Rolling Direction Specimens Research Articles

High‐Cycle‐Fatigue Anisotropy of an Aluminum Alloy Superthick Plate

The effect of anisotropy on high‐cycle fatigue (HCF) property along the rolling direction (RD) and the transverse direction (TD) of a 7××× aluminum alloy super thick plate is mainly investigated in this study. The results show a similar microstructure at different thicknesses, and the HCF properties are close as well. The fatigue fracture morphologies show that the fatigue crack sources are all located on the surfaces of the RD and TD specimens. By considering the differences in the HCF properties, there is only a slight anisotropy effect at the center thickness of the plate, which can be attributed to the tensile anisotropy caused by textures. Besides, the fatigue damage degree along the TD is slightly higher than that along the RD at the center thickness. The reason can be explained by two aspects: one is the higher probability of defect occurrence along the TD compared with that along the RD which is analyzed by the previously proposed Yield strength‐Tensile strength‐Fatigue strength model, and the other is the influence of the textures. The combination of hard and soft orientations may cause fatigue damage localization easily in the soft‐oriented grains which accelerates the fatigue failure.

The effect of texture on the very high cycle fatigue performance and deformation mechanism of rolled AZ31B magnesium alloys

AbstractRolling can result in anisotropy in the microstructure and mechanical properties of the sheet material. This study focuses on the very high cycle fatigue (VHCF) performance of magnesium alloys in the rolling direction (RD), normal direction (ND), and the bisecting angle between the ND and RD (ND–RD). The findings reveal that RD specimens demonstrate superior fatigue performance, while the ND specimens exhibit the lowest fatigue resistance. During the crack initiation stage, the primary influential factor is the maximum shear stress. Due to c‐axis alignment with ND direction in grains, the deformation mode for ND and RD specimens primarily involves first‐order pyramidal slip, while ND–RD specimens primarily undergo basal slip and prismatic slip. In early stable crack propagation, grain size and texture cause variations in the morphology of the rough area among the three directional specimens. Notably, the RD specimens show faster crack propagation during crack initiation than early stable propagation stage.

Crack nucleation and dislocation activities in titanium alloys with the strong transverse texture: Insights for enhancing dwell fatigue resistance

Cold dwell sensitivity of near α titanium alloys has posed a significant challenge to the engineering safety within the aerospace industry. However, there exists inconsistency regarding the critical facet formation mechanism between basal and prismatic nucleation. A key revelation in this paper is that the controversy surrounding the facet nucleation plane primarily arises from variations in texture: when the loading direction is parallel to the c-axis or at a 45 ° angle, it leads to basal plane cracking, whereas loading direction perpendicular to the c-axis results in prismatic plane cracking. What's more, a large anisotropy is observed in the dwell fatigue performance in descending order: rolling direction (RD) > transverse direction (TD) >45° direction. To be specific, the dwell fatigue life of RD specimens was 2 times and 4.07 times longer than that of TD and 45 ° specimens, which exhibits excellent dwell fatigue resistance. Furthermore, the high prismatic dislocation density near the facet of RD specimen was confirmed through the Transmission Electron Microscope (TEM) and Transmission Kikuchi Diffraction (TKD) map, which is evidenced that prismatic slips lead to higher strain hardening during cyclic loading. The basal plane of facet grain is generally parallel to the facet line, indicating that the elliptical facet developed by the transgranular fracture through basal plane. Twinning activation in hard grain to accommodate deformation in Ti60 alloy is firstly observed under dwell fatigue tests, which is a product of high stress level in the hard grain. This paper unveils the significant impact of texture on dwell fatigue resistance, offering novel insights into enhancing dwell fatigue performance through texture control.

Anisotropic deformation mechanisms of rolling-textured Zircaloy-4 alloy by a crystal plasticity model

This study focuses on investigating the anisotropic deformation behavior of rolling-textured Zircaloy-4 alloy under uniaxial tension along the rolling direction (RD) and transverse direction (TD). A dislocation density-based crystal plasticity finite element method is used to study the associated mechanisms. The simulation accurately reproduces the experimental results on stress–strain curves and strain hardening rate. The relationship between relative activities in different slip systems and anisotropic plastic deformation is established. It is revealed that in the tensile deformation, prismatic slip dominates plastic deformation in the RD, while both prismatic slip and basal slip dominate plastic deformation in the TD. The difference in the dominant slip modes leads to a lower yield stress and a higher strain hardening rate in the RD. Furthermore, the stress and strain distributions in the tensile direction are also statistically analyzed. It is found that a certain proportion of hard grains results in more severe stress concentration and lower uniform elongation in the TD specimen compared with the RD specimen. In addition, the strain rate sensitivity of the yield stress is investigated. It is shown that Zircaloy-4 alloy has almost the same yield anisotropy (TD > RD in terms of the yield stress) at different strain rates in the RD and TD.

Quantifying the effect of macrozones on the cold-dwell fatigue response of UD-rolled Ti-6Al-4V using high-energy X-ray diffraction

High-energy X-ray diffraction is used to investigate the evolution of elastic lattice strains in rolled Ti-6Al-4V specimens during cyclic loading in-situ with and without the inclusion of a 120s dwell period. A 1mm segment of the gauge section is monitored throughout the first 100 cycles for specimens extracted along the rolling direction (RD), the transverse direction (TD) and 45° between the two, to explore the effects of texture on the evolution of the micromechanical response. Five families of lattice planes from the hexagonal α phase are analysed with emphasis on lattice strain measured at the peak of each cycle, while macroscopic strain accumulation is simultaneously monitored via Digital Image Correlation. In cyclic loading conditions including a dwell period at load, a prominent increase in elastic strains is observed in prismatic and basal lattice planes with the specimen loaded 45° from the rolling direction. In the absence of dwell, both RD and TD specimen orientations exhibited subtle cyclic hardening in all families of lattice planes probed despite negligible evolution in accumulated macroscopic plastic strain. Estimations of lattice orientation-dependent stresses are also presented using directional moduli to examine redistribution of load across sets of grains with the increasing cycle count.

In Situ EBSD Study on the Microstructural Transformation of the Ni5W Substrate for Coated Conductors.

The microstructure and texture evolution of Ni-5 at%W (Ni5W) alloy substrates were investigated by in situ tensile testing along the rolling direction (RD), transverse direction (TD), and at 45° to the RD (45°-RD), as well as by electron backscatter diffraction characterization. The tensile stress direction had a significant influence on the texture evolution. The cubic texture in the Ni-5 at%W alloy exhibited severe degradation when the tensile angle was 45°-RD. In contrast, the cubic texture was relatively stable under high deformation along the RD or TD. It was found that the slip line system in the 45°-RD specimen was the key to the contrasting behavior. The effect of the tensile testing angle on the cubic texture evolution for Ni–W substrates was investigated, and the corresponding effect on the superconducting properties of coated materials was studied.

Comparative study of Dual-Phase -590 steel on formability at superplastic region and room temperature

A steel alloy DP590 is commonly used for automobile applications because of its outstanding mechanical characteristics. One crucial limitation of this steel forming is that it has limited malleability and ductility. In this study, we compared the experimental forming limit diagram (FLD) for DP590 at RT and 800°C using stretching. An experiment with a strain rate of 0.01/s is carried out with samples cut in four different directions (0°,30°,60°& 90°) as seen from the rolling direction. Rolling direction specimens have been found to be among the stronger samples. FLD can be applied as a method for studying temperature differences in formability characteristics of DP590. Scanning electron microscopy was used for the analysis deformation pattern. Based on these results, it shows that the material has become significantly more formable.

Hardening behavior and deformation microstructure beneath indentation in heavy ion irradiated 12Cr-ODS steel at elevated temperature

Hardness behavior and deformation of the microstructure beneath the indentation in 12Cr-ODS steel after exposure to heavy ion irradiation at 573 K were investigated with combined applications of nano-indentation tests, EBSD analysis, and TEM observation. The inhomogeneous nano-indentation hardness behavior was firstly investigated in both non-irradiated and irradiated specimens and compared to those at room temperature (RT) irradiation. Subsequently, TEM observations were performed to understand the deformation behaviors beneath the indentation tested at typical low-indexed orientations. Obvious irradiation hardening was confirmed in both the normal direction (ND) and rolling direction (RD) specimens, and the hardening effect intensified with an increase in irradiation dose. Meanwhile, various anisotropic hardness behaviors were observed such as a lower hardness value and a weaker hardening effect in the RD specimen compared to the ND specimen, and a lower hardness value but a greater hardening effect in [001] orientation relative to [111] orientation. Furthermore, results from 573 K irradiation showed similar anisotropic hardness behaviors with those obtained from RT irradiation, despite the fact that irradiation at 573 K exhibited a weakened irradiation hardening effect in this steel. TEM observation of the deformation microstructure beneath the indentation reveals that (i) the depth of the deformation affected zone varied with orientation, ranging from ~6-9 times that of the indent depth, and (ii) distinct dislocation-grain boundary (GB) interactions beneath the indentations was confirmed to exhibit dependence on the geometric relation between GB and indenter impression direction. Correlation between the anisotropic hardness behavior and microstructural features is discussed based on Schmid factor analysis, comparison of geometric favorability between indenter and possible slip planes, and TEM observation of deformation microstructure. The results conclude that the anisotropic hardness behaviors in the present 12Cr-ODS steel are ascribed to the combined effect of crystal orientation and the non-uniform grain morphology with the existence of the elongated grains having low aspect ratio in the ND plane and nano-layered grains in the RD plane.

Anisotropic Electroplastic Effects on the Mechanical Properties of a Nano-Lamellar Austenitic Stainless Steel

Effects of electropulsing treatment (EPT) on the microstructural evolution and mechanical properties of a cold-rolled 316L austenitic stainless steel with nano-lamellar structure were investigated. The EPT experiments were carried out with the electric current direction along the rolling direction (RD) and the transverse direction (TD) of the samples, respectively. Significant anisotropic electroplastic effects for the RD and TD specimens, i.e., reduced hardness/strength and enhanced ductility, were obtained owing to the different recrystallization behaviors of the RD and TD specimens during EPT. The RD specimens after EPT with larger recrystallized grain size and higher volume fraction of recrystallization show lower strength and higher elongation than that of the TD specimens. The main reason might be attributed to the change of the current direction in the two kinds of samples, which results in the different sensitivity of the microstructures to thermal and athermal effects during EPT.

Decoding Pattern Dependence of Micro-indentation on Crystal Orientation of Cube-textured Aluminum Foil Using SAXS and Temperature Changes

Recent use of nano-indentation to assess work-hardening of complex microstructure of dual phase steels as a function of deformation together with crystal plasticity finite element method to simulate the bulk properties gives rise to the question of the role of crystallite orientation during indentation. Such studies using nano-indentation on µm-sized grains are difficult. To elucidate this effect, Vickers micro-indentation of cube textured Al capacitor foils were examined. These foils of 106 µm thickness are convenient for small angle X-ray scattering (SAXS) examination and the orientation around the indent can be examined by back-scattered electron diffraction (EBSD). The indentations were carried out with the diagonals parallel to the rolling direction (RD) and 45 ° to it at temperatures from 20 °C (295 K) to 160°C (433 K). The SAXS tests were performed only at 20°C on RD specimens.

Fracture behavior of magnesium alloys – Role of tensile twinning

In this work, Mode-I fracture experiments are conducted using notched compact tension specimens machined from a rolled AZ31 Mg alloy plate having near-basal texture with load applied along rolling direction (RD) and transverse direction (TD). Moderately high notched fracture toughness of JC∼46N/mm is obtained in both RD and TD specimens. Fracture surface shows crack tunneling at specimen mid-thickness and extensive shear lips near the free surface. Dimples are observed from SEM fractographs suggesting ductile fracture. EBSD analysis shows profuse tensile twinning in the ligament ahead of the notch. It is shown that tensile twinning plays a dual role in enhancing the toughness in the notched fracture specimens with reduced triaxiality. It provides significant dissipation in the background plastic zone and imparts hardening to the material surrounding the fracture process zone via operation of several mechanisms which retards micro-void growth and coalescence.

Research Difference of Strain Distribution and Microstructure Evolution between Rolling Direction and Transverse Direction of AM50 Mg Alloy Plate by Digital Image Correlation

The rolling direction (RD) and transverse direction (TD) of AM50 Mg alloy plate were drawn by tensile test while Digital Image Correlation (DIC) was applied to record local strain distribution and evolution. Then, the microstructure in the maximum strain position was observed so as to find the reason causing the difference between RD and TD specimen. Finally, the fracture surface morphology of the broken specimen was observed by scanning electron microscope (SEM) to determine the crack types. Through the analysis, it is found that the critical failure equivalent strains in the RD specimen and TD specimen are 0.1675 and 0.118, respectively, and the maximum equivalent strain position is the crack source; more twinning is generated in the RD specimen than that of the TD specimen, which indicates that twinning plays an important role in affecting its plasticity. The fracture surface morphology indicates that the RD specimen fracture is quasi-cleavage fracture while the TD specimen shows character of cleavage fracture.

Processing maps for hot deformation of rolled AZ31 magnesium alloy plate: Anisotropy of hot workability

Processing maps on rolled AZ31 magnesium plate have been developed in the range 300–550 °C and 0.0003–10 s −1 by hot compression of specimens parallel to the rolling direction (RD), the transverse direction (TD), or the normal direction (ND) with a view to examine whether the hot workability is anisotropic. The processing map for RD specimens exhibited a single wide domain of workability in the temperature range 350–550 °C and strain rate range 0.0003–0.3 s −1 in which dynamic recrystallization (DRX) occurs. The apparent activation energy in this domain is estimated to be 143 kJ/mole, which is close to that for self-diffusion in magnesium. On the other hand, the maps for the TD and ND specimens exhibited two DRX domains, one at lower strain rates (<0.01 s −1) and the other at higher strain rates (>1 s −1). The apparent activation energies estimated in the lower strain rate DRX domain of TD and ND maps are 180 and 168 kJ/mole, respectively, suggesting cross-slip occurs in this domain. In the higher strain rate domain, the apparent activation energy estimated in both TD and ND specimens is 105 kJ/mole, which is close to that for grain-boundary diffusion. The results suggest that the hot deformation behavior is anisotropic and a simple correlation with the known primary rolling texture ( { 0 0 0 2 } 〈 1 0 1 ¯ 0 〉 ) revealed that both the first order and second order pyramidal slip systems are favored in the RD orientation resulting in higher workability. The other two orientations may be considered “harder” as regards hot workability since either the first order or the second order pyramidal slip is likely to dominate. In all the three orientations and within the DRX domains, the grain size varies linearly with the Zener-Hollomon parameter.

Mechanism of Crack Nucleation Analysed by In Situ Observation on Mg-Al-Zn Alloy

An In Situ observation was made on rolled sheet Mg-Al-Zn alloy (AZ31) in SEM. A type of mini-tensile specimens was used in three typical material orientations, RD (Rolling direction), 45 (45 degrees to rolling direction) and TD (transverse direction, 90 degrees to rolling direction). It is found that the plastic deformation occurred unevenly and limited in single grains, shown by micro extruding steps at grain boundaries. Further deformation concentrated at twinning bands and grain boundaries, more and finer twinning bands appeared as secondary twins on the original ones. In different orientations the dislocation slipping mechanism within twinning bands seems to play a role in different degrees. In RD specimens the slipping mechanism seems predominant, whereas in TD specimens the twinned steps were obvious. Micro cracks nucleated at internal interfaces: grain boundaries, interfaces of twinning bands, and intersections of twinning bands as well.

Effect of crystallographic texture on the kinetics of hot deformation of rolled Mg–3Al–1Zn alloy plate

The hot deformation behavior of a rolled plate of Mg–3Al–1Zn (AZ31) alloy has been studied on cylindrical specimens with their compression axis parallel to the rolling direction (RD), the transverse direction (TD) or the normal to the rolling plane (ND) with a view to evaluate the effect of crystallographic texture. Constant true strain rate isothermal hot compression tests were conducted in the temperature range 300–550 °C and strain rate range 0.0003–10 s −1. The temperature and strain rate dependence of steady-state flow stress follows the standard kinetic rate equation. The apparent activation energy is estimated to be 143, 180 and 168 kJ/mole for RD, TD and ND specimens, respectively, the value for RD specimens being close to that for self-diffusion in magnesium. The texture existing in the starting rolled plate ( { 0 0 0 2 } 〈 1 0 1 ¯ 0 〉 ) favors the activation of both first- and second-order pyramidal slip systems during the hot deformation of RD specimens. On the other hand, deformation of TD specimens involves first-order pyramidal slip while in ND specimens the second-order pyramidal slip dominates. The results on RD specimens suggest that the occurrence of extensive slip on both the first- and second-order pyramidal systems along with simultaneous dynamic recovery by cross-slip give rise to a higher rate of nucleation for dynamic recrystallization in comparison with that in ND and TD specimens.