Oxidation of cobalt at high temperature

Precise values of parabolic rate constants of cobalt oxidation have been determined over a wide range of temperature (950–1300°C) and oxygen pressure (6.58× 10^?4?0.658 atm). The dependence of the calculated values of parabolic rate constants k″_p on oxygen pressure and temperature can be described by the following empirical equation: $$k''_p = const. \cdot {\text{p}}_{O_2 }^{{\text{1/n}}} \cdot exp ( - {\text{E}}_{\text{k}} /RT)$$ The exponent 1/n decreases with an increase in temperature from 1/3.40 at 950°C to 1/3.96 at 1300°C, whereas the activation energy E_k decreases with an increase in the oxygen pressure from 41.7 to 38.1 kcal/mole.     

Influence of Interdiffusion in Sn Solution on Growth of Cu<Subscript>3</Subscript>Sn and Cu<Subscript>6</Subscript>Sn<Subscript>5</Subscript> Formed in Semi-infinite and Finite Cu-Sn Diffusion Couples

Reactive diffusion in the Cu-Sn binary system has been studied by using pure Cu/electrically plated Sn with 0.1-0.2 mm thicknesses diffusion couples (EP-couples) at 473 K. The interdiffusion coefficients, \(\tilde{D}\), of the Cu₃Sn and Cu₆Sn₅ diffusion phase layers were determined at the center of these layers by supposing linear concentration (\(C_{\text{i}}\))-distance (X) curves in these layers and by neglecting the interdiffusion in the Sn terminal solution (IDS) as the previous researchers have neglected it. By using \(\tilde{D}\) thus determined, the phase boundary concentrations for the layers obtained in this work and these parameters for the Cu terminal solution chosen appropriately, \(C_{\text{i}}\)-X curves were determined numerically for various values of interdiffusion coefficient, \(\tilde{D}_{\text{in Sn}}\), and the solubility limit of Cu mole fractions, \(N_{\text{Cu}}^{\text{in Sn}}\), in the Sn terminal solution by our method reported previously taking the molar volume change effect into account. The \(C_{\text{i}}\)-X curves obtained experimentally could be reproduced numerically well by neglecting IDS. This result, on the other hand, suggests a large influence of IDS in the semi-infinite diffusion couples (S-couples) or the diffusion couples used by the previous researchers. The quantitative evaluation of the influence in S-couples revealed that it makes the widths of the diffusion layers thinner than those in the present EP-couples in which the influence on the widths is negligibly small. The evaluation of the influence in the diffusion couples used by the previous researchers indicates larger values of \(N_{\text{Cu}}^{\text{in Sn}}\) than those reported as the value of the equilibrium phase diagram.     

Lattice parameters of Ti–4Al–2V alloy with thermal oxidation

In this study, the effect of thermal oxidation on the lattice parameters of Ti–4Al–2V alloy was studied.Samples were oxidized at 450, 600 and 650 °C for 1–7 h in electric furnace under air atmosphere. The lattice parameters were determined using the Cohen method as a function of oxidation time at each temperature. The lattice parameters of as-received alloy are calculated as a = 0.29289 nm and c = 0.46652 nm. The thermal oxidation at 450 °C results in a gradual increase in a-parameter, whereas it goes through a maximum at higher temperatures(600 and 700 °C). The results show that these maximums are reduced to an approximately constant value after a long-time oxidation. The c-parameter generally increases over the whole treatment condition. It is believed that these variations could be due to the dissolution of oxygen atoms in octahedral sites of hcp lattice of titanium.     

A New Finding About Conditions for More Than One Kirkendall Marker Plane in Binary Single Phase Diffusion Couples

It is now well known that there are experimental results of bifurcate, trifurcate or more Kirkendall marker planes (K-plane) in a multiple phase diffusion couple (M-couple). In the case of Au-Zn binary alloy system, for example, even in a β’/β’ single phase diffusion couple (S-couple) there is a possibility of the bifurcate K-planes because the ratio R = D _Zn/D _Au of the intrinsic diffusion coefficients in the β’ phase is smaller than 1 in the Au rich side and larger than 1 in the Zn rich side. It has been reported that the positions of the K-planes in a diffusion zone can be found graphically as intersections between the plot of marker moving distance \(2t\upsilon_{\text{k}}^{\text{D}}\) versus X _k and the plot of a straight line \(2t\upsilon_{\text{k}}^{\text{EX}}\) versus X _k. Here, \(\upsilon_{\text{k}}^{\text{D}}\) is the marker velocity with respect to the volume fixed frame of reference (V-frame) defined by,

$$\upsilon_{\text{k}}^{\text{D}} = \upsilon_{\text{k}} - \upsilon_{\text{V}} = V_{\text{B}} \left( {D_{\text{B}}^{\text{V}} - D_{\text{A}}^{\text{V}} } \right)\left( {\frac{{\partial C_{\text{B}} }}{\partial X}} \right),$$

and \(\upsilon_{\text{k}}^{\text{Ex}}\) is that determined experimentally by the following equation,

$$\upsilon_{\text{k}}^{\text{Ex}} = \upsilon_{\text{k}} - \upsilon_{0} = \frac{{X_{k} - X_{0} }}{2t}.$$

In this work, we studied the alignments of multiple markers (M-Ms) after diffusion anneal embedded in a S-couple for widely different constant values of ratio of intrinsic diffusion coefficients, R = D _B /D _A, with respect to the mole fixed frame of reference (N-frame) by our numerical technique taking the change in molar volume into account. For this purpose, new two plots to know the K-plane(s) for the N-flame were derived. A possibility was indicated that Kirkendall markers can locate not only at the intersection(s) between these new two plots but also at an unexpected place where the intersection cannot be found.

     

Comparative Oxidation Kinetics of a NiPtTi High Temperature Shape Memory Alloy

A high temperature shape memory alloy, Ni–30Pt–50Ti (at.%), with an M _s near 600 °C, was isothermally oxidized in air for 100 h over the temperature range of 500–900 °C. Nearly parabolic kinetics were observed in log–log and parabolic plots, with no indication of initial fast transient oxidation. On average the rates were about a factor of 4 lower than values measured here for a binary Ni–49Ti commercial SMA. The overall behavior could be best described by the Arrhenius relationships: $${\text{Ni}}{\text{Pt}}{\text{Ti}}{:}\,k_{\text{p}} = 1.54 \times 10^{12} \exp \left[(- 250\,{\text{kJ}}/{\text{mol}}) {RT} \right]{\text{mg}}^{2}/{\text{cm}}^{4} {\text{h}} $$ $${\text{Ni}}{\text{Ti}}{:}\,k_{\text{p}} = 6.39 \times 10^{12} \exp \left[(- 249\,{\text{kJ}}/{\text{mol}}) {RT} \right]{\text{mg}}^{2}/{\text{cm}}^{4} {\text{h}} $$ The activation energy was consistent with literature values for TiO₂ scale growth measured for elemental Ti and some NiTi alloys, at ~210–260 kJ/mol. However, a number of other studies produced activation energies in the range of 135–150 kJ/mol. This divergence may be related to various complex scale layers and depletion zones, however, no specific correlation can be identified at present.     

Influence of Hydrogen and Water Vapour on the Kinetics of Chromium Oxide Growth at High Temperature

In support of the selection of structural materials for heat exchangers in helium-cooled high temperature reactors, the oxidation behaviour of the Ni-base chromia-former alloy 230 was investigated at 850 °C in diluted helium atmosphere with a low water vapour content. In such a media, the equivalent partial pressure of oxygen (imposed by the $ P_{{{\text{H}}_{2} {\text{O}}}} $ / $ P_{{{\text{H}}_{2}}} $ ratio) is very low ( $ P_{{{\text{O}}_{ 2} }}^{\text{eq}} $ around 10^?16 Pa). The equivalent partial pressure of oxygen has no straight influence on the parabolic rate constant (k _p); on the other hand, $ P_{{{\text{H}}_{2} }} $ and $ P_{{{\text{H}}_{2} {\text{O}}}} $ demonstrate a complex influence on k _p. Photoelectrochemistry analyses revealed that this oxide could simultaneously contain two types of cationic defects. Specific oxidation tests with D₂O showed that the oxide scale also contains hydrogen. A mechanist model is proposed in order to describe the scale growth using both cationic defects. Those theoretical results show, at least qualitatively, how $ P_{{{\text{H}}_{2} }} $ and $ P_{{{\text{H}}_{2} {\text{O}}}} $ may concurrently influence the oxidation rate.     

Development of Texture in Interstitial-Free Steel Processed by Equal-Channel Angular Pressing

Ti + Nb-stabilised interstitial-free steel is deformed by equal-channel angular pressing (ECAP) adopting a route B_C up to an equivalent strain of 24. Upon ECAP the grain size decreases to ultrafine level and it becomes strongly textured. At ε_vm = 0.6-6, components of both {110} fiber, \( J_{\uptheta } \), \( \bar{J}_{\uptheta } \) and of 〈111〉 fiber, D _1θ, D _2θ with common components of E _θ, \( \bar{E}_{\uptheta } \) are existing but after ε_vm ≥9, only 〈111〉 fiber components are observed. At large strain, ε_vm = 9-24, 〈111〉 fiber texture is recorded with monoclinic symmetry. At ε_vm = 0.6, coarse grains get split into deformation bands. Fragmentation of bands (at ε_vm = 3) suppress \( \bar{J}_{\uptheta } , \) \( J_{\uptheta } \) components. At ε_vm = 6, formation of lamellar structures increases intensity of mainly D _1θ, D _2θ. At ε_vm = 9, oriented ribbon grains result in strong D _1θ, D _2θ components with 〈111〉 fiber. At ε_vm = 15-24, conversion of ribbon grains to near-equiaxed shaped grains maintains 〈111〉 fiber texture with enhanced intensity of D _1θ and D _2θ components.     

Ternary Interdiffusion in <Emphasis Type="Italic">β</Emphasis> (BCC) Phase of the Ti-Al-Nb System

Interdiffusion coefficients are reported at various compositions in the β (BCC) phase of the Ti-Al-Nb system using solid–solid diffusion couples assembled at three different temperatures of 1060 °C, 1100 °C and 1170 °C. The interdiffusion fluxes were determined after fitting the experimental concentration profiles with MultiDiFlux software and the ternary interdiffusion coefficients were evaluated at various compositions using Kirkaldy’s approach. The interdiffusion of Nb was the slowest, while Ti and Al showed similar interdiffusion kinetics. The main interdiffusion coefficients for the three components are positive. The cross interdiffusion coefficients of Ti and Nb are comparable in magnitude to their respective main terms indicating the presence of strong diffusional interactions in this system. The cross coefficient \(\tilde{D}_{\text{TiNb}}^{\text{Al}}\) is positive indicating that the interdiffusion flux of Ti is enhanced down the concentration gradient of Nb. The negative value of the cross-term \(\tilde{D}_{\text{TiAl}}^{\text{Nb}}\) indicates that the interdiffusion flux of Ti is enhanced up the gradient of Al. The tracer diffusion coefficient of Al increases with temperature and decreasing Nb content in binary Ti-Nb alloys. Binary interdiffusivities calculated at Ti-Nb compositions by extrapolation are reasonably consistent with the values reported in the literature.     

Effect of hydrogen intercalation on the critical parameters of YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>

The effect of hydrogenation at T = 150 and 200°C on the electrophysical properties of highly textured YBa₂Cu₃O _y ceramics with different oxygen content has been investigated. Like hydration, hydrogenation results in the deterioration of these properties. However, in samples with high oxygen contents (y = 6.96) hydrogenated at T = 150°C after oxidation (400°C) or recovery annealing with subsequent oxidation, the critical current density and first critical field increase compared to the initial state. The improvement of the properties occurs mainly in a magnetic field applied perpendicularly to the c axis. As after hydration, this is connected with the formation of planar defects in the course of low-temperature annealing. In addition, in the process of the hydrogenation, the partial reduction of copper occurs with the formation of microinclusions of Cu₂O and other products of chemical decomposition, which are extra pinning centers of magnetic vortices.     

Volatilization and Transport Mechanisms During Cr Oxidation at 300 °C Studied In Situ by ToF-SIMS

The oxidation of chromium at 300 °C was investigated in situ by ToF-SIMS for three different oxygen pressures (\(P_{{{\text{O}}_{2} }} = 2.0 \times 10^{ - 7}\), 6.0 × 10^?7 and 2.0 × 10^?6 mbar). Sequential exposure to the ¹⁸O isotopic tracer was performed to reveal the governing transport mechanism in the oxide film. The evolution of the oxide thickness was monitored. Volatilization of Cr₂O₃ was evidenced. A model was used to describe the kinetics resulting from the measurements. Both the parabolic and volatilization constants showed a dependence on oxygen partial pressure like \(P_{{{\text{O}}_{2} }}^{ - 1/n}\), with n = 1.9 ± 0.1, indicating a defect structure mainly consisting of oxygen vacancies. The re-oxidation in ¹⁸O₂ shows a growth of the oxide layer at the metal/oxide interface, demonstrating an oxidation process governed by anionic transport via oxygen vacancies. The diffusion coefficient of oxygen in the oxide was determined by fitting the ToF-SIMS depth profiles. It is 2.0 × 10^?18 cm² s^?1.     

Crystallographic peculiarities of the eutectoid and martensite structures in the U–1.5 % Mo alloy

Using electron microscopy, samples of U–1.5 wt % Mo alloy with a partial structure of eutectoid, which consists of alternating plates of α phase depleted of molybdenum (α-U) and ordered γ’ phase (U₂Mo), have been studied. The structures of a eutectoid and martensite have been obtained by the quenching of samples characterized by delayed cooling from 1000°C. It has been shown that, in the eutectoid, the constant orientation relationships (ORs) are observed between the α-U and U₂Mo phases, namely, \({\left[ {100} \right]_\alpha }{\left\| {\left[ {331} \right]} \right._{\gamma '}},\;{\left( {010} \right)_\alpha }{\left\| {\left( {11\bar 6} \right)} \right._{\gamma '}},\;{\left( {010} \right)_\alpha }{\left\| {\left( {\bar 110} \right)} \right._{\gamma '}}\) These relationships are similar to the ORs observed in the martensite between an orthorhombic α’ martensite and initial bcc γ phase that have been found in low alloys of U–Nb, U–Zr, U–Mo and experimentally confirmed in this work. It has been established that, in the γ’ phase, principal axes a, b, c remain parallel to the principal axes of the matrix γ phase. However, its axis of tetragonality c has the only nonequivalent crystallographic direction at which the plates in the eutectoid colonies that are parallel to the planes of atomic ordering of the γ’ phase have interphase boundaries of \((001)_{\gamma '} ||(130)_\alpha \).     

Diffusion Research in BCC Ti-Al-Ni Ternary Alloys

Interdiffusion in BCC phase of Ti-Al-Ni ternary system was investigated at 1473 K (1200 °C) by employing the diffusion-couple technique. The raw composition profiles resulting from interdiffusion treatment and retrieved from EMPA were first analytically represented by error function expansion (ERFEX), and the ternary interdiffusion and impurity diffusion coefficients were then extracted by the Whittle-Green and generalized Hall methods, respectively. The obtained main interdiffusion coefficients \( \tilde{D}_{\text{AlAl}}^{\text{Ti}} \) and two cross coefficients, i.e. \( \tilde{D}_{\text{AlNi}}^{\text{Ti}} \) and \( \tilde{D}_{\text{NiAl}}^{\text{Ti}} \), were found to increase with increasing composition of diffusing species, whereas the values of \( \tilde{D}_{\text{NiNi}}^{\text{Ti}} \) show no noticeable compositional dependence. The impurity diffusivities \( \tilde{D}_{{{\text{Al}}\left( {\text{Ti - Ni}} \right)}}^{*} \) and \( \tilde{D}_{{{\text{Ni}}\left( {\text{Ti - Al}} \right)}}^{*} \) increase with decreasing the Ni and Al compositions, respectively. The results imply that Al diffusion in β Ti-Al-Ni alloys would occur via an ordinary vacancy diffusion mechanism, whereas Ni diffusion, at least one order magnitude faster than Al, very likely benefits from interstitial diffusion as Fe and Co anomaly diffuse in BCC Titanium alloys.     

Extended Hall–Petch Relationships for Yield,Cleavage and Intergranular Fracture Strengths of bcc Steel and Its Deformation and Fracture Behaviors

Extended Hall–Petch relationships for yield (\( \sigma_{y} \)), cleavage (\( \sigma_{\text{cl}} \)) and intergranular fracture (\( \sigma_{\text{ig}} ) \) strengths of pure iron have been established through the direct calculation of the proportional constant \( (k) \) and the estimation of the friction stress \( (\sigma_{0} ) \). The magnitude orders of \( k \) and \( \sigma_{0} \) are generally \( k_{y} < k_{\text{cl}} < k_{\text{ig}} \) and \( \sigma_{y0} < \sigma_{\text{cl0}} < \sigma_{\text{ig0}} \), respectively. Based on the Hall–Petch relationships, micro-yielding in a bcc steel occurs at the instance that the pile-up dislocations within a specific grain showing the Schmid factor of 0.5 propagate into the neighboring grain. The initial brittle crack is formed at the instance that the flow strength exceeds the brittle fracture strength. Once the brittle crack is formed, it grows catastrophically. Due to the smallest and \( k_{y} \) and \( \sigma_{\text{y0}} \), the cleavage and the intergranular fracture occur always after micro-yielding. The {100} cleavage fracture of the steel is due to the lowest theoretical {100} cleavage strength. Due to the thermal components included in cleavage and intergranular fracture strengths, they show also the temperature and strain rate dependence observed in yield strength. The increase in susceptibility to brittle fracture with decreasing temperature and increasing strain rate is due to the increase in dislocation density which causes the high work hardening rate.     

Effect of the structural state of the FePd equiatomic alloy on the temperature dependence of the initial magnetic susceptibility and the curie temperature

The temperature dependence of the initial magnetic susceptibility of a quenched equiatomic FePd alloy with an A1 structure and the variations of its Curie temperature and anisotropy of hysteresis loops have been studied during the ordering annealing of single-crystal samples at 550°C. The micro- and mesostructure, relief patterns, and magnetic-powder patterns on {100} surfaces of the single crystal were studied using electron microscopy and the polarization-optical method. The correlation between the temperature dependence of the magnetic susceptibility and the Curie temperature of the FePd alloy and the peculiarities of its elastically stressed nanocrystalline state during the A1 → L1₀ transformation is discussed.     

The Effect of Synthesis Conditions on the Phase Composition and Structure of EuBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> Samples

The composition and the structure of ceramic EuBa₂Cu₃O_{6 + δ} (Eu-123) oxide samples annealed in steps with varying processing conditions (in air or oxygen and argon atmosphere at a temperature of 940–960°С for 1–70 h with or without homogenization) were studied by the X-ray phase and chemical analysis, electron diffraction pattern analysis, elemental analysis, and high-resolution transmission electron microscopy. Regardless of the processing conditions, Eu-123 nanostructured oxide with a tetragonal or orthorhombic structure and domains 1–20 nm in size was obtained as a result of annealing. Nanostructuring of the samples, which was revealed by high-resolution electron microscopy, is attributed to their chemical nature: the presence of identical structural elements in members of the homologous Eu _n Ba _m Cu_{m + n}O _y series of oxides allows them to intergrow coherently and create an illusion of a single crystal. Just like any other member of the Eu _n Ba _m Cu_{m + n}O _y series, oxide Eu-123 is disproportionate depending on the annealing conditions to form other members of this series located on either side of the dominant oxide. Temperature T_c of the superconducting transition of each member of the series depends on the average oxidation state of copper \(\overline {Cu} \). At \(\overline {Cu} \) < 2, all members of the series have a tetragonal structure and do not exhibit superconducting properties. At \(\overline {Cu} \) = 2.28, five members of the Eu _n Ba _m Cu_{m + n}O _y series with matrices (Ba : Cu) 5 : 8, 3 : 5, 2 : 3, 5 : 7, and 3 : 4 exhibit superconducting properties with T_c = 82–90 K.     

Oxidation of copper at high temperatures

The kinetics and mechanism of copper oxidation have been measured over the temperature range 900–1050°C and the pressure range 5×10^?3 to 8×10^?1 atm. It has been shown that, at the pressures lower than the dissociation pressure of CuO, the oxide scale formed on flat fragments of the copper specimens is compact and composed of a single layer, adhering closely to the metallic base. Growth of the scale proceeds under these conditions by outward diffusion of metal. The rate of the process under the conditions for which single-phase scales are formed increases with increasing oxygen pressure according to the equation: $${\text{k''}}_{\text{p}}^{} = const {\text{p}}_{{\text{O}}_{\text{2}} }^{{\text{1/3}}{\text{.9}}} $$ . the activation energy for oxidation is 24 ± 2 kcal/mole. On the basis of theFueki-Wagner method and the method proposed in the present work, the self-diffusioncoefficients of copper in cuprous oxide were calculated as a functionof oxygen pressure and temperature. It has been shown that distribution of thedefect concentration in the growing layer of the scale is linear.     

Influences of carbon and silicon on blister formation in scale surface during high temperature oxidation of carbon steels

The in-situ blistering phenomena of the scale ‘surface’ was investigated on three carbon steels with respect to carbon and silicon concentrations, such as 0.05 wt%C, 0.2 wt%C, and 0.2 wt%C-0.2 wt%Si. The oxidation and blistering kinetics and blister area fraction during high temperature oxidation were analyzed. The average thickness of the surface scale by oxidation during isothermal holding from 800 to 1200 °C in dry air was observed to decrease when the amount of carbon increased and/or when Si was inserted additionally. Thus, the blistering behavior depended primarily on a change in oxidation temperature (T _ox ) as well as amounts of carbon and silicon in the matrix. It is also revealed that such blister formation would be triggered by growth of internal stress and active generations of CO and/or CO₂ gases at the interface between the scale and matrix since carbon would result in an increase in the blister formation by generating CO and/or CO₂ gas. In addition, silicon might play an important role in preventing the blister formation at T _ox below 900 °C by reducing the thickness of the surface scale whilst silicon might enhance the blister formation by means of the appreciable micro-void formation in the scale layer at T _ox higher 900 °C.     

Pressure dependencies of copper oxidation for low- and high-temperature parabolic laws

Studies of the oxidation kinetics of copper have been conducted in the thin-film range at temperatures of 383–398 K and in the oxygen pressure range of 0.278–21.27 kPa; whereas in the thick-film regime at 1123 K, studies have been conducted in the oxygen pressure range of 2.53–21.27 kPa. Furthermore, the effect of continuously impressed direct current with oxygen pressure variation in Wagner's parabolic range has been studied also in order to have a better understanding of the effective charge on the migrating species. In the low-temperature range, the rate constant, k_P ∝ \(P_{O_2 }^{1/4} \) , suggesting that the migration of neutral vacancies in the growing film predominates. At high temperature, 1123 K, in the Wagnerian regime, the observed approximate pressure dependencies of the parabolic rate constants are the following: $$\begin{gathered} {\text{k}}_{\text{p}} (normal oxidation) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/7}}} \hfill \\ {\text{k}}_{\text{p}} (sample cathodic) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/5}}} \hfill \\ \end{gathered} $$ and $${\text{k}}_{\text{p}} (sample anodic) \propto \sim {\text{P}}_{{\text{O}}_{\text{2}} }^{{\text{1/10}}} $$ .     

Oxidation of zirconium between 400° and 800°C

The vacuum microbalance method is used to study the oxidation reaction for two surface preparations over the temperature range of 400° to 800°C. The results fit in well with the authors previous work at temperatures of 200° to 425°C and with the work of other groups at higher temperatures. An analysis of the rate data shows that the cubic rate law fits the experimental data best for the abraded specimens. However, the parabolic rate law can be fitted to the data if an initial deviation is disregarded. With chemically polished specimens, a good fit is obtained with the parabolic rate law. The parabolic rate law constant A gives two straight lines when plotted as log A vs 1/T. For the temperature range of 200° to 525°C an energy of activation of 18,200 cal per mol is calculated while a value of 28,600 cal per mol is calculated for the temperature range of 525° to 750°C. The results of this work bring together the previously determined high-temperature oxidation studies of Cubicciotti with the early low-temperature studies of Gulbransen and Andrew.     

Constitutive modeling and understanding of the hot compressive deformation of Mg–9.5Zn–2.0Y magnesium alloy with reduced number of strain-dependent constitutive parameters

The hot compressive flow behavior of the cast Mg–9.5Zn–2.0Y alloy as a function of strain was analyzed, and the degree of dependence of the parameters (A: material constant, n ₂: stress exponent, Q _c: activation energy for plastic flow and α: stress multiplier) of the constitutive equation (\(\dot \varepsilon = A{\left[ {\sinh \left( {\alpha \sigma } \right)} \right]^{{n_2}}}\exp \left( {\frac{{ - {Q_c}}}{{RT}}} \right)\)) upon the strain was examined in a systematic manner. This is to explore the possibility of representing the hot compressive deformation behavior of metallic alloys in a simple way by using a reduced number of strain-dependent constitutive parameters. The analysis results for several different cases can be interpreted as follows: (1) Q _c can be treated as being strain-independent, which is physically sensible; (2) while only the microstructure changes as a function of strain at low flow stresses, as the flow stress increases, the power-law creep deformation and power-law breakdown mechanisms change; (3) the regime where only A is strain dependent expanded to higher strain rates and lower temperatures as the strain increased, suggesting that the number of the strain-dependent parameters decreases as the initial microstructure is refined by dynamic recrystallization, and the microstructure approaches a steady state.