Multilayer Microstructure Research Articles

Electrospun Sulfonated Poly(ether ether ketone) and Chitosan/Poly(vinyl alcohol) Bifunctional Nanofibers to Accelerate Proton Conduction at Subzero Temperature.

Multilayered microstructures can accelerate the proton conduction process in proton exchange membranes (PEMs). Herein, we design and construct PEMs with microstructures based on bifunctional nanofibers and sulfonated poly(ether ether ketone) (SPEEK) nanofibers. Specifically, the bifunctional nanofibers composed of poly(vinyl alcohol) and chitosan are prepared and then combined with the electrospun SPEEK nanofibers. The stable microstructure is derived from the compatible interfacial property of nanofibers and the formed hydrogen bonds. The multilayered microstructure consisting of nanofibers accelerates the proton conduction even at subzero temperature because of regulating the proton conduction pathways. Specifically, the (SKNF/CPNF/SKNF)/PA membrane exhibits the proton conductivities of (0.951 ± 0.138) × 10-2 S/cm at -30 °C and (7.32 ± 0.37) × 10-2 S/cm at 160 °C. Additionally, the fine proton conductivity stability is demonstrated by the proton conductivity in the long-term test and the cooling/heating cycle test, such as 1.67 × 10-2 S/cm at -30 °C (after 1000 h), 4.52 × 10-2 S/cm at 30 °C (after 810 h), 1.12 × 10-2 S/cm at -30 °C, and 1.01 × 10-1 S/cm at 30 °C in the cooling/heating process (5 cycles). The single fuel cell possesses an open-circuit voltage of 0.886 V and a peak power density of 0.508 W/cm2 at 130 °C.

Multi-shell bowl-like carbon microspheres for lightweight and broadband microwave absorption

Carbon materials have made significant progress in the field of microwave absorption (MA), but achieving wide effective absorption bandwidth (EAB) at low filler content still remains a great challenge. In this work, we design multi-shell bowl-like mesoporous carbon microspheres (MBMCs) by a facile hard template method for efficient MA. It is demonstrated that the spacing between inner and outer shell and second shell thickness play a vital role on the configuration of carbon microspheres. By controlling the second addition of silica template, the microstructure of carbon microsphere evolves from spherical to bowl shape geometry. Expanded shell spacing is beneficial for forming bowl-like microsphere. The dielectric loss and MA properties are highly associated with the configuration of MBMCs. Well-proportioned MBMCs with appropriate shell spacing present wide EAB of 7.3 GHz under a low filling ratio of 12 wt.%. This work paves a new way to broaden EAB and lower filling content of carbon materials via asymmetric multilayer microstructure design.

A new type of dolomicrite envelope formed in Oligocene lacustrine sediments and its significance for preserving porosity, Bohai Bay Basin, North China

Micrite envelopes are common early diagenetic features in marine carbonate grains. Most case studies of micrite envelopes focus on those with calcium-carbonate compositions. This paper documents a new type of lacustrine dolomicrite envelopes, coating both terrigenous grains and bioclasts, which developed in the upper Shahejia Formation of early Oligocene age in the middle of the Bohai Bay Basin. These dolomicrite envelopes on grains in a lacustrine mixed sedimentary environment are puzzling for their formation and linkage with the porosity preservation of porosity among grains. We investigate the microstructure and formation mechanism of these dolomicrite envelopes that coat grains through the study of the mineralogy, petrology and porosity characteristics. These studies show that there are two occurrences of the dolomicrite envelopes, i.e., coating on detrital grains and coating on carbonate grains, with a multi-layer microstructure. A potential two stage model to interpret the formation of dolomicrite envelopes incorporates an initial illite coating followed by dolomite encrustation. The illite coating played an important role in the precipitation of the dolomite. Post-envelope diagenetic processes include sparry cementation and destructive dissolution. The quantitative content of dolomicrite envelopes positively correlates with the preserved porosity, which suggests that their formation contributed to resisting compaction and protecting porosity among grains. Indeed, the dolomicrite envelopes appear to have aided in maintaining a kind of extremely high-quality reservoir for hydrocarbon exploration within the Shahejia Formation of the Bohai Bay Basin. In addition, the coating film seems to be conducive to the exchange of anions, thereby resulting in the dissolution of interior feldspar-, bioclast- or ooid-grains. In summary the Shahejia Formation of the Bohai Bay Basin provides a new type of dolomicrite envelope on grains in a lacustrine setting.

Self-assembled rectorite films with remarkable mechanical performance: preparation, structural characterization, and properties

Cohesive flexible rectorite clay films with good mechanical performance were prepared by a simple casting method through the self-assembly of exfoliated natural clay from aqueous dispersions. The multi-layered microstructure of the films consisted of continuous layers of aligned clay platelets parallel to the casting surface. Layers overlap randomly in the lateral direction (plane) and join vertically in an irregular manner by edge-to-face cross-linkages (bridging) to form coherent multi-layered nanostructured films with platelet-void microstructure. The films with the highest mechanical properties had thicknesses below 30 µm. Overall films from rectorite clay with monovalent interlayer content exhibited a higher experimental tensile strength ranging up to 44 MPa and Young’s modulus up to 56 GPa. The corresponding experimental values for films with divalent interlayer cations were 23 MPa for strength and 25 GPa for modulus. The highest experimental values for strength and modulus for neat Na–Ca–rectorite films were 25 MPa and 50 GPa respectively. These two mechanical property values of the best rectorite-based clay films compare favorably with values featured by polymer films typically used for packaging applications.

Investigation on the Microstructure and Mechanical Properties of Multi-layer and Multi-pass Al Alloy Deposition Based on Cold Metal Transfer Technology

Investigation on the Microstructure and Mechanical Properties of Multi-layer and Multi-pass Al Alloy Deposition Based on Cold Metal Transfer Technology

A Breathable, Stretchable, and Self‐Calibrated Multimodal Electronic Skin Based on Hydrogel Microstructures for Wireless Wearables

AbstractBiomimetic electronic skins (e‐skins) are widely used in wearables, smart prosthesis and soft robotics. However, multimodal e‐skins, especially those based on hydrogels, face multiple challenges for practical applications, involving multi‐sensing signal mutual interference, low breathability and stretchability. Here, a breathable and stretchable multimodal e‐skin with a multilayer film microstructure is developed to achieve self‐calibrated sensing of any two of three stimuli: strain, temperature, and humidity, with minimal crosstalk. Hydrogel fibers with different shapes are designed for strain and temperature sensing modules, and the hydrogel film is developed as a humidity sensing module. The multimodal e‐skin exhibits impressive sensing performance, including a low strain detection limit (0.03%), strain linearity (R2 = 0.990), high‐temperature sensitivity (1.77%/°C), and a wide humidity detection range (33–98% RH). Interestingly, due to the directional anisotropy in strain sensitivity of different shaped fibers, the e‐skin realizes self‐calibrated detection of strain and temperature in different directions. By introducing porous elastomer encapsulation membranes, the breathability and wearing comfort of the e‐skin are attained, while the high stretchability (100% strain) is maintained. Furthermore, a personalized human‐machine interaction system is created by integrating the e‐skin with a wireless circuit to realize real‐time and wireless gesture recognition, physiological signals monitoring, and smart prosthesis.

Microstructure and Properties of Multilayer 5052 Aluminum Alloy Sheet by Laser Welding

Microstructure and Properties of Multilayer 5052 Aluminum Alloy Sheet by Laser Welding

Construction of Successive Proton Conduction Channels to Accelerate the Proton Conduction Process in Flexible Proton Exchange Membranes.

Successive proton conduction channels are constructed with the spin coating method in flexible proton exchange membranes (PEMs). In this research, phosphoric acid (PA) molecules are immobilized in the multilayered microstructure of Kevlar nanofibers and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) polymer molecular chains. As a result, successive proton conduction channels can accelerate the proton conduction process in the prepared membrane with the multilayered microstructure. Additionally, the microstructure fractures of the composite membranes from the external force of folding and stretching operations are modified by the inner PA molecules. Notably, numerous PA molecules are further combined through formed intermolecular hydrogen bonding. The stretched membrane absorbs more PA molecules owing to the arrangement of PA molecules, Kevlar nanofibers, and SEBS molecular chains. The stretched membrane thus exhibits the enhanced proton conduction ability, such as the through-plane proton conductivity of 1.81 × 10-1 S cm-1 at 160 °C and that of 4.53 × 10-2 S cm-1 at 120 °C lasting for 600 h. Furthermore, the tensile stress of PA-doped stretched membranes reaches (3.91 ± 0.40)-(6.15 ± 0.43) MPa. A single proton exchange membrane fuel cell exhibits a peak power density of 483.3 mW cm-2 at 120 °C.

Enhancement of ionic transport characteristics and cell performance through multi-layered separator microstructure in Li-ion cells

Enhancement of ionic transport characteristics and cell performance through multi-layered separator microstructure in Li-ion cells

Fabrication of ZTA crowns with simultaneously improved isotropy on mechanical property and surface quality by DLP

AbstractZirconia‐toughened alumina (ZTA) composite ceramics show great potential for use in dental repair applications due to their unique properties. Complex‐shaped ZTA all‐porcelain crowns can be accurately fabricated using digital light processing (DLP) technology. However, effectively controlling both the anisotropy on mechanical property and surface quality of ZTA composites shaped by DLP remains a critical challenge that requires further research and innovation. In this work, we propose an efficient method to synchronously enhance the isotropy on mechanical performance and surface quality of DLP formed ZTA all‐porcelain crowns by controlling contents of yttria‐stabilized zirconia (YSZ) powders. When enhancing contents of YSZ from 5 to 20 wt%, multilayer microstructure with obvious interlayer gaps transformed into uniform microstructure with strong interlayer bonding, and the smaller alumina grain was observed on the stair‐stepping microstructure. Finally, the ZTA composites exhibited flexural and comprehensive strength as high as 640.3 and 6.9 MPa, and dimensional precision as low as 37.5 and 43.5 μm on top and side surface, together with simultaneously enhanced isotropy on mechanical property and surface quality, well satisfying the demands for all‐porcelain crowns fabricating. This study provides thorough understandings on isotropy regulating of DLP‐shaped ZTA all‐porcelain crowns with excellent mechanical performance and surface quality.

Revealing the structure of SiO2 and its effects on electrical properties

In this paper, the effects of vacancies and dopants on α-SiO2 are fully investigated with the first principle calculation and the finite element analysis method. The vacancies and dopants including the oxygen vacancy, silicon vacancy, boron dopant, and phosphorous dopant are considered. The oxygen vacancy, P substituted with O, and Si substituted with B are the most stable in the process of the oxide growth leading to the multi-layer microstructure of the tunneling oxide on the silicon substrate, and their concentrations increase with the temperature. Si substituted with B has larger capture cross sections than the other two types. The SONOS FLASH structure is built with the realistic manufacturing process to clarify the electrical effect of the multi-layer. The programming process with introduced levels from vacancies and dopants will be weakened with less charges storing in the floating gate which can reduce the circuit performance. The theoretical study from the electronic structure to electrical properties has remarkable senses for manufacturing devices and improving device performance in the future.

Mechanistic analysis of improving the corrosion performance of MAO coatings on Ti-6Al-4V alloys by annealing

Titanium and its alloys find extensive application within the realms of dentistry and orthopedics due to their remarkable chemical stability. Nevertheless, they are still susceptible to corrosion in harsh environments. Micro-arc oxidation (MAO) emerges as a potent methodology for enhancing the corrosion resistance of titanium and its alloys, achieved through the generation of a ceramic stratum atop the material's surface. The corrosion resistance of MAO coatings in clinical applications is closely related to their microstructure. This manuscript systematically explores the effect of annealing temperature on the phase composition and microstructure of MAO coatings. Furthermore, the evolution of the surface properties and the crystal structure of coatings is meticulously discussed and illustrated. The results show that the corrosion resistance of coatings exhibits an ascending trajectory followed by a subsequent decline, coinciding with the augmentation of the annealing temperature. This behavior can be attributed to the structural evolution of coatings caused by the gradual increase of the annealing temperature. At the optimum temperature (400 °C), the annealing treatment leads to the crystallization of the coating as well as to a decrease in the surface porosity, resulting in the formation of a compact and continuous multilayer microstructure. The decrease in porosity can be attributed to the diffusion-reaction of oxygen from the air with titanium from the discharge channel (titanium oxide), resulting in the formation of TiO2 particles that effectively fill the pores. The decrease in corrosion resistance of the coatings after annealing at 800 °C is due to the phase transition of TiO2 which leads to the expansion of cracks inherent in the oxide layer to form A-H cracks. Therefore, this study shows that the microstructure of MAO coatings can be adjusted by post annealing treatment (400 °C) to obtain a desirable oxide layer with appropriate porosity, crystallinity and chemical composition, thus improving its corrosion resistance.

Effects of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gear

Bionics research has revealed the remarkable fatigue resistance exhibited by intertidal zone shellfish, attributed to their radial ribs and multi-layered microstructure. Leveraging the analogous stress and working conditions shared by shellfish and gears, we adopted the discrete laser surface melting (DLSM) technology to create discrete laser surface melted (DLSMed) units on gear tooth surfaces. This paper aimed to scrutinize the influence of discrete laser surface melting on the fatigue performance of 20CrMnTi steel gears. In terms of laser selection, we opted for the Nd: YAG pulsed laser. Across various laser parameters, the proportion of DLSMed units on gear tooth surfaces varied. Scanning Electron Microscopy (SEM) facilitated the observation of microstructures and fatigue morphology of the DLSMed gear. X-ray Diffraction (XRD) measurements gauged residual stress along both the surface and cross section of the DLSMed unit, unveiling the residual stress distribution. Microhardness and surface roughness were assessed through a microhardness tester and a surface profilometer, respectively. Fatigue tests were conducted using both the Forschungsstelle für Zahnräder und Getriebebau (FZG) testing machine and a high-frequency fatigue testing machine. Experimental findings disclosed that the DLSMed unit comprised a melting zone and a heat-affected zone. The depth of the residual compressive stress layer increased alongside current intensity, albeit with the unexpected emergence of residual tensile stress. Enhanced current intensity corresponded to a noticeable elevation in the DLSMed gear's hardness value. Differing fatigue behaviors were evident between the as-received gear and the DLSMed gear. The DLSMed gear exhibited reduced fatigue damage compared to the as-received gear. The DLSMed units effectively curbed crack initiation and propagation, markedly enhancing gear fatigue performance. A direct relationship between the DLSMed unit's area proportion on the gear surface and gear fatigue strength was established. Finally, we delved into the anti-fatigue mechanism underlying the DLSMed gear's performance.

Interfacial complex reactions and microstructures in vacuum hot-rolling bonded titanium-steel clad composites dominated by bonding temperature

Vacuum hot-rolling bonded (VHRB) titanium-steel clad composites with high performance are extensively required by both corrosion-resistant and load resistant equipment, and their high interfacial bonding strength strongly depends on an improved microstructure of interfacial reaction layer. This requires continuous exploration of a new solution. For this attempt, VHRB Ti/steel composites were prepared by hot-compression bonding on a thermal-mechanical simulator at two temperatures of 850 °C and 890 °C for typical α-Ti and β-Ti phase domains, respectively, and their interfacial reaction and products were explored mainly via transmission electron microscope (TEM). It was found that with the bonding temperature decreased from 890 to 850 °C, the interfacial multilayer microstructure of TiFe2+TiC (RLi)-TiFe (RLii)-TiC (RLiii) from the steel side to the Ti side of composites was replaced by that of TiFe2+TiC (RLI)-TiC (RLII)-TiFe (RLIII), due to their different competitive diffusion of C, Fe, and Ti atoms and diffusion barrier playing by TiC. In addition, the average thickness of the brittle interface reaction layer decreased from 0.87 to 0.64 μm, while the average thickness of corresponding sublayer changed from 0.30 μm (RLi)-0.27 μm (RLii)-0.30 μm (RLiii) to 0.22 μm (RLI)-0.28 μm (RLII)-0.14 μm (RLIII). This contributed to the increase of interfacial bonding strength from 235 to 410 MPa.

Morphological and structural analysis of iron-rich porcelains excavated from the Jian kiln site of Song dynasty.

Iron-rich porcelains generally embrace relatively high iron concentration in the glaze and body, which have an important position in the history of ancient Chinese high-temperature ceramics. The colour and lustre of glaze patterns are closely related to the orientation and order of crystallisation. In this work, three representative types of iron-rich porcelains (persimmon red-glazed sample, oil spot-glazed sample and mirror black-glazed sample) were analysed by portable energy-dispersive X-ray fluorescence (PXRF), optical coherence tomography (OCT), optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and laser Raman spectroscopy (RS) to determine the morphology, chemical composition and microstructure. Results showed that layered structure was observed in both persimmon red and oil spot glazes, however with respective thickness. Besides, iron-enriched crystals mostly precipitated on glaze surface. For the persimmon red sample, multilayer microstructure consisting of three sublayers beneath glaze surface was identified. Crystals and dark red substrates were all made of ε-Fe2 O3 , implying that it was fired at a strong reducing atmosphere. But for the oil spot sample, large-scale leaf-shaped crystals were well characteristic of ε-Fe2 O3 , while small snowflake-shaped crystals were assigned to α-Fe2 O3 , indicating that the firing environment was partially reduced. In addition, there was no crystalline layer existing on surface of mirror black-glazed porcelain, and plain black glaze layer was featured by a glassy matrix. The Jian kiln is a famous ancient folk kiln in the southern China that is currently located in Jianyang county of Fujian province. Its production of black-glazed porcelain began in the Tang dynasty (618-907 AD), became prosperous in the Southern Song dynasty (1127-1279 AD), and declined and ended in the Yuan dynasty (1271-1368 AD). Black-glazed Jian tea bowls were perfect for highlighting the rich white tea decoction. The thick and lustrous black glaze of Jian bowls sometimes were featured by streaked or mottled patterns, usually recognised by 'hare's fur (HF)', 'oil spot (OS)', 'partridge spot (PS)' and so on, which were the crystalline markings of iron oxide precipitated during firing in the dragon kiln. Iron oxide acted as a colorant for black-glazed porcelain and, thus, was called as iron-rich porcelain. The unique patterns originated from local iron-enrichment raw materials and firing process, and the locally iron-enriched areas generated due to the supersaturated crystallisation of different iron oxide in the cooling period. It was generally believed that research studies on the crystallographic nature and growth mechanism of surface crystals would provide help for the manufacturing of ancient Chinese glazes. With this aim, three types of iron-rich porcelain excavated from the Jian kiln were selected to further study the forming cause and growth process of glaze patterns using a series of characterisation methods, like portable energy-dispersive X-ray fluorescence (PXRF), optical coherence tomography (OCT), optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and laser Raman spectroscopy (RS).

Microstructure and Properties of Monolayer Ta and Multilayer Ta/Ti/Zr/Ta Coatings Deposited on Biomedical Ti-6Al-4V Alloy by Magnetron Sputtering

Two types of coatings, i.e., monolayer Ta and multilayer Ta/Ti/Zr/Ta coatings, were deposited on biomedical Ti6Al4V (TC4) alloy by magnetron sputtering to improve its performance. To evaluate the effect of the two coatings on the alloy properties, the microstructure, composition, mechanical and tribological properties, in vitro biocompatibility, and corrosion resistance were investigated. The results showed that α-Ta exists in the monolayer Ta coating, while α-Ta and β-Ta phases coexist in the multilayer Ta/Ti/Zr/Ta coating. The multilayer Ta/Ti/Zr/Ta coating possessed the highest hardness and the monolayer Ta coating had the lowest friction coefficient compared to the Ti6Al4V alloy. The friction and wear tests revealed that the anti-wear performance of the Ta coating is the best, followed by that of the Ta/Ti/Zr/Ta coating, while the anti-wear performance of TC4 alloy is relatively poor in comparison with the Ta and Ta/Ti/Zr/Ta coatings. The wear resistance of the multilayer Ta/Ti/Zr/Ta coating under low normal load is better than that under high load normal load. Finally, the in vitro and electrochemical corrosion tests showed that the Ta coating modification provides better biocompatibility and corrosion resistance than those of the uncoated Ti6Al4V alloy.

Constructing lamellar low temperature anion exchange membranes based on polymerized ionic liquid and graphene oxide nanosheets

Polymerized ionic liquid (PIL) of poly(1-vinyl-3-methylimidazolium) chloride (poly(vmim)Cl) and graphene oxide (GO) nanosheets were respectively deposited on the surface of Kevlar aramid nanofibers (KANFs) substrates to construct anion exchange membranes (AEMs). The multilayered microstructure resulted in orderly distributed components, which thus improved the mechanical properties and dimension stability of the lamellar low-temperature AEMs. The imidazolium cations in PIL and the polar oxygen functional groups in GO nanosheets constituted the interconnected hydroxide ion conduction channels in the prepared Kevlar/(PIL/GO)60 membrane. Relative to the ionic liquid (IL) monomer of 1-vinyl-3-methylimidazolium chloride, the PIL with polymerized molecular chains could be embedded in GO nanosheets with the formation of a stable microstructure. The Kevlar/(PIL/GO)60 membrane exhibited the enhanced alkaline stability relative to the Kevlar/(IL/GO)60 membrane. Furthermore, the hydroxide conduction behavior in the AEMs at subzero temperatures has been researched in consideration of the long-term exposure in colder conditions of the vehicles equipped with fuel cells. As a result, the Kevlar/(PIL/GO)60 membrane exhibited a hydroxide conductivity of 0.94 mS/cm at −25 °C, 5.25 mS/cm at 30 °C, and 64.7 mS/cm at 80 °C. Meanwhile, good alkaline stability was revealed from the ten-cycle hydroxide conductivities and long-time hydroxide conductivities. In addition, the PIL enhanced the mechanical strength of the Kevlar/(PIL/GO)60 membrane, with the tensile stress at break increasing by 31.3% compared with that of the Kevlar/(IL/GO)60 membrane.

The enhancement of mechanical properties and uniform degradation of electrodeposited Fe-Zn alloys by multilayered design for biodegradable stent applications.

Pure Fe is a potential biodegradable stent material due to its better biocompatibility and mechanical properties, but its degradation rate needs to be improved. Alloying with Zn to form Fe-Zn alloy is anticipated to meet the degradation rate requirements while retaining the iron's inherent properties. Therefore, Fe-Zn alloys with monolayered and multilayered structures were prepared by electrodeposition. The alloys' composition, microstructure, mechanical properties, in vitro degradation and biocompatibility were assessed. Results showed that the Zn content ranged from 2.1 wt% to 11.6 wt%. After annealing at 450°C, all the alloys consisted of α(Fe) solid solution and Zn-rich B2 ordered coherent phase, except for the alloy with 11.6 wt% Zn content, in which a Fe3Zn10 phase appeared. The layered structure consisted of alternating columnar-grain and nano-grain layers, which compensated for the intrinsic brittleness of electrodeposited metals and improved the galvanic effect of the alloy, thus increasing the strength and plasticity and changing the corrosion from localized to uniform while augmenting the corrosion rate. The yield strength of the multilayered alloy exceeded 350 MPa, its elongation was more than 20%, and its corrosion rate obtained by immersion test in Hank's solution reached 0.367 mm·y-1. Fe-Zn alloys with lower Zn content had good cytocompatibility with the human umbilical vein endothelial cells and good blood compatibility. The above results verified that the multilayered Fe-Zn alloy prepared by electrodeposition presented enhanced mechanical properties, higher degradation rate, uniform degradation mechanism and good biocompatibility. It should be qualified for the application of biodegradable stents. STATEMENT OF SIGNIFICANCE: A potential biodegradable Fe-Zn alloy, which is difficult to be obtained by the metallurgical method, was prepared by electrodeposition to solve the low degradation rate of iron-based biomaterials. A multilayered microstructure design composed of alternating columnar-grain and nano-grain layers was achieved by changing the electrical parameters. The layered design compensated for the intrinsic poor plasticity of electrodeposited metals. It increased the galvanic effect of the alloy, thus augmenting the corrosion rate and changing the corrosion mode of the alloy from localized to uniform corrosion. The yield strength of multilayered alloy exceeded 350 MPa; its elongation was more than 20%. Moreover, the layered alloy had good cytocompatibility and blood compatibility. It indicates that the alloy is qualified for biodegradable stent application.

Evolution of microstructures and intermetallic compounds at bonding interface in friction stir welding of dissimilar Al/Mg alloys with/without ultrasonic assistance

Complete understanding of the evolution behaviors of the microstructures and intermetallic compounds (IMCs) along the interface materials flow path in friction stir welding (FSW) of dissimilar Al to Mg alloys is of great significance. In this study, conventional FSW and ultrasonic vibration enhanced FSW (UVeFSW) experiments of Al/Mg alloys were performed, and the instantaneous evolution features of the interface materials around the tool were "frozen" by using the "sudden stop" and simultaneous cooling techniques. The microstructures and IMCs formation at different locations around the exit hole were observed and characterized by scanning electron microscope, energy dispersive spectrometer and transmission electron microscope. It was found that before the materials started to deposit near the back of the tool, “IMC+Mg+IMC+Al” multilayer microstructure and simple IMC layer with (β+γ) sequentially emerged on the Al/Mg interface. With the application of ultrasonic vibration, the multi-layered interface structure only appeared at the middle stage of materials flow around the pin, and ultrasonic vibration just began to play a suppression role on the growth of two sub-layers IMC at a position where the materials deposit. With assistance of ultrasonic vibration in UVeFSW, the tool drove a larger volume of Mg alloy to move toward the retreating side, and the final IMCs thickness was thinner than that in FSW.

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems.