Random Texture Research Articles

Simulated effects of sample size and grain neighborhood on the modeling of extreme value fatigue response

Assessing the size of representative volume elements (RVEs) for fatigue-related applications is challenging. A RVE relevant to random microstructure requires a volume of material that is sufficiently large to capture the grain/phase heterogeneity that captures all statistical moments of the distribution of the driving force for fatigue crack formation at “hot spot” grains. Consequently, the large size of a microstructure RVE required to study fatigue phenomena is largely computationally intractable and difficult to explore. A more realistic objective in this work is to systematically study, as a function of the size of a statistical sample of microstructure, trends towards convergence of the simulated distribution of driving force for fatigue crack formation. The present work accordingly leverages the recently developed open-source PRISMS-Fatigue framework [Yaghoobi et al., npj Comput. Mater., 7, 38 (2021)] to examine the trends in convergence of extreme value distributions (EVD) of Fatigue Indicator Parameters (FIPs) in progressively larger polycrystalline microstructure realizations of FCC Al alloy 7075-T6 using crystal plasticity finite element method simulations. The results are compared to the traditional method in which ensembles of statistical volume elements (SVEs) are simulated to build up statistics intended to approximate those associated with a larger volume of material. The convergence of EVDs with increase of size of a SVE of microstructure is closely related to the extent of grain nearest neighbor (NN) interactions. Accordingly, the sensitivity of the local micromechanical response at hot spot grains is quantitatively investigated by systematically varying the orientations of NN grains. Results indicate that SVEs with cubic crystallographic texture tend towards convergence of the EVD of FIPs with tens of thousands of grains while the random and rolled textures require larger volumes. Simple relationships based on microstructure parameters (e.g., Schmid Factor, grain size, NN misorientation) do not completely correlate to fatigue hot spot grains. Finally, the sensitivity of the extreme value fatigue response at hot spot grains extends to the 3rd NN when a single neighborhood grain orientation is altered.

Hot deformation of cast AZ31 and AZ80 magnesium alloys – Influence of Al content on microstructure and texture development

The present research studies and compares the hot deformation behaviour of the AZ31 and AZ80 magnesium alloys. Uniaxial compression tests using a Gleeble® 3500 thermal-mechanical simulation testing system were conducted at 400 °C and constant true strain rates in the range of 0.001 s−1 to 0.1 s−1. Samples were deformed to various levels of strain to assess the progression of dynamic recrystallization. Detailed microstructure and texture characterization were performed using optical microscopy, XRD macrotexture measurements, and electron backscatter diffraction (EBSD) microtexture measurements. Both the starting materials showed coarse dendritic microstructures and random texture. Both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred in both the alloys during deformation, although the AZ31 alloy showed a higher tendency towards CDRX compared to the AZ80 alloy, while reverse was true for DDRX. The AZ80 alloy showed initiation of DDRX at lower deformation strain levels, had coarser DDRX grain size and a higher DDRX% compared to the AZ31 alloy. These features resulted in the development of a homogeneous fine-grained microstructure in the AZ80 alloy for deformation to an equivalent strain of 1.0, while the microstructure of the AZ31 alloy sample became bimodal. The choice of the alloy also affected the texture development during the deformation, with the AZ31 alloy showing DDRX texture randomization, while the AZ80 alloy showing deformation texture preservation by the DDRXed grains. The study highlights the substantial effect the Al content in the α-Mg solid solution has on the microstructure and texture development during hot deformation of the AZ alloys.

STUDIES ON EFFECT OF Nb SEGREGATION AND FORMATION OF SECONDARY PHASES OF Ni–Cr–Mo CLAD ON 316L SUBSTRATE BY COLD METAL ARC TRANSFER PROCESS

In current scenario, there is an ever increasing demand for alloys with increased wear resistance under severe working conditions. Ni–Cr–Mo alloy is suitable for surface modification and repairing applications. The Ni–Cr–Mo alloy clad region had cellular-dendrite with Laves phase and complex nitrides/carbides (MX) distributed in the interdendritic regions. Microindentation hardness variation was observed on the interdendritic regions as compared to that of dendritic regions. A new solidification path is confirmed through EDS analysis. Ni, Fe and Cr segregate to the dendritic area, whereas Nb and Mo segregate to the interdendritic region. Ni–Cr–Mo microstructure evolution was studied by optical microscope (OM), scanning electron microscope (SEM) and atomic force microscope (AFM). The Laves and G phases were identified in the Ni–Cr–Mo clad region, confirming superior resistance to corrosion. Pin-on-disc abrasion wear technique confirmed that cladding with low base metal dilution possesses better wear resistance. The mechanism of wear depends on load applied and sliding time. EBSD analysis revealed random texture and grains have same crystallographic orientation across the interface boundary line due to epitaxial growth.

An exceptional ductility of AZ31 magnesium alloy sheet achieved by consecutive multi-pass cooperative lowered-temperature rolling

In this study, a novel technique of consecutive multi-pass cooperative lowered-temperature rolling (CMCLR) was proposed for the first time, with the purpose of preparing high performance wrought magnesium alloys. Based on this, a highly ductile magnesium alloy sheet could be effectively produced from ingot. The corresponding microstructure could directly evolve from coarse dendrites to equiaxed grains with an average size of ∼5 μm, which was attributed to the intense dynamic recrystallization (DRX) during isothermal deformation. The equivalent strain gradually decreased from the surface to the interior and edge of the rolled sheet due to the anisotropic plastic deformation. Instead, the temperature of the core of the sheet was slightly higher than that of the surface due to the deformation heat effect. The basal texture in the RD-TD plane generally weakened in the form of the splitting of basal texture toward the RD and the broadening of basal plane away from the pole center due to texture randomization dominated by DRXed grains. The exceptional ductility of more than 28.7% together with acceptable ultimate tensile strength of not less than 267 MPa was ascribed to the progressive work hardening as a result of seamless switching of multiple deformation modes, i.e., basal dislocation-slip-mediated deformation was preferentially operated and then was substituted by twinning-controlled deformation and non-basal dislocation-slip-dominated deformation. The selection of {101‾2} twin variants agreed well with geometrical compatibility factor (m’) criterion instead of Schmid’s law. The activated twin variants nearly engulfed the whole parent grains for the sake of preserving compatible deformation continuity at ambient temperature, giving rise to the formation of TD-split texture. Comparatively, the {101‾2} twinning could randomize the basal texture via reorienting grain orientations which in turn facilitated the reactivation of dislocation slip systems in the case of high temperature deformation.

Slip band formation in low and high solute aluminum: a combined experimental and modeling study

Direct ex situ observations related slip band formation with deformed microstructures in commercial AA1050 and AA2219. The samples from both grades had similar grain sizes (∼250 μm) and nearly random crystallographic textures. However, AA2219 contained significantly more solute. Slip bands, on the internal long transverse (LT) plane in split channel die specimens, were characterized by primary spacings (λ) of 2–9 μm, heights (Z) of 160–360 nm and secondary shear strains (). Higher deformation temperatures for both grades increased λ, decreased, Z and . At all deformation temperatures, AA1050 had smaller λ and higher Z, while AA2219 showed higher . In-grain misorientations, but not residual strains, were larger in grains with finer λ in AA1050, but less so in AA2219. Discrete dislocation dynamics (DDD) simulations reported realistic slip bands with slip localizations. The simulations, initiated with static obstacles and sources, led to dislocation interactions and junction formation. The probability of junction stabilization (p) determined the ratio of dynamic sources to obstacles. Slip band formation appeared to be an outcome of the release of piled up dislocations leading to dislocation avalanches. Slip localization increased weakly with finer active slip plane spacing (λ *), giving higher dynamic obstacle strengths and densities, but strongly with smaller p. In particular, the DDD simulations captured experimental patterns of higher slip localizations and dislocation densities in low solute aluminum with finer λ *.

Antireflective Huygens’ Metasurface with Correlated Disorder Made from High-Index Disks Implemented into Silicon Heterojunction Solar Cells

A large variety of different strategies has been proposed as alternatives to random textures to improve light coupling into solar cells. While the understanding of dedicated nanophotonic systems deepens continuously, only a few of the proposed designs are industrially accepted due to a lack of scalability. In this Article, a tailored disordered arrangement of high-index dielectric submicron-sized titanium dioxide (TiO2) disks is experimentally exploited as an antireflective Huygens’ metasurface for standard heterojunction silicon solar cells. The disordered array is fabricated using a scalable bottom-up technique based on colloidal self-assembly that is applicable virtually irrespective of material or surface morphology of the device. We observe a broadband reduction of reflectance resulting in a relative improvement of a short-circuit current by 5.1% compared to a reference cell with an optimized flat antireflective indium tin oxide (ITO) layer. A theoretical model based on Born’s first approximation is proposed that links the current increase in the arrangement of disks expressed in terms of the structure factor S(q) of the disk array. Additionally, we discuss the optical performance of the metasurface within the framework of helicity preservation, which can be achieved at specific wavelengths for an isolated disk for illumination along the symmetry axis by tuning its dimensions. By comparison to a simulated periodic metasurface, we show that this framework is applicable in the case of the structure factor approaching zero and the disks’ arrangement becoming stealthy hyperuniform.

Thin-gauge non-oriented silicon steel with balanced magnetic and mechanical properties processed by strip casting

Thin-gauge non-oriented silicon steel with high strength was successfully processed using strip casting. Texture evolution and strengthening mechanism via nanoscale Cu-rich precipitates were studied to fundamentally understand the balanced combination of magnetic properties and mechanical properties. Coarse equiaxed grains with average size of ∼190 μm and relatively random texture were formed in the as-cast strip, which contributed to the inhomogeneous deformation, resulting in high density of shear bands. Exact Cube was retained from the initial Cube texture and new Goss was formed during the heavy rolling process in the 0.20 mm cold rolled sheet, which promoted relatively strong Cube and Goss texture after recrystallization annealing. The 0.20 mm annealed sheet exhibited high magnetic induction of 1.709 T, which corresponds to the high texture factor of 0.5. The total iron losses were significantly reduced with decrease in thickness, and the P1.5/50, P1.0/400, and P1.0/1000 in 0.20 mm sheet were as low as 2.63, 15.17 and 55.63 W/kg, respectively, which showed a good match between magnetic induction and iron loss. During the aging process, both the magnetic induction and total iron loss exhibited relatively good stability. With increase in aging time, the yield strength first rapidly increased and then slightly decreased. In 0.20 mm sheet, peak yield strength of ∼630 MPa was obtained on aging at 550 °C for 90–120 min. The key mechanism of precipitation strengthening was attributed to the difference in modulus and coherency strain associated with high density of nanoscale precipitates of ∼5 nm. The study revealed that the nanoscale Cu-rich precipitates can be adopted as effective approach to increase the yield strength over ∼100 MPa without deteriorating iron loss in thin-gauge non-oriented silicon steel by strip casting, which guaranteed the balance of magnetic properties and mechanical properties to meet the requirements of high-speed motor.

A significant toughness enhancement, and microstructural evolution of an electric resistance welded (ERW) microalloyed steel

In this investigation, microstructural evolution and mechanical properties of an X52 microalloyed steel processed by a full scale industrial electric resistance welding (ERW) equipment was studied. The need for adequate level of mechanical properties, in particular toughness, in the welded pipes is discussed due to its industrial prominence. Optical microscopy (OM) and scanning electron microscopy (SEM) were used for microstructural evolution and fractography analysis. Results showed that employing a special annealing treatment of the welded pipe could enhance the mechanical properties and alleviate low toughness problem. Results also showed a significant variation in the microstructure of the pipe as a result of welding and its subsequent heat treatment processes. Electron backscatter diffraction (EBSD) results for the initial plate and the ERW processed cases showed a significant grain size refinement for the case of as weld and after the two-stage heat treatment. A fully random texture component was observed in {111} pole figure of the initial plate. A textured structure, with the components of Copper, Brass, S and Cube, was seen in the as weld condition. These texture characteristics remained in the system, though with lower intensity, after the normalizing stage heat treatment. Hence for its unpredictable toughness behavior. A completely weakened undesirable texture components was detected after the second stage of heat treatment together with smaller amount of second phase particles and smaller grain sizes. Finally, it was concluded that a proper mechanical properties combinations, particularly toughness value, could be attained as a result of this microstructural evolution.

Property Improvement of Additively Manufactured Ti64 by Heat Treatment Characterized by In Situ High Temperature EBSD and Neutron Diffraction

Among various off-equilibrium microstructures of additively manufactured Ti-6Al-4V alloy, electron beam powder bed fusion, in which three dimensional metallic objects are fabricated by melting the ingredient powder materials layer by layer on a pre-heated bed, results in a specimen that is nearly free of the preferred orientation of the α-Ti phase as well as a low beta phase fraction of ∼1 wt%. However, when further heat treatment of up to 1050 ∘C was applied to the material in our previous study, a strong texture aligning the hexagonal basal plane of α phase with the build direction and about 6% β phase appeared at room temperature. In this study, to understand the mechanism of this heat treatment, the grain level microstructure of the additively manufactured Ti-6Al-4V was investigated using in situ high temperature EBSD up to 1000 ∘C, which allows the tracking of individual grains during a heat cycle. As a result, we found a random texture originating from the fine grains in the initial material and observed a significant suppression of α phase nucleation in the slow cooling after heating to 950 ∘C within the α and β dual phase regime but close to the the β-transus temperature at ∼980 ∘C, which led to a coarse microstructure. Furthermore, the texture resulting from phase transformation of the additively manufactured Ti-6Al-4V assuming nucleation at the grain boundaries was modeled, using the double Burgers orientation relationship for the first time. The model successfully reproduced the measured texture, suggesting that the texture enhancement of the α phase by the additional heat treatment derives also from the variant selection during the phase transformation and nucleation on grain boundaries.

Improved strength in wrought Mg–Y–Ni alloys by adjusting the block-shaped LPSO phase and plate-shaped γ′ phase

The microstructure and mechanical properties of two Mg–Y–Ni alloys with different volume fraction of block-shaped LPSO phase and different number densities of plate-shaped γ′ phase were investigated. The volume fraction of block-shaped LPSO phase increases with the content of Y and Ni in the Mg–Y–Ni alloys with Y/Ni atomic ratio of 1. The plate-shaped γ′ phase is formed in the matrix of the as-cast alloys and grows across the matrix during the preheating before extrusion, and its number density increases with increasing content of Y and Ni. After extrusion, the block-shaped LPSO phase is distributed along extrusion direction, and the plate-shaped γ′ phase can be observed in both non-dynamic recrystallized (non-DRXed) grains with strong basal texture and dynamic recrystallized (DRXed) grains with random texture. The increased volume fraction of LPSO phase improves the tensile yield strength of the as-extruded Mg–Y–Ni alloys, accompanied by the decrease in ductility. In addition to the obvious strengthening from the LPSO phase, the plate-shaped γ′ phase is also an effective strengthening phase which can hinder the movement of the slip systems in non-DRXed and DRXed grains of the Mg–Y–Ni alloys. The Mg94Y3Ni3 (at%) alloy containing the highest volume fraction of block-shaped LPSO phase and the highest number density of plate-shaped γ′ phase exhibits the superior tensile yield strength of 502 MPa after extrusion.

Columnar-to-equiaxed grain transition in powder bed fusion via mimicking casting solidification and promoting in situ recrystallization

Columnar grain structure typically formed along the build direction in the electron beam-powder bed fusion (EB-PBF) technique leads to anisotropic physical and mechanical properties. In this study, casting solidification condition was mimicked, and in situ recrystallization was promoted in EB-PBF to facilitate columnar-to-equiaxed grain structure transition in Alloy 718. This is achieved via a unique linear melting strategy coupled with a specific selection of process parameters in EB-PBF. It was found that site-specific melting using line order number (LON) function affected the cooling rate and temperature gradient, which controlled grain morphology and texture. A high LON resulted in a large equiaxed grain zone with a random texture, whereas a fixed LON with a high areal energy density led to a strong texture. The main driving force in the formation of cracks and shrinkage defects during the transition was investigated. A high LON at a fixed areal energy density reduced the average total shrinkage defects and crack length. The hardness was decreased through the transition, which was linked to the reduction in the size of the γ″ precipitates.

Synchrotron Characterisation of Ultra-Fine Grain TiB2/Al-Cu Composite Fabricated by Laser Powder Bed Fusion

Isotropy in microstructure and mechanical properties remains a challenge for laser powder bed fusion (LPBF) processed materials due to the epitaxial growth and rapid cooling in LPBF. In this study, a high-strength TiB2/Al-Cu composite with random texture was successfully fabricated by laser powder bed fusion (LPBF) using pre-doped TiB2/Al-Cu composite powder. A series of advanced characterisation techniques, including synchrotron X-ray tomography, correlative focussed ion beam–scanning electron microscopy (FIB-SEM), scanning transmission electron microscopy (STEM), and synchrotron in situ X-ray diffraction, were applied to investigate the defects and microstructure of the as-fabricated TiB2/Al-Cu composite across multiple length scales. The study showed ultra-fine grains with an average grain size of about 0.86 μm, and a random texture was formed in the as-fabricated condition due to rapid solidification and the TiB2 particles promoting heterogeneous nucleation. The yield strength and total elongation of the as-fabricated composite were 317 MPa and 10%, respectively. The contributions of fine grains, solid solutions, dislocations, particles, and Guinier–Preston (GP) zones were calculated. Failure was found to be initiated from the largest lack-of-fusion pore, as revealed by in situ synchrotron tomography during tensile loading. In situ synchrotron diffraction was used to characterise the lattice strain evolution during tensile loading, providing important data for the development of crystal-plasticity models.

Evaluation of fracture toughness of VN hard coatings: Effect of preferred orientation

The objectives of this study were to evaluate the fracture toughness (Gc) of vanadium nitride (VN) hard coatings using internal energy-induced cracking (IEIC) method, and investigate the effect of preferred orientation on the fracture toughness. VN coatings were deposited on Si (100) substrates by unbalanced magnetron sputtering. Two different nitrogen flow rates were used to prepare coatings with different textures. The fracture toughness of the specimens were assessed using the IEIC method. The results showed that fracture toughness of the VN coatings was texture-dependent, and the Gc values for specimens with random texture and (200) texture were 11.2±0.7 and 19.2±1.2 J/m2, respectively, which were in between those of TiN and ZrN. The higher Gc for the VN coatings with (200) texture was consistent with the higher residual stress in the coatings. The fracture morphology and crack propagation path were examined using a focused ion beam and electron beam system. The fracture morphology of the coatings was similar regardless of random or (200) texture, where the crack path consisted of horizontal (R1) and zigzag (R2) regions. Since the VN coatings possessed a relatively uniform stress gradient, crack initiation may occur inside the coating ahead of the specimen edge due to the edge stress acting at local defects. Similar to the fracture behavior in ZrN coatings, the stress distribution due to free edge effect could move with the crack front and consequently drive the main crack to propagate stepwise.

Unraveling the effect of deformation-induced phase transformation on microstructure and micro-texture evolution of a multi-axially forged Mg-Gd-Y-Zn-Zr alloy containing the LPSO phase

The effect of blocky to lamellar phase transformation on the microstructure and micro-texture of a Magnesium-Rare earth alloy containing long-period stacking order (LPSO) phases were examined comprehensively at the isothermal temperature of 400 °C via multiaxial forging. A very fine-grained microstructure with an average grain size of 1 μm was achieved after applying three multi-axial forging (MAF) passes. Particle stimulated nucleation (PSN) along with continuous dynamic recrystallizations (CDRX) due to the blocky LPSO phases were realized to be the main reasons for the achievement of such fine microstructure. The deformation-induced blocky to lamellar phase transformation began at 1/3 pass and expanded through the whole microstructure after the third pass. Such phase transformation was found to be initiated by the fragmentation of blocky phases. As a result of PSN and CDRX mechanisms, two new rare earth (RE) texture components of <10-11> and <2-1-10> || Transverse Direction (TD) were formed at the second MAF pass that led to a highly randomized deformation texture. Nevertheless, the continuous breakdown of blocky phases and their subsequent phase transformation to lamellar LPSO suppressed PSN at the third deformation pass. Hence, the formed RE texture components were disappeared which in turn increased the texture intensity at this deformation pass.

Utilizing Iron as Reinforcement to Enhance Ambient Mechanical Response and Impression Creep Response of Magnesium

To realize light-weight materials with high strength and ductility, an effective route is to incorporate strong and stiff metallic elements in light-weight matrices. Based on this approach, in this work, magnesium–iron (Mg-Fe) composites were designed and characterized for their microstructure and mechanical properties. The Mg-Fe binary system has extremely low solubility of Fe in the Mg-rich region. Pure magnesium was incorporated with 5, 10, and 15 wt.% Fe particles to form Mg-Fe metal–metal composites by the disintegrated melt deposition technique, followed by hot extrusion. Results showed that the iron content influences (i) the distribution of Fe particles in the Mg matrix, (ii) grain refinement, and (iii) change in crystallographic orientation. Mechanical testing showed that amongst the composites, Mg-5Fe had the highest hardness, strength, and ductility due to (a) the uniform distribution of Fe particles in the Mg matrix, (b) grain refinement, (c) texture randomization, (d) Fe particles acting as effective reinforcement, and (e) absence of deleterious interfacial reactions. Under impression creep, the Mg-5Fe composite had a creep rate similar to those of commercial creep-resistant AE42 alloys and Mg ceramic composites at 473 K. Factors influencing the performance of Mg-5Fe and other Mg metal–metal composites having molybdenum, niobium, and titanium (elements with low solubility in Mg) are presented and discussed.

Mechanism of texture formation in submicron Cu thin films

We successfully fabricated the submicron Cu thin films with different texture components and thicknesses by magnetron sputtering method, and investigated the underlying mechanism of texture formation. The X-ray diffraction, electron backscatter diffraction and transmission electron microscopy were employed to elucidate the {111}, {011}, {001} and random texture components formation mechanism. In addition, the orientation factors were calculated to clarify the influencing mechanism of grain preferential growth in the yielding submicron Cu thin films. The film sputtered at 100 W has a preponderance growth of {111} oriented grains, which is explained by the minimum of surface energy theory. With sputtering power increased to 200 W, the formation of random texture could be attributed to the presence of extensive twinning. Increase the sputtering power to 300 W and simultaneously keep the thickness to 200 nm, then the texture transforms to {001} texture component. Further increased the thickness to 1000 nm, the fraction of {011} texture component reveals preponderantly, which is controlled by the differences of orientation factors during yield process. The qualitative coincidence between the experimental results and theoretical analysis indicated that the underlying mechanism of preferential growth in the submicron Cu thin films was related to the competition of different driving forces. From adjusting the major driving force, different texture components could successfully be manipulated in submicron Cu thin films.

Segregation engineering of grain boundaries of a metastable Fe-Mn-Co-Cr-Si high entropy alloy with laser-powder bed fusion additive manufacturing

Laser-powder bed fusion (L-PBF) additive manufacturing offers unprecedented microstructural fine-tuning capabilities. Naturally, benefitting from such capability requires alloys that are amenable to microstructural heterogeneity and hierarchy (MHH) and that exhibit a low hot-cracking susceptibility (HCS). However, columnar growth, which is characterized by capillary effects and poor strain accommodation capabilities, is prevalent in L-PBF and increases the HCS of the processed alloys. Further, while solute segregation is prominent in cellular and dendritic growth modes during L-PBF, the effects of solute segregation on the alloy HCS and L-PBF processing window remain widely unexplored. Here, we demonstrate that solute segregation affects columnar growth, grain coalescence behavior during solidification, MHH and mechanical properties of a metastable Fe40Mn20Co20Cr15Si5 (at.%) high entropy alloy (CS-HEA) doped with 0.5 wt.% B4C (termed CS-BC). A theoretical framework is proposed, which reveals that a boundary-strengthening segregant may reduce the alloy HCS during L-PBF. In as-built CS-BC, boron, a boundary strengthener, segregated to the solidification cell boundaries, whereas carbon remained in the solid solution. The as-built CS-BC exhibited suppressed columnar growth, more random texture, smaller cell size and higher strength as compared to the as-built CS-HEA. Further, a wide crack-free L-PBF processing window of CS-BC allowed fine-tuning of its MHH and thus the mechanical properties. Upon annealing, as carbon-containing precipitates formed, CS-BC exhibited a metastable microstructure and transformation induced plasticity effect, which led to high synergistic strength-ductility. These findings will foster design of alloys that facilitate application-specific manufacture with L-PBF and thus, an extended outreach of L-PBF for structural applications.

The temperature effect on the plastic deformation of the Mg88Zn7Y5 alloy with LPSO phase studied by in-situ synchrotron radiation diffraction

The temperature dependence of the compressive deformation behavior of the Mg88Zn7Y5 alloy with a high volume fraction (~85%) of the long-period stacking-ordered (LPSO) phase was studied by in-situ synchrotron radiation diffraction. The as-extruded microstructure exhibits a fully recrystallized α-Mg phase with a nearly random texture. The LPSO phase, identified as the 18R polytype, is represented by wavy lamellae elongated along the extrusion direction and has an intensive basal texture. The alloy compressed along the extrusion direction at room temperature shows a superior yield strength of 480 MPa. With increasing deformation temperature, the yield strength is reduced by 15% at 200 °C and by 46% at 300 °C, respectively. At all tested temperatures, the basal slip is activated in the α-Mg matrix far below the yield strength. The macroscopic yielding of the alloy is controlled by the activation of deformation kinking in the LPSO phase. The synchrotron radiation diffraction data indicate the stress localization at kinks with respect to the grains having the same orientation.

Large-area surface wettability patterning of metal alloys via a maskless laser-assisted functionalization method

An innovative laser-assisted functionalization (LAF) method is presented in this work to fabricate a superhydrophobic-superhydrophilic patterned surface on a large-area metal alloy with a high process throughput. The LAF method comprises four steps, including two laser processing steps and two surface chemistry modification steps. Two strategies are demonstrated to fabricate extreme wettability patterns on aluminum alloy without using protective masking. Strategy I fabricates contrasting topography and chemistry where superhydrophobic regions are nanostructured with fluorocarbon chemistry, and superhydrophilic regions contain microchannels with nitrile chemistry. Conversely, strategy II fabricates similar microchannel topography for both wettability regions with contrasting chemistry. Surface topography patterning, from low-roughness, isotropic, random nanostructured texture to highly structured texture, is achieved by adjusting the laser parameters during LAF. LAF constitutes the first known laser-based surface engineering method that decouples extreme wettability from surface topography. In addition, anti-reflection surface property, ranging from moderately reduced reflectivity of about 50% to ultralow reflectivity of less than 10%, is achieved using this process. The processing mechanism, surface chemistry, and surface topography are analyzed to demonstrate the simplicity, robustness, and feasibility of the process.

Study on Microstructure and Mechanical Property in Mg-Gd-Y Alloy by Secondary Extrusion Process

Extruded Mg-Gd-Y alloy tubes were obtained by using cast ingot and extruded bar billets. Microstructure and mechanical properties were also studied with two different cooling methods: air cooling and water cooling. The result shows that by using an extruded bar as billet extruded tubes achieves higher elongation comparing to using cast ingots due to favored texture for the activation of basal slip. Using the water-cooling method, extruded tubes achieve a higher yield strength compared to the air cooling method due to their fine grain size. Using cast ingot billets and the water-cooling method, the elongation is only 6% due to large unrecrystallized grains caused by inhomogeneous deformation and unfavored texture for the activation of basal slip. Using the extruded bar billet and the water-cooling method, the tube has uniformed small grains and much more randomized texture caused by the inhibition of preferred grain growth process. The highest texture intensity is only 1.852 in this kind of tube. Both high yield strength (195.3 MPa) and high elongation (23.9%) are achieved in this tube.