ND Plane Research Articles

DBTT and recrystallization behavior analyses for rolled and forged potassium-doped tungsten alloys

Tungsten-potassium (WK) alloys are regarded as one of the candidates for plasma-facing materials (PFMs) intended for the divertor and first wall of future fusion reactors. Determining the range of the ductile-to-brittle transition temperature (DBTT) and the recrystallization temperature (RCT) for the WK alloy is critical as it is closely related to the safe operational temperature window of the fusion reactor. Variable temperature tensile tests were conducted on rolled and high energy rate forging (HERF) WK alloy specimens to elucidate their DBTT. Additionally, gradient high-temperature isochronal annealing was performed on the HERF samples, coupled with Vickers hardness characterization, to ascertain their distinct RCT for various orientation planes within the same alloy. Subsequently, the DBTT of the as-rolled WK alloy is determined to be approximately between 100 °C and 150 °C, while that of the HERF WK alloy is found to be around lower than 200 °C. Furthermore, the RCT of the ND plane of the HERF WK alloy is approximately 1600 °C, whereas that of the RD counterpart exceeded 1700 °C. The internal mechanisms underlying these phenomena are comprehensively analyzed in this study. This work has identified the safe service temperature window for future fusion reactors with this kind of advanced WK alloy and provided a new perspective for determining the RCT of many other W-based materials.

Texture adjustment approach of magnesium alloys via variable strain path calculated by an integrated finite element-viscoplastic self-consistent model

An integrated calculated approach based on weakly coupled finite element (FEM)-viscoplastic self-consistent (VPSC) model was established to simulate the texture evolution during the variable strain path extrusion process of magnesium alloys. The spiral die extrusion (SDE) process with additional circumferential shear deformation was applied to investigate the effect of path control on texture adjustment and verify the accuracy of the model. The results indicated that the additional spiral shear resulting from the overall inclined flow path effectively reduced the intensity of the {0002}//ED fiber texture by suppressing basal slip activation in the core area, while the local shear deformation along the spiral equal channel strain path led to the formation of an inclined {0002}//ND plane texture on the side. Using the modified Hall–Petch relationship, the correlation between texture and yield strength was quantified. Specifically, the weakening of the texture effectively suppressed {10–12} tensile twinning, which compensated for the deficiency of compressive yield strength without significantly sacrificing tensile yield strength, and thus improved the tension-compression asymmetry. Furthermore, the strongly inclined {0002}//ND plane texture inhibited the widespread activation of basal slip during tensile yielding, thereby enhancing the yield strength.

Effect of anisotropic grain boundaries on the surface blistering of tungsten induced by deuterium plasma exposure

The effect of anisotropic grain boundaries on the surface microstructure changes and deuterium retention behavior in tungsten under deuterium plasma irradiation were studied. The samples named as NDW and RDW were cut from RD × TD plane and TD × ND plane of a rolled W plate (ND: normal direction, RD: rolling direction, TD: transverse direction), respectively. The results suggest that both surface morphology and deuterium retention in the RDW samples are suppressed compared to that of NDW samples for 1 h and 25 h deuterium irradiation. For 1 h exposure, the total deuterium retention in the NDW samples is about 1.6 times as much as that of RDW. However, as the exposure time increased to 25 h, the total deuterium retention in the NDW sample is two times the height of RDW sample. The experimental results show that the special grain structure of RDW can alleviate the surface morphology changes and decrease the deuterium retention in tungsten, which is interpreted by the lateral stress model of blistering.

Effect of hot rolling on microstructure, crystallographic texture, and hardness of AZ31 alloy

In this study, relationships between microstructure, texture, and hardness of hot-rolled AZ31 alloy were investigated. It was found that the grain size decreased into the ultra-fine domain after 60% hot deformation, reaching a grain size of 1 μm. Several dynamic recrystallization (DRX) mechanisms activated after 40% and 60% deformations including discontinuous dynamic recrystallization (DDRX), twin dynamic recrystallization (TDRX), continuous dynamic recrystallization (CDRX), and particle stimulated nucleation (PSN). With increasing the thickness reduction, the intensity of basal texture first increased, then slightly decreased, and finally significantly increased to 15.7 multiple of random density. The average misorientation angle decreased when the thickness reduction increased owing to the formation of a very strong {0001} basal texture. With increasing the strains, the average microhardness increased because of decreasing grain size and increasing twin fraction and shear band density. There were no differences between the hardness values of RD–TD and RD–ND planes for AZ31 samples after 10% and 40% hot rolling and these samples were isotropic. After 60% deformation, the hardness of the RD–TD plane (73.5 HB) was higher than that of the RD–ND one (68.4 HB) that resulted in hardness anisotropy due to the generation of very strong basal texture.

A new 1.2 GPa-strength plain low carbon steel with high ductility obtained by SRDR of martensite and intercritical annealing

In the current research, a new technique to produce ultra-high strength ferrite-martensite dual phase (DP) steels with high ductility was developed for a low-cost plain low carbon steel with 0.16 wt% C. A combination of austenitization, water quenching, single-roll drive rolling (SRDR), and intercritical annealing at 830 °C for three different holding times was used. The microstructure and mechanical properties of DP samples were investigated. It was found that the martensite islands were very uniformly distributed in both RD–TD and RD–ND planes of DP steels due to performing the SRDR process. The average sizes of the martensite islands for the holding times of 1 (DP1), 5 (DP5), and 15 (DP15) min were 7.1, 11.6, and 15.8 μm, respectively. Also, the volume fraction of martensite was about 0.29, 0.47, and 0.68 for the DP1, DP5, and DP15 steels, respectively. With increasing the annealing time, the hardness, strength, and ductility increased. The DP15 showed a superior hardness (354.1 H V) strength (1172.5 MPa) and high ductility (13.5%). The martensite phase in the DP15 steel exhibited remarkable plastic deformation because its hardness decreased by reducing the carbon content and therefore the strain hardening ability of the martensite phase increased. Achieving superior strength with high ductility in the DP15 was attributed to the uniform distribution of martensite caused by the SRDR process. As the holding time increased to 15 min, two stages of strain hardening transformed to one stage owing to increasing the ability of strain hardening of martensite with lower carbon content. All DP steels mainly consisted of dimples indicating the ductile fracture, however, some cleavage facets were observed on the fracture surfaces. In DP1 and DP5 steels voids formed mainly by decohesion at the ferrite-martensite interface. With increasing the holding time to 15 min, the severity of decohesion decreased due to increasing the critical strain required for the formation of voids through interface decohesion.

A study on the dynamic mechanical behavior and microtexture of 6082 aluminum alloy under different direction

The dynamic mechanical behavior and texture of 6082 aluminum alloy along the rolling direction (RD), transverse to the rolling direction (ND), and perpendicular to the rolling direction (TD) were examined within a high strain rate range of 1000 s−1-6000 s−1, using the split Hopkinson pressure bar and X-ray diffraction (XRD). The results indicated that the yield strength and peak flow stress on the RD plane of the material increased as a function of the flow stress, while the flow stresses on the ND and TD planes showed obvious regionalization, with 3900 s−1 being the critical strain rate for regionalization. Analysis of the orientation distribution functions (ODFs) revealed that before dynamic impact, the main textures on the RD, ND, and TD planes were brass {011} <2 1 1>, copper {012} <1 1 1>, and S<123>{634} textures, respectively.

Effect of Microstructure and Texture Evolution During Variable Gauge Rolling on Mechanical Properties of Tailor Rolled Blanks

In this study, anisotropic elastic and plastic mechanical properties of a tailor rolled blank (TRB) with thickness ratio of 0.52 (1 mm/1.9 mm), have been fully studied. To gain a deeper insight into anisotropic mechanical behavior of the studied TRB, continuous changes in microstructure and crystallographic texture of a dual phase steel caused by variable gauge rolling (VGR) were investigated on several points (on RD–ND plane) along longitudinal direction with the aid of EBSD observations. Analysis of grain boundary (GB) maps revealed that ferrite grain refinement is occurred during VGR so that the average ferrite grain size decreases from 4.1 µm for the thicker side to 2.2 µm for the thinner side. Furthermore, it was found out that substructure density is more intense within smaller ferrite grains. Evaluation of inverse pole figures as well as orientation distribution function maps showed that texture of thicker side comprises {001}〈110〉 and {112}〈110〉 components along $$ \alpha $$ -fiber. In addition, it was revealed that orientations of {111}〈110〉 and {111}〈112〉 along $$ \gamma $$ -fiber strengthen along VGR direction by further increase in thickness reduction near thinner side. Accordingly, unprecedented gradual changes in mechanical properties with respect to these changes in microstructure and texture, were obtained. Finally, the correlation between in-plane anisotropic mechanical properties [Young’s modulus (E), yield stress (YS), ultimate tensile stress (UTS) and total elongation] of the studied tailor rolled blank with microstructure and deformation texture was interpreted.

Influence of Grain Orientation on the Corrosion Behavior of Rolled AZ31 Magnesium Alloy

The effect of the grain orientation on corrosion behavior of rolled AZ31 magnesium alloy is investigated in this study. The test samples have a similar surface roughness to the Mg alloy in practical application. The immersion test and electrochemical impedance spectroscopy show that the TD–ND planes dominated by \((10\bar{1}0)\), \((11\bar{2}0)\) and \((10\bar{1}1)\) oriented grains show a higher corrosion resistance compared with these of the RD–TD planes which consist mainly of (0001) oriented grains. Here, RD, ND and TD represent the rolling direction, the normal direction and the transverse direction of the alloy sheet, respectively. The surface morphologies of the alloys at various immersion stages are observed by scanning electron microscopy, and the surface topography of the alloy substitutes is also observed by laser scanning confocal microscopy. The TD–ND planes show a regular corrosion along the TD direction, but the RD–TD plane shows an irregular corrosion.

Texture, Grain Boundary Characterization and Segregation of Phosphorus in an Annealed Interstitial Free Steel

The {111} // ND plane texture, grain boundary characterization and grain boundary segregation of phosphorus are investigated for the phosphorus added high strength interstitial free (IF) steel annealed at 810 °C for 60 s to 180 s. The results show that the maximum volume fraction of {111} // ND plane texture is about 85% and the grain boundary segregation peak of phosphorus is about 14 at. % for the steel annealed at 810 °C for 120 s. The Σ3 and other low-ΣCSL (coincident site lattice) boundaries are lowest for the steel annealed for 120 s. Segregation of phosphorus is also found at low angle grain boundaries.

Hydrogen induced cracking susceptibility in different layers of a hot rolled X70 pipeline steel

Hydrogen induced cracking (HIC) behaviour was investigated in three layers of RD–ND plane. HIC test showed that all cracks initiated from the mid-thickness of the RD–ND plane and propagated in the rolling direction of the steel plate. Hydrogen permeation test results showed a lower permeability and diffusivity coefficient for the third layer resulting in the highest density of traps and consequently HIC susceptibility. Considering the HIC test and crystallographic texture measurements, cracks initiated from the grain boundaries associated with {100} grain orientation and arrested in regions with some strong texture components, such as {110}//ND, {112}//ND, and possibly {332}//ND. The role of HABs and CSLs boundaries was important in crack propagation.

A new consideration on reinforcement distribution in the different planes of nanostructured metal matrix composite sheets prepared by accumulative roll bonding (ARB)

Recently, a number of novel methods based on accumulative roll bonding (ARB) have been introduced to produce particulate metal matrix composites. Nonetheless, the microstructure uniformity from the reinforcement distribution viewpoint in the different planes of ARBed composite sheets has not been focused up to date. This paper aims to compare the evolution of the B 4C particles distribution in nanostructured Al–10 vol.% B 4C composites prepared by ARB in the rolling direction–normal direction (RD–ND) and transverse direction–normal direction (TD–ND) planes. From optical microscopic evaluations quantified by the radial distribution function analysis, it is realized that the homogeneity in the RD–ND planes is in excess of the TD–ND planes. In addition, transmission electron microscopy reveals the development of nanostructures in the Al matrix after seven ARB passes.

Role of initial texture on the plastic anisotropy of Mg–3Al–1Zn alloy at various temperatures

The effect of initial texture on the anisotropic properties of AZ31 Mg alloys was investigated on the basis of microstructure evolution after compression tests and Lankford parameter (r-value) experiments at various temperatures. Two kinds of sheets were used: one is the cast-and-rolled sheet, and the other is the strip-cast sheet. Compression tests were conducted up to a strain of 0.3 at temperatures of 200–400°C, and tensile tests were performed to obtain the r-value at various temperatures (25–450°C). The results showed that, at all test temperatures, the average r-value of the RD plane were greater than those of the ND and TD planes in the cast-and-rolled material. When comparing the average r-value of the RD plane, the cast-and-rolled material revealed much higher values than those of strip-cast material. It was observed that the cross-sectional shape of RD compressive specimens (the compression axis was parallel to the rolling direction) of cast-and-rolled materials changed from an initial circular shape to an ellipsoidal shape due to the plastic anisotropy. Compression processes of specimens were simulated using a finite element method where the Hill's anisotropic yield criterion was adopted. The simulated results were in a good agreement with experimental data.

Recrystallization and Related Phenomena. Microscale Texture and Recrystallized Orientations of Coarse Grained 3%Si-steel Rolled at High Temperature.

Recovered and recrystallized crystal orientations of a coarse grained 3% Si-steel hot rolled at 1280°C were examined. Deformed samples exhibited a recovered structure comprised of subgrains. Recrystallized grains with unique orientations emerged along the original grain boundaries during holding at the rolling temperature for 6.5 s. With the aid of the automated EBSD orientation measurement with two dimensional scan, it became possible to map the orientations of the subgrains which were the minimum units of orientation in the present case. Near the original grain boundary, to an extent of several hundreds of microns, the orientation of the subgrains were scattered or continuously rotated due to the constraint by the grain boundary. The orientations of a number of the subgrains near the original grain boundaries in the deformed sample were measured, and the subgrains having large misorientation with the matrix, which were thought recrystallization nuclei, were found. The recrystallized grains in the sample held for 6.5 s at 1280°C, as well as both the recrystallization nuclei and the continuously rotated subgrains near the original grain boundaries in the immediately quenched specimen, often showed a rotational relationship around an <110> axis on ND plane with the deformed matrices.

Analysis of Grain Colonies in Type 430 Ferritic Stainless Steels by Electron Back Scattering Diffraction (EBSD).

Ridging is a serious problem which occurs in ferritic stainless steel after tensile deformation in the rolling direction, and steel makers are attempting to respond to the surface deterioration caused by this phenomenon. Many authors have suggested that a long distance order in the lattice orientation of a sheet could be responsible for ridging. In this study, the authors performed local orientation measurement on two samples of type 430 stainless steel using orientation imaging microscopy, and analyzed the grain orientations of the RD and ND planes. Data on areas covering more than 5mm 2 are presented here for the first time in the literature. The experimental results prove the existence of grain bands in the ND plane of samples with severe ridging. However, the texture maps for the RD planes are in disagreement with many previously proposed theories. Therefore, a new mathematical model is introduced. The simulated ridging profiles of the samples calculated with this new model agree with the experimental results. Finally, a method of amelioration that can significantly improve the theoretical model is proposed.

A structure oriented model to simulate the shear induced crystallization in injection moulded polymers: a Lagrangian approach

In this work a Lagrangian approach was used to simulate the crystallinity gradients in injection moulded PPS. This was done through the use of markers whose thermomechanical history was traced as they moved in the cavity. The results of the simulation are compared with our earlier experimental observations. It has been found that there is a good quantitative agreement between the experimental and calculated values of gapwise (NDTD plane) and lengthwise (FDND plane) crystallinity distribution. The calculated results for morphological variables such as the thickness of crystalline layers and their overall span agreed well with the experimentally measured values.