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• The three samples manufactured by LPBF had high relative density. • The addition of 2 wt% TiB 2 significantly refined the grain size. • The low-angle grain boundaries increased with increasing proportions of TiB 2. • The strength was improved by introducing TiB 2 particles. The laser powder bed fusion (LPBF) additive manufacturing process has been extensively used to manufacture various nickel-based metal components because it offers the capability of manufacturing three-dimensional structures with complex shapes directly from raw materials. Although LPBF-fabricated Inconel 718 (IN718) superalloys have been successfully applied in the aerospace field, IN718-based composites can offer an alternative pathway to further enhance high-temperature performance. This systematic study examined the effect of various TiB 2 contents on the microstructure and mechanical performance of IN718 fabricated by LPBF. Pure IN718 (IN718-P), IN718-1 wt% TiB 2 (IN718-1) and IN718-2 wt% TiB 2 (IN718-2) composites were nearly fully dense, with relative densities of 99.71%, 99.34% and 99.67% respectively, when fabricated under the optimal process parameters. The degree of grain size refinement was greater for IN718-2 than for IN718-1, and the IN718-1 grains were mainly refined in the width direction, while the IN718-2 grains were refined in both the width and length directions. The proportion of low-angle grain boundaries was significantly higher for the composites than for IN718-P, and it increased with increasing proportions of TiB 2. Compared with the IN718-P sample, the microhardness, yield strength and ultimate tensile strength of IN718-2 at room temperature were increased by 19.93%, 24.83% and 11.07%, respectively, while the yield strength and ultimate tensile strength of IN718-2 at a high temperature of 650 °C were increased by 31.76% and 17.62%, respectively. This indicated that the enhancement of mechanical performance was more noticeable at high temperature than at room temperature. By contrast, less improvement in mechanical properties was achieved by adding 1 wt% TiB 2 particles than by adding 2 wt% TiB 2 particles. These findings indicate an alternative way to manufacture IN718 superalloys with improved mechanical properties through the synthesis of composite materials. [ABSTRACT FROM AUTHOR]

The application of magnesium alloys is rather limited due to their poor corrosion resistance despite of their promising mechanical properties. Alloying is considered one of the most efficient methods to influence the corrosion susceptibility of Mg alloys either by altering the bulk microstructures or by changing the surface chemistries. In the present study, the effects of Sr addition on the microstructure and corrosion properties of a Mg-Zn-Ca alloy were studied. The microstructure characteristics of the alloys were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, while the corrosion properties were evaluated by hydrogen collection method and electrochemical techniques including potentiodynamic polarization and electrochemical impedance spectroscopy. The results indicate that Sr addition significantly deteriorates the corrosion performance of the Mg-Zn-Ca alloy mainly by forming more micro-galvanic couples due to the precipitation of the more populous secondary phase particles. The corrosion product film accumulated on the sample surface marginally affects the corrosion resistance, as their compactness is rather compromised as the immersion time is prolonged. • The volume fraction of the secondary phases increased by adding Sr into the Mg-Zn-Ca alloy; • Sr addition leads to the formation of Mg 17 Sr 2 phase in Mg-1Zn-0.3Ca (wt.%) alloy; • The addition of Sr into the Mg-1Zn-0.3Ca (wt.%) leads to a higher corrosion rate. • Corrosion rates of the Mg-Zn-Ca-(Sr) alloy mainly affected by secondary phases through the microgalvanic mechanism. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is an established metal additive manufacturing technology extensively used in the automotive domain to manufacture metallic components with complex structures from 18Ni-300 maraging steel. However, achieving high-performance 18Ni-300 maraging steel using SLM still presents a challenge in terms of formulation of the processing parameters. The remelting process has the potential to address this challenge during SLM before post-treatments. This paper systematically investigated the effect of remelting on the microstructure and mechanical behaviours of the SLM-built 18Ni-300 maraging steel. The experimental results suggest that increases in the relative density of the as-built samples from 99.12% to 99.93% are achieved by a specific combination of remelting parameters (laser power 200 W, scan speed 750 mm/s, remelting rotation 90° and hatch spacing 0.11 mm) that eliminate large-sized pores. Compared with the as-built condition, remelting can slightly coarsen the average grain sizes and increased the fraction of low-angle grain boundaries (2°–15°). The tensile strength showed no remelting dependence, whereas both the ductility and microhardness increased. Elongation of the as-built sample increased from 10.5 ± 0.8% to 13 ± 3.5% after remelting under the #28 condition. These findings provide a fundamentally new understanding of how a combination of SLM and remelting can aid in the manufacture of high-performing 18Ni-300 maraging steel. • 18Ni-300 maraging steel is manufactured by a combination of selective laser melting and remelting. • Effect of remelting with various parameters on relative density is investigated. • Pore distributions and microstructural characteristics in different conditions are studied. • Remelting enhances the ductility and Vickers hardness compared to as-built samples. [ABSTRACT FROM AUTHOR]

The non-uniform temperature field and cooling rates in the molten pool during solidification process fabricate microstructural and mechanical heterogeneities in fusion zone (FZ) and heat-affected zone (HAZ) of thick titanium alloy weldment. In this study, electron beam welding was used to assemble thick Ti-5Al-2Sn-2Zr-4Mo-4Cr (TC17) alloy plates. Microstructural heterogeneity concerning recrystallized martensitic structures with different morphology and distribution features in FZ and retained microstructures after experiencing thermal exposure in HAZ were analyzed to unravel their effects on multiscale mechanical behavior. It was found that needle-shaped martensite (α') exhibited a comparative high nano hardness and the precipitation of needle-shaped martensite cluster contributed to a more severe tensile strain localization in FZ and premature brittle fracture of the joint. The bottom layer of weldment, where the FZ was verified to be martensitic free, exhibited a better combination of strength and ductility. Mo and Al exhibited a better thermostability than Cr, which held the responsibility for the microstructural stability in HAZ during severe thermal exposure after welding. • Effects of heterogeneous microstructure on nanomechanical and tensile behavior were studied. • The formation of needle-shaped martensite was verified to damage the ductility of the weld joint. • A comparatively lower diffusion rate of Al than Cr contributes to a better thermostability of α P than α L. [ABSTRACT FROM AUTHOR]

Friction stir butt welding was carried out to assemble 6 mm-thick TC17 titanium alloy plates with a W–Re weld tool. Inhomogeneous microstructures were obtained in stir zone (SZ) and heat affected zone (HAZ) of the weldment. A series of tests were conducted to reveal the influence of inhomogeneity of microstructure on mechanical behavior. Comparative refined β phase without precipitating secondary metastable microstructure generated a soft SZ and favored on the ductility of weldment. Strain localization during tension was promoted by the interface of HAZ and SZ that formed by thermal-mechanical coupling effects. Coincidentally, fatal fatigue cracks were verified to nucleate around the same region, and presented in a stress dependent mode. • Comparative refined β grains without lamellar α generate a soft SZ. • W-contaminate traces exhibit higher nano hardness than intermediate banded regions. • Strain localization promoted by the HAZ/SZ interface causes tensile fracture. • Fatal fatigue cracks nucleate around HAZ/SZ interfaces. [ABSTRACT FROM AUTHOR]

• The process parameters of 18Ni-300 maraging steel fabricated by SLM were optimised. • The effect of various heat treatments on phase transformation and microstructure was discussed. • Vertically-built samples exhibited slightly lower tensile strength than those horizontally-built. Selective laser melting (SLM) of 18Ni-300 maraging steel is an important research area in view of its numerous applications in the automotive domain. Heat treatment plays a significant role in the microstructure and mechanical behaviour of maraging steels and is a major area of interest. This paper investigated the effect of heat treatment on microstructure and mechanical behaviour of SLM-built 18Ni-300 maraging steel. The experimental results showed that the densest parts with the smallest number of defects were fabricated at optimum laser energy density of 70 J/mm3 and laser power of 275 W. When the laser power was fixed at 275 W, lower laser energy density resulted in the formation of balling and irregular pores, while higher laser energy density induced spherical pores and microcracks. The as-built samples consisted of cellular and columnar microstructures due to the fast cooling and solidification rates during SLM. However, solution treatment led to changes in the typical microstructure and massive lath martensite phase. The tensile strength and microhardness decreased slightly due to grain growth and residual stress relief upon solution treatment; an opposite effect was observed when the samples were subjected to solution treatment followed by aging at 490 °C for 2 h. With regard to the tensile anisotropy, yield strength and ultimate tensile strength of the horizontally-built samples slightly exceeded those vertically-built. These findings are significant as they allow an informed prediction about the effect of various heat treatments on the microstructure and mechanical behaviour of components manufactured from 18Ni-300 maraging steel using the SLM process. [ABSTRACT FROM AUTHOR]

The design of the trimodal powder feedstock and its feasibility for micro powder injection molding (μ-PIM) were investigated. The feedstock was prepared by mixing Fe micropowder (D 50 = 4 μm) and nanopowder agglomerate composed of a bimodal particle distribution (D 50 = 330 nm and D 50 = 30 nm, respectively) with low viscosity wax-based binders. The homogeneity of the feedstock was evaluated by torque rheometer, microstructure observations, binder burnout analysis, and an extrusion test. The trimodal concept in this study effectively improved the powder loading up to 72 vol%, and the feedstock with 70 vol% powder loading exhibited good homogeneity and flowability. By using the feedstock, the microparts were successfully replicated with sufficient shape retention to be potentially useful for a range of μ-PIM applications. [ABSTRACT FROM AUTHOR]

Electrochemical performance of lithium ion batteries is associated with structural and chemical stability of electrode materials. In the case of nickel-rich layered cathode materials LiNi 0.6 Co 0.2 Mn 0.2 O 2 , cation mixing, which results from the migration of transition metal ions into vacant lithium sites, is accelerated owing to similar ionic radii between nickel and lithium. However, the inevitable lattice distortions and chemical evolution have not been investigated intensely. In this paper, we report the structural evolution localized at surface regions through electron diffraction and high resolution imaging analyses with aberration-corrected transmission electron microscopy and scanning transmission electron microscopy. Repetition of volumetric change generates cracks and voids associated with deterioration of electrochemical performance. Structural change is related with (003) intensity in electron diffraction and it can be presented by dark field transmission electron microscopy imaging at a glance. Drastic structural degradation during early cycling shows relation with rapid capacity and voltage fade. Electron energy loss spectroscopy elucidates that the structural evolution caused by the migration of Ni ions accompanies chemical modification of Mn ions and creation of hole states at the O2p level. This study provides an insight into correlating structural and chemical evolution with degradation mechanism on battery performances of LiNi 0.6 Co 0.2 Mn 0.2 O 2 cathode materials. [ABSTRACT FROM AUTHOR]

Cu/Ni heterogeneous materials integrate excellent thermal conductivity and high-temperature mechanical properties, enabling them to be widely used in the aerospace domain. Differences in the thermal and physical properties of the Cu and Ni materials, however, make them difficult to be processed using the laser powder bed fusion (LPBF) additive manufacturing process. This study systematically examines the effects of various LPBF process parameters on microstructure, element diffusion, bonding strength and microhardness at the Cu/Ni interface, as well as investigating the mechanisms of defect formation within Cu/Ni heterogeneous materials. The results indicate that a reasonable control of laser energy input (<100 J/mm3) facilitates the Cu/Ni components through strong interfacial metallurgical bonding without pore defect formation. Compared to single-material Cu alloy, the ultimate tensile strength (UTS) of the horizontally bonded Cu/Ni specimen increased by 55.25 %, without significant reductions in elongation. The vertically bonded Cu/Ni tensile specimen fractured in the middle of the Cu region rather than the interfacial region, indicating superb interfacial bonding strength. Another advantage lies in the enhancement of thermophysical properties, with a 109.5 % increase in thermal conductivity achieved in the LPBF-fabricated Cu/Ni heterogeneous materials compared to the single-material Ni alloy. Quasi-static compression experiments indicated that the Cu/Ni lattice structure could absorb more energy when compressed parallel to the build direction (BD), compared to being perpendicular to the BD. This study provides guidance for the design and manufacture of high-performance Cu/Ni heterogeneous components via LPBF. [ABSTRACT FROM AUTHOR]

The densification and grain growth behavior of powder injection molded 316L stainless steel micro–nanopowder were investigated in terms of microstructural development. The sintered density of the micro–nanopowder sample increased remarkably in the temperature range of 1000 to 1100 °C due to the sintering effect of nanopowders which increased the number of grain boundaries acting as high material transport path. A near full density of 98% TD was obtained after sintering at 1100 °C for 5 h with the average grain size less than 10 μm, indicating that there was no drastic grain growth. The presence of nanopowders in micro–nanopowder played decisive role in the entire sintering process by enhancing densification but suppressing grain growth. These effects open up the possibility of using micro–nanopowder feedstock to control the sintering behavior of powder injection molding products with full density and fine microstructure. [ABSTRACT FROM AUTHOR]

• High performance of p-type BiSbTe based bimodal structures are fabricated. • bulk fracture displayed a dense & inhomogeneous diversification of mixed. grains. • high scattering rate of carriers/phonons increases α values & reduced κ values. • The Z T max of 1.202, and Z T Avg of 1.14 are obtained for the composite. structures. In this work, we fabricated bimodal structured high performance p-type BiSbTe alloys by combining coarse and sub-micron scale water atomized powder, followed by spark plasma sintering. The bulk fracture analysis revealed a dense and inhomogeneous distribution of mixed grains on the surface, while the texture analysis using EBSD revealed that the bulk specimens had a bimodal microstructure with random grain alignment due to the distribution of initial powder sizes. The coarse grain specimen exhibited high electrical conductivity of 1257 Ω−1cm−1 because of its high carrier mobility and carrier concentration. A high Seebeck coefficient (214 μV/K) and low thermal conductivity (0.95 W/mK) were observed for the bimodal structured specimens because scattering of carriers and phonons was higher compared with the coarse specimen. The maximum thermoelectric figure of merit, Z T of 1.2, and Z T Avg of 1.14 was achieved in the bimodal structure specimen, due to its high-power factor, and low thermal conductivity. [Display omitted] [ABSTRACT FROM AUTHOR]

The primary objective of this study was to produce a TiVNbZrHf high-entropy alloy through powder metallurgy process and characterize its properties. The effect of sintering temperature on the microstructure and mechanical properties of bulk TiVNbZrHf samples was investigated. The resulting microstructure of the bulk samples included two different phase structures: a body-centered cubic (BCC) phase with a composition rich in (Ti-V-Nb)-Hf and a hexagonal close-packed (HCP) phase with a composition rich in (Hf-Zr)-Ti. The particle size and relative density of the bulk sample increased with the rising sintering temperature. The bulk TiVNbZrHf sample exhibited the highest hardness and the lowest wear rate when sintered at 1400 °C. The corrosion resistance of the bulk samples submerged in a 3.5 wt% NaCl solution steadily improved with increasing sintering temperatures. This improvement is attributed to the increased relative density and diminished grain boundaries. Our research highlights the crucial role of precise temperature control during the sintering process to achieve the desired material properties of high-entropy alloys. [Display omitted] • Bulk TiVNbZrHf high entropy alloy was synthesized by powder metallurgy process. • Alloy shows a dual-phase structure: body-centered cubic and hexagonal close-packed. • The highest hardness and the lowest wear rate were observed in the alloy at 1400 °C. • A better corrosion resistance of alloy was achieved at higher temperature (≥1400 °C). [ABSTRACT FROM AUTHOR]

Abstract: For the successful commercial production of CIGS PV modules, a good long-term damp heat stability of solar modules is necessary. The causes for the degradation of encapsulated solar modules are clearly explained. This article investigates the degradation behavior of encapsulated CIGS PV modules combined with the failure analysis of AZO films in CIGS cells. CIGS PV modules were exposed to the damp heat test of the IEC 61646 qualification standard—the modules are discolored from the outside edge to the center. Moreover, each module had its own distinct discolored area. The discolored area of the modules is significantly associated with the degradation of FF and efficiency. To clarify the causes of the degradation of FF and efficiency, failure analysis of AZO films in CIGS cells was performed. Electrical and structural properties as well as observation of the microstructure depending on the position of the AZO layers were characterized to explain the degradation mechanism of the encapsulated CIGS PV modules. It was revealed that the discoloration phenomenon of the modules and the degradation of AZO films were caused by the penetration of water molecules and adsorption of oxygen. By XPS and FT-IR analyses, the causes of degradation were confirmed. It was attributed to the generation of Zn(OH)2 and carboxylic acids by a combination of EVA, AZO and water molecules. [Copyright &y& Elsevier]

[Display omitted] • The synthesis process is customized for single-particle Ni-rich layered cathode materials. • Morphological engineering of cathode materials enhances the rate-capability and cycling stability. • Microcrack formation and particle fracture can be effectively suppressed during cycling. • All-solid-state-battery shows a high capacity retention of 84.9% at 0.5C after 150 cycles. A single-crystalline Ni-rich cathode material is synthesized for high-performance all-solid-state batteries (ASSBs). We customize the morphology and microstructure of the material by optimizing the synthesis process (particle size control and post-heat treatment) and demonstrate the advantages of single-crystalline cathode materials for practical use in ASSBs. The particle density and particle hardness of single-crystalline cathode materials with a particle size of 5 μm are considerably higher than those of the conventional polycrystalline cathode materials that are composed of spherical aggregates of submicron-scale primary particles. These structural features of the single-crystalline cathode materials improve the long-term cycling performance and rate capability of an ASSB configured with an argyrodite–Li 6 PS 5 Cl solid electrolyte. This is mainly attributed to the intimate interfacial solid–solid contacts and enhanced diffusion kinetics induced by the monolithic morphology of the single-crystalline cathode materials in the electrode. Moreover, undesirable microcrack formation and particle fracture in cathode materials are effectively suppressed during cycling. The feasibility of ASSBs configured with single-crystalline Ni-rich cathode materials is examined in detail. [ABSTRACT FROM AUTHOR]

Mixing powders in cold spray is a straightforward method to produce composite coatings, but a direct interpretation of the mixed powder deposition behavior from coating microstructure is often difficult. In this study, to investigate the feedstock deposition behavior in a cold sprayed 316L-10 wt% Fe (10Fe) metal-metal composite coating, splats deposited onto the as-polished 316L and Fe coatings with four types of impact scenarios were studied: (i) 316L on 316L, (ii) 316L on Fe, (iii) Fe on 316L, and (iv) Fe on Fe. The splat flattening ratio and coating crater depth/diameter were measured using a light optical microscope (LOM) and an optical profilometer to evaluate the degrees of particle and coating deformation. Finite element (FE) simulations were performed to obtain the splat rebound behavior during impact. A modified ball bond shear test was performed to determine the adhesion strength/energy of the cold spray splats. Results reveal distinct interparticle bonding features in the 10Fe coating, especially at the mixed 316L/Fe interfaces where a preferential location of inter-lamellar cracks can be seen. Similar bonding features were also observed in the deposited splats, indicating the splat on coating tests to be indicative of the coating build-up process. Finally, the feedstock deposition behavior in the 10Fe coating was explained through splat characterizations and FE simulations from hardness, surface oxide layer and particle morphology. [ABSTRACT FROM AUTHOR]

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi 0.5 Sb 1.5 Te 3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials. [Display omitted] • Novel fabrication of hierarchical structured material with successive arrangement of two different microstructures. • Successful consolidation of well-bonded hierarchical material and confirming by simulating results from COMSOL software. • Highest power factor of 3.8 * 10−3 W/m-K2 obtained by transportation of charge carriers through two different energy levels. • Hierarchical structured sample show highest figure of merit of 1.25 at 400 K which is highest among all reported samples. [ABSTRACT FROM AUTHOR]

An improved efficiency from an encapsulated flexible top-emitting organic light-emitting device (FTOLED) has been demonstrated by integrating a microstructure onto the polymer encapsulation film. Soft-nanoimprint lithography is employed to integrate the microstructure onto the polymer surface, which enables large area fabrication with high quality, low cost, and repeatable use of the poly(dimethylsiloxane) mold. The light extraction of the FTOLEDs has been improved by integrating the microstructure with two-dimensional tapered micropillars array on the polymer encapsulation film, which can suppress the reflection by enhancing the critical angle of total reflection owing to its gradually changed refractive index. Moreover, the microstructured surface exhibits a hydrophobic property owing to its high contact angle, which results in a self-cleaning ability to protect the FTOLEDs from being polluted by water droplets and dust particles in practical applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • The relation between macro/microstructure and mechanical properties was conducted by experiment and simulation. • A surface-tracking TFF model with heat source correction was established to reveal the physics. • The underlying physics of powder adhesion was investigated. The occurrence of structural defects in selective laser melting (SLM) damages the mechanical properties and fabrication accuracy of components and is closely related to the processing parameters. Therefore, having a good grasp of the interaction mechanism between the material and laser is useful for designing an improved process window. In this study, we experimentally investigated the relationship between the samples' macro- and microstructure and their mechanical properties under low energy inputs, and the response behaviour of as-built parts under these parameters was calculated using a thermal fluid flow (TFF) model with a modified and surface-tracking heat source. The results showed that Ti6Al4V parts obtained via SLM under low energy inputs exhibited a strong relationship between the macro- and microstructure and the mechanical properties. Single-track TFF models were built to better understand the underlying phenomena that are influenced by process parameters and then affects the depositing process. The models provided insight into the thermal history, deposition behaviour, densification, size accuracy, and surface morphology and by considering the velocity field, the phenomenon of powder adhesion caused by the Bernoulli effect could be investigated. Interestingly, the TFF model with a volume energy density (E v) of 90 J/mm3 captured the formation of pores, however, high smoothness of the surface and size accuracy was obtained in the sample. It can be proved that densification is hardly related to the surface morphology or the fabrication precision. In addition, our experiments showed that the fabrication process was less sensitive to process parameters at E v = 38 J/mm3. Densification was also more sensitive to the laser power than to the scanning speed. The results suggest that good-quality samples can be synthesised via SLM under low energy inputs, and the TFF model is a powerful tool for the systematic optimisation of the process parameters. Our findings could be applied to improve the controllability of the overhang surface with severe powder adhesion in further studies. [ABSTRACT FROM AUTHOR]

Highlights: [•] Viewing-angle independent WTOLEDs have been fabricated. [•] A microcavity with a periodically and gradually changed cavity length has been constructed. [•] The periodic microstructured cavity has been introduced into the WTOLEDs. [•] The viewing-angle independence in both the spectrum and CIE coordinates are obtained. [•] The microstructured WTOLEDs show comparable efficiency to that of the planar TOLEDs. [ABSTRACT FROM AUTHOR]

Abstract: Introduction of microstructures into an organic light-emitting device (OLED) is being considered as an effective approach to outcouple photons trapped in waveguide (WG) and surface plasmon-polariton (SPP) modes within the devices. However, the attempt has been hampered by the difficulty in applying lithographic patterning technologies on organic materials. Here, we show the end has been simply reached by one-step directly laser ablating the hole-transporting layer of the OLEDs without inducing any optical or electrical deterioration. Three times efficiency enhancement has been experimentally attained from the corrugated OLEDs, which has then been ascribed by numerical simulation to the efficient outcoupling of the SPP and WG modes to radiation. [Copyright &y& Elsevier]