Fiber Deformation Texture Research Articles

Unraveling the heterogeneous evolution of the microstructure and texture in the thermomechanically affected zone of commercially pure titanium during friction stir processing

The microstructure and texture of the thermomechanically affected zone (TMAZ) in friction stir processed (FSPed) CP-Ti material was investigated via electron backscatter diffraction (EBSD), finite element analysis (FEA), and polycrystal modeling. This study aimed to characterize the complicated deformation history in TMAZ and its systematic correlation with the asymmetric deformation and dynamic recrystallization mechanisms during FSP. Microstructure observation of the TMAZ revealed two distinct regions based on grain average misorientation (GAM) criteria: TMAZ-I was characterized by a mixture of deformed, substructured, and recrystallized grains near the stir zone; and TMAZ-II was characterized by only deformed and substructured grains near the bottom section. The texture development in the TMAZ was highly dependent on its deformation history, which differed for different zones. A multi-mechanism of dynamic recrystallization (DRX) was involved in the development of the submicron grain structure in TMAZ-I. A combined study of EBSD and the visco-plastic self-consistent properties (VPSC) revealed multiple fiber textures and deformation texture components in both TMAZ-I and TMAZ-II. High levels of prismatic and basal slip activity were observed throughout TMAZ-II. The texture of the zones was modified by tension twins and slips in the retreating side (RS) and the central zone (CZ) of TMAZ-II, while compression twins and slips were mainly responsible for the texture in the advancing side (AS). The inconsistent evolution of the DRX mechanism, velocity gradient components, and multiple tension and compression twin variants in various regions caused the development of the heterogeneous microstructure, texture, and hardness.

Investigation the effect of strain history on crystallographic texture evolution based on the perspective of macro deformation for high speed machining Ti-6Al-4V

Control of texture evolution of machined surface is an important goal to achieve specific property of workpiece in one macroscopic direction or plane. The present work aims to explore the comprehensive effect of localized strain on the texture variation during high speed orthogonal cutting Ti-6Al-4V. The strain distribution on machined surface is firstly calculated based on finite element (FE) model. Then electron backscattered diffraction experiments are performed to observe the texture variation formation of Ti-6Al-4V machined surface. The FE simulation results show that the strain distribution of machined surface fits with a negative exponential function and the direction of maximum shear strain towards cutting direction varies in the range of 25°–40°. Experimental results show that the grain misorientation distribution exhibits a peak at the angle of 30–45°, which is consistent with the inclination angle of the maximum shear strain in Ti-6Al-4V machined surface. Pole figures and orientation distribution function maps present that C fiber deformation texture is generated evolving from initial texture component of {10−10}〈0001〉. Pyramidal slip system 〈c+a〉 of α-Ti phase begins to be activated under the effects of high strain rate and cutting temperature with the increasing of cutting speed. The findings suggest that lattice rotations leading to the changes of orientation are the direct consequences of imposed deformation strain on machined surface. The results also provide a new avenue for optimizing cutting parameters to control texture variation of Ti-6Al-4V.

超微細繊維状結晶粒組織鋼の強靭化に及ぼす炭素量の影響

(0.2-0.6)%C-2%Si-1%Cr-1%Mo steels were quenched and tempered at 773 K and then deformed by multi-pass caliber rolling (i.e.,warm tempforming) with a rolling reduction of 78% to obtain ultrafine elongated grain (UFEG) structures. Tensile and Charpy impact properties of the warm tempformed (TF) steels were investigated to make it clear the influence of the carbon content on toughening in the UFEG structures. The TF samples consisted of UFEG structures with a strong <110>//RD fiber deformation texture. Transverse grain size and aspect ratio in the UFEG structure tended to reduce with increasing the carbon content while carbide particle size slightly became larger. The increase in carbon content resulted in an increase in yield strength from 1.68 to 1.95 GPa at room temperature, while it was accompanied by a loss of tensile ductility. In contrast to quenched and tempered samples exhibiting ductile-to-brittle transitions, the TF samples exhibited inverse temperature dependences of the impact toughness due to the delaminations, where the cracks branched in the longitudinal direction (//RD) of the impact test bars. The upper-self energy of the TF sample was enhanced as the carbon content decreased, and the higher absorbed energy was also obtained through occurrence of the delamination at lower temperature. The delamination was found to be controlled not only by the transverse grain size, the grain shape, the <110>//RD fiber deformation texture but also by the carbide particle distribution in the UFEG structure.

Influence of Warm Tempforming on Microstructure and Mechanical Properties in an Ultrahigh-Strength Medium-Carbon Low-Alloy Steel

A 0.4 pct C-2 pct Si-1 pct Cr-1 pct Mo steel was quenched and tempered at 773 K (500 °C) and deformed by multi-pass caliber rolling (i.e., warm tempforming). The microstructures and the mechanical properties of the warm tempformed steels were investigated as a function of the rolling reduction. At rolling reductions of more than 28 pct, not only extension of the martensite blocks and/or the packets in the rolling direction (RD) but also a grain subdivision became more significant, and an ultrafine elongated grain (UFEG) structure with a strong 〈110〉//RD fiber deformation texture was formed after 78 pct rolling. The tensile deformation behavior became significantly anisotropic in response to the evolution of UFEG structure. The longitudinal yield strength (σy) of the quenched and tempered sample increased from 1480 to 1860 MPa through the 78 pct rolling, while the transverse σy leveled off at around 1600 MPa up to 28 pct rolling. The transverse true fracture stress was also markedly degraded in contrast to the longitudinal one. Charpy impact properties were enhanced at a rolling reduction of 52 pct or more. The 52 pct-rolled sample underwent a ductile-to-brittle transition in the temperature range from 333 K to 213 K (60 °C to −60 °C), while the 78 pct-rolled sample showed an inverse temperature dependence of the impact toughness because of brittle delamination. The tensile and Charpy impact properties are discussed in association with the microstructural evolution.

Enhancement of Upper Shelf Energy through Delamination Fracture in 0.05 pct P Doped High-Strength Steel

An ultrafine elongated grain (UFEG) structure with strong 〈110〉//rolling direction (RD) fiber deformation texture was produced by warm-caliber rolling at 773 K (500 °C) and final tempering at 823 K (550 °C), namely tempforming in the 1200 MPa-class, medium-carbon, low-alloy steel with phosphorus (P) content of 0.053 wt pct. Charpy impact tests and tensile tests were performed at a temperature range of 77 K (–196 °C) to 623 K (350 °C) on the tempformed (TF) samples along with a conventional quenched and tempered (QT) samples. The QT structure showed a low upper shelf energy of 70 J and a high ductile-to-brittle transition temperature (DBTT) of 373 K (100 °C) as a result of P segregation and intergranular fracture. A remarkable increase in the upper shelf energy to 150 J from 70 J and a low DBTT of approximately 103 K (–170 °C) were obtained in the UFEG structure. P segregation embrittlement disappeared completely in the UFEG structure, and ductile fracture on the planes normal to RD along with delamination fracture on the planes along RD were observed at a temperature range of 123 K (–150 °C) to 423 K (150 °C). The enhanced delamination occurred because of the microstructural anisotropy of the UFEG structure, a strong 〈110〉//RD fiber deformation texture, and interfaces (i.e. ferrite grain boundaries and cementite particles-ferrite matrix interfaces) weakened by P segregation as feasible crack propagation paths. We studied the delamination (crack-arrester-type) fracture in 0.053 pct P doped high-strength steel along with upper shelf energy and DBTT obtained from the UFEG structure.

Tempforming in medium-carbon low-alloy steel

Abstract Deformation of tempered martensitic structure, i.e., tempforming using a caliber rolling at 500 °C was applied to a 0.4%C–2%Si–1%Cr–1%Mo steel to obtain ultrafine elongated grain structure with a strong 〈1 1 0〉//RD fiber deformation texture and then tensile and Charpy impact properties were investigated. An inverse temperature dependence of impact toughness was demonstrated in the tempformed (TF) samples in subzero temperatures, where conventionally quenched and tempered samples showed a ductile-to-brittle transition. The enhancement in the impact toughness of the TF sample was attributed to the occurrence of a delamination, where cracks branched to the longitudinal direction of the impact test bar. The delamination was shown to occur due to the microstructural anisotropy. The dominating factors controlling the delamination were considered to be the transverse grain size, the grain shape and the deformation texture.

Hydrogen Embrittlement of a 1500-MPa Tensile Strength Level Steel with an Ultrafine Elongated Grain Structure

A deformation of a tempered martensitic structure (i.e., tempforming) at 773 K (500 °C) was applied to a 0.6 pct C-2 pct Si-1 pct Cr steel. The hydrogen embrittlement (HE) property of the tempformed (TF) steel was investigated by a slow strain rate test (SSRT) and an accelerated atmospheric corrosion test (AACT). Hydrogen content within the samples after SSRT and AACT was measured by thermal desorption spectrometry (TDS). The tempforming at 773 K (500 °C) using multipass caliber rolling with an accumulative are reduction of 76 pct resulted in the evolution of an ultrafine elongated grain (UFEG) structure with a strong 〈110〉//rolling direction (RD) fiber deformation texture and a dispersion of spheroidized cementite particles. The SSRT of the pre-hydrogen-charged notched specimens and the AACT demonstrated that the TF sample had superior potential for HE resistance to the conventional quenched and tempered (QT) sample at a tensile strength of 1500 MPa. The TDS analysis also indicated that the hydrogen might be mainly trapped by reversible trapping sites such as grain boundaries and dislocations in the TF sample, and the hydrogen trapping states of the TF sample were similar to those of the QT sample. The QT sample exhibited hydrogen-induced intergranular fracture along the boundaries of coarse prior-austenite grains. In contrast, the hydrogen-induced cracking occurred in association with the UFEG structure in the TF sample, leading to the higher HE resistance of the TF sample.

Enhanced upper shelf energy by ultrafine elongated grain structures in 1100MPa high strength steel

Abstract The ultrafine elongated grain (UFEG) structure with strong //RD fiber deformation texture was produced by warm caliber-rolling at 500 °C and final tempering at 550 °C, namely tempforming in the 1100 MPa medium carbon-low alloy steel with ultralow phosphorus and sulfur concentrations. Charpy impact tests were performed at temperature range of −196 °C to 150 °C on the UFEG structure along with a conventional quenched and tempered (QT) structure. A remarkable increase in upper shelf energy of 150 J was obtained in the UFEG structure without delamination, while that of QT structure was 97 J. The UFEG structures tempered at higher temperatures of 625 and 700 °C showed remarkable increase in Charpy absorbed energy from 150 J to 187 J and 203 J. Also, the QT structure absorbed almost same energy as UFEG structure at 700 °C. The enhanced toughness was discussed with tensile ductility, void nucleation and growth, and their relations to microstructure including the //RD fiber deformation texture.

Role of Delamination Fracture for Enhanced Impact Toughness in 0.05 %P Doped High Strength Steel with Ultrafine Elongated Grain Structure

Ultrafine elongated grain (UFEG) structures with strong &lt;110&gt;// rolling direction (RD) fiber deformation texture were produced by warm caliber-rolling at 773 K, namely tempforming in the 1200 MPa-class medium-carbon low-alloy steel with phosphorous (P) contents of 0.001 and 0.053 mass%. Charpy impact tests were performed at temperature range of-196 to 150 °C on the UFEG structure. Regardless of P content, high upper shelf energy about 145 J and a very low ductile to brittle transition temperature (DBTT) of around-175 °C were obtained. P segregation embrittlement completely disappeared in the 0.053 %P steel and both steels showed ductile fracture on the planes normal to RD at temperature range of-150 to 150 °C. The main reason for the high upper shelf energy and very low DBTT in the 0.053 %P steel would be delamination fracture along RD when both 0.001 and 0.053 %P steels showed quite similar microstructures including texture. Since the occurrence of delamination requires relatively weak interfaces or planes, P segregated to the ferrite grain boundaries and interfaces of cementite particles-ferrite matrix and made them feasible paths for crack branching and consequently delamination occurred. We showed in this work the advantage of delamination (crack arrester-type) on the high absorbed energy obtained by 0.053 %P steel in comparison with 0.001 %P steel.

Delamination Toughening of Ultrafine Grain Structure Steels Processed through Tempforming at Elevated Temperatures

The deformation of tempered martensitic structures, namely tempforming treatments, were applied to a 0.6C–2Si–1Cr steel at 500, 600 and 700°C using multi-pass caliber-rolling with an accumulated area reduction of 80%. The tensile and Charpy impact properties were investigated to make clear the relation between the microstructure and the delamination behavior of the tempformed (TF) samples. The tempforming treatments resulted in the evolution of ultrafine grain structures with strong ‹110›//rolling direction (RD) fiber deformation textures and fine spheroidized cementite particles distributions. In contrast to the ductile-to-brittle transition of the conventional quenched and tempered (QT) samples, the TF samples exhibited inverse temperature dependences of the impact toughness due to the delaminations, where the cracks branched in the longitudinal direction (//RD) of the impact test bars. As a result, high strength with excellent toughness was achieved in the TF samples. A yield strength of 1364 MPa and a V-notch Charpy absorbed energy of 125 J were obtained at room temperature in the sample that was tempformed at 500°C. The delamination was shown to occur due to the microstructural anisotropy of the TF samples, and the dominating factors controlling the delamination toughening were the transverse grain size, the grain shape and the ‹110›//RD fiber deformation texture. The discussion also indicated that the ultra refinement of the transverse grain structure was the key to enhancing both the yield strength and the toughness of the TF steel while lowering the ductile-to-brittle transition temperature.

Influence of Cold-Working and Subsequent Heat-Treatment on Young&amp;rsquo;s Modulus and Strength of Co-Ni-Cr-Mo Alloy

Changes in Young's modulus of the Co-31 mass%Ni-19 mass%Cr-10 mass%Mo alloy (Co-Ni based alloy) with cold-swaging, combined with heat-treatment at temperatures from 673 to 1323 K, was investigated to enhance the Young's modulus of Co-Ni based alloy. After cold-swaging, the Co-Ni based alloy, forming 〈111〉 fiber deformation texture, shows the Young's modulus of 220 GPa. Furthermore, after ageing the cold-swaged alloy at temperatures from 673 to 1323 K, the Young's modulus increased to 230 GPa, accompanied by a decrease in the internal fiction and an increase in the tensile strength. This suggests that the increment in Young's modulus is caused by a moving of the vacancies to the dislocation cores and a continuous locking of the dislocations along their entire length with solute atoms (trough model). By annealing at 1323 K after cold swaging, Young's modulus slightly increased to 236 GPa. On the other hand, the tensile strength decreases to almost the same value as that before cold swaging due to recrystallization. These results suggest that the Young's modulus and the strength in the present alloy are simultaneously enhanced by the continuous dislocation locking during aging as well as the formation of 〈111〉 fiber deformation texture.

Co-Ni-Cr-Mo 合金のヤング率および強度に及ぼす冷間加工-熱処理の影響

Changes in Young's modulus of the Co-31 mass%Ni-19 mass%Cr-10 mass%Mo alloy (Co-Ni based alloy) with cold-swaging, combined with heat-treatment at temperatures from 673 to 1323 K, was investigated to enhance the Young's modulus of Co-Ni based alloy. After cold-swaging, the Co-Ni based alloy, forming fiber deformation texture, shows the Young's modulus of 220 GPa. Furthermore, after ageing the cold-swaged alloy at temperatures from 673 to 1323 K, the Young's modulus increased to 230 GPa, accompanied by a decrease in the internal fiction and an increase in the tensile strength. This suggests that the increment in Young's modulus is caused by a moving of the vacancies to the dislocation cores and a continuous locking of the dislocations along their entire length with solute atoms (trough model). By annealing at 1323 K after cold swaging, Young's modulus slightly increased to 236 GPa. On the other hand, the tensile strength decreases to almost the same value as that before cold swaging due to recrystallization. These results suggest that the Young's modulus and the strength in the present alloy are simultaneously enhanced by the continuous dislocation locking during aging as well as the formation of fiber deformation texture.

Toughening of a 1500 MPa class steel through formation of an ultrafine fibrous grain structure

A deformation of tempered martensite, namely tempforming at an elevated temperature, was applied to a medium-carbon low-alloy steel. This thermomechanical treatment led to an evolution of an ultrafine fibrous grain structure with a strong 〈1 1 0〉∥RD fiber deformation texture and to a remarkable improvement in Charpy impact strength (uE = 165 J) at a tensile strength of 1.5 GPa.

Deformation and Recrystallisation Textures in Extruded Cylindrical Aluminium Profiles

Cylindrical profiles of a range of aluminium alloys of the AA6xxx and AA7xxx series have been extruded on a laboratory press. Extrusion was undertaken at elevated temperatures, and the profiles were air cooled after extrusion. Most of the alloys recrystallised during cooling. The alloys that did not recrystallise displayed a combined and fiber deformation texture, in accordance with Taylor theory and experimental investigations reported in the literature. The recrystallisation textures, on the other hand, only displayed the fiber texture. Experimental investigations of the deformation structures demonstrated that the texture component had a larger subgrain size and a lower amount of stored energy than the component. This substructure configuration provides enhanced nucleation and growth of oriented grains into the texture component during recrystallisation. This explains the recrystallisation texture. The sharpness of the recrystallisation texture apparently scales with the amount of oriented grains in the deformation structure, which confirms the suggested nucleation mechanism. Both the sharpness of the deformation texture and the recrystallisation textures decreased with increasing Mg-content and decreasing Zn-content in the 7xxx series alloys.