Aging Temperature Dependence of <Emphasis Type="Italic">α</Emphasis>″-Martensite Decomposition Mechanism in Ti-Al-Fe-Si Alloy

The mechanism by which α″-martensite decomposes in Ti-4Al-4Fe-0.25Si-0.1O alloy is found to change depending on the aging temperature, with Fe-rich α first transforming in twins of α″-martensite. As the aging temperature increases, Fe is segregated at the boundaries between α″ and α. At temperatures >?773 K, the Fe-segregated boundaries provide a nucleation site for B2-structured TiFe intermetallic compounds. This process of α″-martensite decomposition is described as follows: α″?+?α″_Twin?→?α″_Fe-rich?+?α_Fe-rich,V1?→?α_Fe-lean,V2?+?α_Fe-lean,V1?+?TiFe.     

Strain-Induced Phase Transformation and Nanocrystallization of 301 Metastable Stainless Steel Upon Ultrasonic Shot Peening

The following study investigated the strain-induced phase transformation in metastable austenitic 301 stainless steels via an ultrasonic shot peening treatment (USP) for 5 to 30 minutes. Following the USP, the microhardness increased to a depth of 400 μm and from 200 to 400 HV. The deformed grains and the phase transformation were monitored via X-ray diffraction and electron backscattered diffraction analysis. The grain evolution was studied via transmission electron microscopy. Approximately 500 nm α′-martensite grains formed in the top-most region after 5 minutes of the USP treatment. The grains were then further refined to ~?100 nm when the peening time increased to 10 and 15 minutes. The grains refined down to tens of nanometers after the specimen was treated for 30 minutes, where the phases were composed of α′-martensite (~?50 nm). There was a mixture of austenite with α′-martensite (~?25 nm). The grain refinement and the phase transformation of austenite to α′-martensite during ultrasonic shot peening were systematically investigated.     

Microstructure Refinement and Mechanical Properties of 304 Stainless Steel by Repetitive Thermomechanical Processing

Repetitive thermomechanical processing (TMP) was applied for evaluating the effect of strain-induced α′-martensite transformation and reversion annealing on microstructure refinement and mechanical properties of 304 austenitic stainless steel. The first TMP scheme consisted of four cycles of tensile deformation to strain of 0.4, while the second TMP scheme applied two cycles of tensile straining to 0.6. For both schemes, tensile tests were conducted at 173 K (? 100 °C) followed by 5-minute annealing at 1073 K (800 °C). The volume fraction of α′-martensite in deformed samples increased with increasing cycles, reaching a maximum of 98 vol pct. Examination of annealed microstructure by electron backscattered diffraction indicated that increasing strain and/or number of cycles resulted in stronger reversion to austenite with finer grain size of 1 μm. Yet, increasing strain reduced the formation of Σ3 boundaries. The annealing textures generally show reversion of α′-martensite texture components to the austenite texture of brass and copper orientations. The increase in strain and/or number of cycles resulted in stronger intensity of copper orientation, accompanied by the formation of recrystallization texture components of Goss, cube, and rotated cube. The reduction in grain size with increasing cycles caused an increase in yield strength. It also resulted in an increase in strain hardening rate during deformation due to the increase in the formation of α′-martensite. The increase in strain hardening rate occurred in two consecutive stages, marked as stages II and III. The strain hardening in stage II is due to the formation of α′-martensite from either austenite or ε-martensite, while the stage-III strain hardening is attributed to the necessity to break the α′-martensite-banded structure for forming block-type martensite at high strains.     

Load Partitioning and Strain-Induced Martensite Formation during Tensile Loading of a Metastable Austenitic Stainless Steel

In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10^?2 s^?1, as compared to 10^?3 s^?1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson–Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.     

On Shear Testing of Single Crystal Ni-Base Superalloys

Shear testing can contribute to a better understanding of the plastic deformation of Ni-base superalloy single crystals. In the present study, shear testing is discussed with special emphasis placed on its strengths and weaknesses. Key mechanical and microstructural results which were obtained for the high-temperature (T?≈?1000 °C) and low-stress (τ?≈?200 MPa) creep regime are briefly reviewed. New 3D stereo STEM images of dislocation substructures which form during shear creep deformation in this regime are presented. It is then shown which new aspects need to be considered when performing double shear creep testing at lower temperatures (T?<?800 °C) and higher stresses (τ?>?600 MPa). In this creep regime, the macroscopic crystallographic [11?2](111) shear system deforms significantly faster than the [01?1](111) system. This represents direct mechanical evidence for a new planar fault nucleation scenario, which was recently suggested (Wu et al. in Acta Mater 144:642–655, 2018). The double shear creep specimen geometry inspired a micro-mechanical in-situ shear test specimen. Moreover, the in-situ SEM shear specimen can be FIB micro-machined from prior dendritic and interdendritic regions. Dendritic regions, which have a lower γ′ volume fraction, show a lower critical resolved shear stress.     

On the Prediction of <Emphasis Type="Italic">α</Emphasis>-Martensite Temperatures in Medium Manganese Steels

A new composition-based method for calculating the α-martensite start temperature in medium manganese steel is presented and uses a regular solution model to accurately calculate the chemical driving force for α-martensite formation, \( \Delta G_{\text{Chem}}^{\gamma \to \alpha } \). In addition, a compositional relationship for the strain energy contribution during martensitic transformation was developed using measured Young’s moduli (E) reported in literature and measured values for steels produced during this investigation. An empirical relationship was developed to calculate Young’s modulus using alloy composition and was used where dilatometry literature did not report Young’s moduli. A comparison of the \( \Delta G_{\text{Chem}}^{\gamma \to \alpha } \) normalized by dividing by the product of Young’s modulus, unconstrained lattice misfit squared (δ ²), and molar volume (Ω) with respect to the measured α-martensite start temperatures, \( M_{\text{S}}^{\alpha } \), produced a single linear relationship for 42 alloys exhibiting either lath or plate martensite. A temperature-dependent strain energy term was then formulated as \( \Delta G_{\text{str}}^{\gamma \to \alpha } \left( {{\text{J}}/{\text{mol}}} \right) = E\varOmega \delta^{2} (14.8 - 0.013T) \), which opposed the chemical driving force for α-martensite formation. \( M_{\text{S}}^{\alpha } \) was determined at a temperature where \( \Delta G_{\text{Chem}}^{\gamma \to \alpha } + \Delta G_{\text{str}}^{\gamma \to \alpha } = 0 \). The proposed \( M_{\text{S}}^{\alpha } \) model shows an extended temperature range of prediction from 170 K to 820 K (?103 °C to 547 °C). The model is then shown to corroborate alloy chemistries that exhibit two-stage athermal martensitic transformations and two-stage TRIP behavior in three previously reported medium manganese steels. In addition, the model can be used to predict the retained γ-austenite in twelve alloys, containing ε-martensite, using the difference between the calculated \( M_{\text{S}}^{\varepsilon } \) and \( M_{\text{S}}^{\alpha } \).     

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.     

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.     

Kinetics study on non-isothermal crystallization of Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> metallic glass

In this paper, the crystallization kinetics of melt-spun Cu₅₀Zr₅₀ amorphous alloy ribbons has been investigated using differential scanning calorimetry. Moreover, the Kissinger, Ozawa and isoconversional approaches have been used to obtain the crystallization kinetic parameters. As shown in the results, the onset crystallization activation energy E _x is less than crystallization peak activation energy E _p. The local activation energy E _α increases at the crystallized volume fraction α < 0.2 and decreases at the rest, which suggests that crystallization process is increasingly hard (α < 0.2) at first, after which it become increasingly easy (α > 0.2). The nucleation activation energy E _nucleation is greater than grain growth activation energy E _growth, indicating that the nucleation is harder than growth. In terms of the local Avrami exponent n(α), it lies between 1.27 and 8, which means that crystallization mechanism in the non-isothermal crystallization is interface-controlled one- two- or three-dimensional growth with different nucleation rates.     

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.     

Investigation of Deformation Mechanisms in Deep-Drawn and Tensile-Strained Austenitic Mn-Based Twinning Induced Plasticity (TWIP) Steel

The effect of strain on the deformation mechanisms in an austenitic Mn-based twinning induced plasticity (TWIP) steel is investigated using magnetic measurements, XRD, positron beam Doppler spectroscopy, and finite element method simulations. The experimental observations reveal the formation of $ \alpha^{\prime } $ -martensite at specific degrees of deformation, despite the high stacking fault energy (SFE) of the material (52?mJ/m²). The observed fraction $ \alpha^{\prime } $ -martensite is consistent with the estimated fraction of intersected shear bands acting as preferred nucleation sites for $ \alpha^{\prime } $ -martensite formation as a function of accumulated equivalent strain.     

Effect of Cyclic Pre-deformation on Uniaxial Tensile Behavior of Cu-16 at. pct Al Alloy with Low Stacking Fault Energy

To explore the effect of cyclic pre-deformation on static mechanical behavior of materials with different stacking fault energies (SFEs), polycrystalline Cu-16 at. pct Al alloy with a low SFE is selected as the target material in the present work, and the strengthening micro-mechanisms induced by cyclic pre-deformation are compared with the previous studies on pure Al with a high SFE and Cu with an intermediate SFE. The results show that the movement of dislocations exhibits a high slip planarity during cyclic pre-deformation at different total strain amplitudes Δε _t/2, and some nano-sized deformation twins are formed after subsequent tension. The cyclic pre-deformation at an appropriate Δε _t/2 of 1.0 × 10^?3 promotes a significant increase in ultimate tensile strength σ _UTS nearly without loss of tensile ductility, which primarily stems from the introduction of many mobile planar slip dislocations by cyclic pre-deformation as well as the formation of nano-sized deformation twins during subsequent tension. Based on the comparison of the strengthening micro-mechanisms induced by cyclic pre-deformation in Al, Cu, and Cu-16 at. pct Al alloy, it is deduced that a low-cycle cyclic pre-deformation at an appropriate condition is expected to cause a better strengthening effect on the static tensile properties of low SFE metals.     

The Influence of Heat Treatment on Nanoscale Microstructure and Crystal Orientation of 7055 Aluminum Alloy Before and After High-Speed Milling

This paper is intended to examine changes in the microstructure and crystal orientation of 7055 aluminum alloy before and after cutting. Single-factor cutting speed test was designed and implemented to investigate the influence of three heat treatment processes, T6, T87 and T815, on the microstructure and crystal orientation of 7055 aluminum alloy before and after cutting. Results showed that, before cutting, T6-state microstructure had uniform grain size with pinning in θ′ phase; T815-state grains were obviously elongated as a result of predeformation; T87-state grains also displayed some elongation, but their overall elongation was not as long as that of T815-state grains; there was a dislocation in the TEM microstructure after both T87 and T815. After cutting, T6-state initial grains were elongated; their horizontal and longitudinal sizes were 46 and 92 μm, and the low-angle boundary (LAB) and high-angle boundary (HAB) densities of T6, T87 and T815-state grains were \(1. 8 5\times 10^{ - 1}\), \(3. 2 5\times 10^{ - 2}\), \(1. 2\times 10^{ - 1}\), \(2. 2\times 10^{ - 2}\), \(2. 5\times 10^{ - 1}\) and \(4. 3\times 10^{ - 2}\) μm^?1. The crystal structure and orientation relationship of T6-state alloy after aged for 4, 8 and 12 h was θ′′, θ′, and many mixed regions of θ′′ and θ′, were observed along {001}α. After aged for 12 h, the T8-state microstructure along [001]α and [011]α was roughly the same as that after aged for 4 h, except that the share of θ′ particles along [011]α had increased from 55 to 90% while θ′′ particles along [001]α had reduced a little. After aged for 12 h, the precipitated particles of the cutting layer of T815-state alloy along [001]α were all θ′ phase while those along [011]α were composed of θ′ and Ω phases. From the boundary microstructure, before cutting, the grain boundary of T6-state alloy was a continuous one with no obvious non-precipitate zone; the grain boundary of T87-state alloy displayed some discontinuity as a result of predeformation, and quite a lot of the precipitated particles were concentrated on the boundary; the grain boundary of T815-state alloy was a discontinuous one, but the non-precipitate zone on the boundary was not as wide as that of T87-state alloy. After cutting, T6-state alloy had the widest non-precipitate zone of all at about 42 nm. The non-precipitate zone of T6-state alloy was 25 nm wide, and the particles were mainly grown θ′ particles, and θ particles incoherent to the aluminum matrix. The non-precipitate zone of T815-state alloy was the narrowest at approximately 15 nm.     

Effects of microstructural factors on quasi-static and dynamic deformation behaviors of Ti-6Al-4V alloys with widmanstätten structures

The effects of microstructural factors on the quasi-static tensile and dynamic torsional deformation behaviors in Ti-6Al-4V alloys with Widmanstätten structures were investigated in this study. Dynamic torsional tests were conducted using a torsional Kolsky bar for five Widmanstätten structures, in which microstructural parameters such as colony size and α lamellar spacing were varied by heat treatments, and then the test data were analyzed in relation to microstructures, tensile properties, and fracture mode. Under dynamic torsional loading, maximum shear stress was largely dependent on colony size, whereas shear strain at the maximum shear stress point was on colony size as well as α lamellar spacing. Adiabatic shear bands were found in the deformed area of the fractured torsional specimens, and their width was smallest in the structure whose colony size and α lamellar spacing were both large. The possibility of the adiabatic shear band formation was quantitatively analyzed in relation to microstructural factors. It was the highest in the coarse Widmanstätten structure, which was confirmed by the theoretical critical shear strain (υ _c ) condition for the adiabatic shear band formation.     

Crystallographic Orientation of the ε → α′ Martensitic (Athermal) Transformation in a FeMnAlSi Steel

The presence of athermal ε- and α-martensite (α′) in the as-cast structure of a Fe-0.08C-1.95Si-15.1Mn-1.4Al-0.017N alloy has been revealed by electron backscattered diffraction analysis. The alloy exhibited two athermal martensitic transformations described by γ → α′ and γ → ε → α′. The Shoji–Nishiyama orientation relationship was observed between γ-austenite and ε-martensite, while α-martensite nucleated from γ-austenite exhibited a Kurdjumov–Sachs orientation relationship. Six crystallographic variants of α-martensite consisting of three twin-related variant pairs were observed in ε-bands. A planar parallelism of {0001}ε || {110}α′ and a directional relation of \( \left\langle {1\bar{1} 1} \right\rangle \alpha ' \) lying within 1 deg of \( \left\langle {\bar{1} 2\bar{1} 0} \right\rangle \varepsilon \) existed for these variants.     

A micromechanical analysis of the yielding behavior of individual widmanstätten colonies of an <Emphasis Type="Italic">α</Emphasis> + <Emphasis Type="Italic">β</Emphasis> titanium alloy

The yielding behavior of individual Widmanstätten α (hcp) + β (bcc) colonies of Ti-8Al-1Mo-1V has been analyzed theoretically by considering the shearing of β platelets by slip in the α phase. Slip is assumed to initiate in the softer α phase and impinges on the harder β platelets. Under the combined actions of the external stress and impinging slip, yielding of the β platelets occurs when the von Mises effective stress in the β phase exceeds a critical value. The theoretical analysis indicates that the macroscopic slip planes in individual Widmanstätten colonies correspond to those that induce the highest stresses in the β platelets. In addition, the yield stress and the strain-hardening rate both increase with decreasing values of the angle, β _b , between the slip direction and the normal to the β platelets, resulting in soft and hard slip orientations. Soft orientation of the lamellar colony is associated with α slip parallel to the macroscopic, serrated α/β interface, which includes crystallographic interface and ledges, while the hard orientation is associated with slip normal to the thin platelets. This slip anisotropy appears to arise from increasing difficulty of slip transmission across the macroscopic α/β interface when the operative slip vector impinges perpendicular to the β platelets.     

Microstructure,Texture, and Mechanical Properties of <Emphasis Type="Italic">β</Emphasis> Solution-Treated and Aged Metastable <Emphasis Type="Italic">β</Emphasis> Titanium Alloy,Ti-5Al-5Mo-5V-3Cr

The current study describes the aging characteristics and mechanical properties of a metastable β titanium alloy Ti-5Al-5Mo-5V-3Cr. The aged microstructures consist of fine α-phase precipitates (lath morphology) in equiaxed β grains. The sizes of the α-phase precipitates increase with the increasing aging temperature. The β ST WQ and 823 K (550 °C)-aged material exhibits maximum hardness due to precipitation hardening. The low- and high-temperature aging conditions result in strong c-type basal and prismatic textures in the α-phase, respectively. The β-phase of the alloy aged at low temperature reveals the presence of texture with moderate intensity. In contrast, high-temperature-aged material exhibits very strong β-phase texture. The strengths of the alloy under β ST WQ- and 923 K (650 °C)-aged conditions are the maximum and minimum along TD and RD, while the ductility values are the maximum and minimum along the RD and TD direction samples, respectively. The flow curves follow typical Holloman equation along three sample directions, and the work hardening rate curves display two distinctive regimes, namely, stage I and stage II. The yield locus plots of the β ST WQ and aged materials exhibit the presence of anisotropy.     

Stress-Induced Twinning and Phase Transformations during the Compression of a Ti-10V-3Fe-3Al Alloy

A metastable β Ti-10V-3Al-3Fe (wt pct) alloy containing different α phase fractions after thermo-mechanical processing was compressed to 0.4 strain. Detailed microstructure evaluation was carried out using high-resolution scanning transmission electron microscopy and electron back-scattering diffraction. Stress-induced β → α′′ and β → ω transformation products together with {332}〈113〉β and {112}〈111〉β twinning systems were simultaneously detected. The effects of β phase stability and strain rate on the preferential activation of these reactions were analyzed. With an increase in β phase stability, stress-induced phase transformations were restricted and {112}〈111〉β twinning was dominant. Alternatively, less stable β conditions or higher strain rates resulted in the dominance of the {332}〈113〉β twinning system and formation of secondary α′′ martensite.     

Microstructure and High Temperature Impression Creep Properties of Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) Alloys

The current study has investigated the influence of zirconium (Zr) addition to Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) alloys prepared using argon arc melting on the microstructure and impression properties at 448–498 K under constant stress of 380 MPa. Microstructural analysis of as-cast Mg–3Ca–xZr alloys showed grain refinement with Zr addition. The observed grain refinement was attributed to the growth restriction effect of Zr in hypoperitectic Mg–3Ca–0.3 wt% Zr alloys. Heterogeneous nucleation of α-Mg in properitectic Zr during solidification resulted in grain refinement of hyperperitectic Mg–3Ca–0.6 wt% Zr and Mg–3Ca–0.9 wt% Zr alloys. The hardness of Mg–3Ca–xZr alloys increased as the amount of Zr increased due to grain refinement and solid solution strengthening of α-Mg by Zr. Creep resistance of Mg–3Ca–xZr alloys increased with the addition of Zr due to solid solution strengthening of α-Mg by Zr. The calculated activation energy (Q_a) for Mg–3Ca samples (131.49 kJ/mol) was the highest among all alloy compositions. The Q_a values for 0.3, 0.6 and 0.9 wt% Zr containing Mg–3Ca alloys were 107.22, 118.18 and 115.24 kJ/mol, respectively.     

Synthesis and Non-isothermal Carbothermic Reduction of FeTiO<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Solid Solution Systems

To investigate the carbothermic reduction behaviors of xFeTiO₃·(1 ? x)Fe₂O₃ solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 10² kJ/mol was obtained.