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In this study, TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composites were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The phase composition, microstructure, mechanical and thermal expansion behaviour of composite HEAs were investigated. The results reveal that the addition of TiC has no effect on the crystal structure, however, the microstructure and mechanical properties show a strong dependency on the TiC content. Compared to the original HEA, the composite HEA shows decreased grain size, resulting in TiC nanoparticles (NPs) retarding grain growth by pinning the grain boundaries. With increasing TiC content from 0 to 4 wt-%, significant increases in the hardness from 410 to 480 HV and compressive yield strength from 680 to 1100 MPa, which is mainly due to the grain boundary and dispersion strengthening effects. Moreover, the thermal expansion curves show linear increments up to 800°C and decrease with increasing TiC content. [ABSTRACT FROM AUTHOR]

An Al-Ni alloy system with excellent energy density and mechanical performance is regarded as a novel high-energy–density material to enhance the energy emission of explosives or propellants. In this study, we explored the influence of a process control agent (PCA) varying from 0, 0.1, 0.25, 0.5, to 1.0 (wt.%) on the cryomilling of Al and Ni powder mixtures. The structural and morphological evolution of cryomilled Al-Ni powder was determined by X-ray diffraction, scanning electron microscopy, particle size distribution analysis, and transmission electron microscopy. Differential thermal analysis was used to study the exothermic reaction temperature, and activation energy calculations were performed using Kissinger plots. The results indicated that the addition of PCA changed the Al-Ni aggregate shape from oval to granular. The lamellar size also became finer after adding PCA up to 0.25 wt.% but the lamellar shape changed to granular at 1 wt.% PCA. These nanoscale lamellae serve as nuclei to produce Al-Ni reaction compounds, which gradually decrease the activation energy. The optimal concentration of PCA was determined to be 0.25 wt.% as this concentration decreased the activation energy of the Al-Ni alloy because of the fine, homogeneous, and alternate Al-Ni lamellae in the alloy when cryomilled. [ABSTRACT FROM AUTHOR]

In this study, the alloying and phase separation behaviors of AlCoCrFeNi-based high-entropy alloys (HEAs) were investigated. The valence electron concentration (VEC) of the AlCoCrFeNi HEA was modified by adding specific elements (Mg, Ti, Mn, Cu, and Zn) to produce biphasic HEAs. These HEAs were prepared by mechanical alloying for 30 hours, followed by the consolidation of the powders at 1000 °C. The results demonstrated the formation of a body-centered cubic (ordered BCC/B2) phase in AlCoCrFeNi–Mg and AlCoCrFeNi–Ti, while a dual-phase face-centered cubic (FCC) phase and minor BCC phases were observed in AlCoCrFeNi–Cu and AlCoCrFeNi–Zn. AlCoCrFeNi and AlCoCrFeNi–Mn exhibited the precipitation of a σ phase in the BCC matrix and a minor FCC phase. The AlCoCrFeNi–Mn HEA exhibited the highest compressive strength among itself, AlCoCrFeNi–Cu, and AlCoCrFeNi–Zn HEAs, owing to the precipitation of a harder σ phase and a higher ordered BCC/B2 fraction. In addition, the AlCoCrFeNi–Cu and AlCoCrFeNi–Zn HEAs exhibited the maximum fracture strain and absorption energies. We propose that a controlled VEC approach by the addition of suitable elements can be used to tailor the microstructure and phase stability of AlCoCrFeNi HEAs. [ABSTRACT FROM AUTHOR]

In this work, we have studied the displacement reaction of Al and SiO2 powder blends by mechanical alloying (MA) for 20 h and low-temperature sintering. The microstructural evolution of powder and compacted specimens were studied by X-ray diffraction and scanning electron microscopy. The extent of the milling on the displacement reaction was studied by differential thermal analysis (DTA). The results show that the reaction between Al–SiO2 couple does not initiate after milling up to 20 h but occurs after thermal treatment of powders. DTA results indicate a lowering in the reaction temperature of Al–SiO2 couple after milling. Following the DTA results, we densified the Al–SiO2 powder compacts at 700°C to produce an in-situ Al–Si/Al2O3 composite. The physical, mechanical, and tribological performance of the composite at different milling times are also reported here. [ABSTRACT FROM AUTHOR]

In this work, we studied the brazing characteristics of Al2O3 and 3D printed Ti–6Al–4V alloys using a novel equiatomic AlZnCuFeSi high entropy alloy filler (HEAF). The HEAF was prepared by mechanical alloying of the constituent powder and spark plasma sintering (SPS) approach. The filler microstructure, wettability and melting point were investigated. The mechanical and joint strength properties were also evaluated. The results showed that the developed AlZnCuFeSi HEAF consists of a dual phase (Cu–Zn, face-centered cubic (FCC)) and Al–Fe–Si rich (base centered cubic, BCC) phases. The phase structure of the (Cu–Al + Ti–Fe–Si)/solid solution promises a robust joint between Al2O3 and Ti–6Al–4V. In addition, the joint interfacial reaction was found to be modulated by the brazing temperature and time because of the altered activity of Ti and Zn. The optimum shear strength reached 84 MPa when the joint was brazed at 1050 °C for 60 s. The results can be promising for the integration of completely different materials using the entropy driven fillers developed in this study. [ABSTRACT FROM AUTHOR]

In this work, we have attempted to develop the Ag-Cu-Ti filler for bonding ZrO2 to Ti-6Al-4V. The CeO2 nanoparticles were reinforced in the eutectic Ag-Cu-Ti filler via mechanical mixing and melting route. Furthermore, the brazeability, microstructure, and mechanical behavior, as well as brazing performance of the ZrO2/Ti-6Al-4V joints, were assessed. The wettability of the Ag-Cu-Ti matrix was increased from 89 to 98% on Ti-6Al-4V and from 83 to 89% on the ZrO2 substrate after the addition of 0.05% CeO2. Also, there was a depression in the melting point of the composite fillers up to 3°C. The microstructure consists of Cu- and Ag-rich phases and Cu-Ti intermetallic compounds (IMCs). The joint shear strength was improved with the addition of CeO2 up to 0.05 wt.% in the matrix. It was inferred that, for an excellent brazing performance of the ZrO2/Ti-6Al-4V joint, the optimum amount of CeO2 should be 0.05 wt.% in the Ag-Cu-Ti matrix. [ABSTRACT FROM AUTHOR]

A Cu-coated C nanofiber (Cu-CNF) composite is added to a Sn-3.5Ag alloy to fabricate a solder nanocomposite using mechanical stirring and a melting technique. The microstructural features of the samples, i.e., the β-Sn grain size and the distribution and thickness of the Ag3Sn intermetallic compound (IMC), are statistically measured. The wettability of the developed solders is tested on a Cu substrate by contact-angle and spreading-factor measurements. The experimental results indicate that the presence of up to 0.05 wt pct Cu-CNFs in the solder matrix reduces the β-Sn secondary dendritic arm spacing significantly. Additionally, the spread ratio and spread factor are improved to 93 and 96 pct, respectively, owing to the adsorption of surface-active CNFs in the solder matrix. Furthermore, the addition of 0.05 wt pct Cu-CNFs to the Sn-Ag (SA) alloy increases the microhardness, tensile strength, elongation percentage (El pct), and toughness by 40, 35, 11, and 33 pct, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this article, the authors present the synthesis of Sn-1.0Ag-0.5Cu (SAC105) alloy embedded with zirconium oxide nanoparticles using simple mechanical blending and casting route. The cast samples were characterized in terms of microstructural evolution, wetting, microhardness, and drop test reliability. The characterizations were performed by using a tabletop X-ray diffraction, field emission scanning electron microscope, and the compositions were identified by energy dispersive spectroscopy. The results showed that addition of ZrO2 nanoparticles significantly refines the grain size, Ag3Sn, and Cu6Sn5 intermetallic compounds thickness by 46, 14, and 26% respectively as compared to the single component SAC105 alloy. The results were also compared with those of standard Sn-3.0Ag-0.5Cu (SAC305) alloy. Although the spreading and microhardness of SAC105 is found to be slightly poor or comparable to SAC305 yet drop test reliability can be improved significantly after addition of ZrO2 nanoparticles appreciably. This kind of refinement results in a cheap alternative to SAC305 with comparable mechanical strength and high solder joint reliability.Graphical Abstract: [ABSTRACT FROM AUTHOR]

Disks of commercial Al-1050 and ZK60A alloys were stacked together and then processed by conventional high-pressure torsion (HPT) through 1 and 5 turns at room temperature to investigate the synthesis of an Al–Mg alloy system. Measurements of microhardness and observations of the microstructures and local compositions after processing through 5 turns revealed the formation of an ultrafine multi-layered structure in the central region of the disk but with an intermetallic β-Al3Mg2 phase in the form of nano-layers in the nanostructured Al matrix near the edge of the disk. The activation energy for diffusion bonding of the Al and Mg phases was estimated and it is shown that this value is low and consistent with surface diffusion due to the very high density of vacancy-type defects introduced by HPT processing. The results demonstrate a significant potential for making use of HPT processing in the preparation of new alloy systems. [ABSTRACT FROM PUBLISHER]

Aluminum alloys with nanocrystalline (NC) and ultrafine grain (UFG) size are of interest because of their strengths that are typically 30 pct greater than conventionally processed alloys of the same composition. In this study, UFG AA 5083 plate was prepared by quasi-isostatic (QI) forging of cryomilled powder, and the microstructure and mechanical behavior was investigated and compared with the behavior of coarse-grained AA 5083. Forging parameters were adjusted in an effort to strengthen the UFG material while retaining some tensile ductility. Different forging parameters were employed on three plates, with approximate dimensions of 254 mm diameter and 19 mm thickness. The overarching goal of the current effort was to increase strength through minimized grain growth during processing while maintaining ductility by breaking up prior particle boundaries (PPBs) with high forging pressures. Mechanical tests revealed that strength increased inversely with grain size, whereas ductility for some of the experimental materials was preserved at the level of the conventional alloy. The application of the Hall-Petch relationship to the materials was studied and is discussed in detail with consideration given to strengthening mechanisms other than grain size, including dispersion (Orowan), solid solution, and dislocation strengthening. [ABSTRACT FROM AUTHOR]

Abstract: Experiments were conducted to evaluate the microstructural evolution occurring in the Zn–22% Al eutectoid alloy when processed by high-pressure torsion (HPT) over a range of experimental conditions. Processing by HPT reduces the grain size and at the edges of the disks it produces agglomerates of Zn-rich and Al-rich grains lying in bands delineating the torsional straining. Unlike most metals processed by HPT, the measured hardness values are lower than in the initial annealed condition. This is due to a significant reduction during processing in the distribution of Zn precipitates which are visible within the Al-rich grains in the annealed condition. It is shown that all of the hardness measurements are mutually consistent when plotted against the calculated equivalent strain. [Copyright &y& Elsevier]

In this work, we have investigated the role of high-energy ball milling (HEBM) on the evolution of microstructure, thermal, and wetting properties of an Sn-0.7Cu alloy. We ball-milled the constituent Sn and Cu powders in eutectic composition for 45 h. The microstructural studies were carried out using optical and scanning electron microscopy. The melting behavior of the powder was examined using differential scanning calorimetry (DSC). We observed a considerable depression in the melting point of the Sn-0.7Cu alloy (≈7 °C) as compared to standard cast Sn-0.7Cu alloys. The resultant crystallite size and lattice strain of the ball-milled Sn-0.7Cu alloy were 76 nm and 1.87%, respectively. The solderability of the Sn-0.7Cu alloy was also improved with the milling time, due to the basic processes occurring during the HEBM. [ABSTRACT FROM AUTHOR]

We have produced pure Sn coatings from an alkaline bath plating. The plating bath was composed of sodium stannate and sodium hydroxide with sorbitol as an additive. The experiments were performed with a potentiostat/galvanostat at various current densities from 5–25 mA/cm2. The morphology of the coatings, thickness, plating rate, and microhardness were evaluated. Furthermore the wetting of the Sn coatings on a Cu substrate was also assessed by area spread ratio measurements after reflow at 250 °C. The resultant coatings were very smooth and shiny. Initially, the plating morphology was uneven and a nodular type, which further improved with increasing current density up to 15 mA/cm2. The plating rate and thickness were the maximum at a current density of 15 mA/cm2. The coatings had higher strength and solderability at 15 mA/cm2 due to the improved microstructure and plating rate. [ABSTRACT FROM AUTHOR]

Abstract: Experiments were conducted to examine the evolution of microstructure and mechanical properties in a Zn–22% Al eutectoid alloy processed by high-pressure torsion (HPT). Measurements of the Vickers microhardness revealed significant weakening in the alloy after HPT, and microstructural analysis showed that the initial duplex structure, consisting of equiaxed grains and lamellae, was retained at the disk centers after HPT, whereas equiaxed fine grains were observed at the disk edges. Direct evidence is presented for a transformation of the lamellae into equiaxed very fine grains and subsequent dynamic recrystallization in the early stages of HPT. The reduction of the lamellar structure and the loss of Zn precipitates account for the weakening in the alloy in HPT processing. Excellent high strain rate superplasticity was recorded after HPT, with elongations up to ∼1800% at 473K at a strain rate of 10−1 s−1. The experiments show that the maximum elongations are displaced to faster strain rates with increasing numbers of HPT turns. [Copyright &y& Elsevier]

In this study, multicomponent AlCuSiZnFe high entropy alloy (HEA) was fabricated through high energy ball milling (HEBM) of constituent powders, and further densification via spark plasma sintering (SPS). The results show the presence of a predominant face-centered cubic (FCC) phase with a minor body-centered cubic (BCC) phase in (45 h) HEBMed powders which further develop according to the SPS treatment. At a low SPS temperature of 600 °C, the alloying of individual elements was poor. Further, at 650 °C, alloying improves and the liquid Cu–Zn FCC phase separates from the high-temperature Fe–Si-rich BCC phase during SPS. At 700 °C, Al was noticed to stabilize the BCC phase leaving behind soft FCC (Cu–Zn). Further increase in SPS temperature to 800 °C causes a complete melting of HEA compacts and the formation of Cu–Al intermetallic compounds (IMCs). The microhardness of the HEA compacts increases with SPS temperature in the range of 690–974 HV. The compressive properties were found to be optimum at 650 °C, compressive strength ≈1987 MPa and elastic modulus ≈27,945 MPa respectively. The measured densities of HEAs varied from 4.98 to 5.24 g/cm3, comparable to the heaviest of lightweight Ti alloys reported so far. • Novel, Cantor-free, dual-phase AlZnCuFeSi high entropy alloy with ultrahigh strength. • The density of the alloys is close to Ti alloys in the range of 4.9–5.24 g/cm3. • Optimum balance of strength and plasticity is obtained after sintering at 650 °C. [ABSTRACT FROM AUTHOR]

The present study explores the mechanical and tribological properties of AlCrFeNiTi high entropy alloy (HEA) processed by mechanical alloying (MA) and spark plasma sintering (SPS). The results show the formation of a single-phase BCC structure after MA at 30 h, and after SPS a single BCC phase decomposed into dual BCC1; AlNi2Ti, and BCC2; CrFe phases. The maximum hardness of ∼960 ± 10 HV and ultimate compressive strength of ∼1650 ± 50 MPa were achieved. The nano hardness of ∼951 ± 21 HV IT and the elastic modulus of ∼256 ± 22 GPa were observed. Further, the ball-on-disc dry sliding tests were performed to study the friction and wear behavior of HEA at different loads and sliding velocities. The average coefficient of friction is about 0.3 for all the applied loads, suggesting no significant difference with load. In contrast, the average coefficient of friction slightly increased from 0.23 to 0.27 with increasing velocity. The specific wear rate increased from 2.66 to 5.06 × 10−6 mm3/Nm and 2.2 to 3.61 × 10−6 mm3/Nm with increasing load from 5 to 15 N and velocity from 0.08 to 0.12 m/s, respectively. Moreover, a transition in wear mechanism was observed from abrasive to oxidative and delamination wear with increasing load and sliding velocity. • An equiatomic AlCrFeNiTi HEA was prepared by powder metallurgy route and studied the mechanical and tribological properties. • A single BCC phase was achieved after MA at 30 h and decomposed into dual phases as BCC1; AlNi2Ti, and BCC2; CrFe after sintering. • A superior hardness of 960±10 HV and elastic modulus of 256±22 GPa was achieved. • The COF and wear rate of HEAs are influenced by the sliding conditions. • A significant transition in wear mechanism was observed from abrasive to oxidative and delamination wear with increasing load and sliding velocity. [ABSTRACT FROM AUTHOR]

Abstract: Organic thin film transistor (OTFT) chemical sensors rely on the specific electronic structure of the organic semiconductor (OSC) film for determining sensor stability and response to analytes. The delocalized electronic structure is influenced not only by the OSC molecular structure, but also the solid state packing and film morphology. Phthalocyanine (H2Pc) and tetrabenzoporphyrin (H2TBP) have similar molecular structures but different film microstructures when H2Pc is vacuum deposited and H2TBP is solution deposited. The difference in electronic structures is evidenced by the different mobilities of H2TBP and H2Pc OTFTs. H2Pc has a maximum mobility of 8.6×10−4 cm2 V−1 s−1 when the substrate is held at 250°C during deposition and a mobility of 4.8×10−5 cm2 V−1 s−1 when the substrate is held at 25°C during deposition. Solution deposited H2TBP films have a mobility of 5.3×10−3 cm2 V−1 s−1, which is consistent with better long-range order and intermolecular coupling within the H2TBP films compared to the H2Pc films. Solution deposited H2TBP also exhibits a textured film morphology with large grains and an RMS roughness 3–5 times larger than H2Pc films with similar thicknesses. Despite these differences, OTFT sensors fabricated from H2TBP and H2Pc exhibit nearly identical analyte sensitivity and analyte response kinetics. The results suggest that while the interactions between molecules in the solid state determine conductivity, localized interactions between the analyte and the molecular binding site dominate analyte binding and determine sensor response. [Copyright &y& Elsevier]

Abstract: The co-doping characteristics on microstructure and thermal properties of barium titanate (BaTiO3) were investigated to elucidate formation of core–shell structure by dysprosium (Dy) and thulium (Tm) addition in the BaTiO3–Dy2O3–Tm2O3 system. The dielectrics co-doped with 0.7mol% Dy2O3 and 0.3mol% Tm2O3 had the dielectric constant up to 2200 as a function of temperature, which was 30% higher than that of specimen containing only Tm2O3 at the room temperature. It could be explained by the fact that the increase of Dy2O3 addition contributed to the improvement of dielectric constant. On the other hand, the rapid diffusion rate of Dy3+ ions in BaTiO3 showed an adverse effect on temperature stability caused by destruction of core–shell. As the compensation for shell expansion in BaTiO3, the reinforcement of the core–shell structure through the addition of Tm2O3 was confirmed by TEM-EDS analysis and attributed the temperature coefficient of capacitance (TCC) in a reliability condition (−55°C to 125°C, △C=±15% or less). The enhanced electrical properties and temperature stability could be deduced from the generation of electrons and the formation core–shell structure in co-doped BaTiO3 system respectively. [Copyright &y& Elsevier]