Hard Grains Research Articles

Hydrogen diffusion and precipitation influenced by non-uniformly distributed stress in zirconium alloy with different textures

Hydrogen embrittlement is a crucial factor for the performance and life of zirconium alloys in nuclear industry. During service, the residual stress in the materials induces re-distribution of hydrogen, which further affects the fracture behavior. This study is dedicated to investigating the hydrogen diffusion and precipitation under the meso‑scale non-uniform deformation field. The texture effect of hydrogen behavior was examined by considering three different texture scenarios: grains with c-axis deviating from the tensile direction of random angle, 0°and 90° The cases were termed Random, T000, and T0900 respectively. The crystal plasticity finite element method (CPFEM) was employed to simulate the stress-assisted diffusion of hydrogen atoms in the polycrystalline zirconium alloy. It is determined that the T0900 case gets fewer regions with higher hydrostatic stress gradient, which helps relieve the hydrogen concentration. Compared to the T0900 texture, the interaction between soft and hard grains in the Random and T000 texture conditions results in higher stress gradient and severe hydrogen concentration. Statistical analysis was conducted and the hydrogen concentration in the three textures presents a normal distribution. T0900 gets a relatively lower overall hydrogen concentration while the T000 texture gets severe hydrogen concentration larger than 120 wt.ppm. In Random and T000 textures, hydrogen tends to accumulate at grain interior and boundaries, and continuous hydrogen concentration band forms along adjacent GBs. The T0900 scenario is free of large continuous hydrogen concentration zones, which helps reduces the adverse effects of hydrogen diffusion and precipitation. The findings of the work advance the understanding of the hydrogen behavior affected by stress heterogeneity and texture, which is the basis for the exploration of hydrogen embrittlement.

Coercivity enhancement and microstructure optimization of Nd-Fe-Co-B magnets by Dy70Al10Cu20 grain boundary diffusion

The effect of grain boundary diffusion on the magnetic properties and microstructure of Nd-Fe-Co-B sintered magnets is investigated using Dy70Al10Cu20 alloy as the diffusion source. After the secondary annealing of the Nd-Fe-Co-B sintered magnet (Hcj = 7.94 kOe), its coercivity is substantially increased to 13.10 kOe. Following post-diffusion annealing, the coercivity of the sintered magnet significantly increased to 20.86 kOe. Microstructure analysis revealed that after the second annealing, the main phase grains in the magnet were connected but lacked thin intergranular phases. The distribution of Co was uneven, with an abundance of soft magnetic phases rich in Co, which was not conducive to improving coercivity. After diffusion, Dy formed a shell structure with high magnetic crystal anisotropy on the outer side of the main phase grains, leading to a significant increase in coercivity. Al and Cu entered the interior of the magnet, reducing the melting point of the grain boundary phase and promoting the uniform distribution of Co through the flow of the liquid phase. A large amount of thin continuous intergranular phase is generated inside the magnet, which helps reduce the exchange coupling between hard magnetic grains. The experimental results indicate that the Dy-Al-Cu alloy can effectively enhance the grain boundary structure of Nd-Fe-Co-B magnets, reduce the abundance of Co-rich phases, and improve the coercivity of the magnet.

Multi-scale surface folding in metal cutting

In this work, commercially pure small-grained copper is used to investigate the nature of plastic flow through in situ image analysis supported by extensive electron backscatter diffraction characterization of the chip. Non-laminar sinuous flow, manifested with surface perturbations (bumps) and folds, produces a highly heterogeneous strain field during cutting. A series of mushroom-shaped morphology, termed as large bumps, separated by large folds on the free surface of the chip are captured in high-resolution field emission scanning electron microscopy. Large bumps or folds, captured in the high-speed camera, consist of many medium and small-size bumps. While the size of the small bump is comparable with the grain size of the base metal, a cluster of grains takes part in forming medium-size bumps. The pinning points for the small size bumps are either grain boundary or hard grains. The hard grains also act as pinning points for the medium size bump. The bump boundaries (folds) are characterized by higher strain and greater refinement of grains, whereas, less strain and larger elongated grains are the characteristics of the central region of the bumps. The evolution of different length scale features on the free surface is discussed in terms of the orientation of grain, position of the grains on the surface, and induced strain in the chip. This study suggested that the development of folding at different length scales is capable of providing deeper insight into the formation of a wide variety of chip morphology observed during the cutting of metals.

Crack initiation mechanisms of micro-textured Ti60 alloys with different dwell sensitivities subjected to fatigue and dwell fatigue loading

In this work, Ti60 alloys with different micro-texture intensity were designed to elucidate the effect of micro-texture on fatigue life and dwell sensitivity and the difference in crack initiation mechanism for low-cycle fatigue (LCF) and dwell fatigue (DF). It was found that micro-texture region (MTR) significantly reduced LCF and DF lifetimes and increased dwell sensitivity compared to no-MTR samples. However, micro-texture does not change the characteristics of the crack initiation grains, and the fracture initiation region facet of all samples matches the (0001) basal plane and is related to basal slip. Therefore, the [0001] orientation domains for crack initiation in both fatigue states are discussed, and it is found that LCF tends to nucleate along the basal slip bands or basal twist grain boundaries (BTGBs) of the high SF grains, whereas DF nucleation is independent of the basal SF value, and the mechanism of initiation of hard oriented grain cracking is also included. In situ further demonstrated that hard grains can activate basal slip as well as cracking, and the possibility of soft/hard grain pairs generating dislocation pile-up stresses leading to cracking of hard grains was determined by theoretical calculations, providing experimental support and evidence for the soft/hard grain model. Based on these findings, criteria for the angle (θ) of the c-axis with respect to the loading axis and the basal SF range are proposed to determine the differences between LCF and DF with respect to the mechanisms of hard grain cracking and BTGB crack initiation.

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.

3-D FE modelling of residual stress distribution in 3003 aluminium alloy overlapped joints by ARM laser with beam oscillations

Adjustable Ring Mode (ARM) laser technology combined with Beam Oscillation optics module was introduced to effectively enhance weld quality in joining aluminium alloys. This study developed a three-dimensional (3-D) thermo-mechanical finite element (FE) model to analyze the distribution of thermally induced residual stresses in laser-welded 3003 aluminium alloy. The accuracy of model was validated through comparisons with experimental weld cross-sections and further reinforced by X-ray diffraction residual stress measurements. The transient temperature field and stress distribution during the welding process were investigated using the verified model. Additionally, the hardness and microstructure of the welded samples were examined through micro-hardness tests and scanning electron microscopy. Results showed that welding with beam oscillation resulted in less penetration but higher hardness and finer columnar grain size in the fusion zone. Additionally, the influence of varying standoff distances between two sequential weld beads on residual stress distribution was investigated. Numerical findings revealed that higher residual stress concentrations were located at the weld seam and dominated by tensile longitudinal residual stress and compressive transverse residual stress. As the distance between weld beads increased, transverse and equivalent residual stresses decreased, while longitudinal residual stress away from the bead increased.

Heterogeneous Microstructure and Tensile Properties of an Austenitic Stainless Steel

Stainless steel (SS) exhibits excellent ductility; however, its low strength hinders its practical applications. To achieve good synergy between strength and ductility, a heterogeneous structure was introduced into a newly developed nitrogen-alloyed low-nickel austenitic steel, QN1803. The received QN1803 was cold-rolled and annealed at 993 K for different durations, and the microstructural evolution and tensile mechanical properties were investigated. The yield strength (1130 MPa) of the QN1803 annealed at a temperature of 993 K for 15 min was approximately three times higher than that of the as-received sample (314 MPa). The short annealing time of 15 min yielded a heterogeneous structure with grain size distributions ranging from nanoscale to micron-scale. The annealed QN1803 exhibited typical dislocation cells and dislocation walls caused by slipping after cold rolling. During annealing, a step-like lamellar structure is formed. The high yield strength was obtained from the large number of twins and hard ultrafine grains. The good ductility is due to the large number of dislocations generated in the soft grains and the GNDs around the heterogeneous interfaces. Additionally, the lamella structure of the material also contributes to improved ductility to a certain degree. The aim of this paper is to develop new materials with both high yield strength and excellent toughness based on more economical materials cost.

Investigation of neighboring grain effects on load shedding in titanium alloys under cold dwell fatigue

Load shedding under cold dwell fatigue in titanium alloys has been a threat to the safety of the aero-engine since it is responsible for crack formation. The strain incompatibility between the soft-hard grain pair arises from the significant creep in the soft grain during the dwell period, which is fundamentally related to the load shedding. Such deformational heterogeneity is not only affected by the soft-hard grain itself but also by its neighboring grains, but the effect of the latter is rarely reported. In this paper, the effect of neighboring grains, including location, crystal orientation, texture, etc., on load shedding is quantitatively investigated using a three-dimensional rate-dependent crystal plasticity model by controlling the microstructural morphology of the grains. In particular, the mechanism that the dwell fatigue cracks tend to nucleate from the sample's interior rather than the free surface is revealed. Restriction of rigid body rotation from neighboring grains can further enhance load shedding. The crystal orientation of individual and group neighboring grains sitting at different locations with respect to the soft-hard grain pair is evaluated. The grain directly attached to the hard grain has the strongest influence. The statistics of load shedding are analyzed by conducting hundreds of simulations with different textures. Stronger textures are found to be able to enhance load shedding and thus deteriorate the service lifetime. The change of locations showing the highest stress during the dwell period arising from plastic deformation in neighboring grain may lead to the phenomenon of reverse load shedding. Understanding the neighboring grain effects from both the mechanistic basis and the statistical point of view is important in integrity evaluations and service life assessments of titanium components in aero-engines.

〈112̄0〉-orientation-dependent crack initiation in a titanium alloy under dwell fatigue

Soft grains with a “rotation angle” between 15° and 30° are prone to induce cracking in hard grains, for the reason that prismatic dislocation slips in these soft grains exert a higher stress (higher κ value) normal to the basal plane of hard grains.

Comparison between the fodder quality of Algerian Pennisetum and Sorghum

Sorghum and Pennisetum were installed in 2013 in a complete random block. Mowing at the vegetative stage was carried out at 30 cm for sorghum and at 60 cm for Pennisetum. There is a very strong correlation between these two parameters (r= 0.75***). The milky pasty stage is reached at 112 days for Pennisetum and at 119 days for sorghum; height of 3 m while sorghum does not exceed 2.5 m, which offers the best green and dry yield for Pennisetum (r=0.60**). At the same pasty milky stage of sorghum, digestibility varies between 45.09%-57.44% for the Sudanese population, 52.72%-53.28% for Hamra and 58.78%-53.92% for the Beida. At the hard grain stage, the digestibility of sorghum is close to the values of Pennisetum at the milky pasty stage. Such ecotypes can play a role in the conservation and enhancement of fragile soils.

Effect of scan speed on corrosion and tribocorrosion properties of cobalt-chromium alloy in situ produced by selective laser melting

Purpose This paper aims to investigate the influence of scan speed on the corrosion and tribocorrosion features of the CoCrMoW samples fabricated via the selective laser melting (SLM) process. Design/methodology/approach CoCrMoW samples were produced by SLM at different scan speeds. Produced samples were made via structural surveys (X-ray diffraction examinations and scanning electron microscopic analyses), hardness measurements and electrochemical and tribocorrosion experiments. Findings Outcomes displayed that the corrosion and tribocorrosion properties of CoCrMoW alloy were significantly influenced by scanning speeds. Also, these properties of the alloy increased with increasing scanning speeds. CoCrMoW samples produced at a laser scan speed of 1,000 mm/s showed the best resistance to corrosion and tribocorrosion. This could be related to the high hardness and low grain structure of the fabricated samples. Originality/value This paper may be a practical reference and offers insight into the effect of scanning speeds on the increase of hardness, tribological and corrosion performance of CoCrMoW alloys. This study can help in the further advancement of cobalt-chromium alloy in situ produced by SLM for both electrochemical and tribocorrosion behavior for biomedical applications.

Mechanical, tribological, and morphological properties of SiC and Gr reinforced Al-0.7Fe-0.6Si-0.375Cr-0.25Zn based stir-casted hybrid metal matrix composites for automotive applications: Fabrication and characterizations

The main goal of this research is to meet the demanding need for developing lightweight materials with improved properties that are appropriate for several engineering applications. The investigators proceeded to considerable efforts to assess the mechanical, micro-structural, and tribological characteristics of Al-0.7Fe-0.6Si-0.375Cr-0.25Zn/10 wt%SiCP/3 wt%GrP-MMC, Al-0.7Fe-0.6Si-0.375Cr-0.25Zn/15 wt%SiCP/5 wt%GrP-MMC, and Al-0.7Fe-0.6Si-0.375Cr-0.25Zn/20 wt%SiCP/8 wt%GrP-MMC based hybrid metal-matrix nano-composites (HMMC's). These hybrid aluminum matrix nano-composites were fabricated using the liquid processing stir casting method for automobile, aviation, defense, and chemical handling sectors owing to their superior strength, and higher thermal conductive properties. The machinability of Al-0.7Fe-0.6Si-0.375Cr-0.25Zn/(SiCp + Grp) - MMC has received limited attention to date. Owing to its exceptional characteristics, this hybrid composite could take the role of cast iron or aluminum composites in a wide-variety multitude of engineering applications. The Mechanical properties of fabricated Hybrid-MMCs have been examined along with tribological properties & other factors, affecting the tensile strength of cast composites in this study. Additionally, the characterization has been performed through X-ray Diffraction (XRD), Energy Dispersive Spectrum (EDS), Scanning Electron Microscope (SEM), and Optical Microscopy. The fabricated samples of hybrid metal matrix nano-composites of Al-0.7Fe-0.6Si-0.375Cr-0.25Zn matrix have been tested for microstructure analysis, micro hardness test, density, tensile strength, and grain size. Microstructure study clears the claim of uniform distribution of SiC & Graphite particles in Al matrix alloy. An average tensile strength has been recorded as 258 MPa and a percent-elongation of 4.6 during the tensile test. Tensile-fractography findings have portrayed the intrinsic fractured-rupture microstructure of tensile-tested samples that seemed to have particle deformation breakage and pull-outs. The density of Al/(SiCp + Grp)-MMCs have been found to be 2.76 g/cm3 whereas the average hardness has been recorded at 120HV. An increase in graphite content in Al/SiC-MMC's provides a significant improvement in friction coefficient as well as a reduction in wear rate. Findings have observed that the wear rate is increased with increasing the sliding speed, however, it is almost constant between 300 and 600 rpm, and beyond this wear rate increases drastically. Likewise, the coefficient of friction also shows a considerable increase with the increase in sliding speed. As the composition of graphite in the material increases, a considerable decrease in the wear has been noted down because of the presence of tribo-layer formed between mating surfaces. A high value of applied load and high rotating speed imposed high deformation of the surface and increase in frictional force, as a result, an increase in wear rate. Wear rate increases with the increment in load during the wear test, while friction coefficient decreases. Hence, the development of HMMCs with better mechanical, microstructural, and tribological properties that can be utilized as cast iron or aluminum composites in a diverse spectra multitude of engineering applications involving the study's scientific insights and technological developments. Manufacturers in the myriads of industries, including aerospace, ground-transportation, thermal management, industrial, recreational, and infrastructure, could profit inventors/producers from the findings of the current study.

Effect of water cooling assistance on fatigue behavior of laser welded QP980 steel

Quenching and partitioning 980 (QP980) steel has been applied to new energy vehicles, but even laser welding joints show poor fatigue performance. In this study, water-cooling assistance is applied to improve fatigue resistance of welded joints. Hardness, tensile and fatigue tests are performed together with microstructure observation (scanning electron microscope, transmission electron microscope and electron back scattered diffraction). It is found that tempering martensite showing low hardness and small average grain boundary angles are responsible for poor fatigue performance. Results show that water-cooling assistance significantly improves welding softening and fatigue crack growth behavior of welded joints.

On the strain delocalization mechanism of Cu/Nb nanolayered composites with amorphous interfacial layers

Nanostructured metals and alloys possess ultrahigh strength but suffer from severe shear instability (strain localization). Recent experiments have shown that the strength and strain delocalization capability of some novel nanostructured alloys and nanolayered composites can be enhanced simultaneously by introducing nanoscale amorphous interfacial layers. However, the study on the underlying mechanism is still in an embryonic stage due to the ignorance of the complicated elemental composition of the interfacial layers, especially the compositional gradient along the interface thickness. Here, the atomic mechanisms of the tensile deformation of Cu/Nb nanolayered composites with amorphous interfacial layers are systematically investigated by molecular dynamics simulations. Depending on whether the composition of the interfacial layers is invariable or has a gradient distribution along the interface thickness, these samples are classified as amorphous or gradient samples, respectively. The simulations of normal Cu/Nb nanolayered composites with ordinary incoherent Cu‒Nb interfaces are also included for comparison, the results of which show that strain localization occurs due to the inhomogeneous plastic deformation between soft and hard grains in the Cu and Nb layers. The strain localization is inhibited in the amorphous samples mainly through the activation of deformation twinning in the Cu and Nb layers that produces a co-deformation between grains. Intriguingly, the gradient arrangement of the elemental composition of the amorphous interfacial layers gives a further stronger strain delocalization by further promoting the co-deformation between grains through stimulating more nanotwins in Cu layers and hindering twin growth in Nb layers, and by producing a much more uniform von Mises strain distribution in the interfacial layers. In addition, a better strain delocalization capability can be obtained when the thickness of the interfacial layers is closer to that of the crystalline ones in the amorphous sample or the range of gradient composition is larger in the gradient one.

Ti‐Doped Nanocomposite Pr2Fe14B/α‐Fe Ribbons with High Coercivity

Nanocomposite permanent magnetic alloys are prepared by the melt‐spinning technique with wheel speed ranging from 21 to 33 ms−1. X‐ray diffraction results show that the as‐spun ribbon is rich of soft α‐Fe, hard Pr2Fe14B magnetic phases, and no other metastable phases are found in our alloy ribbon. Initial magnetization curves reveal that the coercivity mechanism of the ribbons vary with the content of Ti. For x = 2, coercivity is mainly determined by pure pinning; while for x = 1, 3, and 4, it is mainly controlled by the mixture of nucleation of domain and localized pinning at grain boundaries. The coercivity value of 1026 kA m−1, the highest value reported so far, is mainly generated from a pure pinning mechanism in the ribbon with x = 2. The recoil permeability shows a minimum value range from to for x = 2 alloy, suggesting strong exchange coupling between the magnetic grains and then leading to the concurrent reversal of soft and hard phase grains during the demagnetization process. The Henkel plots demonstrate only exchange interaction for x = 1 and exchange interaction with slightly magnetostatic interaction for x = 2, 3, and 4. The exchange interaction exhibits maximum strength for x = 2, which is the reason for high coercivity.

Effect of Heating Rate on the Annealing Behavior of Aluminium Alloys

This contribution presents a study on the effect of heating rate maintained during annealing treatment on the final microstructure and mechanical properties of cold rolled Al1050 sheet. This study is focused on microstructure and texture evolution of Al1050 annealed at various heating rates, annealing temperatures, and holding times. It was observed that the longer exposure time for deformed microstructure affects the Vickers hardness values, grain size, and texture intensity. It seems that the crystallographic texture evolution is not affected by heating rate on quantitative level since the same set of orientations tended to evolve in all studied cases. The sample annealed at slow heating rate in a box-type furnace produced recrystallized microstructure with fine grain size, and comparatively lower texture intensity & hardness.

Influences of shale microstructure on mechanical properties and bedding fractures distribution

The difference in microstructure leads to the diversity of shale mechanical properties and bedding fractures distribution patterns. In this paper, the microstructure and mechanical properties of Longmaxi marine shale and Qingshankou continental shale were studied by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) with mineral analysis system, and nanoindentation. Additionally, the typical bedding layers area was properly stratified using Focused Ion Beam (FIB), and the effects of microstructure and mechanical properties on the distribution patterns of bedding fractures were analyzed. The results show that the Longmaxi marine shale sample contains more clay mineral grains, while the Qingshankou continental shale sample contains more hard brittle mineral grains such as feldspar. For Longmaxi marine shale sample, hard brittle minerals with grain sizes larger than 20 μm is 18.24% and those with grain sizes smaller than 20 μm is 16.22%. For Qingshankou continental shale sample, hard brittle minerals with grain sizes larger than 20 μm is 40.7% and those with grain sizes smaller than 20 μm is 11.82%. In comparison to the Qingshankou continental shale sample, the Longmaxi marine shale sample has a lower modulus, hardness, and heterogeneity. Laminated shales are formed by alternating coarse-grained and fine-grained layers during deposition. The average single-layer thickness of Longmaxi marine shale sample is greater than Qingshankou continental shale sample. The two types of shale have similar bedding fractures distribution patterns and fractures tend to occur in the transition zone from coarse-grained to fine-grained deposition. The orientation of the fracture is usually parallel to the bedding plane and detour occurs in the presence of hard brittle grains. The fracture distribution density of the Longmaxi marine shale sample is lower than that of the Qingshankou continental shale sample due to the strong heterogeneity of the Qingshankou continental shale. The current research provides guidelines for the effective development of shale reservoirs in various sedimentary environments.

Microstructure, texture and mechanical properties of Al–Zn–Mg–Zr cylindrical part with thin-wall and high-rib formed by integral-accuracy-extrusion

The complex section cylindrical part with thin-wall and high-rib was obtained through integral-accuracy-extrusion, and the microstructure evolution, recrystallization behavior, texture configuration and strengthening and toughening mechanism were investigated. Samples of different positions all exhibit the microstructure of predominant elongated grains along extrusion direction (ED) surrounded by fine equiaxed grains, but the width of elongated grains in the rib is higher than that in the thin-wall. Except for particle-stimulated nucleation (PSN) mechanism due to the MgZn2, the dominant recrystallization mechanism of all samples should be discontinuous dynamic recrystallization (DDRX), and the parent grains with the orientation of (001)//ED are more susceptible to recrystallization than other orientations. Additionally, more prone to continuous dynamic recrystallization (CDRX) results in a higher recrystallization fraction and a lesser average grain size in the thin-wall. Samples in the rib are dominated by strong copper-type texture, showing the feature of deformation texture; as for sample in the thin-wall, a high strength of Cube texture is displayed. The ultimate tensile strength (UTS) of the sample in the rib is 20 MPa higher than that in the thin-wall, which is mainly attributed to texture strengthening caused by hard orientation grains with smaller Schmid factor (SF), but the elongation of sample in the thin-wall is 30% higher than the rib (15.1% vs 11.6%), showing a superior plasticity, which is related to higher SF, higher recrystallization fraction and more homogeneous microstructure. This research will theoretically guide the manufacture of high-performance complex section Al–Zn–Mg–Zr cylindrical part with thin-wall and high-rib.

Investigation on the crystal plasticity of α phase Ti-6Al-4V based on nano-indentation simulation and experiment

Ti-6Al-4V parts are usually hypothesized as isotropic mechanical properties during micro-machining operation. However, the crystal anisotropic mechanical property is an influential factor in the machining of crystals with different sizes and orientations. The hypothesis causes distinct variation in predicting machining force, and consequently the surface integrity cannot be exactly predicted in the micro-machining. Actually, Ti-6Al-4V parts are pseudo isotropy composed of grains with different orientations, elastic modulus, and hardness. Simultaneously, the initiation mode of plastic slip system varies with the grain orientation when the crystal is subjected to an applied load. It is challengeable to evaluate the effect of crystal orientation on its macroscopic properties, either by traditional experimental methods or macroscopic finite element analysis. Nano-indentation provides one novel method to investigate the plastic deformation of selected grains with specific orientations to characterize their mechanical response properties. This research aims to investigate the plastic behavior of α phase Ti-6Al-4V with different orientation grains by means of nano-indentation experiment and crystal plastic finite element method. In the study, single crystals of α phase are classified into “hard grains” (θ < 30°), “soft grains” (θ > 60°) and “normal grains” (30° < θ < 60°) by defining the crystal inclination angle (θ). The elastic modulus and hardness of hard grains are 9% and 28% larger than those of soft grains, respectively. This difference in mechanical properties depends on the slip system that dominates the plastic deformation behavior. The plastic deformation of soft grains is dominated by prismatic slip (48%), while hard grains are accommodated to plastic deformation by basal slip (51%). The average total cumulative shear strain of the soft grains is double that of the hard grains at a maximum load of 10 mN. Meanwhile, the sensitivity analysis is performed to evaluate the effects of the three sets of < a > slip systems and the two sets of < c + a > slip systems on plastic deformation with different grain orientations. The research contributes to the understanding of the plastic deformation mechanism in micro-machining and the exactly predicting the surface integrity generated from micro-machining.

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.