Deformation Recrystallization Research Articles

Stochastic model describing evolution of microstructural parameters during hot rolling of steel plates and strips

Enhancing strength-ductility synergy of materials has been for decades an objective of research on structural metallic materials. It has been shown by many researchers that significant improvement of this synergy can be obtained by tailoring heterogeneous multiphase microstructures. Since large gradients of properties in these microstructures cause a decrease of the local fracture resistance, the objective of research is to obtain smoother gradients of properties by control of the manufacturing process. Advanced material models are needed to design such microstructures with smooth gradients. These models should supply information about distributions of various microstructural features, instead of their average values. Models based on stochastic internal variables meet this requirement. Our objective was to account for the random character of the recrystallization and to transfer this randomness into equations describing the evolution of dislocations and grain size during hot deformation and during interpass times. The idea of this stochastic model is described in the paper. Experiments composed of uniaxial compression tests were performed to supply data for the identification and verification of the model in the hot deformation and static recrystallization parts. Histograms of the grain size were measured after hot deformation and at different times after the end of deformation. Identification and validation of the model were performed. The validated model, which predicts evolution of heterogeneous multiphase microstructure, is the main output of our work. The model was implemented in the finite element program for hot rolling of plates and sheets and simulations of these processes were performed. The model’s capability to compare and evaluate various rolling strategies are demonstrated in the paper.

Hot Deformation Behavior of an As-Extruded Mg-2.5Zn-4Y Alloy Containing LPSO Phases

The hot deformation and dynamic recrystallization (DRX) characteristics of an as-extruded Mg-2.5Zn-4Y alloy containing long-period stacking ordered (LPSO) phases were investigated using a Gleeble 3500 thermal simulator at temperatures (300–400 °C) and strain rates (0.001–1 s−1). The results revealed that low flow stress corresponded to a high temperature and a low strain rate. An increase in the temperature of deformation caused an increase in the amount of dynamic recrystallization. Additionally, as the strain rate decreased at a given deformation temperature, dislocations were less likely to cause pile-up and dynamic recrystallization was more appropriate, resulting in a lower stress value. Kink deformation was clearly minimized as the number of dynamic recrystallizations increased. The test alloy’s activation energy value was determined as 212.144 kJ/mol.

Hot deformation characteristics of Ti-6Al-4V

Abstract The flow behavior and hot deformation mechanisms of Ti-6Al-4Vin both β and (α + β) phase regions have been studied by compression tests in the temperature range 750 – 1100 °C and strain rate range 0.05 –15 s –1. The flow curves displayed discontinuous yielding at temperatures above 850 °C and high strain rates, typically 5 and 15 s–1. Flow oscillations were also observed under such conditions. The relative discontinuous flow stress drop increased with increasing temperature in the (α + β) phase region and reached a steady state in the β phase region. The discontinuous yielding is attributed to the sudden increase in the mobile dislocation density occurring due to the activation of β grain boundary sources during hot deformation. The apparent activation energy estimated using the standard kinetic analysis is about 246 kJ/mol in the β region and 621 kJ/ mol in the (α + β) region while the strain rate sensitivity values are 0.34 and 0.18, respectively. The mechanism in the β region has been suggested to involve grain boundary sliding and dynamic recovery of the β phase while in the (α + β) region a transient mechanism, involving dynamic recovery followed by post deformation recrystallization, has been proposed.

Study on the High-Temperature Deformation and Dynamic Recrystallization Behavior near the Interface of Stainless Steel Cladding

To ensure the long service life of concrete buildings in the marine environment, it is urgent to develop building materials with good corrosion resistance and weatherability. Stainless steel cladding is suitable for a highly corrosive environment and provides cost advantages. This paper investigated the deformation coordination and the microstructure evolution near the cladding interface of stainless steel/carbon steel. The stress-strain curves at different temperatures and strain rates were analyzed on the basis of high-temperature compression experiments. In addition, the sin-hyperbolic constitutive model was constructed, and the optimized parameters were obtained using electron backscatter diffraction characterization technology. The results show that at the deformation temperature of 1100 °C and the strain rate of 1 s−1, the deformation coordination increases significantly near the interface, accompanied by a large number of recrystallized grains, which has a positive impact on the comprehensive performance of the materials.

Simulation of Deformation and Dynamic Recrystallization During Isothermal Compression of Zn-22al Alloy

Simulation of Deformation and Dynamic Recrystallization During Isothermal Compression of Zn-22al Alloy

High Strain Rate Deformation Behavior and Recrystallization of Alloy 718

To study the deformation behavior and recrystallization of alloy 718 in annealed and aged state, compression tests were performed using Split-Hopkinson pressure bar (SHPB) at high strain rates (1000 to 4000 s−1), for temperatures between 20 ^circ C and 1100 ^circ C (293 K to 1373 K). Optical microscope (OM) and electron back-scatter diffraction (EBSD) technique were employed to characterize the microstructural evolution of the alloy. The stress–strain curves show that the flow stress level decreases with increasing temperature and decreasing strain rate. In addition, up to 1000 ^circ C, the aged material presents higher strength and is more resistant to deformation than the annealed one, with a yield strength around 400 MPa higher. For both states, dynamic and meta-dynamic recrystallization occurred when the material is deformed at 1000 ^circ C and 1100 ^circ C, leading to a refinement of the microstructure. As necklace structures were identified, discontinuous recrystallization is considered to be the main recrystallization mechanism. The recrystallization kinetics is faster for higher temperatures, as the fraction of recrystallized grains is higher and the average recrystallized grain size is larger after deformation at 1100 ^circ C than after deformation at 1000 ^circ C.

Zonality of ore-forming chrome spinels of medium-chrome and aluminous chromitites of the Voikaro-Syninsky massif

Relevance of the work. The conditions for the formation of chromium ores in alpine-type ultramafites remain a topical subject of research. In recent years, scientific papers have focused on the issue of changing the chemical composition of ore-forming minerals and chromium ores under the influence of deformation and dynamic recrystallization processes accompanying metamorphism. The results of such studies make it possible to formulate a new model of the formation of chromium mineralization taking into account a significant amount of geological data indicating that alpine-type ultramafic rocks are “mantle tectonites”. In our work, we have studied zonal ore-forming spinels from chrome ores of the Polar Urals. The results of the study make it possible to associate the formation of chemical zoning in minerals and ore bodies with recrystallization under the influence of stress tension. Purpose of the work – study of the conditions for the formation of chemical zoning of chromium spinels from alumina and medium chromium ores of the Voikaro-Syninsky massif. Results. Zonal ore-forming spinels from medium-chromium and aluminous chromitites of the Voikaro-Syninsky massif (Polar Urals) have been studied. It was found that replacement rims are developed along the grains of oreforming spinels with an increased content of Cr2 O3 and an oxidation state of iron in relation to the core, as well as a reduced content of Al2 O3 . The oxidation state of iron in the rims of most grains does not exceed the values typical for unaltered ore-forming spinels. T–fO2 parameters of zoning formation in spinels were determined by oxythermobarometry. Comparison with zoned chrome spinels of the Golyamo Kamenyane massif (Bulgaria). Conclusion. Metamorphic transformations of alumina and medium-chromium chromitites of the Voikaro-Syninsky massif, occurring under subcrustal conditions under the action of directional stress at relatively constant T–fO2 parameters, lead to an increase in the chromium content of the ore mineral.

Influence of strain path change on static recrystallisation behaviour of an extruded pure magnesium

ABSTRACT The present work has examined the influence of strain path change on the deformation behaviour, texture evolution and recrystallisation process in an extruded pure magnesium. The samples were compressed at room temperature along ED, ND and ND–ED directions to the same total strain. Electron back-scattered diffraction (EBSD), hardness testing and X-ray diffraction were utilised to examine the deformed and annealed samples at different conditions. The texture evolution in the ND–ED samples showed a more significant difference than the samples monotonically deformed along ED and ND directions. As-deformed microstructures illustrate the presence of lenticular shaped twins in the ND–ED samples, while the complete flipping of original grains owing to twinning was observed in the ED and ND samples. The recrystallisation of ED deformed sample showed the fastest kinetics followed by the ND–ED and ND samples, respectively. This was rationalised based on the variation in deformation mechanisms. For all the three conditions, the formation of new grains at prior grain boundaries appeared to be the prevalent mechanism for recrystallisation. Additionally, for the ND–ED deformed samples, evidence of recrystallisation within twin was reported.

Effects of Oxide Inclusions on Texture of 1235 Al-Alloy after Deformation

Texture characteristics of compressed 1235 Al-alloy treated by different purification methods are studied by electron backscattered diffraction. The effects of oxide inclusions on texture components of material are studied as well. The main textures in hot-compressed 1235 Al-alloy are Cube texture, R texture, Gross texture, Brass texture, and Rotated cube texture. The lower the content of oxide inclusions in the material, the smaller the total relative ratio of textures. The total relative ratio of textures goes to the smallest by 1.8 % in high-efficient purified 1235 Al-alloy by oxide inclusion content of 0.051 %. The purification results have obvious effects on types and percentage of texture in the deformed alloy. With the decreasing content of oxide inclusion, the ratio of deformation texture decreases and recrystallization texture increases. Brass texture is gradually replaced by Goss texture in the deformation textures. R texture is the main texture in recrystallization textures. Therefore, reducing the content of oxide inclusions is effective for improving the hot deformation properties of 1235 Al-alloy.

Dynamic recrystallization analysis of reduction pretreatment process by multi-phase field method

The reduction pretreatment (RP) process is an effective method to improve billet quality, and the deformation recrystallization plays an important role in the process. Exploring the RP process parameters, a dynamic recrystallization model of GCr15 steel was established by the phase-field method and physical simulation. The recrystallization kinetics and flow stress curves during hot compression were simulated by using this mode. The effects of deformation parameters and initial grain size on the dynamic recrystallization were investigated. Moreover, by using the results obtained by Finite element method (FEM), dynamic recrystallization during the RP process was investigated though this model. It was found that increasing the deformation temperature, deformation rate and decreasing the initial grain size can promote the dynamic recrystallization kinetics. Large Zener-Hollomon parameters can enhance recrystallized grain refinement, while the recrystallized grain size was not affected by the initial grain size. During the RP process, when the reduction is insufficient (10%), partial recrystallization occurs in the billet. With the increase of reduction from 10% to 16%, the area of complete recrystallization increases gradually. When the reduction is the same, the recrystallization in the billet center increases with the decrease of casting speed. When the reduction is 10%, partial recrystallization occurs in the billet center at a casting speed of 0.7 m min−1, and fully recrystallization occurs in the billet center with a casting speed of 0.5 m min−1. Thus, when the reduction is difficult to increase further, the recrystallization in the billet center can be improved by decreasing the casting speed.

Formation of Recrystallization Cube Texture in Highly Rolled Ni–9.3 at % W

In this work the formation of strong recrystallization cube texture in heavily rolled Ni–9.3 at % W has been studied. During the cold rolling (also known as recovery-rolling) process the deformation texture of Ni–9.3 at % W alloy (further notated as Ni9W) transforms to Copper-type rolling texture, and after annealing, a sharp cube texture is generated. It is remarkably strong recrystallization cube texture, as high as 93 vol %, in metallic materials with low stacking fault energy. The formation mechanism of the cube texture is adopted for the rapid recovery of cube nuclei at the early stage of recrystallization as well as fast migration rate of high angle boundaries between cube grains and deformed microstructure at high temperature. Considering the cold rolling texture of Ni9W, oriented nucleation seems to play more important role in the cube texture formation process. In this article, the relationship between the deformation texture and recrystallization cube texture is discussed.

Analysis of the Optical Properties of Plastically Deformed ZnS(O) Using Band-Anticrossing Theory

The cathodoluminescence and absorption of plastically deformed ZnS(O) single crystals are investigated in the light of band-anticrossing theory. The difference in the oxygen content in the surface layer and in the sample bulk is found using a scanning electron microscope and according to cathodoluminescence data. This fact explains the specifics of the spectral position of the fundamental absorption edge and exciton spectra. The shift dynamics of the bands of self-activated luminescence on deep A centers (SA luminescence) during deformation recrystallization with an increase in the dissolved oxygen concentration is presented. Restriction of the spectral range of the appearance of self-activated luminescence at shallow levels—“edge” luminescence—is established. The nature of the emission bands in the wavelength ranges of 336–350 and 364–390 nm is established. These results refine the energy model of ZnS(O) crystals and can be useful in the case of the practical use of their structure-sensitive properties.

Анализ оптических свойств пластически деформированного ZnS(O) с привлечением теории антипересекающихся зон

Abstract The optical properties of plastically deformed ZnS∙0 single crystals have been studied on the basis of bandanticrossing theory. The difference in oxygen concentration in the surface layer and in the bulk of the sample was found from an analysis of the results of cathodoluminescence and scanning electron microscopy. This made it possible to explain the position of the fundamental absorption edge and exciton spectra. Dynamics of the shift of the self-activated luminescence at deep A-centers bands during deformation recrystallization with increasing concentration of dissolved oxygen is shown. The restriction of the spectral range of the appearance of self-activated luminescence at shallow levels is established. The nature of the emission bands in the wavelength range 336-350and 364-390 nm has been discovered. The results can be used both to refine the energy model of ZnS∙O and in the case of practical use of the structure-sensitive properties of zinc sulphide crystals.

Microstructure Evolution of a High Nb Containing TiAl Alloy with (α2 + γ) Microstructure during Elevated Temperature Deformation

In order to verify the correctness of the transition of deformation mechanism with the change in deformation parameters and to reveal the types and mechanism of dynamic recrystallization of γ grains during compression deformation, microstructure characterization of Ti-43.5Al-8Nb-0.2W-0.2B (at. %) alloy after isothermal compression deformation were performed. When the alloy was deformed at 1000 °C/10−2 s−1, the initial γ grains are elongated and significantly refined and the fraction of low angle grain boundaries (LAGB) of γ grains is obviously increased and the texture intensity remains unchanged, which indicates that the compression deformation in dislocation creep region is dominated by intragranular deformation and dynamic recrystallization (DRX) of γ grains. Besides, the lattice rotation at grain boundary serrations may be responsible for the nucleation of new recrystallized γ grains, and the following growth process may be achieved by the migration of γ grain boundaries. However, when the alloy deformed at 1050 °C/10−4 s−1 and 1000 °C/10−4 s−1, the γ grains maintain equiaxed shapes and distribute more uniformly and the fraction of LAGB of γ grains is slightly raised and the texture sharpness decreases, which indicates that the compression deformation in grain boundary sliding (GBS) region is mainly controlled by GBS of γ grains and DRX occurs simultaneously within some coarse γ grains.

Investigation on microstructure evolution of a new disk superalloy under different hot process

Over the course of this paper, a FGH100L nickel based alloy, which was prepared by spray forming, had been treated by hot isostatic pressing, followed by an optimized heat treatment. The microstructure evolution of gamma prime phase under different conditions was systematically analyzed. In conclusion, both the temperature and cooling rate during the heat treatment can affect gamma prime phase on its morphology, size and distribution. By varying solution treatment temperature, size variation of γ′ phase and fine-grain microstructure was obtained at a relatively low solution treatment temperature. As for changing cooling rate, a doublet morphology of splitting γ′ phase appeared at a relatively slow cooling rate under hot isostatic pressing progress. Based on microstructural characterization of γ′ phase, the reasonable heat treatment regime of FGH100L alloy was determined. The deformation recrystallization occurred when the as-deposited alloy was treated by hot isostatic pressing, which results in grain morphology changing from spherical or sphere-like to polygon. It can be obtained multi-sized γ′ precipitates for the hot isostatic pressing alloy which treated by optimized heat treatment regime. The results indicate that the multi-sized γ′ phase microstructure is beneficial to obtain ideal comprehensive mechanical properties.

Influence of Processing Parameters on Microstructural Evolution and Tensile Properties for 7075 Al Alloy Prepared by an ECAP-Based SIMA Process

A modified strain-induced melt activation (SIMA) process consisting of homogenization, equal-channel angular pressing (ECAP) and subsequent heating to the semisolid temperatures was introduced to prepare the 7075 aluminum alloy with superior thixotropic behaviors. The effects of both the homogenization and the number of ECAP passes, as well as the isothermal temperatures on the microstructural evolution, were investigated. The results indicate that ideal microstructure wherein fine and globular solid grains surrounded by uniform liquid films can be achieved through ECAP deformation–recrystallization mechanism. Increasing the number of ECAP passes accelerates the recrystallization of strained grains, thus reducing the average grain size and improving the grain sphericity. Moreover, higher holding temperatures and prolonged soaking time can improve the growth of the solid grains. Two main coarsening mechanisms, viz. coalescence and Ostwald ripening, contribute to the growth of the solid grains simultaneously and independently. The tensile strength of the 7075 alloys after four-pass ECAP-based SIMA and T6 heat treatment is relatively lower than the as-received billet, while the elongation of SIMA processed samples is much higher than that of as-received ones. Increasing the number of ECAP passes improves the tensile strength for alloys with and without T6 treatment due to the fine grain strengthening mechanism.

공정지도를 이용한 AA6082 합금의 연속 동적 재결정 및 고온 변형 거동

공정지도를 이용한 AA6082 합금의 연속 동적 재결정 및 고온 변형 거동

Effect of microstructure softening events on the chip morphology of AISI 1045 steel during high speed machining

The main purpose of this paper is to study the change of chip morphology with increasing cutting speed by considering the role of microstructure evolution in chip root. The orthogonal cutting experiments of AISI 1045 steel showed that the chip morphology would be changed from continuous chip to discontinuous serrated chip as the microstructure softening events occurred in the secondary shear zone with the increasing cutting speed. Based on the principle of cutting force balance and the concept of equilibrium shear angle (ϕe), the influence of the dynamic behavior of deformation and recrystallization in chip material on chip morphology was analyzed and modeled. Three types of chip morphology would be characterized corresponding to the sliding, only severe deformation and dynamic recrystallization behaviors, respectively, in the secondary shear zone. It was concluded that the physical mechanism of the serrated chip morphology is the variation of ϕe controlled by the mechanical properties of workpiece material in the secondary shear zone, which is related to dynamic deformation behavior of material as influenced by microstructural softening events, such as recrystallization or phase transformation.

Formation of Friction Layers in Graphene-Reinforced TiAl Matrix Self-Lubricating Composites

The friction layer structure has been proved to be formed during severe plastic deformation and markedly improves the tribological properties of material. The dry friction and wear performance of graphene-reinforced TiAl matrix self-lubricating composites (GTMSC) at different sliding velocities are systematically researched. GTMSC show the best tribological properties and special friction layer structure containing a wear-induced layer and a grain refinement layer with a nanocrystalline (NC) structure under surface after sliding at a sliding speed of 1.1 m/s. Nanoindentation results show that the grain refinement layer has a higher hardness and elastic modulus than the wear-induced layer. This special microstructure of friction layers beneath the surface after sliding leads to a low coefficient of friction and high wear resistance of GTMSC. Moreover, it is deduced that the appearance of an NC structure results in hardening of the material. The formation mechanisms of friction layers are researched in detail. It can be concluded that the formation of a wear-induced layer results from frictional heat and fracture of the counterpart. The formation of a grain refinement layer is due to severe plastic deformation and dynamic recrystallization. Severe plastic deformation results in the formation of an NC structure and dynamic recrystallization leads to grain refinement.

High temperature deformation behavior and dynamic recrystallization in CoCrFeNiMn high entropy alloy

Microstructure evolution in high-entropy alloy CoCrFeNiMn during uniaxial compression to a height reduction of true strain of ≈1.4 in the temperature interval 600–1100°C was studied. Although some differences was observed in the mechanical behavior of the alloy and the activation energy of deformation in warm (below 800°C) and hot (above 800°C) temperature intervals, microstructure evolution at all studied temperatures was found to be accompanied by discontinuous dynamic recrystallization (dDRX). During hot deformation recrystallization was primary associated with nucleation of new grains on the initial grain boundaries, while in the warm interval dDRX was mainly observed in shear bands. The volume fraction of the recrystallized structure was respectively 0.085 and 0.95 at 600 and 1000°C and the recrystallized grain size was found to be 0.2 and 40.4µm for 600 and 1100°C, respectively.