Effect Of Grain Orientation Research Articles

Grain-scale microtribological behavior of VCoNi medium-entropy alloy

The tribological behavior of equiatomic face-centered cubic (FCC) VCoNi medium-entropy alloy (MEA) remains underexplored despite of the alloy’s notable tensile strength and ductility. In this study, the tribological performance of VCoNi MEA is investigated using microscratching techniques, with emphasis on the effects of grain orientation, normal force, and scratch velocity. The study has demonstrated that the grain orientation in VCoNi MEA determines the activation of slip systems during the scratching processes, which significantly affects the morphology of wear tracks, slip steps and pile-up, as well as changes in microtribological behavior. As the normal force increases, the degree of wear intensifies, which is attributed to the significant material pile-up and more intense plastic flow. The plastic deformation of VCoNi MEA is found to be independent of scratch velocity within the 0.1–2 µm/s range. Ploughing and micro-shearing are identified as the primary wear mechanisms under various friction conditions. Furthermore, during the ploughing process, the deformation mechanism of the alloy is still dominated by dislocations. The direction of dislocation motion aligns with the direction of pile-up resulted from plastic deformation. The present study offers critical insights into the tribological behavior of medium-entropy alloys and broadens the potential for their applications in friction-intensive environments.

Orientation-dependent deformation and failure of micropillar shape memory ceramics: A 3D phase-field study

Some microscopic samples of zirconia-based shape memory ceramics (SMCs) have shown full martensitic phase transformation (MPT) over multiple loading cycles without cracking. However, the occurrence of MPT is strongly influenced by grain orientation. Depending on the specific grain orientation relative to the loading direction, alternative mechanisms such as plastic slip and fracture may emerge. This study introduces a phase-field (PF) based framework that integrates a PF-MPT model, a PF fracture model, and a crystal viscoplasticity model to investigate the effects of grain orientation on MPT, plastic slip, and fracture mechanisms in SMC micropillars. Single crystal micropillars are created to distinguish the orientations that facilitate each mechanism. A wide range of grain orientations are found to predominantly exhibit MPT. Micropillars with grain orientations close to the (100) and (001) directions primarily experience fracture, with minimal plastic slip. Additionally, samples oriented along the (110) direction show a significant amount of plastic slip. A pole figure is constructed to elucidate the interplay between MPT, cracking, and plastic slip under compressive loading conditions. This research provides valuable insights into the intricate behavior of SMCs under different loading scenarios, crucial for optimizing their performance in practical applications.

The correlation between grain structures and the corrosion behaviors of as-extruded Mg-Sm-Zn-Zr alloys

This work investigates the relationship between grain structure and corrosion behaviors of extruded Mg-Sm-Zn-Zr alloys. The results show that the phase composition and distribution are immune to the varied extrusion ratio, however, the grain orientation, grain boundary, and dislocations are changed, resulting in different corrosion behaviors. The corrosion initiates from the grain boundaries, especially low-angle grain boundaries, and dislocations, while the quasi-passivated surface suppresses the effect of grain orientation. The uniform distributed grain boundaries and dislocations generate uniform protective film with higher corrosion resistance, while the concentrated distribution enhances the film breakdown, causing exposed Mg substrate and accelerated corrosion.

Micropillar compression of single-crystal single-phase (Co, Cu, Mg, Ni, Zn)O

Bulk, polycrystalline (Co, Cu, Mg, Ni, Zn)O was synthesized using solid-state sintering. Micropillars were prepared and mechanically deformed along three crystallographic orientations: (001), (101), and (111). Pillars (001) and (111) cracked, while Pillar (101) remained intact. Pillars (001) and (101) exhibited activated slip systems, confirmed by a large stress drop, and the presence of slip bands, respectively. Schmid factor (SF) analysis was performed to examine the effect of grain orientations on dislocation activity and slip behavior. SF values range from 0 to 0.5, with non-zero values indicating potential for slip. Six slip systems exist in the (Co, Cu, Mg, Ni, Zn)O rock salt crystal structure: 1/2⟨110⟩11¯0. For the (001) orientation, four slip systems are potentially active (SF = 0.5). For the (101) orientation, there are four potentially active slip systems (SF = 0.25). For the (111) orientation, no potentially active slips systems exist (SF = 0). Dislocation structures, which were observed post-compression via transmission electron microscopy, demonstrated variations in size, number, and distribution across the pillar, depending on micropillar orientation. Entangled dislocations created misorientation in Pillar (001), which led to the possible formation of subgrains, while singular dislocations were observed in Pillar (101), and a lack of dislocations was observed in Pillar (111). Zener–Stroh type dislocation entanglement-mediated cracking is the proposed cause of the transgranular-type cracks in Pillar (001). The possible subgrain formation, or lack of formation, respectively, caused intergranular-type cracks to additionally form in Pillar (001), while Pillar (111) only exhibited transgranular-type brittle fracture. In combination, these findings highlight the importance of dislocation activity, without the need for elevated temperature, and grain orientation in controlling the mechanical deformation response in single-phase (Co, Cu, Mg, Ni, Zn)O.

The mechanistic origins of heterogeneous void growth during ductile failure

In 1969, Rice and Tracey proposed that the rate of void growth during ductile failure is a strong function of the hydrostatic stress state. Numerous in-situ x-ray computed tomography (XCT) studies demonstrated that the average rate of void growth is well-predicted by modified versions of the Rice-Tracey equation. However, recent in-situ XCT studies of void growth demonstrated that individual voids grow in highly heterogeneous manners in a way that is not predicted by Rice-Tracey or similar models. Model-based studies using crystal plasticity finite element (CP-FE) suggest that local effects of grain orientation play a strong role during void growth, but we lack experimental data to test this hypothesis. The present study leverages recent advances in laboratory-based diffraction contrast tomography (Lab-DCT) and in-situ XCT to systematically examine the effects of grain orientation on void growth experimentally in an Al-2219 alloy. CP-FE modeling was used to assess the local stress states associated with voids and their influence on void growth rates. These data indicate that void growth is not simply controlled by the local hydrostatic stress or stress triaxiality. Additionally, no clear relationship between void growth rates and grain orientation were observed. Instead, void growth rates were highly stochastic in ways that could not be directly linked to the local stress or strain states. The combination of experimental and modeling data suggests that our current assumptions regarding the mechanisms of void growth are flawed and that additional factors, which may include the local dislocation density, affect the rate of void growth.

In-situ synchrotron X-ray diffraction study of the effects of grain orientation on the martensitic phase transformations during tensile loading at different strain rates in metastable austenitic stainless steel

In this work, in-situ high-energy X-ray diffraction was used to analyze the effects of strain rate and austenite (γ) grain orientation on the strain-induced martensitic transformation in metastable austenitic stainless steel 301LN. The diffraction measurements were carried out at strain rates ranging from 10−3 s−1 to 1 s−1 continuously without interrupting the experiment and thus creating nearly adiabatic conditions at the highest studied strain rate. The results indicate that <100>γ fiber-oriented grains preferentially transform at the strain rate of 10−3 s−1 when the true strain is above 0.10, whereas the <111>γ fiber-oriented grains transform only at later stages of plastic deformation. The phase transformation rate of the <111>γ and <100>γ fiber-oriented grains decreases with increase in strain rate. A theoretical model based on stacking fault width as a function of external stress and temperature (stacking fault energy) was used to predict lower-bound estimates for the critical tensile stress needed to start ε-martensite and α’-martensite phase transformations. The model can predict the experimentally observed phase transformation behavior of the <111>γ fiber orientations at all strain rates but is unable to predict the decrease of phase transformation rate of <100> fiber-oriented γ grains with increase in strain rate, which could be related to change in dislocation structure.

Effect of grain orientation on the corrosion behavior of AZ31 alloy sheet

Effect of grain orientation on the corrosion behavior of AZ31 alloy sheet

Effect of grain orientation on the energy absorption performance of Chinese fir wood under quasi-static compression

ABSTRACT The compressive response and energy absorption of Chinese fir wood with different grain orientations along the longitudinal (L) and radial (or tangential) directions were studied through uniaxial quasi-static compression tests. The results indicated that the wood compressive behavior changed from out-of-plane to in-plane, similar to honeycomb materials when the grain orientation was changed from longitudinal to transverse. The initial peak stress (σp ) and plateau stress (σpl ) decreased upon increasing the grain angle (θ), especially below 45°, and more slowly above 45°. The wood compressive failure modes and energy absorption ability were also strongly dependent on the grain orientation, and the energy absorption per unit volume and energy absorption efficiency decreased as θ increased. Energy absorption diagrams and mathematical models were established to evaluate the optimum energy absorption point to guide the selection of energy-absorbing wood.

Delving into the intrinsic co-relation between microstructure and mechanical behaviour of fine-/ultrafine-grained TWIP steels via TEM and in-situ EBSD observation

To illustrate the microstructural factors of grain refinement for enhancing mechanical properties, the fine-/ultrafine-grained TWIP steels with a product of strength and elongation of ∼71 GPa·% were first prepared by combining rolling and stress relief annealing. Subsequently, the evolution of dislocations, stacking faults, and associated substructures of the fine-/ultrafine-grained TWIP steels was analysed by using in-situ EBSD tensile tests and TEM characterisation of the interrupted strain experiments. The results reveal that the excellent mechanical properties of the TWIP steels are attributed to dislocations and associated dislocation cells, dislocation walls, dislocation tangles, stacking faults and associated Lomer-Cottrell locks (LCs), nano-twins, primary and secondary twins and their interactions during plastic deformation. The density of geometrically necessary dislocations (GNDs) was evaluated based on the modified Ashby's model and compared with experimental results, indicating that grain size heterogeneity can promote the accumulation of GNDs, which facilitates the generation of subgrains and new boundaries to reduce the mean free path (MFP) of dislocations, thus enhancing strain hardening. Meanwhile, the interaction of lamellar primary and secondary twins in fine grains and the generation of stacking faults and nano-twins in ultrafine grains at higher strains can further promote strain hardening to elevate strength. Furthermore, the effects of grain orientation and grain size on the activation and evolution of dislocations and twins were elucidated. In ultrafine grains, twinning is strongly inhibited due to the elevated critical shear stress for twinning, resulting in more stacking faults and nano-twins, but fewer dislocation cells. The present work contributes to an in-depth understanding of the mechanical properties of fine-/ultrafine-grained materials to exploit their potential for industrial applications.

Effects of grain orientation and grain size on etching behaviors of high-strength and high-conductivity Cu alloy

Etching is a precise chemical material reduction processing method that can get small and precise components with specific size and pattern. In etching of the high-precision lead frames, microstructure of the Cu alloy plate has become an important factor that affects the etching rate, size accuracy and surface roughness of the etched products. In this study, the CuCrSn alloy samples with different grain size were etched by aqua regia and then comprehensively characterized to reveal the effects of grain orientation and grain size on the etching behavior. The results show that the etching morphologies and rates of the Cu alloy grains are significantly different and dominated by the grain orientation, and etching of the grains with their surface nearly parallel to the {100} crystal planes are the lowest, meanwhile the roughness of these etched surfaces is the lowest. After the etching, the grain surfaces show very fine stepped structures composed of two or more {100} crystal planes along which the Cu atoms dissolve. The priority corrosion is prone to occur at the grain boundaries (GBs), and the etching around the GBs is more significant when the grains are finer. With the increase in grain size, the etching at the GBs become less apparent, and the difference in etching rates between different grains increases, results in height difference and an increase in roughness of the etched surfaces.

Enhancement of magnetoelectric coupling in laminate composites of textured Fe–Ga thin sheet and PZT

Magneto-mechano-electric (MME) generators consisting of piezoelectric and magnetostrictive materials can convert the stray magnetic noise to useful electric energy for the wireless sensor networks utilizing the magnetoelectric coupling effect and magnetic interactions. In this paper, a scalable engineering approach was proposed to fabricate the laminate MME generator composed of a PZT/Fe–Ga/PZT sandwich structure. The Goss-oriented Fe81Ga19 thin sheet with a large magnetostriction of 244 ppm was produced by a simple and low-cost approach, and the commercial polycrystalline piezoelectric ceramic products (PZT-5H) were used as the PZT layers. The effect of grain orientation, device structure, magnetic field amplitude, and resonance frequency on the electrical output of the PZT/Fe–Ga/PZT MME generator was investigated. The electrical output of the MME generator containing the Goss-oriented Fe81Ga19 thin sheet reached an AC voltage of 4.58 V and the ME coefficient of 76.33 V/cm·Oe under a low excitation magnetic field of 26 Oe at a low resonance frequency of 26 Hz. The MME generator with a Goss-oriented Fe–Ga layer shows 4.7 times higher output voltage and ME coupling coefficient than that with the no-oriented polycrystalline Fe–Ga layer, but only 81% of the latter’s resonance frequency. This is related to the significant increase in magnetostriction due to the texture transition after secondary recrystallization annealing at the temperature of 950 °C. This paper provides a very promising solution to meet the self-power supply needs of the Internet of Things utilizing low-value and low-frequency magnetic fields.

Resolving the Dependence of Aluminum Alloy Corrosion on Grain Orientation by Scanning Electrochemical Cell Microscopy

The study of grain-dependent corrosion behaviors of practical polycrystalline metals remains challenging due to the influences of other microstructural features, such as intermetallic particles and grain boundaries. In this work, we employed the oil-immersed scanning electrochemical cell microscopy (SECCM) to investigate the effect of grain orientations of a practical aluminum alloy AA7075-T73 on the surface electrochemical behaviors. Thousands of spatially resolved microscopic potentiodynamic polarization (PDP) measurements were performed, allowing the extraction of information only from grain interior areas excluding intermetallic particles and grain boundaries. The differences in the corrosion behaviors between grains were revealed. Cathodic currents exhibited a strong grain orientation dependence with a decreasing order of {101} > {001} > {111}, agreeing with the prediction from the order of atomic planar density. By contrast, the dependence of anodic currents on grain orientation was weak, and pitting was independent of grain orientation, which could be due to the limited mass transport of ions within the surface oxide film. This work highlights the capability of oil-immersed scanning electrochemical cell microscopy in resolving small electrochemical differences, which will greatly promote the study of grain-dependent behaviors of practical polycrystalline samples.

Electrocaloric behaviour of tape cast and grain oriented NBT-KBT ceramics

We have investigated the effects of grain orientation and tape casting process on the electrocaloric properties of 0.82Na0.5Bi0.5TiO3-0.18 K0.5Bi0.5TiO3 (0.82NBT-0.18KBT) ceramics at the Morphotropic Phase Boundary (MPB), using direct and indirect measurements. We observe a larger electrocaloric response for the template-free ceramics compared to 7 and 10 wt% template containing ones, suggesting that grain orientation along rhombohedral < 100 > does not improve the electrocaloric response. Indirect measurements yielded a large adiabatic temperature change of around 3 K under an electric field of 50 kV/cm, which is significantly higher than 0.9 K reached at a lower electric field of 40 kV/cm using the direct measurement.

Effect of grain orientation and precipitates on the superelasticity of Fe–Ni–Co–Al polycrystalline alloys

In this paper, the evolution of microstructure in Fe–Ni–Co–Al polycrystalline alloys and its effects on mechanical properties were systematically investigated. The results show that the proportion of high-angle grain boundaries (HAGBs) is 98.1 % with 51.2 % of Σ3 GBs during the solid solution (SS) process. The distribution of Σ3 GBs and other HAGBs (non-Σ3 HAGBs) are relatively dispersed, which prevents the formation of a specific orientation. In addition, there is no discernible anisotropy in GB migration during the SS process, ultimately resulting in the absence of texture. In contrast, during the directional recrystallization (DR) process, the directional migration of GBs is driven by the temperature gradient. Random high-angle grain boundaries (RHAGBs) with Σ values exceeding 29 possess higher GB energy and migration rate compared to low-angle grain boundaries (LAGBs) and HAGBs, making them more susceptible to GB migration. In the grain incubation area, the proportion of RHAGBs between grains oriented {111}<214> (grain 2 and grain 5) and their surrounding grains are 90 % and 75 %. These grains have the growth advantage and eventually form the main orientation {111}<214>. While the proportion of RHAGBs between grains oriented {114}<214> (grain 11) and its surrounding grains is only 65 %, characterized by lower GB energy and migration rate. Therefore, these grains eventually form the minor orientation {114}<214>. The coherent L12-Ni3Al (γ′) precipitates were observed in both the SS-AG (SS after aging) and DR-AG (DR after aging) treatments. The DR-AG alloy, characterized by {111}<214> and {114}<214> orientations and γ′ precipitates, exhibited a 3.6 % recoverable strain and a 1.2 % superelastic strain, whereas no evident superelastic behavior was found in the SS-AG alloy, which featured a random texture and γ′ precipitates.

Texture-Induced Corrosion Resistance of Dissimilar AA7204/AA6082 Friction Stir Welded Joints.

The quasi in situ EBSD test was applied to study the effect of grain orientation on corrosion behaviors of the thermomechanically affected zone I (TMAZ I) of dissimilar AA6082/AA7204 friction stir welding (FSW) joints in this work. The results show that the structure with grain orientation close to the brass texture ({110}<112>) has excellent corrosion resistance, which contributes to the better corrosion performance of the TMAZ I of the 7204-AS joint than the 7204-RS joint. Furthermore, the brass texture around by S texture ({213}<364>) in the TMAZ I of the 7204-AS joint is slightly corroded, and the orientation of the remaining structure is closer to the ({110}<112>) than before, which indicates that the corrosion, like deformation, is carried out alongside the {110} plane for the structure with grain orientation near {110}<112>. Those findings could provide new insight into the designed FSW joints and improve the corrosion resistance of the wrought aluminum alloy.

Effect of Grain Orientation on Microstructure and Mechanical Properties of FeCoCrNi High-Entropy Alloy Produced via Laser Melting Deposition.

The long, straight grain boundary of the high-entropy alloy (HEA) produced via laser melting deposition (LMD) is prone to cracking due to unidirectional scanning (single wall). To enhance the competitive growth of columnar grains and improve the overall performance of the alloy, a vertical cross scanning method was employed to fabricate FeCoCrNi HEA (bulk). The influence of grain orientation on the microstructure and mechanical properties of FeCoCrNi-LMD was systematically investigated. Microhardness tests and tensile tests were conducted to assess the mechanical property differences between the single-wall and bulk samples. This study shows that using a single scanning strategy results in monolayer wall grains sized at 129.40 μm, with a max texture strength of 21.29. Employing orthogonal scanning yields 61.15 μm block-like grains with a max texture strength of 11.12. Dislocation densities are 1.084 × 1012 m-2 and 1.156 × 1012 m-2, with average Schmid factors of 0.471 and 0.416. In comparison to the FeCoCrNi-LMD single wall, the bulk material produced through cross-layer orthogonal scanning exhibited reduced residual stress, weakened anisotropy, and improved mechanical properties. These findings are expected to enhance the potential applications of FeCoCrNi-LMD in various industries.

Thermal conductivity assessment of wood using micro computed tomography based finite element analysis (μCT-based FEA)

The paper presents a progressive methodology that combines X-ray micro computed tomography (μCT) and finite element analysis (FEA) to test the thermal conductivity of wood at the mesoscale level. μCT enables the three-dimensional (3D) modeling of real wood material with two-phase components (i.e., earlywood and latewood). The analytical wood conductivities from μCT-based FEA agree well with those from the theoretical analysis and the existing experimental findings. Using μCT-based FEA also enables the numerical evaluation of the effects of grain orientation, porosity, and water saturation degree on thermal conductivity of wood. Compared to current testing methods, the proposed μCT-based FEA has the advantages of high-resolution modeling, rapid evaluation, and high reproducibility of wood thermal conduction.

A new approach to measure fundamental microstructural influences on the magnetic properties of electrical steel using a miniaturized single sheet tester

Magnetic properties of electrical steel are usually measured on Single Sheet Testers, Epstein frames or ring cores. Due to the geometric dimensions and measurement principles of these standardized setups, the fundamental microstructural influences on the magnetic behavior, e.g., deformation structures, crystal orientation or grain boundaries, are difficult to separate and quantify. In this paper, a miniaturized Single Sheet Tester is presented that allows the characterization of industrial steel sheets as well as from in size limited single, bi- and oligocrystals starting from samples with dimensions of 10 × 22 mm. Thereby, the measurement of global magnetic properties is coupled with microstructural analysis methods to allow the investigation of micro scale magnetic effects. An effect of grain orientation, grain boundaries and deformation structures has already been identified with the presented experimental setup. In addition, a correction function is introduced to allow quantitative comparisons between differently sized Single Sheet Testers. This approach is not limited to the presented Single Sheet Tester geometry, but can also be used to compare the results of Single Sheet Testers of various sizes. The results of the miniaturized Single Sheet Tester were validated on five industrial electrical steel grades. Furthermore, first results of differently oriented single crystals as well as measurements on grain-oriented electrical steel are shown to prove the additional value of the miniaturized Single Sheet Tester geometry.

An experimental investigation of formability of inconel sheet plate for different die angles and rolling directions in press brake bending

The formability of Inconel materials is important to be used in engineering applications such as in fields of aircraft and maritime. The aim of study is to investigate bending characteristic and formability of Inconel 625 material having a property of corrosion resistance and high strength. In the paper, spring-back phenomena of Inconel 625 sheets are focused on experimentally. The 4 specimens for each different die angle are prepared to be bent. The press brake is used for forming Inconel 625 sheets. The die angle is altered from 90˚ to 150˚. The different rolling direction such as 0˚ and 90˚ is chosen to investigate the effect of grain orientation on spring-back of Inconel sheets. The bending radius is constant and set as 2 mm for all bending tests. The spring-back angles and amounts are measured. Results show that as the bending angle is increased, the spring-back amount in units of angle is decreased averagely from 3.35˚ to 2.58˚ for 0˚ rolling direction and maximum spring-back angle is obtained at a die angle of 120˚ for rolling direction of 90˚. Finally, Erichsen cupping test is also applied to determine the deformability of Inconel sheets. It is demonstrated that cup height value has been found as 17.20 mm.

Investigation of creep-fatigue crack initiation by using an optimal dual-scale modelling approach

In this work, three dual-scale modelling approaches containing sub-modelling approach, coupled modelling approach and full-field crystal plasticity finite element (CPFE) approach are implemented for notched structures under creep-fatigue loading conditions. Based on the comprehensive comparisons, the sub-modelling approach is determined to be an optimal simulation strategy among them. Furthermore, the combined effects of grain orientation and stress concentration on crack initiation are investigated by adopting the sub-modelling approach. Under low stress concentration factor, the most potential positions of crack initiation randomly locate at the root of geometric discontinuities owing to the influence of grain orientation distribution. With the increase in stress concentration factor and decrease in the number of grains at hotspots, the cooperative relation between grain orientation and stress concentration factor for creep-fatigue crack initiation is revealed through a sequence of simulation results, followed by the competitive relation. On this basis, a feature region map is constructed to distinguish the factor-dominated crack initiation. Finally, a case study of turbine disk is provided to illustrate the engineering meanings of the dual-scale modelling approach. The link from scientific problem to engineering application for the crack initiation prediction is bridged by the damage mechanics approach, which is also expected to be promoted in many high-temperature components.