not affect the short-term strength characteristics and substantially affects the ductility characteristics of the single crystals. The effect of the method of introducing basic components and refractory reaction- and surface-active alloying elements in the alloys on the structure-phase state of Ni3Al-based alloys and their service life is investigated.

Effect of thermal fatigue on the structure and properties of Ni3Al-based alloy single crystals

The effect of thermal fatigue during tests of 〈001〉 and 〈111〉 single crystals according to the schedules 100 ai 850°C, 100 ai 1050°C, 100 ai 1100°C at a peak-to-peak stress Δσtc = 700–1000 MPa (sum of the maximum tensile and compressive stresses in a thermal cycle) on the structure, the fracture, and the fatigue life of an Ni3Al-based VKNA-1V alloy is studied. It is found that, at 103 thermal cycles, the 〈111〉 single crystals have the maximum thermal fatigue resistance at the maximum cycle temperature of 850 and 1050°C, and the properties of the 〈001〉 and 〈111〉 samples are almost the same at the maximum thermal cycle temperature of 1100°C. After thermal cycling at the maximum temperature of 850°C, the γ layers in the two-phase γ′ + γ region in dendrites remain a single-phase structure, as in the as-cast material, and the layer thickness is 100–150 nm. When the maximum thermal cycle temperature increases to 1050 or 1100°C, the discontinuous γ-phase layers in the γ′(Ni3Al) matrix change their morphology and become shorter and wider (their thickness is 300–700 nm). The nickel-based supersaturated solid solution in these layers decomposes with the formation of secondary γ′(Ni3Al)-phase (γ′sec) precipitates in the form of cuboids 50 and 100 nm in size at the maximum cycle temperature of 1050 and 1100°C, respectively. The alternating stresses that appear during thermal cycling cause plastic deformation. As in nickel superalloys, this deformation at the first stage proceeds via the slip of screw dislocations along octahedral {111} planes. Networks of 60° dislocation segments form at γ′/γ interfaces in this case. Fracture begins at the lines of intersection of the slip planes of the {111} octahedron with the sample surface. During fractional, a crack passes from one octahedral plane to another and forms terraces and steps (crystallographic fracture); as a result, the fracture surface bends and becomes curved. In all cases, the fracture surfaces have a mixed brittle-ductile character with a combination of crystallographic and ductile (dimple) fracture elements.

Structure of a Welded Joint of Directedly Crystallized Metal Based on Ni3Al

The structure of a welded joint obtained by argon-arc welding with the use of a composite electrode wire of a Ni3Al-base alloy after directed crystallization is studied. It is shown that the use of composite electrode wire containing nanoparticles of tungsten carbide for argon-arc welding promotes formation of a quality weld metal and a defect-free transition zone between the latter and the directedly crystallized alloy based on Ni3Al.

Fabrication of Ni–Al nanoparticles via vacuum arc plasma evaporation and their catalytic properties for CO oxidation

Ni–Al nanoparticles were fabricated from Ni3Al-based alloys using vacuum arc plasma evaporation, and their catalytic activities for carbon monoxide (CO) oxidation were examined. The synthesized nanoparticles were characterized in detail using synchrotron radiation X-ray diffraction analyses, scanning transmission electron microscopy, and surface area measurements based on nitrogen adsorption. The as-fabricated nanoparticles were composed of Ni, Ni3Al, and a small amount of NiAl, with Al2O3 and NiO phases formed on their surfaces. The nanoparticles exhibited a much higher activity than that of a conventional atomized Ni3Al powder. It was found that the Ni phase is oxidized to NiO during CO oxidation, while the Ni3Al phase remains unchanged. It is likely that the NiO phase serves as the active species for CO oxidation, and the Ni3Al and Al2O3 phases serve as supports for the NiO phase.

Hot Corrosion Behavior of a Ni3Al-Based IC21 Alloy in a Molten Salt Environment

Ni3Al-based alloys have become important candidates for hot components in turbine engines, owing to their low densities and outstanding mechanical properties in service environments. The hot corrosion behavior of a Ni3Al-based IC21 alloy in a molten salt environment of 75 wt% Na2SO4 and 25 wt% NaCl at 900 °C was studied, via oxidation kinetics analyses, scanning electron microscope observations and energy dispersive as well as diffraction analyses by X-ray. A multilayer corrosion oxide scale and dendritic morphology internal corrosion zone formed after hot corrosion, and inter-phase selective corrosion phenomena were also observed. Salt fluxing and oxidation-sulfidation processes were inferred to be the essential hot corrosion mechanisms of the alloy. Moreover, additions of Cr and Y proved to be beneficial to the hot corrosion resistance of the IC21 alloy, while the Mo content should be strictly controlled.

Hot Deformation Behavior of Ni3Al-based Alloy MX246A

The hot deformation behavior of homogenized Ni3Al-bascd alloy MX246A has been characterized on the basis of its flow stress variation obtained by isothermal constant true strain rate compression testing on the MTS 810 machine in the temperature range of 1150–1225 °C and strain rate range of 0.001–0.1 s−1. Microstructural observation revealed striped secondary γ′ phase which was vertical to compression axis, and precipitation of fine ternary γ′ phase. The amount of striped secondary γ′ phase reduced and that of fine ternary γ′ phase increased with increasing temperature and decreasing strain rate. The material exhibited peak stress followed by flow softening, but no obvious steady-state flow behavior. Microstructural investigations have shown no dynamic recrystallization happened. TEM studies indicated that the flow softening was controlled by dynamic recovery mechanism.

Yield anisotropy and tension/compression asymmetry of a Ni3Al based intermetallic alloy

In order to investigate the yielding behavior of the newly developed Ni3Al-based intermetallic alloy IC10, yield stresses have been measured in tension and compression with different orientations. The specimens were cut from a sheet with different angles inclined from the solidification direction. The inclined angles were taken to be 0°, 22.5°, 45°, 67.5° and 90°. All experiments were conducted at room temperature except for orientation 0°, whose deformation temperatures ranged from 298 to 1273K. Experimental results show that the yield strength of alloy IC10 has the anomalous behavior which has been observed for other Ll2-long-range ordered intermetallic alloys, but it is less pronounced. The abnormalities show the following characteristics: (i) the yield strength increases as the temperature is raised below the peak temperature, (ii) yield strength anisotropy, (iii) tension/compression asymmetry. Compared to Ni3Al single crystals, the polycrystalline exhibits some different yielding behaviors which may be due to the high volume fraction of γ phase.

Heat Treatment of a Ni<sub>3</sub>Al-Based Single Crystal Alloy IC32

C32 is a new type of Ni3Al-based single crystal alloy, which has been designed to serve at 1200. The effect of heat treatment on the microstructure of single crystal superalloy IC32 was investigated. The microstructure after heat treatment under different solution and aging temperature was examined by using optical microscope (OM), scanning electron microscopy (SEM) and electron probe microscopic analyzer (EPMA). The as-cast microstructure of IC32 consisted of a two-phase γ/γ microstructure, and primary bulky γ phase which priciptated in the interdendritic region. The incipient melting temperature of IC32 is 1360, and the heat treatment window is about 40. Considering high contents of refractory elements Re and Ta, a complicated 18 hours solution heat treatment at different temperatures was conducted to elimate the segregation and dissolove the primary bulky γ phase. The optimum heat treatment of IC32 alloy is 1325/4h+1335/4h+1345/10h, ac + 1165/2h, ac + 870/32h, ac.

Effect of Cr and Re on the Oxidation Resistance of Ni<sub>3</sub>Al-Base Single Crystal Alloy IC21 at 1100

The oxidation kinetic curves of three Ni3Al-based single crystal alloys (IC21, IC21C and IC21CR) with different Cr and Re content were examined at 1100. The microstructures and element distributions of the oxide scales on these alloys were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectrometry (EDS). Results revealed that the oxidation resistance of these alloys was improved in the order of IC21 < IC21C < IC21CR. The oxide products of IC21 mainly consisted of NiO, α-Al2O3, NiAl2O4 and a small amount of NiMoO4 and MoO2. The volatilization of Mo oxides led to the oxide scale spallation from IC21C, thus deteriorated the oxidation properties. While for IC21C and IC21CR, the oxidation resistance was significantly improved. The Mo oxides in the oxide layer were greatly reduced and a continuous α-Al2O3 layer was formed.

First-principle calculation of yield stress anomaly of Ni3Al-based alloys

This paper studies the impact of 5d transition metals Re and Pt on yield stress anomaly of Ni3Al-based alloys by evaluating the anisotropy ratio for the APB energies using first principles calculations. The completely relaxed {111} and {100} APB energies of the Ni3Al-based alloys are calculated. It is found that alloying element Re prefers to occupy the Al site, but Pt prefers to occupy the Ni site. Both Pt and Re can increase {111} and {100} APB energies of the Ni3Al-based alloys. It is found that only when the coverage of alloying element Re or Pt in the slip plane of APBs is less than a certain critical value the anisotropy ratio for the APB energies of the corresponding alloy can meet the cross-slip condition within the Paidar–Pope–Vitek model and the yield stress anomaly can occur. The paper gives an approach which can calculate the antiphase boundary energy of the multi-component alloys. These results can provide a good reference to selection, preparation and application of the Ni3Al intermetallics.

Tensile Creep Behavior of Two NiAl-Based Alloys

The tensile creep behaviors of two NiAl-based alloys (HIPed NiAl-33.5Cr-0.5Zr and DS NiAl-28Cr-5.8Mo-0.2Hf) have been investigated. The creep results indicated that the creep curves of both alloys have similar shapes, which are composed of primary creep stage, steady-state creep stage, longer accelerated creep stage, and about 25-45% creep strain. The apparent stress exponents are in the range of 4.8-7.5 and the apparent activation energies of 520-584 kJ/mol were also analyzed. The creep deformations were controlled by the sub-grain boundary formation for the HIPed NiAl-Cr(Zr) and dislocation climb for the DS NiAl-Cr(Mo,Hf). The creep rupture data of both alloys obey the Monkman-Grant relationship.