Crystal NiAl Research Articles

Enhanced mechanical properties of Ni3Al composites reinforced with single-walled and multi-walled carbon nanotubes: An atomistic modeling study

In this study, the mechanical properties of a Ni3Al matrix composite reinforced with single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) were investigated using atomistic modeling. The analysis focused on the behavior of the composite under uniaxial tensile strain across a range of temperatures (100–900[Formula: see text]K). The results demonstrated that the incorporation of any type of carbon nanotubes (CNTs) significantly enhanced Young’s modulus, yield strength, and tensile strength of the Ni3Al matrix. Notably, the reinforcement with MWCNTs resulted in superior mechanical properties compared to SWCNTs. Additionally, an increase in temperature led to a reduction in Young’s modulus for all composite samples. Among the tested configurations, the composite reinforced with MWCNTs exhibited the highest tensile modulus and yield strength, outperforming both the SWCNT-reinforced composite and the unreinforced Ni3Al crystal. These findings underscore the potential of MWCNTs as effective reinforcements in improving the mechanical performance of Ni3Al-based composites, especially at elevated temperatures.

Effects of alloying elements on the super-lattice intrinsic stacking fault energy and ideal shear strength of Ni3Al crystals

The effects of alloying elements (Re,W,Ti,Ta,andMo) on the super-lattice intrinsic stacking fault energy and ideal shear strength (σmax) of Ni3Al crystals at 0 K was studied through first-principles calculation. The calculated formation enthalpy of point defects reveals that single solute atoms (i.e., Re,W,Ti,Ta,andMo) tend to occupy the Al site, while solute–solute complex defects (i.e., Re-Re, Re-W, Re-Mo, Re-Ta, Re-Ti, W-Mo, W-Ta, W-Ti, Mo-Ta, Mo-Ti, and Ta-Ti) tend to occupy the Al-Al site. The addition of single solute atom can increase the unstable stacking fault energy and ideal shear strength (σmax) of perfect Ni3Al crystals. Therefore, the doping of a single solute atom is beneficial for the creep strengthening of Ni3Al crystals. Compared with the doping of W,Ti,Ta,andMo, the doping of Re can more effectively impede the nucleation and movement of dislocations of Ni3Al crystals. Through the careful comparison of the creep properties of Ni3Al crystals with solute–solute complex defects, a conclusion can be drawn that the doping of alloy elements W and Re exhibit similar strengthening effects on the creep properties of Ni3Al crystals. W can be preliminarily predicted to replace part of Re in Ni3Al crystals without affecting creep properties. In addition, comprehensive evaluation reveals that the weak interaction between solute–solute complex defects should improve the strengths of Ni3Al crystals to a certain extent.

Crystal plasticity modeling of non-Schmid yield behavior: from Ni3Al single crystals to Ni-based superalloys

A crystal plasticity finite element (CPFE) framework is proposed for modeling the non-Schmid yield behavior of L12 type Ni3Al crystals and Ni-based superalloys. This framework relies on the estimation of the non-Schmid model parameters directly from the orientation- and temperature-dependent experimental yield stress data. The inelastic deformation model for Ni3Al crystals is extended to the precipitate (γ′) phase of Ni-based superalloys in a homogenized dislocation density based crystal plasticity framework. The framework is used to simulate the orientation- and temperature-dependent yield of Ni3Al crystals and single crystal Ni-based superalloy, CMSX-4, in the temperature range 260–1304 K. Model predictions of the yield stress are in general agreement with experiments. Model predictions are also made regarding the tension–compression asymmetry and the dominant slip mechanism at yield over the standard stereographic triangle at various temperatures for both these materials. These predictions provide valuable insights regarding the underlying (orientation- and temperature-dependent) slip mechanisms at yield. In this regard, the non-Schmid model may also serve as a standalone analytical model for predicting the yield stress, the tension–compression asymmetry and the underlying slip mechanism at yield as a function of orientation and temperature.

Excitation of Soliton-Type Waves in Crystals of the A3B Stoichiometry

Using the method of molecular dynamics and taking Ni3Al and Pt3Al as examples, crystals of the A3B composition are considered for the possibility of excitation of soliton-type waves in them. The potentials obtained by the embedded-atom method were used to describe interatomic interactions. It is shown that the harmonic external stimulus can excite waves of the soliton type in a Pt3Al crystal, but not in Ni3Al. Such compression–expansion waves are generated because of excitation of discrete breathers with soft nonlinearity that cannot exist in a Ni3Al crystal near the affected region. The detected waves are capable of propagating to thousands of nanometers along the Pt3Al crystal without losses of integrity and speed. The shape of the obtained wave corresponds to the kink solution of the sine-Gordon equation. The aggregate amount of energy transferred by a wave is determined by the number of rows of atoms involved in fluctuations; this may involve dozens and hundreds of electron volts.

Возбуждение волн солитонного типа в кристаллах стехиометрии A-=SUB=-3-=/SUB=-B

In the work, using the molecular dynamics method, the crystals of composition А3В are considered, for example Ni3Al and Pt3Al, for the possibility of excitation of soliton-type waves in them. To describe the interatomic interactions, the potentials obtained by the immersed atom method were used. It is shown that under a harmonic external action, excitation of soliton-type waves is possible in a Pt3Al crystal, but not in Ni3Al. The occurrence of such compression-extension waves is due to the excitation near the zone of action of discrete breathers with a soft type of nonlinearity, the existence of which is impossible in a Ni3Al crystal. The detected waves can propagate thousands of nanometers along a Pt3Al crystal without any loss of shape or speed. The shape of the received wave corresponds to the kink solution of the sin-Gordon equation. The total amount of energy carried by the wave is determined by the number of rows of atoms involved in the oscillations, we can talk about tens and hundreds of electron volts

Coating in the Ni-Al system using the SHS method

Using the method of self-propagating high-temperature synthesis, coatings based on aluminum nickelides were obtained. The processes occurring in the layers of a powder mixture of nickel and aluminum are studied. The influence of the coating thickness and the degree of dilution of the powder mixture with aluminum oxide on the maximum temperature of the combustion wave and the rate of its propagation is established. The coating consists of small crystals of NiAl, Ni3Al, fused together. The coating has good electrical conductivity and can be used as electric heaters.

Fracture toughness evaluation of NiAl single crystals by microcantilevers—a new continuous J-integral method

Abstract

Atomistic simulations of the nanoindentation-induced incipient plasticity in Ni3Al crystal

In this work, the indentation-induced incipient plasticity of Ni3Al crystal is investigated by performing molecular dynamics (MD) simulations. Simulation results reveal that the incipient plasticity of Ni3Al is originated from the homogeneous nucleation of the 1/6〈112〉-type Shockley partial dislocation. The critical load, critical contact pressure, dislocation nucleation site and active slip system are significantly affected by crystallographic orientation, model size, indenter radius and temperature. The choice of interatomic potential has significant implications for the indentation behavior of Ni3Al. Some benchmarks for evaluating the credibility of interatomic potentials are presented. The pop-in phenomena are correlated with dislocation generation, multiplication and reactions. The formation mechanisms of complex stacking faults (CSFs), antiphase boundaries (APBs) and superlattice intrinsic stacking faults (SISFs) are clarified. The highest indentation modulus is obtained in (111) indentation followed by the (110) and (100) cases. The indentation modulus and the depth of nucleation sites increase with increasing indenter radius but the maximum shear stress decreases. The maximum shear stress and indentation modulus decrease linearly with increasing temperature, reflecting the stress-assisted and thermally activated nature of dislocation nucleation.

Nanoindentation of NiAl and Ni3Al crystals on (100), (110), and (111) surfaces: A molecular dynamics study

Molecular dynamics simulations were performed to study the nanoindentation of NiAl and Ni3Al crystals on three surfaces: (100), (110), and (111). The calculated load-displacement curves show discrete drops at certain indentation depths, indicating dislocation bursts during indentation. The hardness values for the two materials were found to depend significantly on the indented crystallographic plane: the (100) surface is the softest for NiAl and the hardest for Ni3Al. We also found distinctive deformation activities in the subsurface region in Ni3Al crystals, while dislocation loops propagate deep into the substrate in NiAl systems.

Microstructure evolution and mechanical properties of Ni3Al/Al2O3 composite during self-propagation high-temperature synthesis and hot extrusion

The Ni3Al/Al2O3 composite was fabricated by self-propagation high-temperature synthesis with and without hot extrusion methods. Its microstructure and mechanical properties were investigated by using combination of optical microscope, transmission electron microscope and compression test. The results show that the Ni3Al/Al2O3 composite without hot extrusion has relative coarse microstructure, which contains γ-Ni and Ni4Al3 phases along the Ni3Al phase boundary. In addition, κ-Al2O3, θ-Al2O3, α-Al2O3 and cavities are observed in the composite without hot extrusion, which segregate greatly in original powder boundary. The hot extrusion process densifies the composite; eliminates the element segregation and redistributes Al2O3 particles homogeneously. Moreover fine Ni3Al crystalline with high density of dislocations and twinned Ni3Al crystals are observed in the extruded part. The hot extrusion improves the mechanical properties of the Ni3Al/Al2O3 composite significantly, especially its ductility.

Microstructure and mechanical properties of Ni 3Al and Ni 3Al–1B alloys fabricated by SHS/HE

The well-densified Ni 3Al alloys without and with boron addition were fabricated by self-propagation high-temperature synthesis and hot extrusion (SHS/HE) technology. Microstructure investigation showed that Ni 3Al and Ni 3Al-1B alloys contained fine grain structure. Analysis of X-ray spectra as well as transmission electron microscopy studies revealed that three phases present in all alloys: γ-Ni, Ni 3Al and dispersoids of α- Al 2O 3 and γ- Al 2O 3. However, β-NiAl, Ni 3B phase and twinned Ni 3Al crystal are observed in the Ni 3Al-1B alloy. In addition, dislocations with high density exist in all alloys. The mechanical test showed that the B addition leads to obvious improvement in yield strength and compressive ductility, and compared with the ones synthesized by combustion, SHS/HE synthesized Ni 3Al and Ni 3Al-1B alloys exhibit more excellent mechanical properties.

Positron annihilation study of the influence of doping on the 3d electron states in the Ni3Al intermetallic compound

The 3d electron states in Ni3Al single crystals doped with Fe, Co, and Nb have been investigated using angular correlation of annihilation radiation (ACAR). The ACAR spectra contain information on the momentum distribution of valence electrons and strongly bound 3d electrons of the intermetallic compound. It has been established that the positrons in the Ni3Al crystals predominantly annihilate in the nickel sublattice from delocalized states. The doping of the compound by the third element leads to a variation in the momentum distribution of Ni 3d electrons due to the change in the character of interatomic bonds. An analysis of the momentum distribution has demonstrated that the niobium atoms increase the covalent component of the chemical bond as compared to the binary compound due to the dNb-dNi hybridization. The doping with cobalt atoms also enhances the tendency toward the formation of the covalent bond. At the same time, iron atoms have a weak effect on the electronic structure of the intermetallic compound.

The hyperbolic sine relation and dip test data in constant strain rate compression experiments

Single crystals of Ni3Al, intrinsic Ge, Cu, Cu with 5at%Al and 7.5at%Al are submitted to constant strain rate compression tests and stress reduction experiments. Curves of the initial creep rate as a function of the amount of stress reduction are analysed in terms of a hyperbolic sine relation based on the thermal activation of the dislocation velocity. It is shown that this relation satisfactorily fits the curves of the two first crystals. However, this is not observed for the three last ones. Reasons for this behaviour are proposed as well as a method for the effective stress evaluation.

Equation of state of solid nickel aluminide

The pressure-volume-temperature equation of state of the intermetallic compound NiAl was calculated theoretically, and compared with experimental measurements. Electron ground states were calculated for NiAl in the CsCl structure, using ab initio pseudopotentials and density functional theory (DFT), and were used to predict the cold compression curve and the density of phonon states. It was desirable to interpolate and smooth the cold compression states; the Rose form of compression curve was found to reproduce the ab initio calculations well in compression but exhibited significant deviations in expansion. A thermodynamically-complete equation of state was constructed for NiAl, which overpredicted the mass density at standard temperature and pressure (STP) by 4%, fairly typical for predictions based on DFT A minimally-adjusted equation of state was constructed by tilting the cold compression energy-volume relation by �7GPa to reproduce the observed STP mass density. Shock waves were induced in crystals of NiAl by the impact of laser-launched Cu flyers and by launching NiAl flyers into transparent windows of known properties. The TRIDENT laser was used to accelerate the flyers, 5mm in diameter and 100 to 400µm thick, to speeds between 100 and 600m/s. Point and line-imaging laser Doppler velocimetry was used to measure the acceleration of the flyer and the surface velocity history of the target. The velocity histories were used to deduce the stress state, and hence states on the principal Hugoniot and the flow stress. Flyers and targets were recovered from most experiments. The effect of elasticity and plastic flow in the sample and window was assessed. The ambient isotherm reproduced static compression data very well, and the predicted Hugoniot was consistent with shock compression data.

Orientation dependence and tension/compression asymmetry of shape memory effect and superelasticity in ferromagnetic Co 40Ni 33Al 27, Co 49Ni 21Ga 30 and Ni 54Fe 19Ga 27 single crystals

In the present study the effects of crystal axis orientation, stress state (tension/compression) and test temperature on shape memory effect and superelasticity of Ni 54Fe 19Ga 27(I), Co 40Ni 33Al 27(II), Co 49Ni 21Ga 30(III) (numbers indicate at.%) single crystals were investigated. The shape memory effect, the start temperature of superelasticity T 1 and the mechanical hysteresis Δ σ were found to be dependent on crystal axis orientation and stress state. Superelasticity was observed at T 1 = A f ( A f, reverse transformation-finish temperature) in tension/compression for [0 0 1]-oriented Ni–Fe–Ga crystals and in compression for [0 0 1]-oriented Co–Ni–Ga crystals, which all displayed a small mechanical hysteresis (Δ σ ≤ 30 MPa). An increase in Δ σ of up to 90 MPa in the Co–Ni–Al and the Co–Ni–Ga crystals lead to stabilization of the stress-induced martensite, and an increase in to T 1 = A f + Δ. The maximal value of Δ (75 K) was found in [0 0 1]-oriented Co–Ni–Al crystals in tension. A thermodynamic criterion describing the dependencies of the start temperature of superelasticity T 1 on crystal axis orientation, stress state and the magnitude of mechanical hysteresis is discussed.

Cross-sectional TEM studies of plastic wave attenuation in shock loaded NiAl

The role of plasticity and overall shear strength of metals subjected to weak and moderate shock waves is not well understood. The plastic response of shocked metals is known to vary with applied pressure although these variations are different for each material. Weakly shocked single crystals will tend to display plastic anisotropy and anisotropic Hugoniots at least up to the overdrive pressure. In the current study, cross-section transmission electron microscopy (XTEM) has been used to elucidate these effects in single crystals of nickel aluminide (NiAl). Single crystals of NiAl (5 mm diameter) were cut and polished down to 100–300 μm along three loading directions 〈0 0 1〉, 〈1 1 0〉, 〈1 1 1〉. Each of the three samples was subjected to laser induced shocks of around 15 GPa. Cross-sectional transmission electron microscopy (XTEM) samples were extracted from shocked samples and were used to observe dislocation structures and lattice rotations with selected area diffraction patterns. Regions within 2 μm of the drive surface exhibited lattice rotation gradients up to about 1400°/mm in 〈1 1 0〉 samples. Following the first few microns, the lattice rotations were found to decay rapidly over the next 5 μm. These trends were also seen in orientation imaging microscopy (OIM) data. The lattice rotation gradients correlated well with pressure decay from 1D hydrodynamic calculations.

Deexcitation of sputtered metastable aluminum atoms

An experimental system was set up incorporating pulsed ion beam sputtering, two Nd:YAG pumped dye lasers and an imaging time-of-flight (TOF) analysis system. The system was used to perform state-selective analyses of neutral atoms sputtered from surfaces using resonant one-color and two-color ionization schemes. We have measured, for the first time, TOF mass spectra of Al atoms sputtered into the ground state 2 P 1 / 2 0 and first excited state 2 P 3 / 2 0 (with an excitation energy of 0.014 eV) from single crystals of Ni 3Al and NiAl. The population ratio of the first excited state to the ground state in the sputtered flux was estimated to be 0.91 for Ni 3Al and 0.95 for NiAl, respectively. This indicates that the magnitude of the excitation energy plays an important role even in the deexcitation rate of sputtered metastable state atoms with an open outer shell.

Two-step temperature dependence of the yield stress in crystals

The temperature dependence of the critical resolved shear stress (CRSS) of single crystals often exhibits a two-step change. On the basis of the Peierls mechanism of the dislocation glide, a two-step change can theoretically be expected for (1) a depressed-top or a flat-top Peierls potential, (2) the Peierls mechanism of a narrowly dissociated dislocation and (3) two stable core configurations with different Peierls stresses and different kink energies. In this paper, after discussing the CRSS versus T relations for bcc metals and tetrahedrally coordinated crystals, detailed discussion has been made on the two-step CRSS versus T curves reported for (1 0 0)[0 1 0] and (1 0 0)[0 0 1] slips in tetragonal β-Sn reported by Kirichenko [Phys. Met. Metallogr. 63 (1) (1987) 144] and on that reported for single crystals of NiAl with the hard orientation.

Point-defect properties of and sputtering events in the {001} surfaces of Ni3Al I. Surface and point-defect properties

Constant-area and fully relaxed molecular dynamics methods are employed to study the properties of the surface and point defects at and near {001} surfaces of bulk and thin-film Ni, Al and Ni3Al respectively. The surface tension is larger than the surface energy for all {001} surfaces considered in the sequence: Al (1005 mJ m−2)< Ni3Al (mixed Ni–Al plane outermost, 1725 mJ m−2)< Ni3Al (all-Ni-atoms plane outermost, 1969 mJ m−2)< Ni (1993 mJ m−2). For a surface of bulk Ni3Al crystal with a Ni–Al mixed plane outermost, Al atoms stand out by 0.0679 Å compared with the surface Ni atoms and, for the all-Ni-atoms surface, Al atoms in the second layer stand out by 0.0205 Å compared with Ni atoms in the same layer. Vacancy formation energies are about half the bulk values in the first layer and reach a maximum in the second layer where the atomic energy is close to the bulk value but the change in embedding energy of neighbouring atoms before and after vacancy formation is greater than that in the bulk. Both the vacancy formation energy and the surface tension suggest that the fourth layer is in a bulk state for all the surfaces. The formation energy of adatoms, antisite defects and point-defect pairs at and near {001} surfaces of Ni3Al are also given.

Deformation behavior of Ni 3Al single crystals during nanoindentation

The deformation behavior of (1 1 1), (1 1 0) and (0 0 1) oriented Ni 3Al single crystals was investigated by means of nanoindentation. Upon loading with the blunt and sharp indenter tips, the crystal deforms elastically in the initial stage followed by plastic deformation of which the onset is characterized by an obvious displacement burst (or pop-in) in the loading curve. This pop-in corresponds to homogeneous nucleation of dislocation loops under the indenter. When a sharp indenter tip was used, a major pop-in can be identified at a large load (∼7 mN for (1 1 1) crystal) in the plastic regime on loading. The major pop-in may be correlated with the special dislocation structure of the K–W locks in the Ni 3Al crystals that are formed during loading. The pop-in behavior during plastic deformation of Ni 3Al crystals is found to be closely related to the crystal orientation, pre-existing dislocation density in the sample surface, loading rate, and holding (at a constant sub-critical load) time as well. Pop-ins were also observed at critical loads in unloading processes.