Effect Of Grain Orientation Research Articles

Effect of build orientation on fracture behaviour of AlSi10Mg produced by selective laser melting

PurposeA key challenge found in additive manufacturing is the difficulty to produce components with replicable microstructure and mechanical performance in distinct orientations. This study aims to investigate the influence of build orientation on the fracture toughness of additively manufactured AlSi10Mg specimens.Design/methodology/approachThe AlSi10Mg specimens were manufactured using the selective laser melting (SLM) technology. The fracture toughness was experimentally determined (under ASTM E399-09) using C(T) specimens manufactured in different orientations. The microstructure of the specimens was examined using metallography to determine the effects of grain orientation on fracture toughness.FindingsThe fracture toughness magnitude of manufactured specimens ranged between 36 and 50 MPam, which closely matched conventional bulk material and literature values regarding AlSi10Mg components. The C(T) specimens printed in the T-L orientation yielded the highest fracture toughness. The grain orientation and fracture toughness values confirm the anisotropic nature of SLM parts where the T-L-oriented specimen obtained the highest KIC value. A clear interaction between the melt pool boundaries and micro-slipping during the loading application was observed.Originality/valueThe novelty of this paper consists in elucidating the relationship between grain orientation and fracture toughness of additively manufactured AlSi10Mg specimens because of the anisotropy generated by the different melting pool boundaries and orientations in SLM. The findings show that melt pool boundaries can behave as easier pathways for cracks to propagate and subsequently reduce the fracture toughness of specimens with cracks perpendicular to the build direction.

Technical Note] The Effect of Variables on Laboratory Termite Testing: Part II—Effect of Grain Orientation of Test Blocks

Abstract The effect of test-block grain orientation on laboratory termite tests using American Wood-Preservers' Association Standard E1-97 was evaluated using Coptotermes formosanus. This research revealed that testing of samples with the 6-mm direction in either the longitudinal or the tangential direction was appropriate. The E1 standard was subsequently modified to allow either.

Modeling of material deformation behavior in micro-forming under consideration of individual grain heterogeneity

Abstract This study aims to develop a model to characterize the inhomogeneous material deformation behavior in micro-forming. First, the influence of individual grain heterogeneity on the deformation behavior of CuZn20 foils was investigated via tensile and micro-hardness tests. The results showed that different from thick sheets, the hardening behavior of grains in the deformation area of thin foils is not uniform. The flow stress of thin foils actually only reflects the average hardening behavior of several easy-deformation-grains, which is the reason that thinner foils own smaller flow stress. Then, a composite modeling method under consideration of individual grain heterogeneity was developed, where the effects of grain orientation and shape are quantitatively represented by the method of flow stress classification and Voronoi tessellation, respectively. This model provides an accurate and effective method to analyze the influence of individual grain heterogeneity on the deformation behavior of the micro-sized material.

On enhancing surface wear resistance via rotating grains during selective laser melting

Abstract Selective laser melting (SLM) enables fast and reliable fabrication of metallic parts. Yet post-processing techniques are still required to achieve desirable surface properties, such as wear resistance, surface quality, before the components are ready for deployment in the field. Given the complexities associated with post-processing, alternative approaches are needed. To this end, tailoring process parameters during SLM could be an efficient way to increase wear resistance. However, the relationship between process parameters, microstructure, and wear mechanism must be clarified first. In this study, three scanning strategies are applied to tailor the microstructure of SLM fabricated 316 L stainless steel samples. They are: without remelting (zigzag), remelting with a 0° (zigzag-R0), and 90° (zigzag-R90) rotation and different hatch spacings. The effects of grain orientation on wear resistance are studied by performing scratch tests. It is shown that remelting with small hatch spacings results in the transition of crystallographic texture from the single fiber texture to cubic textures, causing the remelted samples to have high wear resistance through aligning the grains orientations to resist slip. The intensity of textures tends to increase with decreasing the hatch spacings. The maximum enhancement of wear resistance is found in the zigzag-R90 samples using a hatch spacing of 10 μm, leading to 90.8 % and 96.7 % reductions in scratch depth and wear rate, respectively. Such a method can be used in increasing surface wear resistance of SLM fabricated components.

Modeling the two-way shape memory and elastocaloric effects of bamboo-grained oligocrystalline shape memory alloy microwire

Recent experimental studies reported that the bamboo-grained oligocrystalline shape memory alloy (SMA) microwire showed excellent two-way shape memory effect (TWSME) and elastocaloric effect (eCE) due to the reduced constraints from grain boundary. In this paper, a theoretical model is established to predict the TWSME and eCE of such a kind of SMAs. At single crystal scale, an anisotropic thermo-mechanically coupled constitutive model is proposed to describe the thermo-elastic martensitic transformation based on the crystal plasticity theory. The driving force of martensite transformation, the internal heat release/absorption, and the evolutions of internal variables and temperature are deduced within the framework of irreversible thermodynamics. To calculate the temperature, stress and strain fields in the bamboo-grained oligocrystalline SMA microwire and obtain the overall thermo-mechanical response of the microwire, the proposed constitutive model is implemented into the finite element program ABAQUS/Explicit by writing a user-defined material subroutine. Meanwhile, to reduce the computational cost faced in the fully coupled thermo-mechanical analysis by using the finite element method, a scale transition rule from single crystal scale to macroscopic oligocrystalline one is constructed based on a new proposed sub-region integral method by considering the special geometric characteristics of the microwire. The capability of proposed model to describe the TWSME and eCE of bamboo-grained oligocrystalline SMA microwire is validated by comparing the predictions with the experimental data. In addition, the effect of grain orientation is discussed. The proposed model can provide a theoretical guidance for the optimal design of grain microstructures to obtain the SMAs with excellent TWSME and eCE.

Texture modification and mechanical properties of AZ31 magnesium alloy sheet subjected to equal channel angular bending

Analysis of the recently proposed equal channel angular bending (ECAB) process is provided on thin hot-rolled AZ31 magnesium alloy sheets. In particular, effects of deformation temperature and strain path on the texture evolution and mechanical properties are systematically investigated under single pass ECAB at various temperatures and multi-pass ECAB process that involves changes in strain paths. It is found that simultaneous activation of multiple twinning types is successfully introduced during ECAB, which results in obvious tilted component of basal texture. Attributed to the domination of extension twins, weaker basal textures are detected after both single pass ECAB at 150 °C and three cross passes ECAB at 200 °C. After annealing, the basal texture is further weakened via twin-related recrystallization and the annealed microstructure is featured with mixture of basal and non-basal orientated grains. Additionally, the effect of grain orientation on the mode of plastic deformation and the roles of grain orientation and grain boundary on the local strain accommodation are coherently studied. This study reveals that over 60 % increase of uniform elongation with marginal reduction of tensile strength less than 5 % can be achieved for single pass ECAB at 150 °C and three cross passes ECAB at 200 °C, which is the result of larger fraction of grains favored with extension twinning and better local strain accommodation.

Control of grain orientation and its impact on carrier mobility in reactively sputtered Cu2O thin films

Grain orientation can be particularly important in devices such as thin film transistors (TFTs) where grain boundaries present a barrier to lateral carrier transport. This paper demonstrates that thin films of nanocrystalline cuprous oxide (Cu2O) can be grown with control of the grain orientation in the direction of either [111] or [100] perpendicular to the substrate surface using a high target utilization sputtering system. This allows a systematic study of the effect of grain orientation on the carrier mobility in Cu2O films. It is shown that the carrier mobility in as-deposited films is similar for both grain orientations while [100]-oriented thin films exhibit a higher carrier mobility for lateral conduction than films with a [111] orientation after annealing, which is discussed from the viewpoint of the Urbach energy, crystallinity and surface morphology. This experimental finding suggests that Cu2O thin films with a [100] surface grain orientation are favorable for device applications such as p-type TFTs where a high in-plane carrier mobility is desired.

Finite element analysis of effect of grain orientation on the thermal conduction of h-BN ceramics

Study of thermal conduction process of ceramics by experimental and theoretical model analysis methods is complicated and non-intuitive. In this work, to analyze the influence mechanism of h-BN grain orientation on the thermal conduction of h-BN ceramics, new mesoscale finite element models considering the anisotropy in the thermal conductivity of h-BN grain were established based on random sequential adsorption method and periodic boundary condition. And the accuracy of the finite element models was verified by theoretical model and experimental results. The heat flux vector and temperature distributions intuitively show that the orientation of h-BN grains will significantly affect the thermal conduction process of the ceramics by affecting the heat flow path. The heat flow will propagate mainly along the “thermal conducting pathways” formed by the h-BN grains when the h-BN layer direction shows small angle with the external temperature difference direction, otherwise, h-BN grains will act as barriers to the heat conduction.

Effect of Grain Orientation on the Compressive Response of Highly Oriented MAX Phase Ti <sub>3</sub>SiC <sub>2</sub>

Effect of Grain Orientation on the Compressive Response of Highly Oriented MAX Phase Ti <sub>3</sub>SiC <sub>2</sub>

Formation Mechanism of Strip Defects in Anodizing AA5252 Aluminium Alloy Sheets

Processed by sulfuric acid anodizing, several unexpected strip defects exhibited on the anodizing film of AA5252 aluminium alloy sheets. Their formation mechanism was studied in detail. The normal zone and strip zone were compared, with respect to surface brightness, porosity of anodizing film, and microstructures of the corresponding aluminium substrate tested by spectroscopic colorimeter and SEM, and SEM-EBSD. Results showed that the brightness of strip zone was lower than that of normal zone. Additionally, compared with normal zone, the porosity of anodizing film was higher, and cubic grains fewer, which located in the corresponding surface layer of aluminium substrate in strip zone. In order to further clarify the effect of grain orientation on the brightness of anodizing film, single crystal aluminium sheet with (100), (110) or (111) orientation was anodized. Results showed that the anodized (100) oriented specimen, i.e., cubic grain was brighter, whose anodizing film had lower porosity, compared with (110) and (111) oriented ones. Therefore, the formation mechanism of strip defects was proposed as uneven distribution of cubic grains. The zones with fewer cubic orientated grains were darker, and were visible as strip defects after anodizing.

Micromechanical modeling of polycrystalline high manganese austenitic steel subjected to abrasive contact

This study focuses on microstructural and micromechanical modeling of abrasive sliding contacts of wear-resistant Hadfield steel. 3D finite element representation of the microstructure was employed with a crystal plasticity model including dislocation slip, deformation twinning, and their interactions. The results showed that deformation twinning interacting with dislocations had a key role in the surface hardening of the material, and it was also important for the early hardening process of the sub-surface grains beyond the heavily distorted surface grains. The effects of grain orientation and microstructural features were discussed and analyzed according to the micromechanical model to give a perspective to the anisotropy of the material and the feasibility of using micromechanics in virtual material design.

Effects of grain orientations and pre-existing defects on mechanical properties and deformation mechanisms of polycrystalline yttria-stabilized tetragonal zirconia

Experimental and computational studies have revealed that the mechanical properties and phase transformation behavior of single crystalline zirconia-based shape memory ceramics are significantly dependent on their crystal orientation with respect to the loading direction. However, such effects have not been studied in polycrystalline zirconia-based ceramics. In this work, we utilize molecular dynamics simulations to investigate the effects of grain orientations and manufacturing-produced sub-surface defects on the mechanical properties and deformation mechanisms of polycrystalline yttria-stabilized tetragonal zirconia (YSTZ). Polycrystalline models are generated according to the dominant plastic deformation mechanisms of each individual grain utilizing the single crystal deformation data, and the polycrystalline models mainly comprise phase transformation-dominated grains (P-grain), combined phase transformation- and dislocation-dominated grains (P-D-grain), and dislocation-dominated grains (D-grain). Grain orientations are noted to play a significant role in determining the strength of polycrystalline YSTZ. Martensitic phase transformation is the dominant deformation mechanism in P-grain dominated polycrystals, while in P-D-grain and D-grain dominated cases amorphization and sliding of grain boundaries become the main deformation mechanisms, which can significantly degradate the shape memory behavior. The strength values of polycrystals are considerably decreased due to the addition of a void. Dislocations and phase transformation are observed to nucleate around the void, which accordingly alter the deformation mechanisms observed in defect-free polycrystals.

Nanoscale investigation of deformation characteristics in a polycrystalline silicon carbide

In this paper, we study the mechanical behaviour of silicon carbide at the nanoscale, with a focus on the effects of grain orientation and high-dose irradiation. Grain orientation effect was studied through nanoindentation with the aid of scanning electron microscopy (SEM) and EBSD (electron backscatter diffraction) analyses. Mechanical properties such as hardness, elastic modulus and fracture toughness were assessed for different grain orientations. Increased plasticity and fracture toughness were observed during indentations on crystallographic planes which favour dislocation movement. In addition, for SiC subjected to irradiation, increases in hardness and embrittlement were observed in nanoindentations at lower imposed loads, whereas a decrease in hardness and an increase in toughness were obtained in nanoindentations at higher loads. Transmission electron microscopy (TEM) analyses revealed that the mechanical response observed at a shallow indentation depth was due to Ga ion implantation, which hardened and embrittled the surface layer of the material. With an increased indentation depth, irradiation-induced amorphization led to a decrease in hardness and an increase in fracture toughness of the material.

Experimental and crystal plasticity study on deformation bands in single crystal and multi-crystal pure aluminium

Deformation bands (DBs) formed in metals even in single crystals are known to give rise to the microstructural heterogeneities, thus contributing to some long-standing microstructure formation problems, such as the occurrence of recrystallization on the basis of deformed microstructure. Previous experimental transmission electron microscope (TEM) work has identified two types of DBs in the microscopic scale, i.e. kink bands and bands of secondary slips, showing the importance of understanding the slip activation for DBs. To extend the theory in mesoscale, single crystal and multi-crystal pure aluminium, as well as their corresponding crystal plasticity finite element (CPFE) models, are used in this paper to explore the effect of grain orientation, strain level and neighbouring grains on the formation of DBs. It is demonstrated that slip band intersection of primary and secondary slips is predicted to constrain the lattice sliding but facilitate the lattice rotation for the formation of DBs regarding the wall of DBs and its orientation. It is found that the impact of the above factors on the formation of DBs is caused by the slip field of primary slips. A sufficient amount of primary slips activated inside grains would be the key to the formation of distinct DBs with high area fraction and aspect ratio.

Electromigration in Bi-crystal pure Sn solder joints: Elucidating the role of grain orientation

Intermetallic compound (IMC) and void growth are electromigration (EM) damage mechanisms that are controlled by the anisotropic diffusion of Cu in β-tetragonal Sn solder joints. Single crystal fast diffusion, slow diffusion, and bicrystal solder joints were fabricated and tested under thermal aging and EM conditions to investigate the effect of grain orientation on microstructure evolution including IMC growth, void growth and grain structure. Sample and testing geometry ensured there were no effects from current crowding or joule heating so that crystallographic effects could be isolated. Microstructure characterization by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and X-ray microtomography revealed interface-nucleated and bulk-nucleated IMC growth, particle stimulated nucleation (PSN) of recrystallized grains, and two unique voiding behaviors, void faceting and void burrowing. The relationship between these features and β-Sn grain orientation and implications for EM damage mitigation are discussed.

Varestraint Testing of Selective Laser Additive Manufactured Alloy 718—Influence of Grain Orientation

The effect of grain orientation on hot cracking susceptibility of selective laser additive manufactured Alloy 718 was investigated by Varestraint testing. Electron backscattered diffraction showed that cracks in heat affected zone (HAZ) of the welded samples occurred in high angle grain boundaries. The extent of HAZ cracking was smaller in samples tested parallel to the elongated grain orientation and larger in samples transverse to the elongated grain orientation. However, for solidification cracking in the weld metal, no significant difference with respect to grain orientation in the base metal was found.

Modeling Effect of Grain Orientation on Degradation in Tin-Based Solder—Part II: Electromigration Experiments

In a series of articles, we consider the effects of the microstructure and the associated anisotropy of Sn grains on electromigration in lead-free solder bumps. In this article, we carried out experiments to characterize microstructures of tin-based solder bumps and to investigate their effects on electromigration-induced failure. Accelerated electromigration tests and electron backscatter diffraction (EBSD) tests are performed on tin-based solder bumps in wafer-level chip-scale packages (WLCSPs). EBSD analysis, together with the results of time to failure from accelerated electromigration tests, provides valuable information on the effects of the microstructure on electromigration-induced failure that can be used for predictive modeling. For Ni-based metallization, we find that tin self-diffusion is the dominant degradation mechanism and a strong effect of the grain orientation in the solder on the time to failure.

Effect of Grain Orientation on Indentation Induced Creep in Pure Zinc

Abstract The study presents the anisotropy in the indentation creep response of zinc. Indentation creep tests were conducted on grains with three different orientations, namely, 〈0001〉, ⟨112¯0⟩, and ⟨101¯0⟩. Indentation creep along the 〈c〉 axis showed a pronounced creep exhibiting a 25% higher creep displacement as compared with indentation perpendicular to the 〈c〉 axis. However, the recovery observed was the highest for basal-oriented grains wherein a recovery of 50% to its indented depth was observed, whereas for ⟨112¯0⟩ the recovery observed was 30%. The stress exponent, n, was obtained by employing two different approaches for each of the orientations and a difference in the stress exponent value was also observed, highlighting the anisotropic creep response. Basal and non-basal oriented grains showed a lower (n ≅ 1.6) and higher stress exponent (n ≅ 5), respectively, highlighting the different operable creep mechanism. Surface topography using atomic force microscope (AFM) revealed twinning and sink-in for ⟨112¯0⟩ and ⟨101¯0⟩, whereas uniform pile up was observed for basal grain.

Finite element analyses of single particle crushing tests incorporating computed tomography imaging and damage mechanics

Fracture of individual grains within a granular assembly affect the strength and deformation behavior of granular materials under large stress states. Interparticle forces, leading to contact stresses and ultimately fracture initiation, are influenced by particle morphology. A numerical method that incorporates both particle fracture and morphology can provide a more accurate model of a granular material’s macro-scale response. This research investigates an approach to modeling fracture initiation and propagation within individual grains, utilizing high resolution X-ray computed tomography (CT) imaging to consider grain morphology and an explicit finite element code optimized for high performance computing which incorporates damage mechanics. Using precisely measured force-displacement curves from single particle crushing tests of manufactured quartz spheres, the method is validated, and the effects of fracture properties on grain fragmentation are determined. This approach is then used to simulate single particle crushing of Ottawa sand, with grain morphology incorporated through discretized CT images. The effect of grain orientation on the force and applied displacement at catastrophic splitting is also explored. The proposed discrete particle based finite element framework can be applied to modeling granular assemblies, considering the effect of individual particle shape and fracture on the assembly’s deformation response through well calibrated numerical simulations.

Effect of grain orientation and local strains on void growth and coalescence in titanium

Ductile fracture has been extensively studied in metals with weak mechanical anisotropy such as copper and aluminum. The fracture of more anisotropic metals, especially those with a hexagonal crystal structure (e.g. titanium), remains far less understood. This paper investigates the ductile fracture process in commercially pure titanium (CP-Ti) with particular emphasis on the influence of grain orientation and local state of strain on void growth. An experimental approach was developed to directly relate the growth of a void in three dimensions to its underlying grain orientation. Grain orientation was obtained by electron back scattered diffraction on void-containing CP-Ti sheets prior to their diffusion bonding. Changes in void dimensions were measured during in-situ straining within an x-ray tomography system. The strong influence of the embedded grain orientation and that of its neighbors on void growth rate and coalescence has been experimentally quantified. Finite element crystal plasticity simulations that take into account both grain orientation and the local strain state were found to predict the experimental void growth. Grains where basal slip dominates show the largest void growth rates because they are closer to a plane strain condition that favors void growth and coalescence.