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The flow softening behaviors of a nickel-based superalloy with δ phase are investigated by hot compression tests over wide ranges of deformation temperature and strain rate. Electron backscattered diffraction (EBSD), optical microscopy (OM), and scanning electron microscopy (SEM) are employed to study the flow softening mechanisms of the studied superalloy. It is found that the flow softening behaviors of the studied superalloy are sensitive to deformation temperature and strain rate. At high strain rate and low deformation temperature, the obvious flow softening behaviors occur. With the increase of deformation temperature or decrease of strain rate, the flow softening degree becomes weaken. At high strain rate (1s−1), the flow softening is mostly induced by the plastic deformation heating and flow localization. However, at low strain rate domains (0.001-0.01s−1), the effects of deformation heating on flow softening are slight. Moreover, the flow softening at low strain rates is mainly induced by the discontinuous dynamic recrystallization and the dissolution of δ phase (Ni3Nb).

The texture evolution of a near β-Ti alloy (Ti-55511) is investigated by hot compressive deformation experiments in β region. A visco-plastic self-consistent (VPSC) model is employed to elaborate the correlation between plastic deformation mechanisms and texture evolution. The experimental results show that the types of textures are insensitive to the deformation temperature and strain rate, while the true strain dramatically affects the type of textures. The developed textures include {001}<100>, {012}<100> and η-fiber textures. In VPSC model, the bi-plane and pencil slip modes are selectively activated to match the experimental textures at different deformation strains. With an increase in strain, there is a gradual transition in the slip mode from bi-plane slip to pencil slip. The common textures in β phase of Ti alloys are strongly correlated with the active {112}<111> slip ({112} slip) and {123}<111> slip ({123} slip) modes. Additionally, to explain the effect of initial orientation on texture formation, various initial orientations in Ti alloys are employed in VPSC simulations. The results reveal that starting with a random orientation initially promotes the formation of {110}<111>, {001}<100> and η-fiber textures, accompanied by an increase in texture intensity as the strain level increases. Moreover, {110}<110> orientation undergoes rotation leading to develop {110}<111> texture with a decrease texture intensity, while {110}<112> orientation undergoes rotation inducing {110}<223> texture with an increased texture intensity. • Texture evolution of a near β-Ti alloy is investigated by hot compressive deformation experiments in β region. • A visco-plastic self-consistent model is developed to elaborate the correlation between plastic deformation mechanisms and texture evolution. • Texture types are insensitive to the deformation temperature and strain rate, while the true strain dramatically affects the type of textures. • The common textures in β phase of Ti alloys are strongly correlated with the active {112} and {123} slip modes. • Starting with a random orientation initially promotes the formation of {110}<111>, {001}<100> and η-fiber textures. [ABSTRACT FROM AUTHOR]

In this study, the continuous dynamic recrystallization (CDRX) behaviors of a hot-deformed Ti-55511 alloy are investigated in β single-phase domain. CDRX is found to play a dominant role in the microstructure evolution during thermomechanical forming of the Ti-55511 alloy. In order to quantitatively and visually simulate the hot forming process, a probabilistic cellular automata (CA) method is established. This CA technology integrates the dislocation evolution model, subgrain nucleation rate model, misorientation evolution model, grain boundary (GB) migration model, and topology deformation model. The results of a systematic study of both microstructural evolution and macroscopic mechanical response at various strains, strain rates, and temperatures are presented. The average absolute relative error (AARE), correlation coefficient (R), and root-mean squared error (RMSE) values between the experimental and simulated stresses are 4.63 %, 0.9963, and 3.81 MPa, respectively. The deviation values of subgrain size range from 1.27 % to 17.25 %, when the temperatures varies from 920 to 980 °C. The predicted results well agree with the measured results, demonstrating the transition from a coarse and static recrystallized structure to a refined and continuous dynamic recrystallized structure. A low Zener-Hollomon (Z) parameter can effectively enhance the progress of CDRX. Higher temperatures and lower strain rates result in a larger volume fraction of CDRX. Quantitative analyses confirm that the incubation period for CDRX is significantly longer than that for subgrain formation, indicating a sustained transformation from the low-angle grain boundaries (LAGBs) to the high-angle grain boundaries (HAGBs) through the absorption of dislocations. • A probabilistic CA model is developed to study continuous dynamic recrystallization (CDRX) behaviors of a Ti alloy. • Coarse and static recrystallized structures are transformed to refined and CDRX structures. • A low Zener-Hollomon (Z) parameter can effectively enhance the progress of CDRX. • The subgrain size depends on the Z parameter and follows an inverse logarithmic relationship. • The incubation period for CDRX is significantly longer than that for subgrain formation. [ABSTRACT FROM AUTHOR]

Simulating the evolution of microstructures and the mechanical response of alloys with cubic and hcp structures is crucial for the industrial manufacturing of key alloy components. In this work, a modified Voce (ME-Voce) model is proposed, based on the extended Voce hardening model, to depict the variations of hardening rate with cumulative shear strain. Also, an orientation-dependent weight that describes the neighboring grain-induced 'drag' effect is evaluated. These improvements are numerically implemented in a standard viscoplastic self-consistent (VPSC) model. The ME-Voce parameters are determined through multi-parameter optimization using Matlab software. The influences of grain shape and neighboring grains on the hot deformation behavior of alloys are investigated. The proposed ME-Voce model is validated through hot compression experiments of alloys with cubic and hcp structures. The results show the VPSC embedded in the ME-Voce can reasonably predict the mechanical response under different deformation conditions. This enhances the predictive capability of the VPSC model and provides more options for crystal plasticity simulation of alloys with different crystal structures. • A modified Voce model is proposed to depict the variations of hardening rate with cumulative shear strain. • An orientation-dependent weight describing neighboring grain-induced 'drag' effect is evaluated. • Viscoplastic self-consistent model including ME-Voce can reasonably predict the mechanical response of alloys. • More choices for crystal plasticity simulation of alloys with different crystal structures are provided. [ABSTRACT FROM AUTHOR]

The flow behavior of a high‐strength Ti alloy (Ti‐55511) in the β region is studied by hot compressive experiments. A dislocation density–based constitutive equation, together with processing maps, is established to describe the flow behavior and hot workability of the studied Ti alloy. It is found that the strain rate (ε˙) and temperature (T) distinctly influence the hot compressive deformation behavior. The flow stress increases distinctly with a rising ε˙ or reducing T. The main softening mechanism in the β region is dynamic recovery (DRV). The established constitutive equation based on the work hardening (WH) and DRV mechanisms has the desired prediction accuracy, and the correlation coefficient between the predicted and experimental results is 0.9912. The processing maps indicate that a high strain rate (0.4–10 s−1) easily causes unstable deformation, whereas low and medium strain rates (0.001–0.2 s−1) are suitable for hot compressive deformation of the studied alloy. [ABSTRACT FROM AUTHOR]

The precipitation behavior of α phase in a β-quenched Ti-55511 alloy during high-temperature compression is investigated. The influences of deformation parameters on the flow characteristics, microstructural evolution, as well as the precipitation behavior of α phase, are discussed. Results show that the flow stress features and the dominant softening mechanism are sensitive to the deformation parameters. At low strain rates or high deformation temperatures, the main softening mechanism is dynamic recovery. But, the dynamic recrystallization becomes the dominant softening mechanism at high strain rates or low temperatures. At low strain rates, the continuous strengthening, induced by the pinning effect of α precipitates, happens at the late period of deformation. Distribution of α precipitates is not greatly affected by deformation parameters. In the region near β grain boundary, α precipitates are densely distributed with few orientations. While in the central region of β grain, the α precipitates are distributed a bit more sparsely with several scattering orientations. In addition, with increasing deformation temperature, the content, aspect ratio and size of α phases decrease. However, with increasing strain rate, the content, aspect ratio and size first increase and then decrease. Furthermore, the peak value of aspect ratio appears at 0.01 s−1. • Precipitation behavior of α phase in a β-quenched Ti-55511 alloy during hot compression is studied. • At low strain rates or high deformation temperatures, the main softening mechanism is dynamic recovery. • Dynamic recrystallization is the dominant softening mechanism at high strain rates or low temperatures. • α precipitates are distributed a bit more sparsely with several scattering orientations within β grains. • With increasing deformation temperature, the content, aspect ratio and size of α phases decrease. [ABSTRACT FROM AUTHOR]

Abstract The effects of solution temperature and cooling rate on microstructure and micro-hardness of a hot compressed Ti-6Al-4V alloy are investigated. The microstructure observations reveal the occurrence of static recrystallization during solution treatment. The lamellar α phases firstly decompose into the short-rod phases, and then gradually spheroidize. The increased solution temperature can accelerate the transformation of α grain boundary from the low-angle grain boundaries (LAGB) to the high-angle grain boundaries (HAGB). So, the growth and spheroidization of α grains become more and more obvious. Meanwhile, the precipitation of secondary α phases is promoted. The micro-hardness is significantly improved after the solution treatment, i.e., the micro-hardness undergoes the rapid decrease and slow increase with raising the solution temperature. In addition, the cooling rate has great impact on the microstructures and micro-hardness. With reducing the cooling rate, the mean size of equiaxed α grains and the thickness of lamellar α phases obviously increase. Highlights • Effects of post-deformation heat treatment on microstructures and micro-hardness of Ti-6Al-4V alloy are studied. • Lamellar α phases firstly decompose into the short-rod phases, and then gradually spheroidize. • The increased solution temperature accelerates the transformation of α grain boundary from LAGB to HAGB. • Micro-hardness undergoes the rapid decreases and slow increase with the increase of solution temperature. • The mean size of equiaxed α grains and the thickness of lamellar α phases increase with reducing cooling rate. [ABSTRACT FROM AUTHOR]

The isothermal compressive experiments of a Nb containing Ni-Fe-Cr-base superalloy are carried out. The influences of initial δ phase (Ni 3 Nb) upon dynamic recrystallization (DRX) behavior are discussed. By analyzing the experimental data, the DRX kinetics models are constructed by considering the synthetical influences of initial δ phase, strain rate and deformation temperature. The proposed DRX kinetics model quantitatively reveals the influences of δ phase on the DRX behavior, which is further verified by transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) observations. δ phase impedes the dislocation movement and supports preferential nucleation sites for DRX during hot deformation. Moreover, due to the pinning effect of δ phase, the DRX grain boundary migration can hardly proceed and the growth of DRX grain is restricted. However, with deformation temperature increasing, δ phase gradually dissolves and the influences upon DRX behavior become weaken. [ABSTRACT FROM AUTHOR]

Two-stage stress-aging experiments of an Al–Cu–Mg alloy were performed over wide range of external stress. The effects of external stress on corrosion resistance of the two-stage stress-aged Al–Cu–Mg alloy are investigated by cyclic potentiodynamic polarization experiments, electrochemical impedance spectroscopy (EIS) tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. It is found that the external stress significantly affects corrosion resistance, which is ascribed to the evolution of aging precipitates. The corrosion resistance can be enhanced by two-stage stress-aging processing at the relatively low external stress. This is because the fine aging precipitates of the stress-aged alloy are more uniformly distributed than those of the as-received and stress-free aged alloys. However, the high external stress easily induces the obvious stress-orientation effects, and enlarges aging precipitates. The coarse precipitates increase the potential difference between aging precipitate and aluminum matrix, as well as the level of distortions of crystal lattice. Then, the corrosion resistance is deteriorated. Furthermore, the optimized external stress for the studied Al–Cu–Mg alloy is about 185 MPa within the tested conditions. [ABSTRACT FROM AUTHOR]

Two-stage stress-aging experiments of an Al–Cu–Mg alloy were performed. The effects of stress-aging temperature on corrosion resistance of the two-stage stress-aged Al–Cu–Mg alloy are discussed. It is found that the stress-aging temperature significantly affects corrosion resistance, which is ascribed to the evolution of aging precipitates. The aging precipitates uniformly nucleate in the first stage of two-stage stress-aging. Increasing stress-aging temperature can enhance the uniform distribution of precipitates, but precipitates easily become coarse in the second stage of two-stage stress-aging. The coarsen precipitates enlarge the potential difference between aging precipitate and aluminum matrix, and decrease the corrosion resistance. So, the corrosion resistance of the stress-aged alloy decreases with the increase of the second stage stress-aging temperature. Furthermore, the optimized stress-aging temperature is about 433 K within the tested conditions. [ABSTRACT FROM AUTHOR]

The strain hardening effect and dynamic recovery behavior of a Ni-based superalloy are studied by isothermal compressive tests. A new unified dislocation-density based constitutive model is developed to characterize the strain hardening effect and dynamic recovery behavior of the studied superalloy. In the developed constitutive model, some material parameters (yield stress, strain hardening coefficient, and dynamic recovery coefficient) are assumed as functions of initial grain size, deformation temperature, and strain rate. An iterative algorithm is designed to predict the high-temperature deformation behaviors under time-variant hot working conditions. The hot deformation parameters and material parameters can be updated in each strain increment. Comparisons between the experimental and calculated flow stresses indicate that the developed constitutive model can accurately describe the high-temperature deformation behavior of the studied superalloy. Furthermore, the developed constitutive model is also successfully used for analyzing time-variant hot working processes. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Corrosion resistance of Al–Zn–Mg–Cu alloy is sensitive to creep-aging processing. [•] The increase of applied stress can enhance the corrosion resistance. [•] The increased temperature first increases and then decreases corrosion resistance. [•] Discontinuous GB precipitate and narrow PFZ improve can corrosion resistance. [Copyright &y& Elsevier]

Abstract: Creep-aging forming, combining both the aging treatment and forming process, has recently drawn much attention of researchers. In this study, the effects of creep-aging processing on the corrosion resistance and mechanical properties of a typical Al–Cu–Mg alloy (2024 aluminium alloy) are investigated by electrochemical corrosion, exfoliation corrosion and uniaxial tensile experiments. The results show that the corrosion resistance and mechanical properties of the studied Al–Cu–Mg alloy are strongly sensitive to the creep-aging processing parameters. The creep-aging processing can change the dimension and density of nanoprecipitates, which greatly affects the corrosion resistance and mechanical properties of the studied Al–Cu–Mg alloy. With the increase of creep-aging temperature, the corrosion resistance and the elongation decrease, while the yield strength and ultimate tensile strength increase. For the materials creep-aged in “under aging” and “peak aging” conditions, the applied stress can increase the ultimate tensile strength, but deteriorate the corrosion resistance. [Copyright &y& Elsevier]

Abstract: We have studied the temperature dependence of the band gap and the decay dynamics of isoelectronic ZnSe1−x O x (x=0−0.053) semiconductors, using photoluminescence (PL) and time-resolved PL spectroscopy. The temperature dependence of the band gap of ZnSe1−x O x decreases with the increase in O concentration. The Kohlrausch law is in good agreement with the O-induced complex decay profiles. As temperature increases, the mechanism of carrier decay undergoes a complicated change from trapped to free excitons. These findings are consistent with the temperature dependence of the stretching exponent β. [Copyright &y& Elsevier]

Abstract: High-entropy alloys with a wide range of novel microstructures and properties are under extensive development. In this study, two equimolar powder mixtures of NiCrAlCoW and NiCrAlCoSi were prepared as cladding materials. They were clad by gas tungsten arc welding on AISI 1050 medium carbon steel substrate to form an in situ synthesized multicomponent clad layer. The microstructure, chemical composition and constituent phases of the clad layers were characterized by FESEM, EPMA and XRD, respectively. A rotating tribometer was employed to evaluate the tribological properties of the clad layers. Experimental results demonstrate that the NiCrAlCoW clad layer is composed of W (precipitates and residual particles), AlNi and Cr15.58Fe7.42C6. The NiCrAlCoSi clad layer contains only a BCC phase. The two clad layers exhibit high hardness, caused by precipitation hardening with different precipitates. The NiCrAlCoW clad layer exhibits strong mechanical interlocking, which results from the complex phase and microstructure of the NiCrAlCoW clad layer. During rubbing, the in situ phase transformation of the NiCrAlCoSi clad layer induces the softening of the matrix. Therefore, the wear performance of the NiCrAlCoW clad layer is better than that of the NiCrAlCoSi clad layer. [Copyright &y& Elsevier]

• The microstructure evolution of a hot deformed Ti-55511 alloy is studied. • A unified constitutive equation is established to model the flow behaviors and microstructure evolution. • The discontinues and geometric DRX mechanisms are dominant. • Increasing the deformation temperature can increase the DRX fraction and sub-grain size. • The chain-like small DRX grains and the flow location occur at high strain rates. The microstructure evolution of a Ti-55511 alloy deformed at high temperatures (from 1163 K to 1253 K) and wide strain rate range (from 10 s−1 to 0.001 s−1) is studied by isothermal compression tests. Based on the sensitivity of dislocation density to deformation conditions, a unified constitutive equation is established to describe the evolution of flow stress, grain size and dynamic recrystallization (DRX) fraction. The results show that the initial grain boundaries are serrated, and the sub-grains and DRX grains are formed with the further deformation. Furthermore, the discontinuous and geometric DRX mechanisms are dominant recrystallization mechanism. Increasing the deformation temperature can increase the DRX fraction and sub-grain size. However, the abnormal growth of β grains occurs at 1253 K. The DRX fraction decreases with the increased strain rate. Meanwhile, the chain-like small DRX grains and the flow localization occur at high strain rates. Also, the established constitutive model is verified by the experimental results, and the correlation coefficient is 0.9929, indicating the excellent prediction ability of the established constitutive model. [ABSTRACT FROM AUTHOR]

A three-stage process, i.e., solution treatment, pre-tensile deformation at intermediate temperatures and aging treatment, is designed to optimize the microstructures and improve the mechanical properties of an Al–Cu alloy. The interactions between the aging temperature (T), aging time (t), precipitation features and mechanical properties of the pre-tensile deformed Al–Cu alloy are investigated by TEM and DSC analysis. The precipitation of phases is largely influenced by T and t. As T is raised from 408 K to 428 K, the contents of θ′′ phases and G.P. zones decrease, while these of θ′ phases increase. If T is further raised, almost all the G.P. zones and θ′′ phases will transform to θ′ phases. However, θ′ phases easily coarsen at high temperature. So, the yield and ultimate tensile strengths first increase and then decrease. In addition, increasing t can enhance the precipitation process, i.e., G.P. zones→θ′′ phases→θ′ phases, which results in the increased content of θ′ phases. Due to the enhanced pinning effect of θ′ phases on dislocations, the yield strength is improved. Based on the comprehensive analysis, the appropriate T and t for the pre-tensile deformed Al–Cu alloy are about 428 K and 24 h, respectively. Image 1 • Interactions between aging, precipitation and mechanical properties of the deformed Al–Cu alloy are studied. • Increasing aging time and temperature can raise the content and size of θ ' phase. • The rise of aging time and temperature can enhance the precipitation process G.P. zones.→θ" phases→θ′ phases • Yield and ultimate tensile strengths first increase and then decrease with the increase of aging temperature. • The appropriate aging temperature and time are about 428 K and 24 h, respectively. [ABSTRACT FROM AUTHOR]

Hot tensile tests are performed on an Al-Zn-Mg-Cu alloy at larger temperature and strain rate ranges. The influences of deformation parameters and stress triaxiality on hot tensile fracture characteristics, fracture mechanisms and microstructural evolution are discussed. It is found that the maximum tensile load increases with raising stress triaxiality. The fracture strain rises with increasing strain rate or decreasing stress triaxiality. When the deformation temperature is raised, the fracture strain firstly increases and then decreases. Dynamic recovery (DRV) is the main softening mechanism. At low strain rates or high deformation temperatures, the partial dynamic recrystallization (DRX) behavior occurs, and continuous dynamic recrystallization (CDRX) is the main DRX mode. The dominant fracture mechanism is the coalescence of micro-voids at the tested deformation conditions. Due to the occurrence of DRX, the intergranular fracture also occurs at low strain rates or high deformation temperatures. The low strain rate or high stress triaxiality easily induces the appearance of micro-voids, which accelerate the fracture failure. • Effects of deformation conditions and stress triaxiality on hot tensile fracture features and microstructures are studied. • The fracture strain rises with increasing strain rate or decreasing stress triaxiality. • At low strain rates or high temperatures, continuous dynamic recrystallization (CDRX) is the main DRX mode. • Dominant fracture mechanism is the coalescence of micro-voids at the tested deformation conditions. • Low strain rate or high stress triaxiality easily induces the appearance of micro-voids, accelerating the fracture. [ABSTRACT FROM AUTHOR]

Spheroidization and dynamic recrystallization (DRX) mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. It is found that the spheroidization of lamellar α phases and DRX of β phases, which are obviously influenced by deformation conditions, are the main softening mechanisms. The spheroidization fraction of lamellar α phases first increases with the raised temperature or strain rate. However, the spheroidization fraction of lamellar α phases begins to drop at about 700 °C as the strain rate is higher than 0.01 s−1, and the maximum spheroidization fraction of lamellar α phase is about 2.3%. This phenomenon is attributed to the Implanting-Mechanism, which is induced by the common or close orientation relationships of the spheroidized and equiaxed α phases, as well as few dislocations between the spheroidized and equiaxed α phases. Contrarily, the lamellar α phases are obstructed from equiaxed α phases by a mass of dislocations. Additionally, the DRX degree of β phases increases with the reduced temperature or the raised strain rate. • Spheroidization and DRX mechanisms of a Ti-55511 alloy during hot compression in α+β region is investigated. • Spheroidization fraction of lamellar α phase first increases then drops with the raised strain rate. • The maximum spheroidization fraction of lamellar α phase is about 2.3% near 700 °C and 0.01 s−1. • Implanting-Mechanism, induced by the close orientation relationships of spheroidized and equiaxed α phases, is proposed. • The DRX extent of β phases increases with the reduced temperature and raised strain rate. [ABSTRACT FROM AUTHOR]

The hot deformation behavior and microstructural evolution of a Ti-55511 alloy in α+β region are investigated by uniaxial compressive tests at elevated temperatures. Transmission Electron Microscope (TEM) and Electron Backscattered Diffraction (EBSD) are employed to observe the microstructures. The spheroidization of lamellate α phases and the dynamic recrystallization (DRX) of β grains are analyzed. It is observed that the flow characteristics are prominently affected by deformation parameters, i.e., the flow stress, peak stress and flow softening stress decrease with the reduced strain rate or the increased deformation temperature. When the deformation temperature is slightly raised or the strain rate is properly reduced, the fraction of spheroidized α phase greatly increases. The substructures are formed in the lamellate α phase, and the β phase wedges into the lamellate α phase. Then, the lamellate α phase is fragmentized and spheroidized. The DRX of β grains is promoted with the raised strain rate or the reduced deformation temperature. Additionally, the higher dislocation density and obvious dislocation pile-ups can be noticed at the α/β interface, which induces the DRX nucleation of β grains at the α/β interface. • Hot deformation behavior and microstructure evolution of a Ti-55511 alloy in α+β region are investigated. • The fraction of spheroidized α phase increases with increasing deformation temperature or reducing strain rate. • The substructures are easily formed in the lamellate α phase, and the β phase wedges into the lamellate α phase. • The DRX of β grains is promoted with the raised strain rate or the reduced deformation temperature. • The obvious DRX of β grains easily nucleate at the α/β interface. [ABSTRACT FROM AUTHOR]

The metadynamic recrystallization (MDRX) characteristics of a Ni-Cr-Mo alloy are investigated using the double-pass thermal compression tests. The impacts of double-pass compression parameters on the kinetic features and microstructural changes are clarified. Results signify that the MDRX softening behaviors are remarkably accelerated with increasing of compression temperature, first-pass strain or strain rate. The bulging of the MDRX grain boundary and the annihilation/interaction of substructures become weaken at low compression temperature or small first-pass strain, enhancing the grain refining during MDRX. However, the MDRX grains coarsen rapidly with decrease of strain rate. Based on the comprehensive impact of double-pass compression parameters on softening fraction and grain size, the MDRX kinetic model and MDRX grain size model are developed. The predicted results are well matched the experimental data, which suggests that the established models can precisely characterize the changes of softening characteristics and grain size of the researched alloy during MDRX. • The kinetic behaviors and microstructural evolution of a Ni-Cr-Mo alloy during MDRX are revealed. • Softening behavior caused by MDRX are prominently affected by the evolution of substructures and MDRX grains. • The annihilation/interaction of substructures exert a significant influence on the bulging and serrated behaviors of MDRX grain boundary. • The proposed kinetic equation and grain size model can precisely forecast the variation of softening fraction and grain structure during MDRX. [ABSTRACT FROM AUTHOR]

The flow characteristics of a Ni-Mo-Cr base alloy are researched by the double-stages hot compression with step-strain rates. Electron backscatter diffraction (EBSD) as well as transmission electron microscopy (TEM) are adopted to systematically comprehend the influences of compressed parameters on microstructural changes. To forecast the hot compressed behaviors, a physically-based constitutive model with considering the evolution characteristics of dislocation density, subgrain and the grain structure is developed. Experimental results indicate that the elevated compressed temperature can exacerbate the dislocation consumption, subgrain rotation/interaction and dynamic recrystallization (DRX) grains coarsening. However, the prominent dislocation accumulation, subgrain generation and the refinement of DRX grains come up as the strain rates at the first or second stage of hot compression are ascended. The discontinuous DRX characterized by the bulging/serrated of grain boundaries is the major DRX nucleation mechanism of the researched alloy. The forecasted compressed stress, grain size and DRX fraction well match the tested results, which indicates the constructed physically-based constitutive equations can be employed to model the high-temperature features and microstructural changes of the studied Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates. • The flow characteristics of a Ni-Mo-Cr base alloy in double-stages hot compression with step-strain rates are revealed. • With increasing strain of first stage, high density substructures are formed and the bulging of DRX grain boundary is inhibited. • The consumption of substructures and coarsening of DRX grains are enhanced with raising of compressed temperature. • The major DRX nucleation mechanism of the researched alloy in double-stages hot compression with step-strain rates is DDRX. • The developed physically-based constitutive model can precisely reproduce the flow behaviors and microstructural changes. [ABSTRACT FROM AUTHOR]

Three alloys with the same molybdenum equivalent (Mo [eq] , Mo [eq] ≈9) were prepared by adjusting the Mo and Cr contents in novel Ti–3Al-1.2V–1Zr–2Nb–1Sn- x Mo- y Cr (x = 6,4,1; y = 2.7,4,5.7, wt.%) alloys. Differences of microstructures, mechanical properties and deformation mechanisms in the three alloys under the same solution and aging treatment conditions were investigated. Effect of Mo on grain refinement during quenching is more notable than Cr in multi-element alloys. The change of elements ratio has little effect on the strengths of these alloys, but a significantly impact on their ductilities. After solution treated at 780°C and aged at 530°C, three alloys show similar strength (UTS~1400 MPa) but the difference of their ductilities is more than 5%. The alloy with the same Mo and Cr contents exhibits the best elongation (El~14.0%). Moreover, detailed analyses of transmission electron microscopy (TEM) results indicate that the dislocation slipping is the main deformation mechanism in β matrix, and the slipping hindered by various boundaries (grain boundaries and α GB , α s /β and α p /β interface) is the main strengthening mechanism. The ductility difference in the three alloys is mainly caused by the deformation ability of α phase. Formation of α-twin, α sub-boundary and other deformation products could accommodate local deformation and relieve stress concentration. This study provides a good guidance for high strength and toughness titanium alloy design. ● The effect of Mo on grain refinement during quenching is more notable than Cr in multi-element alloys ● The change of elements ratio has little effect on the strength of these alloys, but shows a significantly impact on ductility ● The difference of fracture mode and cracks propagation pathway under solution and aging treatment were compared ● The differences of deformation mechanism in three alloys with the same Mo [q] under the same heat treatment conditions were investigated [ABSTRACT FROM AUTHOR]

In this paper, the Ti-55511 (Ti-5Al-5Mo-5 V-1Cr-1Fe) alloy was cross-rolled in β field with various rolling reductions, following by short-time aging at 600 °C. The evolution of microstructures and mechanical properties during cross rolling was investigated, and the effect of the deformation features on the precipitation behavior of α phase was elucidate. The results indicated that cross rolling can effectively promote the grain refinement of the β phase, which results in increased tensile strength and weakened texture. Kink bands, stress/strain-induced martensite phases and β-twins were activated in the cross-rolled β matrix, which have a positive influence on the increase of ductility. Besides, the β twin was observed near the β grain boundaries where a high density of dislocations was developed, and the formation of β twins was dependent on the local element content. As a result of soaking in the α + β field, the α phase prefers to precipitate from the pre-existing dislocation structures and martensite phase. • The refinement process of the β phase was revealed. • Some deformation features, such as kink band, SIM phase and β-twins, were observed in the cross-rolled sample. • The mechanical properties were highly dependent on the microstructure changes. • The formation of β-twin has a close relationship with the local element content. • The α phase preferred to precipitate from the pre-existing dislocation structures and SIM phases. [ABSTRACT FROM AUTHOR]

A lamellar near β-Ti alloy was subjected to cyclic tensile loading at room temperature. Transmission electron microscopy (TEM) and high resolution TEM (HRTEM) investigation revealed that the deformation mechanisms of α-phase were found to be changing with increasing loading cycles, from mechanical twinning to martensite transformation. To be specific, at the beginning of straining, the formation of mechanical α-twins was the dominant deformation mechanism to accommodate the applied strain. As the increasing cycles, the secondary twin and hierarchical structure formed in α laths. During further straining, the noticeable groove was observed at the α/β grain boundary. Meanwhile, dispersed nanosized α" martensite phase formed in the α plate and the number of α-twins sharply decreased at this stage. This work will provide a basis for the enhancement of load bearing capabilities of near β-Ti alloys. [ABSTRACT FROM AUTHOR]

This work systematically investigates the microstructural evolution and deformation mechanism of lamellar and equiaxed Ti-55511 alloys during hot deformation. For textural discrepancies, the classical Burgers orientation relationship in lamellar microstructures broke down owing to dynamic recrystallization (DRX) of the α phase during hot deformation, while the intensities of micro-textures increased due to the elongated α phase parallel to the rolling direction. The anisotropies of the mechanical properties in deformed lamellar microstructures were influenced by the DRX of the α phase and inhomogeneous deformation, such as the formation of shear bands. With regard to equiaxed microstructures, dynamic recovery (DRV) of the α phase predominated, forming elongated α grains perpendicular to the loading direction, which increased the anisotropy. However, the anisotropy from DRV was compensated for by the DRX of the β phase. DRV α grains with serrated boundaries promoted the DRX of the β phase due to the accumulation of dislocations. The localized shear band found in the lamellar α plate during spheroidization comprised two ribbon-like { 1 1 ¯ 01 } twins, which are abreast but non-parallel and play critical roles in the evolution of α phases. The activation of this type of twin is heavily dependent on the aspect ratios of the α phases. These studies provide insight into the deformation behavior of lamellar and equiaxed near β-Ti alloys, which paves the way for the development of ultra-fine-grained microstructures with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

Cross rolling (CR) process was successfully applied to solve the grain refinement of the equiaxed microstructure. In this work, microstructural evolution, textural discrepancy, mechanical properties and twin-accommodated mechanisms were studied in the equiaxed near β titanium alloy for different modes of rolling i.e. unidirectional rolling (UR) and cross rolling (CR). The results showed that CR can effectively promote the grain refinement of both the α and β phases as compared to UR, which leads to weaker texture intensities of the CR sample, and results in an elevated ductility. The { 10 1 ‾ 1 } twinning is the major twin-accommodated mechanisms observed in near β-Ti alloys. The { 10 1 ‾ 1 } twinning accommodated the rotation of subgrains and tailored subgrains orientation during the UR process. In comparison, during the CR process, accumulated stress increases the volune fraction of residual activated twins. Furthermore, with the increasing deformation, the α phase was progressively fragmented into fine grains by the thickening and extension of { 10 1 ‾ 1 } twins. The results in the present study can be applided to optimize deformation processes to achieve ultra-fine grained microstructures, and to figure out the refinement of massive-grained microstructures. [ABSTRACT FROM AUTHOR]