Effect Of Crystal Orientation Research Articles

Effect of crystal orientation on the scratching behavior of γ-TiAl alloy nanowires by molecular dynamics simulation

In micro-and-nanomachining, crystal orientation effects significantly influence the plastic deformation, mechanical response, and temperature profile of nanowire materials. This study utilizes molecular dynamics simulation to investigate the process of surface scratching on γ-TiAl alloy nanowires under six different crystal orientations. The results reveal that the evolution of internal microscopic defects during the surface scratching process is heavily affected by crystal orientation, resulting in distinct dislocation motion-induced shear deformation and extrusion removal by the tool. These factors determine variations in both the shape of the nanowire's surface pile-up and the overall degree of workpiece deformation. Among all cases examined, crystal orientation exhibits easier removal of atoms with minimal internal defects, while crystal orientation shows maximum atom removal without significant overall deformation, both cases demonstrate superior surface morphology and subsurface quality. Furthermore, stress and temperature profiles within abraded atoms and inside the workpiece depend on crystal orientation. These findings provide valuable insights for characterizing surface damage in γ-TiAl alloy nanowires as well as facilitating the preparation of surface nano-channels.

Mechanical and vibrational behaviors of bilayer hexagonal boron nitride in different stacking modes

Hexagonal boron nitride (h-BN) is a semiconductor material with a wide band gap, which has great potential to serve as a nanoresonators in microelectronics and mass and force sensing fields. This paper investigates the mechanical properties and natural frequencies of bilayer h-BN nanosheets under five different stacking modes, which have been rarely studied, using molecular dynamics simulations. The mechanical properties, including Young’s modulus, the ultimate stress, ultimate strain, Poisson’s ratio and shear modulus, are studied for all five stacking modes. And the effects of strain rate, crystal orientation and temperature to bilayer h-BN nanosheets’ tensile properties have also been studied. Our findings suggest that bilayer h-BN nanosheets are basically an anisotropic material whose tensile properties vary substantially with stacking modes and temperature. Moreover, the natural frequencies are proposed in an explicit form based on the nonlocal theory. The differences of the fundamental natural frequencies among different stacking modes are affected by the constraint condition of bilayer h-BN sheet. The theory results match well with the simulation results. These findings establish elementary understandings of the mechanical behavior and vibration character of bilayer h-BN nanosheets under five different stacking modes, which could benefit its application in advanced nanodevices.

The effects of crystal orientation on the ferroelectric and optoelectronic properties of Pt/Na0.5Bi0.5TiO3/La0.5Sr0.5CoO3 heterostructures

Due to their excellent ferroelectric, semiconducting, and optoelectronic properties, perovskite ferroelectric thin films have attracted increasing attention in the photovoltaic field. Using La0.5Sr0.5CoO3 (LSCO) as the bottom electrode, flake, strip and pyramidal Na0.5Bi0.5TiO3 (NBT) films were prepared on (001), (110) and (111) SrTiO3 (STO) substrates by off-axis magnetron sputtering and pulsed laser deposition, respectively. XRD and Phi scan results show that both LSCO and NBT are perovskite structures and satisfy the epitaxial growth along the substrate STO. NBT orientation has a significant effect on the ferroelectric properties of Pt/NBT/LSCO heterostructures. The remnant polarization 2Pr values for NBT(111), NBT(110) and NBT(001) are 87.5, 62.6 and 28.5 μC/cm2, respectively, and thus 2Pr(111)>2Pr(110)>2Pr(001). NBT(111) shows the best ferroelectric properties (Pr=41.3 μC/cm2), excellent fatigue-resisting (up to 1010 cycles) and retention performance (duration 104s). The 2Pr-T association 2Pr=41.72+16.05*T0.35 for NBT(111) was obtained according to the curve fitting, it is found that the NBT orientation has a significant effect on the PV effect for PT/NBT/LSCO photovoltaics and the open-circuit voltage ∆Voc. The short-circuit current ∆Jsc of polarization regulate intensity follows the laws of ∆Voc-111>∆Voc-110>∆Voc-001 and ∆Jsc-111>∆Jsc-110>∆Jsc-001, the Jsc for Pt/NBT(111)/LSCO heterostructures increases linearly with the illumination Ip increasing, while the Voc decreases linearly. The ferroelectro-polarized modulation PV mechanism was investigated by analyzing band structure of the Pt/NBT/LSCO heterostructures, which is attributed to the coupling effect of the ferroelectric depolarization field and the interfacial Schottky barrier.

Surface roughness evolution and heterogeneous plastic deformation of austenitic stainless steel during micro deep drawing: Modeling and experiment

The present work involves the numerical simulation and experimental study on the surface roughness evolution and heterogeneous plastic deformation (strain localization and concomitant surface morphology evolution) in grain scale of micro deep drawn parts of austenitic stainless steel (ASS) 304 foils. A three-dimensional modeling framework was used to simulate the micro deep drawing (MDD) process. The simulation involved the development of a Voronoi-based polycrystalline geometry model (VPGM), a multi-stress-strain response model, and a crystal plasticity finite element methods (CPFEM) model. The results indicate that CPFEM model exhibits higher accuracy in the localized stress and strain, thickness distribution fluctuation and surface roughness evolution of the fabricated parts compared to multi-stress-strain response model. Therefore, the plastic deformation heterogeneity in MDD is in-depth discussed based on CPFEM model. The results show that the coarse-grained foils correspond to the intense strain localization, which is the main cause of surface roughening. Considering the average grain size is close to the thickness of ASS foils, mounding features on the rough surface may readily develop further into potentially fractured sites during deformation. On the other hand, crystal orientation influence plastic deformation by affecting the slip behavior of materials. The effect of crystal orientations including {011} 〈211〉 (Brass), {011} 〈100〉 (Goss), and {112} 〈110〉 components on deformation is discussed. The results indicate a strong correlation between the magnitude of the Schmid's factor and the ease of deformation. Additionally, variations in Schmid's factor across different directions result in differences in deformation accumulation, which affects the thickness distribution along the radial direction and the distribution of earrings and wrinkles along the circumferential direction of the fabricated micro parts.

Disequilibrium oxygen isotope distribution among aqueously altered minerals in Ryugu asteroid returned samples

AbstractOxygen 3‐isotope ratios of magnetite and carbonates in aqueously altered carbonaceous chondrites provide important clues to understanding the evolution of the fluid in the asteroidal parent bodies. We conducted oxygen 3‐isotope analyses of magnetite, dolomite, and breunnerite in two sections of asteroid Ryugu returned samples, A0058 and C0002, using a secondary ion mass spectrometer (SIMS). Magnetite was analyzed by using a lower primary ion energy that reduced instrumental biases due to the crystal orientation effect. We found two groups of magnetite data identified from the SIMS pit morphologies: (1) higher δ18O (from 3‰ to 7‰) and ∆17O (~2‰) with porous SIMS pits mostly from spherulitic magnetite, and (2) lower δ18O (~ −3‰) and variable ∆17O (0‰–2‰) mostly from euhedral magnetite. Dolomite and breunnerite analyses were conducted using multi‐collection Faraday cup detectors with precisions ≤0.3‰. The instrumental bias correction was applied based on carbonate compositions in two ways, using Fe and (Fe + Mn) contents, respectively, because Ryugu dolomite contains higher amounts of Mn than the terrestrial standard. Results of dolomite and breunnerite analyses show a narrow range of ∆17O; 0.0‰–0.3‰ for dolomite in A0058 and 0.2‰–0.8‰ for dolomite and breunnerite in C0002. The majority of breunnerite, including large ≥100 μm grains, show systematically lower δ18O (~21‰) than dolomite (25‰–30‰ and 23‰–27‰ depending on the instrumental bias corrections). The equilibrium temperatures between magnetite and dolomite from the coarse‐grained lithology in A0058 are calculated to be 51 ± 11°C and 78 ± 14°C, depending on the instrumental bias correction scheme for dolomite; a reliable temperature estimate would require a Mn‐bearing dolomite standard to evaluate the instrumental bias corrections, which is not currently available. These results indicate that the oxygen isotope ratios of aqueous fluids in the Ryugu parent asteroid were isotopically heterogeneous, either spatially, or temporary. Initial water ice accreted to the Ryugu parent body might have ∆17O > 2‰ that was melted and interacted with anhydrous solids with the initial ∆17O < 0‰. In the early stage of aqueous alteration, spherulitic magnetite and calcite formed from aqueous fluid with ∆17O ~ 2‰ that was produced by isotope exchange between water (∆17O > 2‰) and anhydrous solids (∆17O < 0‰). Dolomite and breunnerite, along with some magnetite, formed at the later stage of aqueous alteration under higher water‐to‐rock ratios where the oxygen isotope ratios were nearly at equilibrium between fluid and solid phases. Including literature data, δ18O of carbonates decreased in the order calcite, dolomite, and breunnerite, suggesting that the temperature of alteration might have increased with the degree of aqueous alteration.

Incipient Dissolution of Emplaced Forsterite and Fayalite Records the Effects of Climate, Mineral Composition, and Crystallographic Orientation

To investigate the effects of environment, composition, and crystal orientation on incipient surface alteration of forsterite and fayalite in a natural environment, polycrystalline forsterite and fayalite samples were emplaced in Mg/Fe-rich and Al-poor ultramafic soils under subarctic (Tablelands in Newfoundland, Canada; 3.9 ⁰C and ∼120 cm precipitation/year), Mediterranean (Klamath Mountains, California;≤12.8 ⁰C and ∼101-118 cm precipitation/year), and desert (Pickhandle Gulch, Nevada; ∼14.1 ⁰C and ∼14.4 cm/year) climates for one year. Incipient alteration after one year was examined using scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, X-ray photoelectron spectroscopy, and visible and near-infrared reflectance spectroscopy.Alteration features on forsterite surfaces included flat-bottomed pits with steeply dipping walls likely developing on grain faces and representing surface retreat of individual grains and lining features likely developing along grain boundaries. Mg-leached surface layers formed under acidic to slightly alkaline conditions while Mg-enrichment was observed under alkaline conditions. Flat bottomed pit formation preferentially occurs on surfaces within 30° of perpendicular to the b-axis (on the [010] plane) of the olivine crystal lattice. Depth of flat-bottomed pits on forsterite surfaces follows the order Klamath Mountains > Tablelands >> Pickhandle Gulch, reflecting the importance of environmental conditions. Warm, wet, and relatively acidic conditions enhanced forsterite dissolution over cold, wet, and slightly alkaline conditions, with minimal alteration observed under hot but arid and alkaline conditions. Greater surface roughness on flat-bottomed pit floors on Klamath Mountain forsterite surfaces are consistent with less-saturated soil-pore water reaction conditions.In contrast, fayalite disks buried in the Klamath Mountains show no evidence for etch-pit formation despite the warm, wet, and slightly acidic conditions. Elevated Fe/Si ratios from X-ray photoelectron spectroscopy measurements and evidence of M-OH bonds in visual and near infrared spectra are consistent with formation of a Fe-enriched hydroxylated layer limiting fayalite surface area available for water-rock interaction and retarding fayalite dissolution during aqueous alteration under oxidizing conditions. These results differ from previous laboratory experiments that show enhanced dissolution of fayalite relative to forsterite, showing the effect of natural, oxic, unsaturated weathering zones. These results will be helpful for interpreting observations of this widely studied mineral, including from the planet Mars.

Preparation of HFCVD spherical diamond films and the effect of crystal orientations on adhesion and tribological properties

The different coefficients of thermal expansion of WC-Co cemented carbide and diamond have limited the development of spherical diamond-coated tools. In this study, diamond sphere films with different crystal orientation and texturing were successfully prepared by hot filament chemical vapor deposition (HFCVD). The adhesion and friction characteristics of the films were investigated by indentation and friction tests. The results show that the adhesion of the (111) orientation micron diamond (111MDF) spherical film, (110) orientation micron diamond (110MDF) spherical film, and (110) orientation texturized micron diamond (110TDF) spherical film increase sequentially at the same position. Under dry friction conditions, the average coefficient of friction of 110TDF spherical film was reduced by 28%, the wear resistance was increased by 80%, the surface roughness of the workpiece was reduced by 23%, and the material removal rate was reduced by 23.6% compared with that of 111MDF spherical film.

Anisotropic and heterogeneous acoustoplasticity of α-Ti during ultrasonic vibration assisted compression: Modeling and experiments

Introducing ultrasonic vibration (UV) into the plastic deformation process is a promising and efficient way to improve the formability of metallic materials. However, the acoustoplasticity of α-Ti with pronounced anisotropic behavior during UV-assisted deformation is still not well understood, and the underlying mechanisms associated with the ultrasonic effect on multiple slip/twinning systems remain ambiguous. In this research, the anisotropic and heterogeneous acoustoplasticity of α-Ti was investigated through modeling and experiments. A novel acoustic crystal plasticity model considering the anisotropic ultrasonic response of multiple slip/twinning systems was proposed, in which the ultrasonic softening is determined by the coupling effect of crystal orientation, mechanical threshold, and ultrasonic energy density. The proposed model was validated through the mechanical response of the UV-assisted compression and the twin volume fraction of α-Ti specimens along RD, TD, and ND directions. Full-field crystal plasticity simulations regarding UV-assisted compression were carried out. Then the mechanism of the acoustoplasticity of α-Ti was explored via the analysis of ultrasonic activation on multiple slip/twinning systems and the grain scale deformation behavior. A considerable anisotropic and heterogeneous ultrasonic softening effect of α-Ti was found, and the anisotropy as well as the magnitude of ultrasonic softening increase with the ultrasonic energy density. The ultrasonically activated deformation modes gradually change from prismatic slip and tensile twinning to basal slip and compressive twinning from RD, TD to ND specimens, which results in a higher average CRSS decrease and more pronounced ultrasonic softening macroscopically. The grain scale stress inhomogeneity of α-Ti is relieved under UV, and the local deformation and grain rotation are both enhanced. The dislocation motion and twinning behavior are both promoted by UV. The facilitated twinning behavior can be attributed to the enhanced dislocation assisted nucleation and propagation of deformation twins under UV. These findings provide a fundamental understanding of the anisotropic and heterogeneous acoustoplasticity of α-Ti during the UV-assisted deformation process.

Crystal Orientation Regulation of Spin-Orbit Torque Efficiency and Magnetization Switching in SrRuO<sub>3</sub> Thin Films

Spintronic devices utilize the spin property of electrons for the storage, transmission, and processing of information, inherently possessing advantages such as low power consumption and non-volatility, thus attracting widespread attention from both academia and industry. Spin-orbit torque(SOT) is an efficient method of manipulating magnetic moments using electric current for writing, harnessing the spin-orbit coupling (SOC) effect within materials to achieve the mutual conversion between charge current and spin current. Enhancing the efficiency of charge-spin conversion is a critical issue in the field of spintronics. Strontium ruthenate (SRO) in transition metal oxides(TMO) has attracted significant attention as a spin source material in SOT devices due to its large and tunable charge-to-spin conversion efficiency. However, current research on SOT control in SRO primarily focuses on utilizing substrate strain, with limited exploration of other control methods. Crystal orientation can produce various novel physical properties by affecting material symmetry and electronic structure, is one of the important means to control the properties of TMO materials. Given the close correlation between the SOT effect and electronic structure as well as surface states, crystal orientation is expected to affect SOT properties by adjusting the electronic band structure of TMO. This work investigates the effect of crystal orientation on the SOT performance of SrRuO<sub>3</sub> films and develops a novel approach for SOT control. (111)-oriented SRO/CoPt heterostructures and SOT devices were prepared using pulse laser deposition, magnetron sputtering, and micro-nano processing techniques. Through harmonic Hall voltage(HHV) measurements, we found that the SOT efficiency reached 0.39, and the spin Hall conductivity reached 2.19×10<sup>5</sup><i>ħ</i>/2e Ω<sup>−1</sup> m<sup>−1</sup>, which were 86% and 369% higher than those of the (001) orientation, respectively. Furthermore, current-driven perpendicular magnetization switching was achieved in SrRuO<sub>3</sub>(111) devices at a low critical current density of 2.4×10<sup>10</sup> A/m<sup>2</sup>, which was 37% lower than that of the (001) orientation. These results demonstrate that crystal orientation is an effective approach to significantly enhance the comprehensive performance of SrRuO<sub>3</sub>-based SOT devices, providing new insights for developing high-efficiency spintronic devices.

Effect of Crystal Orientation and Crystallographic Anisotropy on Shear Band Formation During Ductile Fracture in Fe Single Crystals

Effect of Crystal Orientation and Crystallographic Anisotropy on Shear Band Formation During Ductile Fracture in Fe Single Crystals

Random crystal orientation and tensile strength of nanocrystalline dumbbell-shaped copper thick films electrodeposited from acidic aqueous solutions containing polyethylene glycol

Nanocrystalline thick copper films with the thickness of ∼250 μm were electrochemically synthesized from an acidic aqueous solution containing polyethylene glycol (PEG) with the average molecular weight of 3,000 to investigate the preferential crystal orientation and mechanical properties such as microhardness and tensile strength. By addition of PEG to the electrolytic bath, the cathode potential was shifted to a less noble direction during the electrodeposition and the average crystallite size of electrodeposited copper thick films was decreased. The copper thick films electrodeposited from the solution without PEG exhibited a preferentially orientation in (220) texture while that obtained from the solution containing PEG was composed of nanocrystals with random crystal orientation that containing (111) and (200) textures. The micro-Vickers hardness, tensile strength, and elongation of the electrodeposited copper thick films reached up to 133 HV, 234 MPa, and 13.1%, respectively. These improvements in mechanical properties can be explained by the grain refinement effect and the random crystal orientation effect.

Effect of crystal orientation and temperature on the mechanical properties and fracture mechanism of silicon carbide nanowires

Effect of crystal orientation and temperature on the mechanical properties and fracture mechanism of silicon carbide nanowires

Stress intensity factors analysis for crack around film cooling holes in Ni-based single crystal with contour integral method

PurposeThis paper aims to provide SIF calculation method for engineering application.Design/methodology/approachIn this paper, the stress intensity factors (SIFs) calculation method is applied to the anisotropic Ni-based single crystal film cooling holes (FCHs) structure.FindingsBased on contour integral, the anisotropic SIFs analysis finite element method (FEM) in Ni-based single crystal is proposed. The applicability and mesh independence of the method is assessed by comparing the calculated SIFs using mode of plate with an edge crack. Anisotropic SIFs can be calculated with excellent accuracy using the finite element contour integral approach. Then, the effect of crystal orientation and FCHs interference on the anisotropic SIFs is clarified. The SIFs of FCH edge crack in the [011] orientated Ni-based single crystal increases faster than the other two orientations. And the SIF of horizontal interference FCHs edge crack is also larger than that of the inclined interference one.Originality/valueThe SIFs of the FCH edge crack in the turbine air-cooled blade are innovatively computed using the sub-model method. Both the Mode I and II SIFs of FCHs edge crack in blade increase with crack growing.

Study of the effect of crystal orientation on the mechanical response and fatigue life of solder joints under thermal cycling by crystal plasticity

Electronic products are subjected to thermal cycling caused by power cycling in service processes. Owing to the difference in the coefficients of thermal expansion (CTEs) of solder joints and other packaging materials, solder joints suffer from thermomechanical fatigue, and cracks appear at their bonding interfaces. Solder joints are usually a single grain or three grains with Beachball morphology, and their composition is Sn-based Pb-free SAC305 (96.5Sn–3.0Ag–0.5Cu wt.%) solder, which exhibits obvious anisotropic mechanical behavior. This study investigated a thermal cycling simulation of Plastic Ball Grid Array (PBGA) packaging, in which the Anand model was used for solder joints, and the outermost solder joint was found to be a dangerous point. Sub-models were then established for this solder joint with several typical crystal orientations. The effect of crystal orientation under thermal cycling was simulated using thermomechanical crystal plasticity. When the c-axis of Sn crystal was perpendicular to the substrate, the deformation resistance was the largest, and the accumulation of equivalent plastic strain and strain energy dissipation was the slowest; hence, the fatigue life was the longest. As the angle between the c-axis and the substrate decreased, the deformation accumulated faster. When the c-axis was parallel to the substrate, the deformation of the solder joint was the fastest, and thus this joint was the first to fail and had the shortest fatigue life. In addition, the simulation of three grains indicated that orientations and their distributions had an influence on the shear strain accumulation of slip systems and fatigue life.

Effect of crystal parameters and orientation on the angular distribution of diffracted transition radiation from relativistic electrons

The influence of the finiteness of the width of the total X-ray reflection region on the angular distribution of diffracted transition radiation of relativistic electrons in crystals is analyzed. Such an effect is investigated for different reflecting planes, diffracted X-ray energies, and electron beam energies and is found to be non-negligible and to substantially change the angular distributions of diffracted transition radiation under certain experimental conditions. The difference between the reflectivity and the δ function is shown to distort the angular distribution of the detected radiation and to limit the possibility of using this type of radiation to diagnose the parameters of beams of relativistic electrons and positrons with energies greater than 50 GeV.

Effect of crystal orientation of AlN coatings on its high temperature oxidation in wet air

Aluminum nitride is discussed for different high temperature applications, due to its unique properties. Lately it also received attention as a coating for different substrate materials. Within the present study oriented AlN-coatings with two different crystal orientations were produced via reactive magnetron sputtering and a high temperature CVD process on SiC-based substrates. The oxidation resistance of these coatings in comparison to bulk AlN was investigated in wet synthetic air at 1200 °C. Both, the bulk AlN and (101¯0)-oriented AlN-coating formed a porous Al2O3-scale, which was not protective and resulted in high oxidation rates. In contrast, the (0001)-oriented coatings were able to form a thin oxide scale and remained protective for the total exposure time of up to 200 h at 1200 °C. The underlying mechanism of the oxidation of AlN in wet air was discussed, considering the strong influence of the crystal orientation.

Non-equilibrium molecular dynamics studies of thermal diffusion of hydrogen isotopes in low concentration zirconium hydrides

Tritium permeability in zirconium-based tritium getter critically impacts tritium storage and environmental safety during operation of tritium-producing burnable absorber rods (TPBARs). Previous experiments indicated that during irradiation operation, the hydrogen equilibrium pressured is increased. Further experimental and modeling studies suggested that the enhanced tritium release observed for reactor scale assemblies might be related to a thermal diffusion known as the Soret effect. A direct measurement of the Soret factor, however, has not been performed. To improve TPBAR and other nuclear applications, here we have applied two non-equilibrium molecular dynamics methods to study thermal diffusion of hydrogen isotopes in low-concentration zirconium hydrides. One of the methods produces sufficiently converged results to distinguish crystal orientation, isotope type, and concentration effects. With this method, crystal orientation, isotope type, and concentration effects are discussed.

Boron-doped {113}, {115} and {118}-oriented single-crystal diamond electrodes: Effect of surface pre-treatment

In this study, the effect of vicinal crystal orientation ({113}, {115}, and {118}), boron doping level, and surface termination induced by various pre-treatments on electrical and electrochemical properties of single crystal boron-doped diamond (SC-BDD) electrodes was carefully investigated. van de Pauw measurements confirmed Hall concentration to increase with increasing vicinal angle, {118} < {115} < {113}. As-deposited H-terminated surfaces were converted to predominantly O-terminated surfaces (confirmed by X-ray photoelectron spectroscopy) using hot acid, ozone and anodic pre-treatments, or by spontaneous oxidation in air. This conversion was recognized by inhibited heterogeneous electron transfer kinetics of inner-sphere redox markers ([Fe(CN)6]3−/4− and dopamine), by an increase in double layer capacitance and charge transfer resistance values. The most pronounced surface oxidation was recognized for electrodes with the lowest boron content as a result of blocked boron atoms by oxygen functionalities and loss of superficial hydrogen on the surface. Reverse conversion from oxidized to H-terminated surfaces using cathodic pre-treatment led mainly to restoration of electrochemical parameters. Moreover, spontaneous oxidation of electrode surfaces in ambient atmosphere was confirmed, with the fastest being within the first five days. The results show the key role of boron content, and hence the crystal orientation and superficial hydrogen in affecting conductivity and performance of SC-BDD electrodes, which is demonstrated by changes in heterogenous electron transfer kinetics of surface sensitive redox systems.

Orientation Dependence of B19’-Martensite Reorientation Stress and Yield Stress in TiNi Single Crystals

This paper deals with the effect of crystal orientation on the B19’-martensite reorientation stress and yield stress in compression in TiNi single crystals with different Ni contents varying from 50.4 to 51.2 at.%. It was experimentally shown that the martensite yield stress appears to be higher for the [111]B2-oriented single crystals than for the [001]B2-oriented single crystals regardless of Ni content. The difference between martensite yield stress for the two investigated orientations increases with the growth of Ni content. The maximum difference between martensite yield stress σcrM for two investigated orientations is 996 MPa at Ni content of 51.2 at.% (σcrM = 1023 MPa for the [001]B2-orientation and σcrM = 2019 MPa for the [111]B2-orientation). As a result of comparison with the B2-austenite yield stress, it was found that this is not an ordinary case. The [001]B2 orientation is a high-strength in B2-austenite and a low-strength in B19’-martensite. It was experimentally shown that the B19’-martensite reorientation stresses weakly depend on the orientation and chemical composition compared with the martensite yield stress. The reasons for the orientation dependence of the martensite yield stress in compression and the deformation mechanisms of B19’-martensite are discussed.

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.