Deformation Temperature Range Research Articles

The influence of phosphorus microalloying on the structure formation of CuZn32Mn3Al2FeNi multicomponent brass

Phosphorus in brass can have both a positive effect, such as improving mechanical properties, increasing corrosion resistance and machinability, and a negative effect, such as adversely affecting weldability and causing cracking. The study of the role of phosphorus in the processes of brass structure formation is of practical relevance, since it helps optimise the properties of the material, reduce the risk of defects, improve treatment processes and control properties and quality. The work covers the study of the role of phosphorus in brass, the need to control its content during production by limiting the share of secondary use. The study revealed the possibility of a positive effect of modifying copper alloys with phosphorus in order to improve performance properties, as well as the prospects of using phosphorus as a safe replacement for lead in brass. The authors assessed the content and distribution of phosphorus impurity at a concentration of 0.005% in a brass sample of the CuZn32Mn3Al2FeNi grade, studied the nature of its interaction with other components of the alloy and the changes occurring at different temperatures of heat treatment. It has been found that phosphorus actively participates in diffusion processes and forms phosphides in both defective and defect-free blanks. When heated to the hot deformation temperature range, phosphorus redistribution occurs, phosphide locally dissolves, and metastable inclusions form. Due to differences in the concentration of elements in areas adjacent to the phosphide, the brass structure changes leading to the formation of areas different from the matrix β-phase. Manganese phosphide in brass can improve its mechanical properties and cutting ability, but an excess of this compound can lead to problems with strength, crack resistance, and moulding.

EVALUATION OF TECHNOLOGICAL PLASTICITY OF HIGH BORON CORROSION-RESISTANT STEEL DURING HOT DEFORMATION OF PIPES USED FOR SPENT NUCLEAR FUEL STORAGE

Statement of the problem. The sustainable development of the global nuclear power industry in the future depends on how effectively the problems of radiation safety and nuclear proliferation are addressed. Such problems occur, among other things, at the final stage of the nuclear fuel cycle – spent fuel management. This task is currently on the agenda of both the international community and national governments of countries that develop or intend to develop nuclear energy [1−3]. Today, in connection with ensuring the safety of nuclear energy, boron-containing steels are widely used in the world practice as a material for biological protection and for the manufacture of special equipment parts. This is due to the fact that the B10 isotope in steels provides neutron capture [4]. Hexagonal pipes made of high-boron steel were needed to shield the support cover of the compacted spent fuel storage facility at nuclear power plants. Corrosion-resistant steels alloyed with boron are widely used in the nuclear power industry due to their special nuclear properties. During the operation of nuclear power plants, fuel assemblies that have served their useful life must be stored in special storage facilities using containers – hexagonal tubes made of 04Сr14Ti3B2V steel. To reduce costs during in the construction and operation of NPPs, part of the spent nuclear fuel management should be performed at Ukrainian enterprises. This will provide a significant import substitution effect. To manufacture hexagonal tubes from 04Сr14Ti3B2V steel according to the ingot-hot deformation-profiling-heat treatment scheme, it is necessary to develop the parameters of hot deformation and subsequent technological operations. The use of these pipes in compacted spent fuel storage facilities of NPPs will allow to increase the storage capacity by 2 times, which will give a significant national economic effect Material and methods of research. Material used for the study was steel 04Сr14Ti3B2V (CS-82), smelted using two variants (vacuum-induction – “VI” and vacuum-induction followed by vacuum-arc remelting – (“VD”). Steel grade 04Сr14Ti3B2V belongs to high-alloy, corrosion-resistant ferritic steels with a high boron content of up to 2 %. The method of differential thermal analysis was used to study the phase transformation temperatures in the steel. X-ray diffraction and micro-X-ray spectral analysis were used to assess the phase state. The steel samples were tested for weldability After cooling, the welded samples were subjected to X-ray transmission [5]. Hot twisting tests and mechanical tests at high temperatures were also performed. The macro- and microstructure of the metal was studied. Results. The macro- and microstructure of steel was evaluated depending on the smelting method. The phase composition of the steel was studied. The study of the plastic properties of steel ChS-82 by means of penetration and hot twisting tests showed that the temperature range of maximum plasticity is in a wide range (from 1 025 to 1 150 0C) with a rather low resistance to deformation. During hot deformation in the temperature range of 1 175 0C and above, metal fracture was observed along the grain boundaries at the melting points of the Cr−Fe−B boride phase. The optimal temperature range for hot deformation of steel ChS-82 is 1 000−1 050 ⁰С. Scientific novelty. For corrosion-resistant high boron steel used for spent nuclear fuel storage, the temperature range of hot deformation was selected and the structural and phase composition was estimated, which will allow deforming the metal on the piercing mill and manufacturing pipes.

Determination of Hot Workability of 5Cr5MoSiV1 Steel Based on Hot Processing Map

The evaluation of the hot workability of 5Cr5MoSiV1 steel with high deformation resistance is crucial for the controllability of the hot forging process. Based on the isothermal compression at deformation temperature of 950–1200 °C and strain rate of 0.01–10 s−1, the flow behavior of 5Cr5MoSiV1 steel is demonstrated. As the strain rate increases, the typical characteristics of the true stress–strain curve indicate that the dynamic softening mechanism changes from dynamic recrystallization to dynamic recovery. Moreover, the hot working window determined by the hot processing map from the modified J–C constitutive model is constructed for the forging process of the material. Through microstructure verification, the optimal hot working window is within the range of deformation temperature from 1000 to 1185 °C and strain rate from 0.01 to 0.202 s−1. Furthermore, the forging upsetting tests of the large cylindrical specimens are used to confirm the insecurity of hot deformation parameters outside the optimum hot working window. The implementation of this study can provide a theoretical basis for the determination of hot forging process parameters for 5Cr5MoSiV1 steel.

Effect of Ti micro-addition on the hot tensile behaviour, microstructure and fractography of low-C high-manganese steels

The aim of the work was to determine the effect of Ti micro-addition on the hot tensile behaviour, microstructure and fractography of two low-C high-manganese steels with additions of Si and Al. The hot tensile tests were performed using the Gleeble 3800 thermomechanical simulator. Samples were stretched at a temperature range from 1050 ℃ to 1200 ℃ at a strain rate of 2.5·10 3 s−1. The microstructure of the tested high-manganese steels under conditions of hot deformation was influenced by strain hardening and simultaneous dynamic recrystallization, as well as precipitation processes-depending on the chemical composition of the alloy and plastic deformation parameters. The analysis of the curves registered in the hot tensile tests indicated that a decrease of strain hardening was the result of the dynamic recrystallization. Hot tensile curves of the Ti-micro-alloyed steel were characterized by higher yield stress compared to the Ti-free steel. The Ti micro-addition with a concentration of 0.075 wt.% guaranteeing stable TiN-type nitrides eliminated the possibility of precipitating AlN-type nitrides and complex MnS-AlN type non-metallic inclusions, which are harmful to hot ductility. Fracture modes of the Ti-free steel showed a mixed nature from 1050 ℃ to 1150 °C, i.e. ductile fracture and numerous cavities and voids were identified. As the deformation temperature increased to 1200 °C, the fracture character was brittle with numerous inter-crystalline cracks along austenite grain boundaries. The addition of Ti improved significantly the hot ductility behaviour characterized by higher values of flow stress and reduction in area as well as ductile fracture modes in the entire high deformation temperature range.

On the influence of iron and silicon content on the phase composition of the Al-Fe-Si system

Increasing interest in intermetallic phases of the Al-Fe-Si system is associated with their high specific strength, corrosion and wear resistance, as well as the low cost of their production. To exhibit the most successful combination of properties, it is necessary to impart a specific compact morphology to the precipitated intermetallic phases. It is important to create an alloy with a composition capable of accepting plastic deformation. The purpose of the work is to develop the composition of an Al-Fe-Si system alloy capable of withstanding plastic deformation and determining the corresponding deformation interval. Based on computer modeling, an alloy composition capable of accepting plastic deformation was developed and the corresponding deformation interval was determined. The simulation was carried out in the ThermoCalc software package, TCAL8 database. It has been revealed that alloys with a high content of both silicon and iron are not characterized by the formation of a single-phase region, however, with a certain combination of alloy components, it is possible to achieve a quasi-single-phase structure, when the content of one phase is observed to be more than 90%. The solidus temperatures for different alloy compositions and the boundary conditions for the existence of phases have been determined. The α phase is present in the system from a temperature of 770°C up to a temperature of 446°C. In composition, it is found in the range from 5 to 35% iron with an amount of silicon of 10% and from 0 to 15% silicon with an iron content of 30%. The maximum amount of α phase was obtained for the Al60-65 alloy; Fe30-32; and Si5-10%, deformation temperature range is 600-450°C. Deformation in this region will ensure processing in a quasi-single-phase region without melting.

Hot deformation behaviors and microstructure evolution of a supersaturated nickel-based superalloy

The hot deformation behaviors and microstructure evolution of a supersaturated Ni-based superalloy GH4742 were investigated by isothermal compression tests. The deformation temperature range encompassed γ' sub-solvus (1000–1075 °C) and super-solvus (1100–1150 °C), with strain rates ranging from 0.001 s−1 to 1 s−1. Separate Arrhenius-type constitutive equations were established considering the re-precipitation of the γ' phase. The correlation coefficient between the calculated stresses and the experimental data was as high as 0.997, which indicated that the rheological behaviors of the material during hot deformation processes could be accurately analyzed by the constitutive relationship. Additionally, the activation energies for the γ + γ' two-phase region and the γ single region were calculated to be 949.08 kJ.mol−1 and 437.66 kJ.mol−1, respectively. Microstructural analysis revealed that the partial dynamic recrystallisation (DRX) occurred in the γ' sub-solvus regime whereas the full DRX occurred in the γ' super-solvus regime. The low DRX fractions in the γ' sub-solvus regime were attributed to the presence of near-spherical re-precipitated γ' phase, which effectively suppresses the nucleation and growth of new grains. The deformed grains were oriented in the <101> direction parallel to the compression direction. Meanwhile, the non-monotonic relationship between the degrees of DRX and strain rate was observed due to the adiabatic temperature rise. The retarding effects of solute elements on the grain growth in the γ' super-solvus regime were determined by comparing the recrystallized grain sizes from theoretical analysis and experiment values. This work can provide guidance for understanding the deformation behaviors of the alloy and achieving desired microstructures.

ОСОБЛИВОСТІ НЕОДНОРІДНОСТІ ПЛАСТИЧНОЇ ДЕФОРМАЦІЇ ГЕТЕРОФАЗНИХ НЕМЕТАЛЕВИХ ВКЛЮЧЕНЬ В СТАЛЯХ

The nature and level of plasticity of microcomposite heterophase inclusions in steels under pressure treatment condition was investigated. Plastic phases in heterophase inclusions of various types under the conditions of hot and cold deformation of steels were investigated. It is shown that each type of inclusions, which are microcomposite formations in steels, is characterized by its own laws of the development of deformation processes, which are determined by their chemical and phase composition, structure, deformation capacity of inclusion phases. The generalized of the plastic behavior of heterophase inclusions of various types with a complex structure have been established and inhibitory effect of non-deformable inclusion phases on the behavior of plastic phases in a wide range of deformation temperatures of steels has been established. The peculiarities of the nature of plasticity of heterophase inclusions with different compositions and structures are discussed. The use of the obtained results will make it possible to develop technologies for obtaining steels with a regulated content and types of heterophase non-metallic inclusions, which will significantly increase their technological plasticity, as well as prevent the formation of various types of defects during pressure treatment of steels.

Thermal Mechanical Behavior and Microstructure Characteristics of As‐Cast FeCrNiAl Steel

To find the suitable deformation temperature range for the as‐cast Fe–5.5Cr–5.5Ni–3.0Al–0.27C high‐strength lightweight steel, the thermal mechanical behavior and the dependent microstructure characteristics are studied to investigate the high‐temperature mechanical response of the steel. In the results, it is shown that the microstructure of the steel owns a dendrite framework consisting of the martensite dendrite and the interdendritic austenite, among which precipitations of NiAl, Ni3Al, and δ‐Fe are induced by high‐temperature deformation. The flow stress dependence of deformation temperature shows two different variation tendencies, corresponding to the varied deformation mechanisms of strain‐induced precipitation of second phases and δ‐Fe nucleation, and then resulting in different variation of dislocation density. It is found that a periodical fluctuation of flow stress appears as the alternative occurrence of first rise and then drop followed by drop and rise, and the phenomenon is inferred to be caused by local dynamic recrystallization in the dendrites and the neighboring interdendritic spacings.

Effect of hydrogen on thermal deformation behavior and microstructure evolution of MoNbHfZrTi refractory high-entropy alloy

The study examined the thermal-deformation behavior of an MoNbHfZrTi refractory high-entropy alloy (RHEA), which were hydrogenated using a liquid hydrogenation method and then subjected to high-temperature uniaxial compression in the deformation temperature range of 1100–1250 °C and strain rate range of 0.5–10−3 s−1. Test results showed that: (1) When the deformation temperature was between 1100 and 1250 °C, hydrogen addition led to increased high-temperature peak stress of the alloy at higher strain rates of 0.5 and 10−1 s−1. At a low strain rate of ∼10−2 s−1, the addition of hydrogen causes a decrease in the high-temperature peak stress. However, at a lower strain rate of ∼10−3 s−1, hydrogen addition has insignificant effects on the high-temperature peak stress. (2) At a higher strain rate of ∼0.5 s−1, the major reasons for hydrogen-induced hardening of the peak stress were solution strengthening and dislocation pinning. (3) At a low strain rate of 10−2 s−1, the reason for decrease of the peak stress was that the hydrogen addition promoted the formation of precipitated phases, thereby facilitating dynamic recrystallization (DRX), and making the microstructure more uniform at high temperatures.

Study on the precipitation behavior of the hot deformed 2195 Al–Li alloy after online quenching and its relation to the age-hardening response

The fine-grained structures following deformation would be retained by using online quenching treatment which would achieve the purpose of simplifying formation process and reducing energy consumption. This study examined the effects of hot deformations on grain morphology, dynamic precipitation behavior and age-hardening response of the alloy after online quenching. And the dynamic precipitates re-solution behavior after online assisted heating were analyzed. The results indicated that the age-hardening response of the alloy was primarily controlled by the deformation temperature, and the appropriate deformation temperature range for online quenching was determined as 475–500 °C. Most of the deformed grains exhibited <110>Al//CD orientation. The increase in deformation temperature induced the transformation of the deformed grains from <110>Al//CD to <100>Al//CD orientation. A number of coarse second phases would be observed when the alloy was deformed below the optimal temperature range (e.g. 450 °C). For this case, it was suggested that the deformed alloy was heated by online assisted heating for a short time with the remaining heat after hot deformation, promoting most of the dynamic precipitates to be re-dissolved before online quenching. As a result, the deformation temperature window suitable for online quenching in 2195 Al–Li alloy could be broadened to 450–500 °C.

Constitutive Modeling for Flow Stress and Processing Maps of a 0.2C–2.0Mn–0.5Cr Microalloyed Steel

Low‐carbon microalloyed steel with the microstructure of bainite is frequently utilized to produce automotive parts. The systematic investigation of the hot deformation behavior can serve as a reference for the optimization of deformation process parameters. The hot deformation of 0.2C–2.0Mn–0.5Cr microalloyed steel is studied. Based on the stress–strain curve, an Arrhenius model with strain compensation is established. The correlation coefficient R2 and the average absolute relative error calculated according to this model are 0.962 and 4.871%. The microstructure evolution at the strain of 0.90 is studied. In the stable region with substantial power dissipation, the microstructure is uniformly fine. The strain rate is high in the stable region with low‐power dissipation, and the room‐temperature microstructure after deformation retains a large amount of deformation storage energy and fine substructures. During deformation, the banded structures are formed in the instable region. The difference in dislocation density between the band structure and the nearby regions promotes the formation of necklace microstructures. Therefore, the 0.2C–2.0Mn–0.5Cr microalloyed steel has an ideal deformation process window in the range of a hot deformation temperature of 880–920 °C and a strain rate of 0.1–0.3 s−1.

Dependence of Electrochemical Characteristics of a Biodegradable Fe-30Mn-5Si wt.% Alloy on Compressive Deformation in a Wide Temperature Range

Fe-30Mn-5Si alloy subjected to a compression test at various deformation temperatures ranging from 350 to 900 °C with a strain rate of 1 s−1 are studied. It was found that the Fe-30Mn-5Si alloy exhibits high resistance to the dynamic recrystallization process in a whole studied range of deformation temperatures. There are no differences in structure formation in the zone of action of tangential tensile stresses and peripheral and central zones of localized compressive stresses. The room-temperature X-ray diffraction study shows the presence of a single-phase state (FCC γ-austenite) after deformation temperature range from 350 to 700 °C and a two-phase state (FCC γ-austenite + HCP ε-martensite) after deformation test at 900 °C. The presence of a two-phase state provides a higher rate of biodegradation compared with a single-phase state. The changes in the biodegradation rate dependence on the structure change with an increase in the deformation temperature are explained. Favorable temperature regimes for subsequent thermomechanical processing are proposed based on the relationship between structure formation and biodegradation rate to obtain semi-products from the Fe-30Mn-5Si alloy.

Constitutive Modeling of Hot Deformation Behaviors and Processing Maps of Mg–4.83Gd–2.36Nd–0.21Zr Alloy

Accurately assessing the hot workability and flow behavior is crucial in the preparation of high‐performance wrought Mg–rare earth (RE) alloys. The hot deformation behaviors and workability of Mg–4.83Gd–2.36Nd–0.21Zr alloy are examined via Gleeble 3500 thermosimulation tests across a range of deformation temperatures from 350 °C to 450 °C and strain rates ranging from 0.001 to 1 s−1. The experimental results reveal that the flow stress of the experimental alloy decreases as the temperature increases and the strain rate decreases. The activation energies for deformation (Q) of the experiment alloy are calculated by the hyperbolic constitutive equation and range from 186.78 to 234.97 kJ mol−1. Strain compensation is incorporated in constitutive modeling, resulting in the correlation coefficient (R) of 0.9865 and the average absolute relative error (AARE) of 5.4639%. Further, the processing maps are constructed at different strains based on dynamic material models, from which the feasible processing window of the experimental alloy is determined in the areas of deformation temperatures of 425–450 °C and strain rates of 0.01–0.1 s−1.

Dynamic recrystallisation behaviour and intrinsic workability of 12%Cr USC rotor steel during hot deformation

ABSTRACT Hot deformation of 12%Cr USC rotor steel was investigated by hot compression testing over a temperature range of 900 °C to 1,200 °C at strain rates of 0.001 s−1–1 s−1 with the use of a Gleeble–1500D thermal-mechanical simulator. The true stress–strain curves were obtained and showed that the stress increased with a decrease in temperature, an increase in strain rate, or both. Based on the stress–strain curves, processing maps of 12%Cr USC rotor steel under various strains were established, and the Zener-Hollomon (Z) parameter was calculated, it increased with decreasing temperature or increasing strain rate. Combining the values of the Z parameter and the microstructure after thermal compression, it was found that dynamic recovery was the main softening mechanism at lnZ > 39.09, and dynamic recrystallisation (DRX) became the main softening mechanism at 39.09 > lnZ > 32.56. When lnZ < 32.56, DRX occurred completely, and a small amount of recrystallised grains formed. The deformed microstructures showed that 12%Cr USC rotor steel incurred a continuous dynamic recrystallisation mechanism, a discontinuous dynamic recrystallisation mechanism, and a geometric dynamic recrystallisation mechanism during the hot deformation process. The intrinsic workability of 12%Cr USC rotor steel was explored by analysing the processing maps. It was found that the best forging process parameters range of the material in the actual production process was a deformation temperature range of 1,100 °C to 1,200 °C and a strain-rate range of 0.01 s−1–0.1 s−1.

STUDY OF LOW-TEMPERATURE THERMOMECHANICAL BEHAVIOR OF THE Ti-18Zr-15Nb SUPERELASTIC ALLOY UNDER DIFFERENT TEMPERATURE-RATE CONDITIONS

The biomedical alloy Ti-18Zr-15Nb (at.%) with shape memory was subjected to a true deformation e = 0.7 in three different modes: in the temperature range from 20°C to 600°C at deformation rate ξ = 0. 1 s-1; at temperatures 250°C and 300°C with strain rates ξ = 0.1, 1 and 10 s-1; deformation at 300°C and strain rate ξ = 0.1 s-1 after annealing at 300°C (τ = 10, 60, 300, 600 and 1200 s). It is established that with increasing temperature the conditional yield strength σ0.2 continuously decreases, at that in the temperature range of deformation temperatures 250°С-300°С the increase of maximum stress σmax is observed. In the temperature range from 200°С to 400°С fluctuations are observed on the flow curves, the amplitude of which increases with increasing temperature. The change σ0.2 and σmax, as well as the presence of oscillations on the strain diagrams are connected with the course of dynamic strain aging accompanied by the release of excess ω-phase particles at temperatures 200°С - 400°С. Increasing the strain rate at temperatures of 250°С - 300°С has a strong effect on the deformation behavior of the alloy due to a significant increase in temperature during the deformation process. Thus, increasing the strain rate up to ξ = 10 s-1 leads to a stepwise decrease in stress, starting from e ≈ 0.3, after which the plastic flow curve acquires a wave-like form with a low frequency of stress fluctuations. The main phase after all modes of thermomechanical tests is the BCC β-phase. At annealing of 300°С and an exposure of more than 300 s weak ω-phase lines are observed, and at deformation after aging significantly broadened ω-phase lines are observed only after prolonged exposure (1200 s).

Analysis on the Key Parameters to Predict Flow Stress during Ausforming in a High-Carbon Bainitic Steel

Since flow stress is an important parameter in the processing and application of metallic materials, it is necessary to trace the flow stress during austenite deformation. Thermal compression deformation of austenite in a high-strength bainitic steel was conducted using a Gleeble-3500 thermo-mechanical simulator, within the deformation temperature range of 400 °C~900 °C. By analyzing the stress–strain curves and strain-hardening exponent, the effects of strain hardening and dynamic recovery on the dislocation density of the material during the thermal processing were considered in the present work. Based on the general form of the Kocks–Mecking–Estrin (KME) model, the effects of deformation temperature and strain on the key parameters of the model were clarified. Differing from other work which commonly terms m (strain rate sensitivity exponent) and k2 (dimensionless parameters for dynamic recovery) as constants, the current models consider the quantitative relationship between key parameters and deformation temperature and strain. The results show that m is an exponential function related to temperature and strain, which decreases with the increase in strain. Meanwhile, k2 is a temperature-dependent polynomial function that increases as the deformation temperature increases. Finally, a modified constitutive KME model was proposed to predict the austenitic plastic stress with strain. Using established m-ε and k2-T models, the predicted curves are in good agreement with the experimental measurements.

Fatigue life and failure mechanism of nylon 66 cord/rubber composites under wide temperature range

This work simulates the real harsh service conditions of Fiber-reinforced polymer composites (FRPC), and the dynamic adhesion and failure mechanism of nylon 66 (PA66)-reinforced natural rubber (NR) composites under large deformation and wide temperature range are deeply studied by comprehensive analysis of the interfacial adhesion evolution, microstructure and failure damage location of the composites, interfacial heating rate, and modulus ratio of PA66/NR. The failure mechanism of PA66/NR composites is interfacial debonding at −20 °C, 25 °C and 80 °C, whereas that at 120 °C is matrix cracks. Interestingly, at −20 °C, the crack expansion at the interface is slow, and the samples show two-stage damage during fatigue, resulting in the highest fatigue life. At 80 °C, the interface heating rate and modulus ratio of the PA66/NR composites is the lowest, and thus the fatigue life is higher than that at 25 °C and 120 °C. Keywords: fiber reinforced polymer composites, fatigue life, failure mechanism.

Hot working processing and microstructure characterisation of as-cast high manganese TWIP steel

ABSTRACT The hot compression of the as-cast Fe-21Mn-0.7C–0.1Si twinning induced plasticity (TWIP) steel was investigated at the deformation temperature range of 950–1100 °C and strain rates of 0.01–5 s−1, using a GleebleTM thermo-mechanical simulator, to determine the hot deformation behaviour and analyse the recrystallisation mechanism. The results showed that the flow curves were characterised by yield-point-elongation (YPE) and dynamic recrystallisation (DRX) as the principal restoration mechanisms. The activation energy (Q) was calculated to be 394.975 KJ mol−1, which implies that the recrystallisation is sluggish in the whole range of the deformation conditions. Furthermore, the processing maps were generated according to the dynamic material model (DMM). The processing map was subdivided into different domains for the microstructural observations. The ideal hot deformation parameters of as-cast high Mn TWIP steel were obtained in the deformation condition range of 1087–1098 °C/10−1.2-10−0.17 s−1. Moreover, the microstructure analysis revealed that the DRX grains were twinned and nucleated through the bulging mechanism at the serrated grain boundaries, accompanied by twin boundaries migration created in the DRX grains by growth accidents, which contributed significantly to the growth of the DRX.

Relationship between β→α dynamic transformation and dynamic recrystallization under thermomechanical coupling in Ti-5Al-5Mo-5V-1Cr-1Fe alloy

The thermal simulation compression tests of near-β titanium alloy Ti-5Al-5Mo-5V-1Cr-1Fe were performed within the range of deformation temperatures of 710–860 °C and strain rates of 0.001–1 s–1. Based on electron backscatter diffraction (EBSD) characterization and analysis technology, the interaction between dynamic phase transformation (DPT) of β-to-α and dynamic recrystallization (DRX) under thermal-mechanical coupling is deeply and systematically explored. We clarify the effects of temperatures and strain rates on the orientation relationship during dynamic precipitation of α-phase within β grain interiors possessing special orientation. The results show that the intragranular α-phase precipitated on the subgrain boundaries near {001}β with a high degree of dynamic recovery (DRV) deviates more from Burgers Orientation Relationship (BOR) than the α-phase that precipitates near {111}β as temperature increases. The proportion of α-phase precipitated by strain-induced on β recrystallized equiaxed grains for the deviating angle from BOR (θBOR) in the range of 20°–30° increases to 40% with the increase of strain rates below 800 °C. In addition, the α-phase is dynamically precipitated on the grain boundaries with {110}β orientation, which undergoes continuous dynamic recrystallization (CDRX), exhibiting epitaxial recrystallization, namely {110}β//{0001}α. Furthermore, the morphology of grain boundaries α phase (αGBs) precipitated by strain-induced phase transformation (SIPT) on specific types of β grain boundaries (βGBs), as well as the crystallographic orientation relationship and variant selection effect between adjacent α-variant within β grains are elucidated. The orientation relationships between α variants in {111}β grain are related with each other by 50°–60°/<–12–10> and 60°–70°/<–48–43> rotation. The “necklace” αGBs of recrystallization exhibit mainly the rotation of 50°–70° around the 〈2–310〉 zone axis, while the adjacent α-variant in the grain interiors is mainly 60° or 90°/<12−30>. In summary, the study has contributed to a deeper understanding of the deformation behavior and DPT laws of β-to-αp in near-β titanium alloy, which lays a foundation for the optimization of the hot deformation process and mechanical properties.

Hot Deformation Behavior and Processing Maps of Pure Copper during Isothermal Compression.

In this study, pure copper's hot deformation behavior was studied through isothermal compression tests at deformation temperatures of 350~750 °C with strain rates of 0.01~5 s-1 on a Gleeble-3500 isothermal simulator. Metallographic observation and microhardness measurement were carried out of the hot compressed specimens. By analyzing the true stress-strain curves of pure copper under various deformation conditions during the hot deformation process, the constitutive equation was established based on the strain-compensated Arrhenius model. On the basis of the dynamic material model proposed by Prasad, the hot-processing maps were acquired under different strains. Meanwhile, the effect of deformation temperature and strain rate on the microstructure characteristics was studied by observing the hot-compressed microstructure. The results demonstrate that the flow stress of pure copper has positive strain rate sensitivity and negative temperature correlation. The average hardness value of pure copper has no obvious change trend with the strain rate. The flow stress can be predicted with excellent accuracy via the Arrhenius model based on strain compensation. The suitable deforming process parameters for pure copper were determined to be at a deformation temperature range of 700~750 °C and strain rate range of 0.1~1 s-1.