Influence Of Crystal Orientation Research Articles

The Influence of Crystal Orientation and Thermal State of a Pure Cu on the Formation of Helium Blisters

The factors that influence the formation of helium blisters in copper were studied, including crystallographic grain orientation and thermomechanical conditions. Helium implantation experiments were conducted at 40 KeV with a dose of 5 × 1017 ions/cm2, and the samples were then subjected to post-implantation heat treatments at 450 °C for different holding times. A scanning electron microscope (SEM) equipped with an electron backscatter diffraction (EBSD) detector was used to analyze the samples, revealing that the degree of blistering erosion and its evolution with time varied with the crystallographic plane of the free surface in different ways in annealed and cold rolled copper. Out of the investigated states, rolled copper with a (111) free surface had superior helium blistering durability. This is explained by the consideration of the multivariable situation, including the role of dislocations and vacancies. For future plasma-facing component (PFC) candidate material, similar research should be conducted in order to find the optimal combination of material properties for helium blistering durability. In the case of Cu selection as a PFC, the two practical approaches to obtain the preferred (111) orientation are cold rolling and thin layer technologies.

Influence of crystal orientations on the creep fracture of a nickel-based single crystal superalloy

Due to the anisotropy of the modulus of face-centered cubic cells, the nickel-based single crystal alloys exhibits substantial anisotropy at high temperatures. Their creep properties, especially the creep rupture lives, are related to the actuation of the slip system and the magnitude of the shear stress on the slip plane. The creep orientation sensitivity has been analyzed through creep experiments, as well as the microstructure and morphology of the fracture. On the macroscale, the necking sections of [001], [011] and [111] orientations are circular, elliptical and circular, respectively. Meanwhile, on the microscopic scale, the damage evolution caused by the expansion of the internal micropores in the single crystal alloy under the three orientations shows fourfold symmetry, double symmetry and triple symmetry, respectively. Based on the crystal plasticity theory, an anisotropic creep constitutive model and damage model are established to reflect the difference in creep deformation and damage evolution caused by orientation. The numerical simulations of the whole creep process of a second generation nickel-based single crystal superalloy show that the creep constitutive model and damage model can simulate the deformation and damage of the specimen under different orientations, and the creep life can be obtained.

Quasi in-situ investigation on kinking behavior of Fe-Cr-Al alloy during thermal compression

As a rare plastic deformation mechanism, kinking has attracted substantial attention because of its additional softening effect on the matrix and its heterogeneous refinement on the original grains. However, the details of kinking deformation and the influence of crystal orientation on itself have not been sufficiently elucidated yet, thereby resulting in inadequate microstructure optimization associated with kinking. In this work, the kinking formation process in Fe-Cr-Al alloy during thermal compression deformation has been investigated by using quasi in-situ electron backscatter diffraction (EBSD). By employing the average Schmid factor (Average-SF) model, the influence of crystal orientation on kinking behavior is predicted accurately. The results suggest that the softening effect of kinking on the matrix can be attributed to the fact that the nucleation of pre kink bands (pre-KBs, misorientation <15°) leads to a pronounced reduction in geometrically necessary dislocations (GNDs) density within them. Besides, the ripening behavior of pre-KBs is closely associated with the variation of GNDs density and the overall slip activation capability of the matrix, and is essentially dependent on crystal orientation. The harder the crystal orientation, the smaller the Average-SF, the higher the increment rate of GNDs density, the larger the ripening rate pre-KBs. Under equivalent strain, orientations close to 〈111〉// compression direction (CD) have the highest probability of forming mature KBs with high angle grain boundaries (HAGBs, >15°), whereas KBs in those close to 〈001〉//CD almost always remain as pre-KBs with low angle grain boundaries (LAGBs).

Monocrystalline Nickel Nanogrinding Subsurface Deformation-Layer Depth Study Based on Orthogonal Tests

Nanogrinding is one of the main technologies for machining complex surface shapes with nanometer-level precision. The subsurface deformation depth, as an important index of machining quality, directly affects the service life and mechanical properties of machined parts. In order to explore the factors that influence subsurface deformation depth, this work investigated the effects of three factors, namely, grinding speed, grinding depth and crystal orientation, along different crystal planes at the depth of the subsurface deformation layer in a monocrystalline nickel nanofabrication process. By combining molecular dynamics simulation and orthogonal tests, the results showed that, among the three aforementioned factors, the influence of crystal orientation at the depth of the subsurface deformation layer was the greatest, followed by that of grinding depth, while the influence of grinding speed was the weakest. Through the orthogonal tests, the factors affecting the significance of subsurface deformation depth were analyzed, and the results were found to be more meaningful compared with those of current single-factor studies. Meanwhile, in-depth exploration of the nanogrinding mechanism can provide the necessary theoretical basis for the development of nanomachining technology, which is of great significance for the improvement of ultra-precision cutting technology.

Crystal plasticity analysis of the evolutions of temperature, stress and dislocation in additively manufactured tungsten

Additive manufacturing (AM) has brought new opportunities for the fabrication of refractory metal tungsten (W). However, the cracking issue in additive manufactured pure W has not been solved, restricting its application. The cracking behavior is associated with the high residual stress, which is caused by the high temperature gradient and cooling rate during AM, as well as the internal brittleness of W. In order to solve this problem, the evolution of the internal microstructure and the corresponding thermal and loading conditions during AM has to be systematically investigated, but the related work is very rare. In the current work, a thermal-mechanical coupled dislocation-based crystal plasticity model is developed, which considers the temperature dependent plasticity induced by the thermal-activated kink-pair mechanism of screw dislocation. This model is applied to investigate the evolution of temperature, stress, and dislocation behaviors in single crystal and polycrystalline W during AM. The influences of crystal orientation and adding alloying element Ta are also discussed from the microscopic and macroscopic perspectives.

Influence of crystal orientation on twinning in austenitic stainless-steel during single micro-asperity tribology and nanoindentation

Wear induced deformation has been the focus of numerous studies but the fundamental understanding of the influence of wear direction and crystal anisotropy on microstructure evolution has only been handful. We investigate the influence of wear direction on the deformation mechanisms in single grains with {001} and {111} normal orientation. We observe multivariant twin structures below the wear track. The extent of deformation and the twin density are found to be dependent on the wear direction and normal load. This study also addresses why some grains show twinning while others do not show twinning at identical external loads.

Crystal orientation-dependent scribing of A-, C-, and M-plane sapphires by an ultraviolet laser

The ultraviolet nanosecond laser processing of microgrooves was conducted on A-, C-, and M-plane sapphire sheets along different crystal orientations. The influences of crystal orientation on the mechanical cleaving of sapphire sheets containing laser-processed microgrooves were investigated. Experimental results revealed that laser-induced cracks within the microgrooves, ablation threshold, and material removal rate of sapphire were closely related to crystal orientation. The removal energies of aluminum and oxygen ions per unit length along different crystal orientations were theoretically calculated; the difference in material removal rates along different crystal orientations was explained. Mechanical cleaving indicated that sapphire sheets could be separated along the A-M, C-A, C-M, and M-A orientations, whereas cleaving sapphire along A-C and M-C orientations was difficult. Moreover, the changes in the structure of laser-processed sapphire were also analyzed.

Phonon transport properties depending on crystal orientation analyzed by nanoindentation using single-crystal silicon wafers

The influences of crystal orientation on phonon transport properties were analyzed by nanoindentation using single-crystal Si wafers. The elastic moduli and group velocities of [100]-oriented Si were lower than those of [111]-oriented Si. The phonon mean free path (MFP) exhibited the opposite trend. Phonon transport properties were calculated using Hooke’s law with a stiffness tensor. The measured phonon MFP of the [100]-oriented Si were approximately 13% different from the corresponding semi-theoretical values, while those of the [111]-oriented Si were comparable to the corresponding semi-theoretical values, according to the difference in atomic density of each crystal plane of Si.

Influence of crystal orientation on stretching induced void formation in poly(4‐methyl‐1‐pentene) investigated by in‐situ small‐angle and wide‐angle X‐ ray scattering

In this work, the void formation of poly(4-methyl-1-pentene) (P4MP1) during solid-state stretching was investigated by in-situ small-angle and wide-angle X-ray scattering. By controlling the heating temperature, P4MP1 specimens with different orientation degrees were obtained. The results showed that: (1) specimens with high orientation presented hard elastic deformation behavior. Before the voids were induced, a density decrease in the amorphous phase was detected due to the extension of chain network. Once voids were formed, their longitude direction was aligned perpendicular to the stretching direction. With the increase of crystal orientation, the volume fraction of voids was greatly enlarged; (2) specimen with random orientation showed cold drawing deformation. As the Hencky strain was larger than 0.13, the void scattering was strengthened in the vertical direction whereas weakened in the horizontal direction, indicating that the longitude direction of the voids was changed to the stretching direction. With further stretching, the length of the voids was enlarged and the orientation of the voids was enhanced, but the volume fraction of the voids was reduced slightly due to the collapse of small voids. After stretching, the length and width of the void evaluated from SEM were 382 and 81 nm.

Influence of Substrate Orientation and Oxygen Partial Pressure on the Morphology, Structure, and Electrical Property of Epitaxial Indium Tin Oxide Films

Indium tin oxide (ITO, tin-doped indium oxide) has been widely used in optoelectronic and other research fields because of its excellent electrical conductivity. However, there is a lack of systemic research on the influence of crystal orientation on the electrical properties of epitaxial ITO films. In this work, the epitaxial ITO films were deposited on low index planes of yttria-stabilized zirconia substrates by direct current magnetron sputtering at different oxygen partial pressures ranging from 0 to 3 Pa. The carrier concentration of the ITO film decreased with the increase of the oxygen partial pressure and further leading to the increase of overall resistivity. In addition, we also found that the Hall mobilities of ITO (100) films rapidly decreased with the oxygen partial pressure, while the Hall mobilities of ITO (111) films remained unchanged. The anisotropy of the carrier mobility was the main factor for the resistivity difference of ITO films with different orientations at high oxygen partial pressure.

The Influence of Crystal Orientation on Subsurface Damage of Mono-Crystalline Silicon by Bound-Abrasive Grinding.

Subsurface damage (SSD) produced in a grinding process will affect the performance and operational duration of single-crystal silicon. In order to reduce the subsurface damage depth generated during the grinding process by adjusting the process parameters (added), experiments were designed to investigate the influence of machining factors on SSD. This included crystal orientation, diamond grit size in the grinding wheel, peripheral speed of the grinding wheel, and feeding with the intention to optimize the parameters affecting SSD. Compared with isotropic materials such as glass, we considered the impact of grinding along different crystal directions <100> and <110> on subsurface damage depth (added). The Magnetorheological Finishing (MRF) spot technique was used to detect the depth of SSD. The results showed that the depth of SSD in silicon increased with the size of diamond grit. SSD can be reduced by either increasing the peripheral speed of the grinding wheel or decreasing the feeding rate of the grinding wheel in the <100> crystal orientation, if the same size of diamond grit was employed. In addition, we proposed a modified model around surface roughness and subsurface crack depth, which considered plastic and brittle deformation mechanisms and material properties of different crystal orientations. When the surface roughness (RZ) exceeded the brittle-plastic transition’s critical value RZC (RZC<100> > 1.5 μm, RZC<110> > 0.8 μm), cracks appeared on the subsurface. The experimental results were consistent with the predicted model, which could be used to predict the subsurface cracks by measuring the surface roughness. However, the model only gives the approximate range of subsurface defects, such as dislocations. The morphology and precise depth of plastic deformation subsurface defects, such as dislocations generated in the fine grinding stage, needed to be inspected by transmission electron microscopy (TEM), which were further studied.

Nano mechanical property analysis of single crystal copper using Berkovich nano indenter and molecular dynamic simulation

Nanoindentation analysis of FCC single crystal copper with different crystal orientations under Berkovich indenter was carried out by molecular dynamics simulation. The influence of crystal orientation on load distribution under Berkovich indenter was studied and compared with the experiment. Simultaneously, by establishing the relationship between the load–displacement curve and the instantaneous defect structure, the defect formation and slip processes under different crystal orientations were analyzed. Finally, the dislocation density of different orientations was calculated. Meantime, the relationship between the dislocation density and the hardness was explored. The results show that the 〈100〉 orientation shows a slightly different anisotropy difference, and the load value is lower than the 〈110〉 and 〈111〉 orientations. The 〈111〉 load value is slightly greater than 〈110〉 and the hardness values also show the same trend as the load value. The launch time of the initial dislocation loop of 〈100〉 orientation is earlier than 〈110〉, 〈111〉. The crystallographic orientation has a great influence on the change of dislocation morphology during the indentation process. With different orientations, the main plastic deformation is incomplete dislocation nucleation. Under different orientations, different forms of dislocation proliferation, such as quadruple, double and triple symmetry, and different stacking slip directions activated during indentation are observed. The 〈110〉 orientation has a relatively small dislocation density value, the dislocation density ρ0.5 is proportional to the hardness, and the coefficient values are different with different orientations.

Influence of crystal orientation and Berkovich tip rotation on the mechanical characterization of grain boundaries in molybdenum

In this study, nanoindentation experiments with a continuously measured stiffness are performed in the vicinity of grain boundaries in technically pure molybdenum. A significant change in hardness as a function of indentation depth is put in context with the corresponding deformation patterns in the indented crystals. The difference in hardness increase of 18% compared to 5% of two different grain boundaries with similar misorientation angle could be explained in this way. Five degrees of freedom have to be determined to fully describe a grain boundary. However, the influence of the rotation angle of a pyramidal indenter geometry around the loading axis as yet another loading parameter is assessed by backscattered electron micrographs and orientation deviation maps. Indentation experiments with different rotation angle at the same grain boundary confirm that a hardness increase close to the grain boundary is only apparent if a significant amount of plastic deformation is introduced towards the interface.

Oxidative decomposition of volatile organic compound on hydroxyapatite with oriented crystal structures

Hydroxyapatite (HAp) exhibits superior biocompatibility, ion-exchange ability and high adsorption property has attracted much attention as one of the most well-known ceramic functional materials. We have previously reported the efficient oxidative decomposition of volatile organic compounds (VOC) on commercial HAp powders, which makes HAp a promising alternative material of precious metal nanoparticle catalyst for environmental purification. In this work, HAp with oriented crystal growth of a-plane and c-plane were synthesized via air-liquid interface precipitation in solution, and the influence of crystal orientation on VOC decomposition performance was systemically investigated. As a result, HAp with preferential growth of c-plane performs higher catalytic VOC decomposition activity, which can be attributed to the large number of active radicals generated on surface despites the relative smaller sufficient surface area. The results in this study highlight the important relation between crystal structure of HAp and the decomposition activity of VOC, which also provide useful information for the structure design of ceramic functional materials.

Influence of crystal orientation and surface termination on the growth of BiSb thin films on GaAs substrates

We investigate the crystal growth of BiSb thin films on various GaAs substrates with different crystal orientation and surface termination. We found the non-trivial growth mode of BiSb which depends on the crystal orientation/surface termination of GaAs. While BiSb(0 0 1) can be grown epitaxially on GaAs(1 1 1)A, only textured BiSb(0 1 2) can be grown on GaAs(1 1 1)B even with the help of an ultrathin Bi buffer layer, indicating the critical role of surface termination of the GaAs(1 1 1) substrates. Meanwhile, only textured BiSb(0 0 1) thin films grow on GaAs(0 0 1) instead of BiSb(0 1 2), indicating that symmetry matching plays a little role on the growth of BiSb on GaAs(0 0 1).

Influence of surface energy and elastic strain energy on the graphene growth in chemical vapor deposition

Polycrystalline metal substrates such as copper (Cu) have been intensively used to grow graphene in chemical vapor deposition (CVD) technique. It has been observed that crystal orientations affect the quality of graphene produced to some degree. The existence of crystal orientations caused graphene to grow randomly on top of Cu which also resulted on the formation of polycrystalline graphene. Despite this, the influence of crystal orientations on the quality of graphene produced are not yet fully understood. There are two possible factors that could affect graphene growth from crystal orientation point of view; surface energy and elastic strain energy. The understanding towards these both factors might beneficial to control the quality of graphene. This paper thus aims to highlight the influence of surface energy and elastic strain energy on the graphene growth in CVD. Substrate used were single crystal Cu with (111), (110) and (100) orientations. The graphene was grown inside a closed reaction chamber with the presence of argon (Ar), hydrogen (H2) and methane (CH4) gases with partial pressure ratio of 0.6: 0.2: 0.2 at 1 atm, 1000 ˚C in 30 minutes. The quality of the as-grown graphene was identified using Raman spectroscopy. The Raman spectra show the existence of graphene peak for all the Cu substrates. The calculation of ID/IG ratio revealed that the Cu (100) possessed the lowest amount of defects compared to Cu(110) and Cu(111). While I2D/IG ratio fluctuated between 0.22 to 0.34 suggested that the crystal orientation does not control the thickness of graphene layer at these reaction conditions. The usage of higher CH4 partial pressure produced a thicker graphene. It is assumed that the thickness of the graphene exceeded the critical thickness thus elastic strain energy becomes the dominant factor in controlling graphene growth. Larger lattice mismatch causes major defects on graphene and this result has been shown in graphene grown on top of Cu(111). These findings thus would give a new insight to tailor the high-quality large-area graphene growth in CVD.

Influence of crystal orientation on the magnetostriction behavior of Fe films formed on MgO single-crystal substrates

Abstract Fe thin films are prepared on MgO substrates of (001), (110), and (111) orientations by ultra-high vacuum magnetron sputtering. The magnetostriction behaviors under rotating magnetic fields are observed by using a cantilever method. The relationship between in-plane magnetic anisotropy and magnetostriction behavior is investigated. An Fe(001)bcc single-crystal film is obtained on MgO(001) substrate. A four-fold symmetry in in-plane magnetic anisotropy is observed for the Fe(001)bcc film, where the easy magnetization directions are parallel to bcc[100] and bcc[010]. An Fe(211)bcc bi-crystalline film is formed on MgO(110) substrate and the film also shows an almost four-fold symmetric magnetic anisotropy. The reason is interpreted to be due to an influence of overlap of magnetic anisotropies of two bcc(211) variants with two effective easy magnetization directions which are obtained by projecting bcc[010] and bcc[001] on the bcc(211) plane. An Fe(110)bcc film is epitaxially grown on MgO(111) substrate with two types of variant with the crystallographic orientation relationships similar to Nishiyama-Wasserman and Kurdjumov-Sachs. The Fe(110) film shows an isotropic in-plane magnetic property due to an influence of the variant structure. Usual sinusoidal waveforms of magnetostriction are observed for the Fe(110) film. On the other hand, waveforms measured for the Fe(001) and the Fe(211) films are deformed from sinusoidal shape under low in-plane rotating magnetic fields and the magnetostriction behaviors are similar between the two films. Rectangular waveforms are observed for the bending parallel to easy magnetization directions, whereas triangular waveforms are recognized for the bending parallel to hard directions. The phenomenon is related to the direction difference between applied magnetic field and magnetization in magnetically unsaturated films with in-plane anisotropies. The magnetostriction behavior is influenced by the symmetry of in-plane magnetic anisotropy.

Effects of crystal orientation and diameter on the mechanical properties of single-crystal MgAl2O4 spinel nanowires

The influence of crystal orientation (including [100], [110], and [111]) and diameter (ranging from 2 to 10 nm) on the tensile deformation behavior and mechanical properties of single-crystal spinel (MgAl2O4) nanowires is investigated using molecular dynamics simulations. Varied deformation characteristics and fracture modes are revealed when the tensile loading is applied in the differently oriented nanowires. Mechanical properties including elastic modulus and ultimate tensile strength of spinel nanowires are distinctly dependent on size in each crystal orientation. This study advances the understanding of spinel nanomechanics which can help the development of high-strength spinel materials and their potential nanodevice applications.

Effects of Crystal Orientations on the Low-Cycle Fatigue of a Single-Crystal Nickel-Based Superalloy at 980 °C

The influence of crystal orientations on the low-cycle fatigue (LCF) behavior of a 3Re-bearing Ni-based single-crystal superalloy at 980 °C has been investigated. It is found that the orientation dependence of the fatigue life not only depends on the elastic modulus, but also the number of active slip planes and the plasticity of materials determine the LCF life, especially for the [011] and [111] specimens. The [011] and [111] specimens with better plasticity withstand relatively concentrated inelastic deformation caused by fewer active slip planes, compared to the [001] specimens resisting widespread deformation caused by a higher number of active slip planes. Additionally, fatigue fracture is also influenced by cyclic plastic deformation mechanisms of the alloy with crystal orientations, and the [001] specimens are plastically deformed by wave slip mechanism and fracture along the non-crystallographic plane, while the [011] and [111] specimens are plastically deformed by planar slip mechanism and fracture along the crystallographic planes. Moreover, casting pores, eutectics, inclusions and surface oxide layers not only initiate the crack, but also reduce the stress concentration around crack tips. Our results throw light upon the effect of inelastic strain on the LCF life and analyze the cyclic plastic deformation for the alloy with different orientations.

The influence of crystal orientation on corrosion behavior of iron in liquid PbLi

Using first principles calculations combined with molecular dynamics simulations, the corrosion behavior of iron in liquid PbLi has been investigated by calculating the packing and exchanging properties of atoms at typical iron - liquid PbLi interfacial region. The equilibrium structure of interfaces showed that the Pb/Li atoms that directly bind to iron atoms were found all have 5 or 6 same layer Pb/Li neighboring atoms. By exchanging the atoms near the interfacial region, Pb atoms were found to be more stable than Li atoms when directly bind to iron matrix, and Cr had lower solution formation energy than Fe atom. Through dragging the interface Fe atom to liquid PbLi region, Fe <110> crystal orientation was found to be more corrosive than others, and the formation energy of an interface Fe atom migrate to the PbLi region for concerned cases were all in range of 1.6–1.7 eV. These resulting data can provide basic information for understanding the dissolution corrosion behavior of RAFM steel in liquid PbLi.