Effect Of Crystallography Research Articles

Estimation of Yield Function for Anisotropic Aggregate of FCC Crystallites

In this paper, we give an simple but approximate yield surface for single FCC crystals in Hill’s criterion form by Schmid’s law and nonlinear optimization theory. Assuming that all FCC crystallites in a polycrystal have the same (current) critical resolved shear stress τc for slip, we derive two closed but approximate yield functions through the orientational averaging of all FCC crystallites’ yield surfaces in the polycrystal. The effect of crystallography on the two yield functions are described by the orientation distribution function.

Crystallographic effects on transgranular chloride-induced stress corrosion crack propagation of arc welded austenitic stainless steel

The effect of crystallography on transgranular chloride-induced stress corrosion cracking (TGCISCC) of arc welded 304L austenitic stainless steel is studied on >300 grains along crack paths. Schmid and Taylor factor mismatches across grain boundaries (GBs) reveal that cracks propagate either from a hard to soft grain, which can be explained merely by mechanical arguments, or soft to hard grain. In the latter case, finite element analysis reveals that TGCISCC will arrest at GBs without sufficient mechanical stress, favorable crystallographic orientations, or crack tip corrosion. GB type does not play a significant role in determining TGCISCC cracking behavior nor susceptibility. TGCISCC crack behaviors at GBs are discussed in the context of the competition between mechanical, crystallographic, and corrosion factors.

Effect of crystallography on residual stresses during ultra-precision machining of sapphire

Residual stresses play an important role in determining the quality of a machined surface during ultra-precision machining (UPM) of ceramics by initiating cracks at premature loads. In this study, the anisotropy in residual stresses resulting from UPM of two crystallographic planes of sapphire is investigated using micro-Raman spectroscopy. An analytical model is then used to improve our understanding of plastic deformation during UPM and its contribution to residual stress. Results show a strong dependence of residual stress magnitude on the slip and fracture systems activated during machining which are anisotropic based on the cutting direction.

Effects of crystallography on hot-spot formation in porous RDX single crystals

The thermomechanical behavior of porous RDX single crystals is studied under dynamic loading using an anisotropic dislocation-based crystal plasticity model that accounts for deformation-induced heating. A micromechanics-based framework is proposed to account for micro-inertially confined dynamic collapse of pores. A suite of finite element calculations are carried out to systematically elucidate the role of crystallographic orientation on hot-spot formation. Under particular loading orientations, the porous RDX crystals are found to be quite sensitive to deviatoric and volumetric strain localizations, even for loading situations that do not particularly promote strain localization in isotropic materials. Due to the anisotropy-induced strain localizations, fairly severe hot-spots are predicted even under moderate applied strains. The susceptibility of porous RDX to strain localize and form severe hot-spots under particular loading orientations has important implications for accidental detonation of these energetic materials.

Phase Transformation Prediction Considering Crystallographic Orientation in Microgrinding Multiphase Material

AbstractThis investigation proposes a physics-based model to predict the solid-state phase transformation of maraging steel subjected to microgrinding. In microgrinding, the effect of crystallography is significant on the grinding phase transformation in light of the fact that the depth of cut is on the same order of magnitude as the grain size. This paper proposes a predictive model of phase transformation considering crystallographic orientation (CO) with respect to the grinding direction based on the Taylor factor model. In addition, the flow stress model is modified by adding a CO sensitive term and incorporating the mechanical-thermal loadings. Furthermore, the temperature, temperature rate, strain rate, and Taylor factor are also combined in the model of phase transition. The kinetics parameters of the models are obtained by a regression analysis against experimental data. Finally, the modified models are validated with experiments data and compared with the previous prediction.

Micro-grinding Temperature Prediction Considering the Effects of Crystallographic Orientation and the Strain Induced by Phase Transformation

This paper proposes a physical-based model to predict the temperature in the micro-grinding of maraging steel 3J33b with the consideration of material microstructure and process parameters. In micro-grinding, the effects of crystallography on the grinding machinability become significant, since the depth of cut is of the same order as the grain size. In this research, the Taylor factor model for multi-phase materials is proposed to quantify the crystallographic orientation (CO) with respect to the cutting direction by examining the number and type of activated slip systems. Then, the flow stress model is developed, in which both the athermal stress resulted from the COs and the strain induced by the phase transformation are taken into account. On the basis of the flow stress model, the grinding forces are predicted followed by the calculation of the grinding heat. In the investigation, the triangular heat flux distribution and the reported energy partition model are applied in the calculation of workpiece temperature. Furthermore, the temperature model is validated by conducting an orthogonal-designed experiment, with the predictions of the maximum temperature in good agreement with the experimental data. Moreover, the predictive data is compared with the predictions resulted from the two other previously reported models. The results indicate that the proposed temperature model with considering the effect of CO and the phase transformation improved the prediction accuracy of the micro-grinding temperature.

Force prediction in micro-grinding maraging steel 3J33b considering the crystallographic orientation and phase transformation

In micro-grinding, the effects of crystallography on grinding force become significant since the depth of cut is of the same order as the grain size. In this research, the Taylor factor model for multi-phase materials is proposed based on the previously reported Taylor factor model for monocrystalline material. Based on this model, the flow stress model is developed, which takes both the effect of CO on the athermal stress and the stress induced by the phase transformation into account. Based on the flow stress model, the predictive model of chip formation force is proposed by adapting parallel-sided shear zone theory. The rubbing force is modeled by applying Waldorf’s worn tool theory. Furthermore, the plowing force is predicted based on previously reported model by the authors. Subsequently, a comprehensive model of the micro-grinding force is proposed by considering mechanical-thermal loading, the effects of crystallography, and phase transformation. Finally, the model is validated by conducting an orthogonal-designed experiment with the result proving that the prediction of the model is capable to capture the magnitude and trend of the experimental data. Moreover, the proposed analysis are compared with the predictions of two other previously reported models with the result, indicating that the model that considers the effect of CO and the phase transformation improves the accuracy of the micro-grinding force.

Effect of crystallography on the calculation energies of equilibrium and enthalpies of formations at first-principles calculations (DFT)

Effect of crystallography on the calculation energies of equilibrium and enthalpies of formations at first-principles calculations (DFT)

Forces prediction in micro-grinding single-crystal copper considering the crystallographic orientation

In the micro-grinding of single-crystal copper, the effect of crystallography becomes significant as the wheel works intra-crystalline. To quantify the effect of crystallographic orientation (CO) related to the cutting direction on the micro-grinding process, this article presents a Taylor factor model by examining the number and style of activated slip systems. Then, the flow stress model of monocrystalline material is developed considering the variation of the Taylor factor. Furthermore, the models of chip formation and rubbing forces are derived from the flow stress model, while the plowing force is predicted by the Vickers hardness. Then, the overall grinding force model of the whole wheel is developed by incorporating the process parameters and the wheel properties. Finally, micro-grinding experiments are conducted to verify the model, using only the Taylor factor as the variable. The proposed analysis is also compared with the previously reported model, which considers the Taylor factor as a constant of 3.06. The comparison between the two predictions and experimental data shows that the consideration of Taylor factor variability improves the accuracy of prediction.

Atomistic Studies of Nanoindentation—A Review of Recent Advances

This review covers areas where our understanding of the mechanisms underlying nanoindentation has been increased by atomistic studies of the nanoindentation process. While such studies have been performed now for more than 20 years, recent investigations have demonstrated that the peculiar features of nanoplasticity generated during indentation can be analyzed in considerable detail by this technique. Topics covered include: nucleation of dislocations in ideal crystals, effect of surface orientation, effect of crystallography (fcc, bcc, hcp), effect of surface and bulk damage on plasticity, nanocrystalline samples, and multiple (sequential) indentation. In addition we discuss related features, such as the influence of tip geometry on the indentation and the role of adhesive forces, and how pre-existing plasticity affects nanoindentation.

In Situ investigation of Interfacial Transformations Between Oriented Transition Metal Dichalcogenides and Metals

Layered materials, such as transition metal dichalcogenides (TMDCs), are attractive for energy storage, nanoelectronics, and electrochromic devices. Layered TMDC materials feature a strongly anisotropic crystal structure, with basal planes and edge sites within the structure exhibiting divergent chemical and bonding properties. The interaction of external metals and ions with TMDCs is critical for their use in batteries and electronic devices; metal ions are reversibly intercalated between TMDC layers when used as battery electrodes, and thin film metal electrical contacts must be interfaced with TMDCs in next-generation electronics. In both cases, the crystallographic orientation of the TMDC likely influences the interfacial reaction and/or ion intercalation pathways and kinetics, but the effect of crystallography on these phenomena is not well understood. Here, we use in situ x-ray photoelectron spectroscopy (XPS) to determine how the crystallography and structure of TMDCs (MoS2 and TaS2) influence interfacial transformation pathways and kinetics when interacting with different metals of interest for energy storage and electronic contacts. This work is enabled by the synthesis of MoS2 and TaS2 with controllably aligned crystal structure: thin films with vertically aligned layers are grown via a sulfidation process, and single crystals with horizontally aligned layers are also utilized. In situ XPS is carried out by sputter depositing thin metal films (lithium, silver, or gold) onto the oriented TMDC material within an XPS instrument, and photoelectron spectra are acquired at different times to probe near-surface chemical changes and reaction kinetics in the TMDC material. The results show that lithium reacts with both edge planes and basal planes in MoS2 at similar rates to form reduced Mo and S species. This indicates that the conversion reaction of MoS2 in Li-ion batteries is not strongly dependent on the crystalline anisotropy of the lattice. In contrast, less reactive metals (silver and gold) were observed to intercalate in low concentrations, and this intercalation behavior is strongly dependent on the orientation of MoS2­ and TaS2. Interestingly, despite the relatively unreactive nature of Ag and Au, these materials also induce slight chemical reduction at the TMDC interface. This study emphasizes the importance of using in situ experiments for understanding interfacial reaction mechanisms and kinetics, which are generally difficult to study in buried interfaces. Future work will focus on tuning interfacial interactions via crystallographic control.

Initial transient structure and chemistry of intergranular glassy films in ferric-oxide doped strontium titanate ceramics

Intergranular glassy films (IGFs) often play a key role in the formation of microstructure and the resultant properties in titanate-based materials. In this article, a systematic study of IGF structure and chemistry is reported in Fe2O3-doped SrTiO3 ceramics sintered under different temperatures and dwelling times. IGFs exhibit a large variation in their thicknesses, although majority of them are still formed by the lower energy {100}, {110}, and {111} planes from one side, which is also true for those grain boundaries (GBs) without IGF and reveals no particular effect of crystallography on IGF width. Furthermore, two trends of IGF chemical composition were found coexisting in each sample, one rich in Ti and the other in Sr, and both containing Fe segregants. The change of sintering temperature did not show significant effect on the distributions for both trends. However, increase of the dwelling time is effective to turn some Sr-rich IGFs to Ti-rich IGF, indicating that the former is in a transient state and the equilibrium IGF has most likely a TiO2-based composition.

The cellular interlamellar and growth-front interphase boundaries in Cu-3 Wt pct Ti

Examination of the cellular colony interlamellar and growth-front interphase boundaries in Cu-3 wt pct Ti reveals an influence of crystallography at both of these interface types. Analysis of the interlamellar boundaries demonstrates that different arrangements of interphase misfit-compensating defects exist and combinations of misfit dislocations (MDs), structural ledges (SLs), or direction steps (DSs) were observed to dominate strain reduction between lamellae, even within the same colony. Detailed analysis also demonstrated that the actual interlamellar orientation relationship (OR) is (111) α ‖ (010) β with [-101] α ‖ [501] β , which is 0.28 deg in misorientation from the reported OR. The effect of crystallography was also apparent at the cellular growth front, as evidenced by the misfit-compensating structure observed with transmission electron microscopy (TEM) at the grain-boundary segments and the sharp faceting of all β precipitate-growth interfaces.

The equilibration of high-angle grain boundaries in dynamically recrystallized quartz: the effect of crystallography and temperature

Dynamically recrystallized and sutured quartz grains from metamorphic rocks with different strain intensities and temperature conditions ranging from ca. 350°C to ca. 700°C have been studied. Universal-stage measurements on quartz–quartz high-angle grain boundaries show that they are never curved but always consist of straight segments which preferentially occupy specific crystallographic orientations in relation to both neighboring crystals. With increasing temperature the segments preferentially concentrate in a decreasing number of orientations, mainly near the rhombohedral {101̄1} planes. The crystallographic data and the observations on grain boundary geometries suggest that: (i) grain boundary orientations are strongly crystallographically controlled, (ii) this control is the main factor on the textural equilibration of quartz–quartz grain boundaries in metamorphic rocks, and (iii) grain boundaries from dynamically recrystallized quartz should be regarded as annealed and equilibrated fabrics that are stable against subsequent annealing as long as the material is not re-deformed.

Crystallographic effects on the fatigue fracture of copper-sapphire interfaces

Abstract Interfacial fatigue cracks were propagated in copper-sapphire bicrystals with the boundary perpendicular to the load axis and (110)Cu||(1010)Al2O3 – [001]Cu||[0001]Al2O3 to study the effect of crystallography in the fracture process. Cylindrical samples with a circumferential notch were loaded in compression–compression and compact tension specimens in tension–tension. Three interfacial cracks in the cylindrical sample nucleated simultaneously at sites corresponding to the maximum slip length, under local single slip conditions, for three of the four slip vectors expected for the loading axis in the copper crystal. These cracks arrested with continued cycling, while two new cracks nucleated at 0° and 180° from [110]Cu, which also self-arrested. Then another crack started at 90° from [110]Cu and grew with an inclined front. Striations could be observed on the copper fracture surfaces; however, they did not coincide macroscopically with traces of {111} slip planes. Large areas were also relat...

Grain Boundary Migration in Alumina

ABSTRACTThe sintering process of ceramics involves grain-boundary migration (GBM) that is accompanied by mass transport across an interface. In this study, electron backscatter diffraction (EBSD) has been used to examine grain-boundary migration in alumina bicrystals with liquid films at the interface. EBSD patterns, taken near the sintered interface, have been used to study the effects of crystallography on GBM and to study the orientation relationships within the migrated regions of the crystal. Results indicate that the direction of migration is not always the same as that predicted by the current theories on GBM. It was also found that there may be small-angle misorientations in the migrated regions.

Surface segregation on Fe–Si single crystals: the effect of crystallography

The kinetics of solute segregation was measured at the (001), (0 1 14), (017), (015), (014) and (013) surfaces of an Fe–6 at% Si alloy at 873 K. Individual stages of segregation kinetics can be explained on the basis of mutual interaction among the principal segregants (silicon, nitrogen, sulfur and potassium). Strong attractive interaction between silicon and nitrogen results in the formation of stable Si x N y two-dimensional surface compounds at all surfaces studied including (001). Formation of these Si–N bonds is accompanied by a shift in the kinetic energy of the Si LVV Auger peak. Analysing the segregation behaviour of individual surfaces indicates that it can be considered as a combination of the two principal (001) and (013) planes.

Grain size effect on noise properties in CoCrTa thin film media

Grain growth of Cr and CoCrTa thin film was examined using high resolution transmission electron microscopy (HRTEM) and high resolution scanning microscopy (HRSEM). The effect of crystallography on media noise was studied. The grain size of the CoCrTa thin film increases with thickness and retains a bi-crystal structure over a range of Cr grain size. Media noise at a high recording density seems to increase with the grain size of Cr underlayer surface. This suggests that the micromagnetization process can be influenced by a bi-crystal structure of Co alloy films at their initial layers.

The influence of crystallography and oxide and metallic types on the structure and properties of metal-ceramic interfaces

Metal-ceramic oxide interfaces were investigated systematically to determine the role of reactivity of the metal and the oxide on the structure and mechanical properties of the interface. Electron microscopy was used to examine the structure of metal-ceramic interfaces between a non-reactive metal and a non-reactive ceramic (PtAl 2O 3), between a non-reactive metal and a reactive ceramic (PtNiO) and between a reactive metal and a non-reactive ceramic (TiAl 2O 3). The effect of crystallography, impurities and processing conditions on the interfacial morphology was also studied. For PtAl 2O 3, diffusion bonding in air produces a thin amorphous layer while bonding in argon produces a layer of grains of metastable crystalline alumina compounds such as ιAl 2O 3. It is believed that impurities play an important role in the formation of metastable phases in the PtAl 2O 3 system. For NiOPt, the relative geometry across the interface plane influences its structure. The morphology of the NiPt intermetallic compound formed by low temperature anneals is sensitive to the relative geometry between the NiO and platinum, and to the presence of silicon impurities. For TiAl 2O 3, heat treating at low temperatures produces no reaction layer and the strongest interfacial bonding, while heat treating at high temperatures (800°C and above) produces an interlayer of intermetallic compounds and weak bonding.

The effects of crystallography and lateral intermixing on the subband structure and optical anisotropy in quantum-wire arrays on vicinal substrates in the layer-orbital model

Materials-characterization studies indicate a high degree of lateral intermixing in quantum-wire arrays grown on vicinal substrates. In this study, the layer-orbital model, which is a variation of the effective bond-orbital model, is used to calculate the zone-center conduction- and valence-subband energies and optical matrix elements of recently grown epitaxially buried GaAs/AlGaAs/AlAs quantum wires and quantum-wire arrays. The lateral intermixing effect is included using a compositional profile that has the merit that it is appropriate for the entire range of lateral intermixing, whether small or large, and that is computationally efficient. The effect of the orientation of the quantum wires on the subbands and the optical matrix elements is also investigated. For uncoupled quantum wires, the orientation mainly affects the positions of the valence subbands; the optical matrix elements are nearly independent of the orientation. The situation for the quantum-wire array is more complicated due to its intermediate nature between one and two dimensional. It is found that only the position of the light-hole subband is appreciably affected. It is also found that quantum-wire arrays misoriented from the [011] ([01̄1]) direction display somewhat reduced optical anisotropy.