Co Effect on As-cast and Heat-Treated Microstructures in Ru-Containing Single-Crystal Superalloys

The effect of Co on the as-cast and heat-treated microstructures was investigated in two experimental Ni-based single-crystal superalloys containing low levels of Re and Ru. The experimental results indicated that increasing the Co content from 7.9 to 15.8 wt pct decreased the volume fraction of (γ + γ′) eutectic and the solidification segregation ratio of W. High levels of Co additions were also found to decrease the solvus temperatures of the γ′ phase and (γ + γ′) eutectic as well as the solidus temperature. During the long-term thermal exposure at 1373 K (1100 °C), no TCP phases precipitated in either alloy. However, the coarsening and coalescence of γ′ precipitates in the alloy containing 15.8 wt pct Co was slower than that in the other alloy with 7.9 wt pct Co. In the current study, high levels of Co additions decreased the equilibrium volume fraction of γ′ phase, leading to a change in the partitioning ratios of TCP-forming elements Cr, Mo, Re, and W between the γ and γ′ phases. This change resulted in a lower degree of elemental supersaturation in the γ matrix and improved the phase stability of the γ/γ′ microstructure. These experimental results were then compared with those obtained from multi-component thermodynamic calculations, and good agreement was observed.     

Mechanical Behavior of Three-Dimensional Braided Nickel-Based Superalloys Synthesized <Emphasis Type="Italic">via</Emphasis> Pack Cementation

Braided tubes of Ni-based superalloys are fabricated via three-dimensional (3-D) braiding of ductile Ni-20Cr (wt pct) wires followed by post-textile gas-phase alloying with Al and Ti to create, after homogenization and aging, γ/γ′ strengthened lightweight, porous structures. Tensile tests reveal an increase in strength by 100 MPa compared to as-braided Ni-20Cr (wt pct). An interrupted tensile test, combined with X-ray tomographic scans between each step, sheds light on the failure behavior of the braided superalloy tubes.     

Improvement of Creep Resistance at 950 °C and 400 MPa in Ru-Containing Single-Crystal Superalloys with a High Level of Co Addition

Microstructural features, including γ′ volume fraction and size, γ-γ′ lattice misfit, γ channel width, and dislocation substructure, are known to significantly influence the creep performance in Ni-base single-crystal superalloys. In this study, the microstructural characteristics of Ru-containing single-crystal superalloys with different levels of Co, Mo, and Ru additions were quantitatively investigated after ruptured and interrupted creep tests conducted at 1223 K (950 °C) and 400 MPa. The creep lifetime was slightly increased with the high level of Co addition and significantly increased with the coadditions of Mo and Ru. A minor effect of Co content on the γ channel width and γ′ volume fraction was found in experimental alloys. The alloy with high levels of Mo and Ru additions was determined to possess a more negative γ-γ′ lattice misfit, and a high density of stacking faults (SFs) was formed in the γ channels during creep. The combined effects of the SFs in the γ matrix serving as the barriers to dislocation movement, as well as the dense interfacial dislocation networks preventing dislocation to shear the γ′ phase, were considered as the main mechanism responsible for the improvement of creep resistance. Results from this study are helpful to understand the effect of microstructural features on creep performance and contribute to the knowledge of physical metallurgy in Ru-containing single-crystal superalloys.     

Determination of <Emphasis Type="Italic">γ</Emphasis>/<Emphasis Type="Italic">γ</Emphasis>′ Lattice Misfit in Ni-Based Single-Crystal Superalloys at High Temperatures by Neutron Diffraction

Constrained γ/γ′ lattice misfit as a function of temperature (room temperature, 871 °C, 982 °C, 1093 °C, and 1204 °C) is measured by neutron diffraction on the first-generation Ni-based single-crystal superalloy René N4 and second-generation superalloys René N5, CMSX4, and PWA1484. All the alloys studied show negative misfit at temperatures above 871 °C. For René N4, René N5, and PWA1484, the misfit becomes less negative at temperatures above 1093 °C, possibly due to either the chemistry effect or internal stress relaxation. The magnitude of the misfit shows a qualitative agreement with Caron’s misfit model based on Vegard’s coefficients. The Re-free alloy René N4 was found to have a larger γ lattice parameter and γ/γ′ misfit due to higher fractions of Cr, Ti, and Mo. After 100 hours of annealing at high temperatures, René N5 shows a more negative misfit than the misfit after the standard heat treatment.     

Microstructural Degradation and the Effects on Creep Properties of a Hot Corrosion-Resistant Single-Crystal Ni-Based Superalloy During Long-Term Thermal Exposure

In the present study, the kinetics of microstructural degradation during long-term thermal exposure (LTTE) and the effects on creep deformation mechanisms of a hot corrosion-resistant single-crystal Ni-based superalloy with a low γ′ volume fraction and γ/γ′ lattice misfit were investigated in detail. The kinetic of γ′ coarsening in the experimental alloy conforms well to the Lifshitz–Slyozov–Wagner theory during LTTE at 900 °C up to 10,000 hours. The evolution of γ/γ′ lattice misfit during the LTTE was also investigated by a first attempt. The focused research emphasized on the influences of γ/γ′ lattice misfit evolution after the LTTE on the microstructural degradation, dislocation motion, and different creep mechanisms during high-temperature low-stress creep and high-temperature high-stress creep. The results show that the decreasing of the absolute values of γ/γ′ lattice misfit and change of γ′ size and morphology after the LTTE contribute to the weakening of barrier to the dislocation cutting process into γ′ precipitates during creep and the sharp reduction of stress-rupture lifetime at 950 °C/280 MPa after 1000 hours exposure. As the applied stress decreased to 230 MPa at 950 °C, the creep mechanisms change from the dislocation cutting through γ′ precipitates at high applied stress to the dislocation glide and climb around γ′ precipitates. The dislocation glide and climb by-pass deformation mechanism were not significantly influenced by the change of γ′ precipitates morphology and magnitude of γ/γ′ mismatch within 1000 hours thermal exposure, and the minimum creep rate and creep lifetime after 1000 hours thermal exposure were similar to that of the original heat-treated samples.     

History Dependence of the Microstructure on Time-Dependent Deformation During <Emphasis Type="Italic">In-Situ</Emphasis> Cooling of a Nickel-Based Single-Crystal Superalloy

Time-dependent plastic deformation through stress relaxation and creep deformation during in-situ cooling of the as-cast single-crystal superalloy CMSX-4^® has been studied via neutron diffraction, transmission electron microscopy, electro-thermal miniature testing, and analytical modeling across two temperature regimes. Between 1000 °C and 900 °C, stress relaxation prevails and gives rise to softening as evidenced by a decreased dislocation density and the presence of long segment stacking faults in γ phase. Lattice strains decrease in both the γ matrix and γ′ precipitate phases. A constitutive viscoplastic law derived from in-situ isothermal relaxation test under-estimates the equivalent plastic strain in the prediction of the stress and strain evolution during cooling in this case. It is thereby shown that the history dependence of the microstructure needs to be taken into account while deriving a constitutive law and which becomes even more relevant at high temperatures approaching the solvus. Higher temperature cooling experiments have also been carried out between 1300 °C and 1150 °C to measure the evolution of stress and plastic strain close to the γ′ solvus temperature. In-situ cooling of samples using ETMT shows that creep dominates during high-temperature deformation between 1300 °C and 1220 °C, but below a threshold temperature, typically 1220 °C work hardening begins to prevail from increasing γ′ fraction and resulting in a rapid increase in stress. The history dependence of prior accumulated deformation is also confirmed in the flow stress measurements using a single sample while cooling. The saturation stresses in the flow stress experiments show very good agreement with the stresses measured in the cooling experiments when viscoplastic deformation is dominant. This study demonstrates that experimentation during high-temperature deformation as well as the history dependence of the microstructure during cooling plays a key role in deriving an accurate viscoplastic constitutive law for the thermo-mechanical process during cooling from solidification.     

Atomic Species Associated with the Portevin–Le Chatelier Effect in Superalloy 718 Studied by Mechanical Spectroscopy

In many Ni-based superalloys, dynamic strain aging (DSA) generates an inhomogeneous plastic deformation resulting in jerky flow known as the Portevin–Le Chatelier (PLC) effect. This phenomenon has a deleterious effect on the mechanical properties and, at high temperature, is related to the diffusion of substitutional solute atoms toward the core of dislocations. However, the question about the nature of the atomic species responsible for the PLC effect at high temperature still remains open. The goal of the present work is to answer this important question; to this purpose, three different 718-type and a 625 superalloy were studied through a nonconventional approach by mechanical spectroscopy. The internal friction (IF) spectra of all the studied alloys show a relaxation peak P₇₁₈ (at 885 K for 0.1 Hz) in the same temperature range, 700 K to 950 K, as the observed PLC effect. The activation parameters of this relaxation peak have been measured, E_a(P₇₁₈)?=?2.68?±?0.05 eV, τ₀?=?2·10^{?15 ± 1} s as well as its broadening factor β?=?1.1. Experiments on different alloys and the dependence of the relaxation strength on the amount of Mo attribute this relaxation to the stress-induced reorientation of Mo-Mo dipoles due to the short distance diffusion of one Mo atom by exchange with a vacancy. Then, it is concluded that Mo is the atomic species responsible for the high-temperature PLC effect in 718 superalloy.     

Effect of Microstructure and Alloy Chemistry on Hydrogen Embrittlement of Precipitation-Hardened Ni-Based Alloys

The sensitivity to hydrogen embrittlement (HE) has been studied in respect of precipitation size distributions in two nickel-based superalloys: Alloy 718 (UNS N07718) and Alloy 945X (UNS N09946). Quantitative microstructure analysis was carried out by the combination of scanning and transmission electron microscopy and energy dispersive x-ray spectroscopy (EDS). While Alloy 718 is mainly strengthened by γ″, and therefore readily forms intergranular δ phase, Alloy 945X has been designed to avoid δ formation by reducing Nb levels providing high strength through a combination of γ′ and γ″. Slow strain rate tensile tests were carried out for different microstructural conditions in air and after cathodic hydrogen (H) charging. HE sensitivity was determined based on loss of elongation due to the H uptake in comparison to elongation to failure in air. Results showed that both alloys exhibited an elevated sensitivity to HE. Fracture surfaces of the H precharged material showed quasi-cleavage and transgranular cracks in the H-affected region, while ductile failure was observed toward the center of the sample. The crack origins observed on the H precharged samples exhibited quasi-cleavage with slip traces at high magnification. The sensitivity is slightly reduced for Alloy 718, by coarsening γ″ and reducing the overall strength of the alloy. However, on further coarsening of γ″, which promotes continuous decoration of grain boundaries with δ phase, the embrittlement index rose again indicating a change of hydrogen embrittlement mechanism from hydrogen-enhanced local plasticity (HELP) to hydrogen-enhanced decohesion embrittlement (HEDE). In contrast, Alloy 945X displayed a strong correlation between strength, based on precipitation size and embrittlement index, due to the absence of any significant formation of δ phase for the investigated microstructures. For the given test parameters, Alloy 945X did not display any reduced sensitivity to HE compared with Alloy 718 when considering high-strength conditions despite the absence of intergranular δ phase.     

γ′ Precipitation Study of a Co-Ni-Based Alloy

A Co-Ni-based alloy strengthened by γ′-(L1₂) precipitates was utilized to investigate the precipitation evolution after various cooling rates and several aging conditions. In this study, the precipitate size and volume fraction have been studied via scanning electron microscopy and transmission electron microscopy. The influence of the precipitation evolution was measured via microhardness tests. The cooling rate study shows a more sluggish γ′ precipitation reaction compared to that observed in a Ni-based superalloy. Following a rapid cooling rate, the application of appropriate double aging treatments allows for the increase of the γ′ volume fraction as well as the control of the size and distribution of the precipitates. The highest hardness values reach those measured on supersolvus cast and wrought Ni-based superalloys. The observed γ′ precipitation behavior should have implications for the production, the heat treatment, the welding, or the additive manufacturing of this new class of high-temperature materials.     

Effect of Co on Discontinuous Precipitation Transformation with TCP Phase in Ni-based Alloy Containing Re

The effect of Co on discontinuous precipitation (DP) transformation involving the formation of topologically close-packed (TCP) phase was investigated in three Ni-Cr-Re model alloys containing different levels of Co. One typical TCP phase, σ, was generated within DP cellular colonies along the migrating grain boundaries in experimental alloys during aging treatment. As a result of the increased solubility of Re in the γ matrix and enlarged interlamellar spacing of σ precipitates inside of growing DP colonies, Co addition suppressed the formation of σ phase and associated DP colonies. This study suggests that Co could potentially serve as a microstructural stabilizer in Re-containing Ni-base superalloys, which provides an alternative method for the composition optimization of superalloys.     

Very High Cycle Fatigue of Ni-Based Single-Crystal Superalloys at High Temperature

Very high cycle fatigue (VHCF) properties at high temperature of Ni-based single-crystal (SX) superalloys and of a directionally solidified (DS) superalloy have been investigated at 20 kHz and a temperature of 1000 °C. Under fully reversed conditions (R = ? 1), no noticeable difference in VHCF lifetimes between all investigated alloys has been observed. Internal casting pores size is the main VHCF lifetime-controlling factor whatever the chemical composition of the alloys. Other types of microstructural defects (eutectics, carbides), if present, may act as stress concentration sites when the number of cycles exceed 10⁹ cycles or when porosity is absent by applying a prior hot isostatic pressing treatment. For longer tests (> 30 hours), oxidation also controls the main crack initiation sites leading to a mode I crack initiation from oxidized layer. Under such conditions, alloy’s resistance to oxidation has a prominent role in controlling the VHCF. When creep damage is present at high ratios (R ≥ 0.8), creep resistance of SX/DS alloys governs VHCF lifetime. Under such high mean stress conditions, SX alloys developed to retard the initiation and creep propagation of mode I micro-cracks from pores have better VHCF lifetimes.     

Fracture Mode of a Ni-Based Single Crystal Superalloy Containing Topologically Close-Packed Phases at Ambient Temperature

The fracture mode of an experimental Ni-based single crystal superalloy containing topologically close-packed phases at ambient temperature was investigated by a simple and practical testing method. Microstructural investigation and compositional analyses were performed on the matching fracture surfaces of a small scale specimen after the impact experiment. It is suggested that the weak TCP/γ′ interface coherency resulted in the interfacial decohesion, which was the main fracture mode for the investigated superalloy under the impact load at ambient temperature.     

Mechanical and Microstructural Characterization of AF955 (UNS N09955) Nickel-Based Superalloy After Different Heat Treatments

The mechanical and strain-hardening behaviors of the new AF955 nickel-based superalloy were investigated through two different heat treatments. The first consisted of a solubilization with a subsequent precipitation heat treatment at 746 °C for 4 hours, while the second included an additional precipitation treatment at 621 °C for 8 hours, which further increased the AF955 yield stress by about 15 pct and the ultimate stress by about 9 pct. However, through analyzing the true stress and true strain flow curves, the Considére’s stresses of AF955 after the heat treatments were similar and the strain-hardening behaviors at high stresses were surprisingly comparable. The AF955 microstructures were observed after the two different heat treatments through transmission electron microscopy. The dimensions and volume fractions of the strengthening γ″ and γ′ particles were quantified through the imaging analysis technique, finding that there were only γ″ particles in AF955 with heat treatment at 746 °C, while with the additional heat treatment at 621 °C, there was a higher total volume fraction of the γ″?+?γ′ phases. The microstructure quantification allowed modeling of the different yield behaviors of the alloy after the heat treatments through the Orowan model for nondeformable particles and the weak coupled dislocation (WCD) and strong coupled dislocation models for deformable particles. The WCD model for deformable particles described the yield behaviors of AF955 very well after both heat treatments. Moreover, the deformability of the γ″ and γ′ particles also explained the comparable strain-hardening behaviors at high stresses of AF955 after the two different heat treatments. Although mechanical properties are correctly assumed to be key parameters for classifying materials, the analysis of true stress and true strain flow curves always should be performed to properly rationalize the mechanical behaviors of metallic alloys.     

Microstructure and Properties of Plasma-Nitrided Fe-Based Superalloy Fe-25Ni-15Cr

Fe-based superalloy Fe-25Ni-15Cr was plasma nitrided at a low temperature of 723 K (450 °C). The nitrided layer was characterized by optical microscopy (OPM) and scanning electron microscopy (SEM) and X-ray diffraction (XRD) through stepwise mechanical polishing and transmission electron microscopy (TEM). The results indicated that the double expanded austenite (γ _N1 and γ _N2) was developed on the nitrided surface. Energy-dispersive X-ray spectrum (EDS) revealed that separate expanded austenite layers with distinctly different nitrogen contents occurred: high (18.98 to 11.49 at. pct) in the surface layer and low (5.87 to 5.32 at. pct) in the subsurface. XRD analysis indicated that large lattice expansion and distortion relative to the untreated austenite of an idea face-centered-cubic (fcc) structure occurred on the γ _N1, but low expansion and less distortion on the γ _N2. No obvious lattice distortion on the γ _N1 was determined by calculating its electron diffraction pattern (EDP), except for detectable lattice expansion. Inconformity between XRD and EDP results suggested that the high compressive residual stress in the γ _N1 was mainly responsible for the lattice distortion of the γ _N1. TEM indicated that the γ _N1 layer exhibited the monotonous contrast characteristic of an amorphous phase contrast to some extent, and corresponding EDP showed a strong diffuse scattering effect. It was suggested that the pre-precipitation took place in the γ _N1 in the form of strongly bonded Cr-N clusters or pairs. Decomposition of the γ _N1 into CrN and γ occurred at the grain boundaries, and the orientation of both phases remained cubic and cubic relationship, i.e., the planes and the directions with identical Miller indices in both phases were parallel. The nitrided surface was found to have significantly improved wear resistance. Further, the nitrided surface showed no adverse effect in the corrosion resistance but slight improvement in the 3.5 pct NaCl solution.     

Morphological Stability of <Emphasis Type="Italic">δ</Emphasis>-Ferrite/<Emphasis Type="Italic">γ</Emphasis> Interphase Boundary in Carbon Steel

The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results.     

Structural heat-resistant β-NiAl + γ′-Ni<Subscript>3</Subscript>Al alloys of the Ni–Al–Co system: I. Solidification and structure

When analyzing the ternary Ni–Al–M phase diagrams, where M is a group VI–VIII transition metal, we chose the Ni–Al–Co system, where the γ′ and γ phases are in equilibrium with the β phase, as a base for designing alloys with the following physicochemical properties: a moderate density (≤7.2 g/cm³) and satisfactory heat resistance at temperatures up to 1300°C. The structure formation in heterophase β + γ′ alloys during directional solidification is studied. It is found that, in contrast to cobalt-free β + γ′ alloys (where the γ′-Ni₃Al aluminide forms according to the peritectic reaction L + β ? γ′), the alloys with 8–10 at % Co studied in this work during directional solidification at 1370°C contain the degenerate eutectic L ? β + γ. The transition from the β + γ field to the β + γ′ + γ field occurs in the temperature range 1323–1334°C, and the γ′ phase then forms according to the reaction β + γ ? γ′.     

Nano-scale Mechanical Properties and Microstructure of Irradiated X-750 Ni-Based Superalloy

This study investigates the effect of irradiation on the mechanical properties of a Ni-based superalloy, X-750. 40 MeV Ni⁺ ions were used to irradiate the X-750 up to 1 dpa with and without 5000 appm helium pre-implantation at room temperature and 400 °C. Nano-indentation hardness tests were carried out at room temperature in the depth range of 200 to 1400 nm before and after irradiation. Cross-sectional TEM observations were performed on the irradiated materials to correlate the mechanical results with the microstructural evolution. The results show that helium pre-implantation enhances the irradiation-induced hardening due to generating a high density of small cavities and promoting the formation of larger Frank loops. In addition, nano-scale mechanical tests reveal that changing the subsequent Ni ion irradiation temperature from room temperature to 400 °C, leads to changing of the mechanical response from a softening behavior to an irradiation-induced hardening. The γ′ precipitates became disordered after irradiation at room temperature, whereas the γ′-phase remained ordered during irradiation at 400 °C. The softening effect of the γ′ instability outweighed the hardening impact of irradiation-induced defects such as cavities and Frank loops, leading to a hardness reduction for the room-temperature-irradiated material. Three different obstacle-hardening models were employed to assess the individual impact of each type of defect on the material’s overall strength enhancement. Furthermore, the superposition principle was used for each model to estimate the overall irradiation-induced strengthening, which is compared to the results from the nano-hardness measurements.     

Simulation of the sulfide phase formation in a KhN60VT alloy

The conditions of the existence of sulfide phases in Fe–Ni–S alloys and four-component Fe–50 wt % Ni–0.001 wt % S–R (R is an alloying or impurity element from the TCFE7 database) systems are studied using the Thermo-Calc software package and the TCFE7 database. The modification of nickel superalloys by calcium or magnesium is shown to increase their ductility due to partial desulfurization, the suppression of the formation of harmful sulfide phases, and the uniform formation of strong sulfides in the entire temperature range of metal solidification. The manufacturability of superalloys can decrease at a too high calcium or magnesium content because of the formation of intermetallics with a low melting temperature along grain boundaries.     

Effects of N/C Ratio on Solidification Behaviors of Novel Nb-Bearing Austenitic Heat-Resistant Cast Steels for Exhaust Components of Gasoline Engines

In order to comply with more stringent environmental and fuel consumption regulations, novel Nb-bearing austenitic heat-resistant cast steels that withstand exhaust temperatures as high as 1,323 K (1,050 °C) is urgently demanded from automotive industries. In the current research, the solidification behavior of these alloys with variations of N/C ratio is investigated. Directional solidification methods were carried out to examine the microstructural development in mushy zones. Computational thermodynamic calculations under partial equilibrium conditions were performed to predict the solidification sequence of different phases. Microstructural characterization of the mushy zones indicates that N/C ratio significantly influenced the stability of γ-austenite and the precipitation temperature of NbC/Nb(C,N), thereby altering the solidification path, as well as the morphology and distribution of NbC/Nb(C,N) and γ-ferrite. The solidification sequence of different phases predicted by thermodynamic software agreed well with the experimental results, except the specific precipitation temperatures. The generated data and fundamental understanding will be helpful for the application of computational thermodynamic methods to predict the as-cast microstructure of Nb-bearing austenitic heat-resistant steels.     

Creep of Single Crystals of Nickel-Based Superalloys at Ultra-High Homologous Temperature

The creep behavior of single crystals of the nickel-based superalloy CMSX-4 was investigated at 1288 °C, which is the temperature of the hot isostatic pressing treatment applied to this superalloy in the industry. It was found that at this super-solvus temperature, where no γ′-strengthening occurs, the superalloy is very soft and rapidly deforms under stresses between 4 and 16 MPa. The creep resistance was found to be very anisotropic, e.g., the creep rate of [001] crystals was about 11 times higher than that of a [111] crystal. The specimens of different orientations also showed a very different necking behavior. The reduction of the cross-sectional area ψ of [001] crystals reached nearly 100 pct, while for a [111] crystal ψ?=?62 pct. The EBSD analysis of deformed specimens showed that despite such a large local strain the [001] crystals did not recrystallize, while a less deformed [111] crystal totally recrystallized within the necking zone. The recrystallization degree was found to be correlated with deformation behavior as well as with dwell time at high temperature. From the analysis of the obtained results (creep anisotropy, stress dependence of the creep rate, traces of shear deformation, and TEM observations), it was concluded that the main strain contribution resulted from 〈\( 0 1\bar{1} \)〉{111} octahedral slip.