Influence Of Crystal Orientation Research Articles

Influence of crystal orientation on cellular growth of a nickel-base single crystal superalloy

The cellular pattern evolution during directional solidification of a nickel-base single crystal superalloy has been studied in different crystallographic orientations using re-oriented seed crystals. Under the same thermal gradient and solidification velocity, the microstructures of differently oriented cellular single crystals are schematically investigated. It is concluded that the cellular growth direction is less affected by the seed orientation and depends on the heat flow, and is usually along heat flow direction. Cellular interface stability and microstructure are greatly influenced by the crystallographic orientation. When increasing the misorientation, the cell spacing increases correspondingly and the cellular growth interface becomes more unstable.

Influence of Crystal Orientation on the Freckle Formation in Directionally Solidified Superalloys

Freckle occurrence is known to be dependent on the casting size and the superalloy components with large cross section are more prone to freckle formation. In our directional solidification experiment of superalloys freckles are observed in some thin samples, while some significantly thicker samples in the same shell mould cluster remain freckle free. The EBSD analysis shows that the samples with freckles have a good <001> axial orientation, while in freckle free samples the primary dendrite stems diverge from the sample axis. In an analogue system the flow behaviour through a mushy zone was simulated, in which the dendrite network was placed in different orientation. The <001> dendrite array shows the lowest resistance to the vertical melt flow. As the dendrite alignment diverges from <001> orientation, the flow speed slows down and reaches the minimum at the <111> orientation. This orientation effect of the interdendritic permeability explains well why the crystal orientation plays such an important role in the occurrence of freckles in superalloy castings.

Characterization at a local scale of a laser-shock peened aluminum alloy surface

The influence of a laser shock peening mechanical surface treatment on 2050-T8 aluminum alloy has been investigated, mostly using Scanning Kelvin Probe Force Microscopy. Volta potential difference maps around Al(CuFeMn) precipitates were performed before and after laser-shock peening to determine the influence of laser treatment versus galvanic coupling near precipitates, and resulting pit initiations. It has been shown that laser shock peening either preserves or reduces precipitate-matrix Volta potentials gradients, which in this later case, and correlated to recent corrosion electrochemical investigations, could explain corrosion improvement obtained after laser-shock peening treatments of aluminum alloys. The influence of crystal orientation and plastic deformation, and more specifically the effect of laser-induced compressive residual stresses or work-hardening, on the Volta potential values and on the pitting corrosion behavior was also addressed.

Influence of TiN High-tensile Stress Coating on Magnetic Properties in Grain oriented Electrical Steel.

The influence of crystal orientation on the magnetic properties of 3% Si-Fe single crystals was investigated by measuring iron losses and observing magnetic domain patterns in TiN-coated and chemically polished specimens. The iron loss was reduced in a TiN-coated sample whose β angle was less than 4 degrees and increased in a sample whose β angle was larger than 4 degrees. The improvement in the iron loss was due to a decrease in eddy current loss that corresponded to a decrease in the magnetic domain width caused by the tensile stress effect of the TiN coating. In the sample whose β angle was larger than 4 degrees, the eddy current loss did not change due to the TiN coating because the magnetic domain width was almost the same under alternate magnetization. Additionally, hysteresis loss increased because of increase magnetic coercive force.

Influence of crystal orientation on hardness and nanoindentation deformation in ion-irradiated stainless steels

The influence of crystal orientation on hardness and the range of plastic deformation caused by nanoindentation was investigated in a solution annealed type 316 stainless steel irradiated with Fe2+ ions. The hardness was a function of grain orientation and was correlated with the Taylor factor averaged over three normal directions of the contact surface of the Berkovich indenter. The transmission electron microscope observations of the deformation microstructure under the indentations showed that the range of plastic deformation reached up to 10 times the indent depth for unirradiated material and depended on the orientation relation between the contact surface of the indenter and the slip directions. The range of plastic deformation decreased as the damage structure developed in ion irradiation.

Influence of Crystal Orientations on the Bendability of an Al-Mg-Si Alloy

Aluminum alloy sheets are being increasingly used to reduce the weight of an automotive body. Al–Mg–Si alloys have been used because they have favorable properties for automotive bodies. One of the important requirements of these alloys is the ability to resist fracture while bending. In this study, the influence of crystal orientations on the bendability of an Al–Mg–Si alloy is investigated using single-crystal specimens from the viewpoint of the shear band formation. The bendability and the formation of shear bands are clearly dependent on the crystal orientation, and ‹001›//ND-oriented specimens exhibit the highest bendability. The formation of denser shear bands is observed with a decrease in bendability. The shear bands behaved as the origin of the cracks and the propagation path. It is concluded that the inhibition of the formation of shear bands by controlling the orientations is very important to improve the bendability. Moreover, there exists a relation between the Taylor factor and the bendability because the bendability tended to decrease with an increase in the Taylor factor.

Influence of crystal orientations on the bendability of an Al–Mg–Si alloy

Aluminum alloy sheets are being increasingly used to reduce the weight of an automotive body. Al–Mg–Si alloys have been used because they have favorable properties for automotive bodies. One of the important requirements of these alloys is the ability to resist fracture while bending. In this study, the influence of crystal orientations on the bendability of an Al–Mg–Si alloy is investigated using single-crystal specimens from the viewpoint of the shear band formation. The bendability and the formation of shear bands are clearly dependent on the crystal orientation, and ‹001›//ND-oriented specimens exhibit the highest bendability. The formation of denser shear bands is observed with a decrease in bendability. The shear bands behaved as the origin of the cracks and the propagation path. It is concluded that the inhibition of the formation of shear bands by controlling the orientations is very important to improve the bendability. Moreover, there exists a relation between the Taylor factor and the bendability because the bendability tended to decrease with an increase in the Taylor factor.

Laser-induced damage of KDP crystals by 1ω nanosecond pulses: influence of crystal orientation

We investigate the influence of THG-cut KDP crystal orientation on laser damage at 1064 nm under nanosecond pulses. Since laser damage is now assumed to initiate on precursor defects, this study makes a connection between these nanodefects (throughout a mesoscopic description) and the influence of their orientation on laser damage. Some investigations have already been carried out in various crystals and particularly for KDP, indicating propagation direction and polarization dependences. We performed experiments for two orthogonal positions of the crystal and results clearly indicate that KDP crystal laser damage depends on its orientation. We carried out further investigations on the effect of the polarization orientation, by rotating the crystal around the propagation axis. We then obtained the evolution of the damage probability as a function of the rotation angle. To account for these experimental res ts, we propose a laser damage model based on ellipsoid-shaped defects. This modeling is a refined implementation of the DMT model (Drude Mie Thermal) [Dyan et al., J. Opt. Soc. Am. B 25, 1087-1095 (2008)], by introducing absorption efficiency calculations for an ellipsoidal geometry. Modeling simulations are in good agreement with experimental results.

Influence of crystal orientation on copper oxidation failure

The influences of crystal orientation on copper oxidation were investigated. The results indicated that crystal orientation of copper substrate has a great effect on the growth rate, the morphology of oxide film and the extent of oxidation failure. Shear test showed the adhesion strength between Cu(1 1 0) and its oxide film was the highest, whereas, the adhesion strength between Cu(3 1 1) and its oxide film was the lowest. SEM observations revealed that the oxide film grown on Cu(3 1 1) delaminated from substrate seriously, while the oxide film grown on Cu(1 0 0) and Cu(1 1 0) did not reveal such a phenomenon. Cu(1 0 0) and Cu(1 1 0) exhibited thinner oxide thickness compared to those on Cu(3 1 1) and Cu(1 1 1). The activation energy for oxide growth on Cu(1 0 0) and Cu(1 1 0) was calculated to be the highest while that on Cu(3 1 1) was the lowest.

OS0801 Ni基単結晶超合金の引張変形挙動に及ぼす結晶方位の影響(ガスタービン材料の各種力学特性,オーガナイズドセッション)

OS0801 Ni基単結晶超合金の引張変形挙動に及ぼす結晶方位の影響(ガスタービン材料の各種力学特性,オーガナイズドセッション)

The influence of crystal orientations on fatigue life of single crystal cooled turbine blade

A method based on the orthotropic elastic finite element analysis (FEA) has been presented to analyze the fatigue life of cooled turbine blades made of nickel-based single crystal superalloy (SC). Special attention was put on the influence of the crystallographic orientations on the strength and fatigue life of SC cooled turbine blades. It is shown that, due to the influence of the temperature distribution and complexity of cooling tunnel, the place of the maximum resolved shear stress in the blade is not corresponding to the most dangerous place, where results in the minimum fatigue life. For the SC cooled turbine blades studied in the paper, as the same of the most commercial SC blades in the world market, the axial direction is cast to [0 0 1] crystallographic orientation within 15° deviation, and the other two directions are in random. It is found that the randomness of the two directions has only limited influence on the distributions of Mises stress and the maximum resolved shear stress in the blade. But the deviation of the axial direction of the blade has obvious influence on the stress distribution, and the influence of the deviation and randomness orientations on the fatigue life is also obvious. Finally, the benefit of the optimization of the crystallographic orientations of SC cooled turbine blades on the fatigue life is highlighted.

Influence of crystal orientation and surface topography of aluminum substrate on pore nucleation of anodic porous alumina

Pore nucleation and growth processes of anodic oxide films formed on aluminum substrate were investigated by atomic force microscopy with focusing on the crystal orientation and surface topography of aluminum substrate. Nanotopographies of electropolished aluminum were extremely affected by the crystal orientation of aluminum substrate. For as-received aluminum, regularly aligned striped structure appeared after electropolishing. On the other hand, aluminum substrate annealed at 300°C exhibited isotropic hexagonal cell structure. From X-ray diffraction patterns, it was confirmed that the preferential crystal orientation of aluminum was changed from (110) to (100) when annealing temperature was higher than 300°C. In the initial stage of anodization, specific nanotopography of electropolished aluminum surface was served as the initiation sites for pore generation, and accordingly it influenced cell arrangement. Using planarized aluminum with less than 0.3 nm asperities, however, a large number of fine pores initiated on the oxide film surface. Thus, the growth of anodic oxide films was seriously influenced by the surface topography of aluminum substrate.

Influence of crystal orientation on the processing of copper single crystals by ECAP

Single crystals of high-purity copper, having two different orientations, were pressed through one pass in equal-channel angular pressing (ECAP) at room temperature and then examined using several different analytical techniques. For both orientations, it is shown that elongated arrays of cells or subgrains are formed in the first pass with their long axes aligned parallel to the primary \({(\bar {1}\bar {1}\bar {1})[\bar {1}10]}\) slip system. The average width of these subgrains was measured as ∼0.2 μm which is similar to the equilibrium grain size reported in polycrystalline Cu after processing by ECAP. These results confirm earlier observations using an aluminum single crystal except only that the subgrain width in copper is significantly smaller. This difference is attributed to the lower stacking-fault energy in copper and the consequent low rate of recovery.

Crystal-Orientation Dependent Evolution of Edge Dislocationsfrom a Void in Single Crystal Cu

The micro-void growth by dislocation emission under tensile loading isexplored with focus on the influence of crystal orientations. Based onthe elastic theory, a dislocation emission criterion is formulated. Itis predicted that the preferential location of dislocation nucleationand its threshold stress are dependent on the crystal orientation.Large-scale molecular dynamics (MD) simulations are also performed forsingle crystal copper to illustrate the dislocation evolution patternassociated with a nano-void growth. The results are in line with thosegiven by the theoretical prediction. As revealed by MD simulations, thecharacteristics of void growth at micro-scale depend greatly on thecrystal-orientation.

The influence of crystal orientation on the bacterial dissolution of pyrite

In order to understand the influence of crystallographic orientation on the mechanism of pyrite bioleaching, single crystals cut to expose plane orientations of (100), (111) and (110) were used for the study. Experiments to compare the extent of dissolution of the pyrite surfaces in the presence and absence of Acidithiobacillus ferrooxidans under similar solution conditions were undertaken by matching the conditions in abiotic solutions to those in bacterial leaching solutions using an electrolysis cell. The microbial corrosion patterns generated on the surfaces were further used to study the leaching process. Differences in the reaction rates of the pyrite surface planes in both abiotic and bacterial solutions have been observed. The results for the comparison between the bacterial and abiotic leaching of pyrite samples under similar conditions indicate higher dissolution rates in the presence of bacteria. In addition, the morphologies of corrosion patterns arising from microbial leaching were distinct from those of abiotic leached samples and were found to slightly differ from one crystal plane to another, while those in abiotic leaching generally reflected the symmetrical arrangement of the crystallographic planes in the lattice on which they formed. The results show that the surface properties of mineral sulphides control the evolution of corrosion patterns and the initial oxidation kinetics in acid bacterial leaching.

Improved method for determining inversion layer mobility of electrons in trench MOSFETs

Trench sidewall effective electron mobility (μeff) values were determined by using the split capacitance–voltage (CV) method for a large range of the transversal effective field (Eeff) from 0.1 up to 1.4 MV/cm. The influences of crystal orientation, doping concentration and, for the first time, temperature were investigated. Results show that the split CV method is an accurate method for determining μeff (Eeff) data in trench MOSFETs; the {100} μeff data approaches published data on planar MOSFETs for high Eeff; and mobility behaviour can be explained with generally accepted scattering models for the entire range of Eeff. The results are important for the optimisation of trench power devices.

Homoepitaxial mesa structures on 4H–SiC (0 0 0 1) and [formula omitted] substrates by chemical vapor deposition

Selective epitaxial mesas of SiC were successfully grown on masked 4H–SiC (0 0 0 1) and (1 1 2 ̄ 0) substrates using a carbon mask by a CVD method. The carbon mask was removed by thermal oxidation without surface degradation, resulting in the successful formation of SiC epitaxial mesa structures on SiC substrates. The influences of crystal orientation, “step-flow growth” on SiC mesas, and polytypes of grown layers have been investigated. The external lateral growth on the carbon mask was observed along the 〈 1 1 2 ̄ 0 〉 direction on the off-axis (0 0 0 1) and along the 〈0 0 0 1〉 direction on the on-axis (1 1 2 ̄ 0) 4H–SiC substrates. Both on the off-axis (0 0 0 1) and the on-axis (1 1 2 ̄ 0) substrates, the main portion of epitaxial mesas is homoepitaxially grown 4H–SiC. Cross-sectional transmission electron microscopic analysis revealed that 3C–SiC existed at the upstream side of step-flow on the off-axis (0 0 0 1) substrate and in the external lateral growth region along the 〈0 0 0 1〉 direction on the on-axis (1 1 2 ̄ 0) substrate.

Investigating the influence of fabrication process and crystal orientation on shear strength of silicon microcomponents

A summary of the influence of microfabrication processes (wet and dry etching) and crystal orientation on the effective shear strength of microridges is addressed in this paper. Test results indicate that both crystal orientation and geometry plays an important role in determining the strength. The largest shear strengths obtained were for triangular and rectangular ridges fabricated with wet etching and deep RIE respectively. Both of these structures had similar crystal orientations. These strength values were approximately 3.5 times larger than the lowest strengths measured for wet etching structures. Using Chlorine RIE, we were able to demonstrate the influence of crystal orientation on strength, with microridges of {110} sidewall made on a (100) wafer the largest. For wet etching, we found that the strength was concentration dependent. For example, a 45% KOH fabricated structure produced strength values 65% higher than 30% KOH fabricated ones (note crystal orientation the same). This was attributed to a geometric effect, that is the 45% KOH solution had a “V” shaped bottom while the 30% KOH had a flat bottom. EDP and TMAH values had similar strengths to the 30% KOH solution (note similar crystal orientation). Therefore, microcomponent strength is strongly dependent upon fabrication process as well as crystal orientation.

Deep plasma silicon etch for microfluidic applications

Various microfluidic devices like micro pumps, micro dispensers, micro pipettes, etc. are produced by the GeSiM mbH Großerkmannsdorf. Fabrication of such microsystems includes the realization of three-dimensional silicon substrates. Plasma-based silicon etch processes are key technologies for exact patterning the substrates from both surfaces.Typically, etch depths of 10 to 500 μm, aspect ratios >25 and the application of conventional mask systems are required. Etch rates between 2 and 6 μm/min, a uniformity (3σ) below 5%, an excellent anisotropy and a selectivity of >50:1 for photoresists and >150:1 for SiO2 can be realized using an etch system produced by Surface Technology Systems Limited (STS), UK and the ASE™ process based on fluorine etch chemistry. This technique overcomes the disadvantages of conventional wet silicon etch processes, like the influence of crystal orientation on etch rate.Our intention was to investigate the influence of gas flow rates, process gas pressure, supplied power and time sequence on etch rate and edge profile. The results should be used to vary process parameters according to the requirements of application.

Deformation microstructures and textures in steels

Experimental evidence concerning the evolution of textures and substructures during cold rolling of low–carbon steel is presented and reviewed with some reference to the importance of these during subsequent annealing. Attention is paid to the orientation dependence of microstructure and stored energy of deformation. These are considered in relation to the Taylor factors for grains of different orientations in homogeneous deformation, and to the occurrence of different types of heterogeneity. Certain grain–scale heterogeneities appear to be important in defining the textures, which can now be predicted with some success using so–called relaxed constraint models. Intragranular heterogeneities also play a role and these especially affect the variation in substructure between grains. The strain–rate sensitivity of flow stress is an important parameter, which, depending on its sign and magnitude, may cause either severe strain localization in shear bands or lead to very homogeneous deformation structures where the influence of crystal orientation almost disappears.