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High-purity and bulk Ta4AlC3 ceramics were successfully fabricated by spark plasma sintering (SPS) and subsequent heat treatment, using the raw materials including TaC and Ta2AlC powders. These raw materials were first synthesized by self-propagation high temperature synthesis from elements tantalum, aluminium and carbon black powders, followed by pressure-less sintering. The as-fabricated bulk Ta4AlC3 was relatively stable when subjected to heat treatment at elevated temperature of 1500°C. Moreover, prolonging the heat treatment time resulted in bigger grain sizes and higher densities of the Ta4AlC3. The flexural strength and the fracture toughness of the Ta4AlC3 fabricated by SPS were found to be 411MPa and 7.11MPa•m1/2, respectively. After the heat treatment at 1500°C for 8 h, the flexural strength and the fracture toughness of the Ta4AlC3 could reach 709MPa and 9.23MPa•m1/2, respectively. The special structural characteristics of the ternary ceramics and the increase of density after the heat treatment are the main reasons for the variation in mechanical properties of ternary ceramics.

More and more attention is being paid to the influence of powder mixing on the mechanical properties and corrosion resistance of WC-based cemented carbides. In this study, WC was mixed with Ni and Ni/Co, respectively, by chemical plating and co-precipitated-hydrogen reduction, which are labelled as WC-NiEP, WC-Ni/CoEP, WC-NiCP and WC-Ni/CoCP, respectively. After being densified in a vacuum, the density and grain size of CP were denser and finer than those of EP were. Simultaneously, the better mechanical properties of flexural strength (1110 MPa) and impact toughness (33 kJ/m2) were obtained by WC-Ni/CoCP due to the uniform distribution of WC and binding phase and solid solution enhancement of the Ni-Co alloy. In addition, the lowest self-corrosion current density of 8.17 × 10−7 A·cm−2, a self-corrosion potential of −0.25 V and the biggest corrosion resistance of 1.26 × 105 Ω in 3.5 wt % NaCl solution were obtained by WC-NiEP because of the presence of the Ni-Co-P alloy. [ABSTRACT FROM AUTHOR]

In this research, thermoplastic polyimide (TPI) were welding via friction stir spot welding (FSSW) in order to evaluate the feasibility of the technology. The welding tool with a tri-flute pin was used for keeping the welding effectiveness. The effect of the rotation speed and dwell time on the microstructure and shear strength was studied. The results shows that the number of gap defects between the shoulder affect zone and the pin affect zone decreased with the increase of the rotation speed. The boundary of the shoulder affect zone and the pin affect zone was no clear when increasing the dwell time from 10 s to 20 s. Long dwell time could increase the mixing time and reduce the materials viscosity, which made the structure was denser. The maximal shear strength was obtained 85.5% of the base materials. The differential scanning calorimetry (DSC) results indicated that the melting behaviour of different regions was no obvious difference. It indicated that FSSW had a feasible and potential technology to join the high temperature resistant engineering plastics. [ABSTRACT FROM AUTHOR]

For a long time, people believed that the Pt/C particles aggregation in proton exchange membrane fuel cell (PEMFC) catalyst layer will inevitably lead to lower catalyst utilization. However, our research showed that Pt/C particles aggregation sometimes made catalyst utilization increases. PEMFC catalyst layer microstructure two-phase lattice models, in which we hypothesized that these catalyst layers was composed of C phase (Pt/C particles) and IP phase (the mixture phase of pore and ionic polymer), were used to simulate the effect of Pt/C particles aggregation on catalyst utilization, IP phase tortuosity and cell performance. It was found that when IP phase volume fraction ε < 0.6, catalyst utilization indeed decreased with the increase of aggregation coefficient φ . But, when ε > 0.65, the catalyst utilization of electrodes with Pt/C particles aggregation was larger than the electrode without Pt/C particles aggregation. At the same time, IP phase tortuosity decreased with increasing Pt/C particles aggregation coefficient. In overall consideration of the above factors, the best value of Pt/C particles aggregation coefficient was 5. [ABSTRACT FROM AUTHOR]

A high performance near eutectic Al–Si–Mg alloy profile is developed by micro alloying with 0.1wt.% Ti. The tensile properties of near eutectic Al–Si–Mg alloy with and without Ti in different processing conditions are tested for comparison. Microstructure evolution is observed by optical, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Results show that the yield strength (YS), ultimate tensile strength (UTS) and elongation of 0.1wt.% Ti alloyed A2 alloy reach up to 193 MPa, 296 MPa and 12.3% respectively, the tensile strength of which is about 50% higher than that of as-extruded base alloy and even stronger than that of the base alloy micro alloyed by 0.1wt.% Zr or 0.1wt.% V. Addition of 0.1wt.% Ti has obvious refine effect on the microstructure of as-cast Al–Si–Mg alloy, however, it has minor strengthening effect on the as-cast mechanical properties. [ABSTRACT FROM AUTHOR]

Fe-based coatings with a high amorphous content were firstly developed by the traditional twin wires arc spray technology. In consideration of empirical rules, including the multi-component system, an optimal concentration of small atoms, negative heat of mixing and an appropriate atom size mismatch among the main components, the cored wires were designed to contain eight elements, which have an optimized atomic volume strain criterion λ n , in range of 0.14–0.21, to render the coatings a high glass forming ability. Then the coatings were prepared using the above-designed cored wires through a rapid arc spray melting and solidification process. Crystalline phases could not be identified from the XRD patterns within the XRD resolution limits, suggesting that the as-sprayed coatings were approximately comprised of fully amorphous phases. With a dense structure and a low porosity of only 2%, the amorphous Fe-based coatings exhibited an attractive combination of high hardness (900–1100 HV 0.3 ) and superior bonding strength (44.9–54.8 MPa). The coating at λ n = 0.21 had the lowest Gibbs free energy difference Δ G , exhibited the largest super-cooled liquid region Δ T x , Lu’s criterion factor γ value and the heat of crystallization (Δ H ) values, which indicating the highest GFA. [ABSTRACT FROM AUTHOR]

The development of surface microstructure with specific features in electrospun nanofibers has attracted more and more attention in recent years. In this article, a common biological polyester, poly(3-hydroxybutyrate- co-3-hydroxyvalerate) (PHBV) was electrospinning into nanofibers with 'coral-like' surface microstructure by a conventional-electrospinning setup. The effect of the process parameters on the microstructure in electrospun nanofibers were investigated via a series of experiments. The formation mechanism of this feature structure and cytotoxicity assays of PHBV membrane were also discussed. The water contact angle of the electrospun PHBV membrane was higher than that of the PHBV cast film due to a very-rough fiber surface including porous beads when PHBV was electrospun from the concentration of 4 wt %. Because of special hole shape and size distribution, the physical structure of surface of PHBV electrospun fibers offered it special properties, such as specific-surface area, hydrophilic-hydrophobic properties, adhesion properties of cells and biological substances, etc. The demonstrated method of form coral structure would contribute to the areas such as filtration, sensor, tissue engineering scaffolds, and carriers of drugs or catalysis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

Abstract: SiO2–cBN composites were consolidated by spark plasma sintering at 1473–1973K. The effects of cBN content and sintering temperature on the relative density, phase transformation, microstructure and mechanical properties of the SiO2–cBN composites were investigated. The relative density of the SiO2–cBN composites increased with increasing SiO2 content. The phase transformation of cBN to hBN in SiO2–cBN composites was identified at 1973K, showing the highest transformation temperature in cBN-containing composites. The SiO2–20vol% cBN composites sintered at 1673K showed the highest hardness and fracture toughness of 12.5GPa and 1.5MPam1/2, respectively. [Copyright &y& Elsevier]

Abstract: Al2O3–cBN/Ni composites were consolidated by spark plasma sintering (SPS) using α-Al2O3 and Ni nanoparticle precipitated cBN (cBN/Ni) powders. The Ni nanoparticles, 10–100nm in diameter and 0.5–2.2mass% in content, were precipitated on cBN powder by rotary chemical vapor deposition. The effect of sintering temperature (T SPS) and Ni content (C Ni) on the densification, phase transformation, microstructure and hardness of the Al2O3–cBN/Ni composites were investigated. The highest relative density of Al2O3–30vol% cBN composite was 99% at T SPS =1573K and C Ni =1.7mass%. At T SPS =1673K, the relative density decreased due to the phase transformation of cBN to hBN. The Vickers hardness of Al2O3–30vol% cBN/Ni at T SPS =1573K and C Ni =1.7mass% showed the highest value of 27GPa. [Copyright &y& Elsevier]

Abstract: Spark plasma sintering technique was used to in situ fabricate high dense Ti3SiC2–TiC composites. The calculated TiC volume content from X-ray diffraction (XRD) is close to the theoretical one. It is found from fracture surface observation that TiC is about 1μm, and Ti3SiC2 is about 2–10μm in grain size. The fracture modes consist of intergranular mainly for Ti3SiC2 and transgranular fracture mainly for TiC. With the increasing of TiC volume content, Vickers hardness increases to the maximum value of 13GPa for Ti3SiC2-40vol.%TiC. Fracture toughness and flexural strength of the composites are also improved compared with those of monolithic Ti3SiC2 except for Ti3SiC2-40vol.%TiC composite. The main reasons for the sudden decrease of fracture toughness and flexural strength of Ti3SiC2-40vol.%TiC composite can be attributed to the relatively lower density, some clusters of TiC in the composite and the transition of fracture mode from intergranular to transgranular. The thermal conductivities decreased with the addition of TiC. The minimum thermal conductivity is 22Wm°C−1 for Ti3SiC2-40vol.%TiC composite. [Copyright &y& Elsevier]

Abstract: Ti/Si/C powders were used to fabricate high purity Ti3SiC2 with the aids of Al by spark plasma sintering (SPS). The results showed that the dense Ti3SiC2 samples with <2wt.% TiC could be rapidly synthesized from Ti/Si/C/Al mixtures at 1280°C for 6–36min. The sintering temperature and the sintering time was lower and shorter than that by hot isostatic pressing (HIP) or hot pressing (HP) from Ti/Si/C mixtures. The microstructures of Ti3SiC2 depend on the sintering temperature and holding times of SPS and can be controlled accordingly. The technological implication of this work is that, with the aids of Al, Ti/Si/C can be suggested to be the powder mixture to synthesize high purity Ti3SiC2 in addition to Ti/Si/TiC powder mixture. [Copyright &y& Elsevier]

A mixture of Ti, C, Si powders and Al (as a sintering aid) was adopted to synthesize the Ti3SiC2–SiC nanocomposite using the spark plasma sintering-reactive synthesis method. SiC did not form directly from Si and C, but from intermediate phases TiC x and Ti5Si3C y , leaving C. The grain size of Ti3SiC2 is about 5μm, but the average grain size of SiC is about 100nm. With its fine microstructure, the Ti3SiC2–20vol.%SiC composite shows improved mechanical properties at room temperature. [Copyright &y& Elsevier]

Flow pattern defects (FPDs) is one kind of grown-in defects in large diameter Czochralski silicon (Cz-Si) crystals. The evolution of FPDs in lightly doped Cz-Si crystals during secco etchant (50% HF: 0.15 mol L-1K2Cr2O7=2:1) etching process, was studied in detail firstly. The results also showed that the outline of FPDs became larger and the void on the tip of FPDs changed into a shallow hole with the increasing of etching time. A parabola model was firstly put forward to explain the evolution of FPDs in Cz-Si wafers during the procedure. Furthermore, the microstructure of FPDs was observed by optical microscopy and atomic force microscopy, the results showed that the outline of FPDs was parabola with several steps and two heaves were firstly found on the left and right sides of the void on the tip of FPDs. All the results provide forceful evidence to that FPDs is one kind of void-type as-grown defects. These are very useful to investigate FPDs in Cz-Si wafers further and explain the annihilation of FPDs during high temperature annealing processes. [Copyright &y& Elsevier]

Two pieces of plate glass were brazed into a composite of glazing with a vacuum chamber using PbO-TiO 2 -SiO 2 -R x O y powder filler alloys to develop a new type of vacuum glazing. The brazing process was carried out by laser technology. The interface characteristics of laser brazed joints formed between plate glass and solder were investigated using optical microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The results show that the inter-diffusion of Pb/Ti/Si/O elements from the sealing solder toward the glass and O/Al/Si elements from the glass toward the solder, resulting in a reaction layer in the brazed joints. The microstructure phases of PbTiO 3 , AlSiO, SiO 2 and PbO in the glass/solder interface were confirmed by XRD analysis. The joining of the sealing solder to the glass was realized by the reaction products like fibrous structures on interface, where the wetting layer can help improve the bonding performance and strength between the sealing solder and the plate glass during the laser brazing process. [ABSTRACT FROM AUTHOR]

Because inadequate control of the temperature of vacuum glazing may cause changes in form, stress, microstructure, or performance and thereby affect its lifetime, vacuum welding has been adopted to seal the vacuum glazing from the side, and experiments using different sealing temperatures have been executed. The impact of different sealing temperatures on the microstructure of the sealing layer was analyzed to evaluate the combination of material science features on the interface and to reveal the influence of the sealing temperature on the hardness and residual stress of the sealing layer. The results show that a sufficiently high sealing temperature will drive the sealing layer to transform from a hybrid structure to the liquid phase, accelerate the element migration, eliminate pores, stabilize and compact the structure and improve the sealing performance of the vacuum glazing. As the sealing temperature increases, the residual stress and hardness substantially increase. However, when the sealing temperature reaches 460 °C, the residual stress and hardness begin to plateau, and when the sealing temperature reaches 470 °C, no further change can be detected. Therefore, a sufficiently high sealing temperature is beneficial to the bonding of glass and sealing solder and can promote the sealing performance of the vacuum glazing. [ABSTRACT FROM AUTHOR]

Abstract: A WC–Co–Cr coating was deposited by a high velocity oxy-fuel thermal spray (HVOF) onto a 1Cr18Ni9Ti stainless steel substrate to increase its cavitation erosion resistance. After the HVOF process, it was revealed that the amorphous phase, nanocrystalline grains (Co–Cr) and several kinds of carbides, including Co3W3C, Co6W6C, WC, Cr23C6, and Cr3C2 were present in the coating. The hardness of the coating was improved to be 11.3GPa, about 6 times higher than that of the stainless steel substrate, 1.8GPa. Due to the presence of those new phases in the as-sprayed coating and its higher hardness, the cavitation erosion mass loss eroded for 30h was only 64% that of the stainless steel substrate. The microstructural analysis of the coating after the cavitation erosion tests indicated that most of the corruptions took place at the interface between the un-melted or half-melted particles and the matrix (Co–Cr), the edge of the pores in the coating, and the boundary of the twin and the grain in the stainless steel 1Cr18Ni9Ti. [Copyright &y& Elsevier]

The development of excellent performance coarse-grained WC-Co cemented carbides has emerged as a hot topic for cutting tools, drills, molds, wear-resistant parts, etc. In this study, the WC powder was coated by Co and La 2 O 3 simultaneously using a new coprecipitation strategy, and its beneficial effects on the densification, microstructure and mechanical properties of WC-10Co was systematically investigated. Firstly, due to the successful introduction of La 2 (C 2 O 4) 3 precursor, the surprising transformation of rod-like loosely CoC 2 O 4 to regular-spherical-like dense one was observed, further inducing the dense and uniform coating of La 2 O 3 with Co on the surface of WC after the H 2 reduction treatment. The addition of La 2 O 3 by this way was found to improve the grain uniformity of WC in the sintered cemented carbide, inhibiting the appearance of abnormally grown grains, and preventing the conversion of Co FCC to Co HCP effectively, which should be ascribed to the segregation of La 2 O 3 on the grain boundary of WC, produced pinning effect and inhibited the dissolution and growth of WC grains. The mechanical properties of coarse-grained WC-Co cemented carbides, including hardness, strength, fracture toughness and elastic modulus were systematically investigated, validating the beneficial effects of Co and La co-precipitation apparently. In general, this study presents a new strategy for enhancing the performance of coarse-grained WC-Co cemented carbides by both powder mixing design and grain boundary tailoring. • A novel is adopted to achieve two-dimensional growth of CoC 2 O 4 • The pinning of La 2 O 3 at grain boundaries tailors the grain distribution of WC • The successful introduction of La 2 O 3 prevents the transformation of Co FCC to Co HCP • The enhanced performance of cemented carbides by both powder mixing design and grain boundary tailoring are obtained [ABSTRACT FROM AUTHOR]

Nickel-based superalloys, owing to their superior resistance against mechanical and chemical degradation, have been widely applied in the aerospace, turbine engine, nuclear reactor, and chemical industries. The microstructure recognition plays a key role in the characterization and design of new superalloys. Although deep learning techniques have achieved satisfactory performance in the microstructure recognition, these methods usually suffer from generalization when the alloy composition or process changed, especially in the high-throughput experiments. In this paper, we propose a semi-supervised deep transfer learning framework for the microstructure recognition of nickel-based superalloys with different compositions and heat treatment procedures. To be specific, we achieve the knowledge transfer of recognition models from one condition (source domain) to another (target domain) by feature distribution alignment (FDA). To avoid the over-fitting, we design a dynamic alignment strategy to achieve the feature alignment based on the label guidance. Additionally, we effectively utilize the unlabeled samples in the target domain and achieve the distribution alignment between the two domains by adversarial training. The experimental results show that our method is superior to the commonly used deep transfer learning methods. In spite of few labeled samples, it can also approach the satisfactory accuracy. Codes are available at: https://github.com/yangchuanwu/FDA. • A semi-supervised deep transfer learning framework for high throughput characterization was developed. • For labeled and unlabeled samples, the feature distribution alignment method is used to transfer knowledge from the source domain to the target. • By learning from small samples, our method can approach the accuracy obtained by training a large number of samples. [ABSTRACT FROM AUTHOR]

Abstract: Low-temperature aging treatments at 120°C for 8h, with and without deep cryogenic pretreatments, were conducted for friction-stir-welded joints of 2024-T351 aluminum alloys. The microstructures and mechanical properties of the welded joints after the above treatments were investigated. Two obvious soft zones were found to be located at the retreating and advancing sides of the heat-affected zone (HAZ) in the as-welded joint. After a single low-temperature aging treatment (LTA), the soft regions close to the base metal in the HAZ almost vanished, while the soft regions close to the thermal-mechanical-affected zone were not significantly affected. Moreover, tensile fracture occurred along the segregation bands of the precipitates in the nugget zone (NZ). This resulted in a decrease in the elongation of the as-welded joint from 74% to 38% that of the base metal. After low-temperature aging with a deep cryogenic pretreatment at 77K, the features of the soft zones were similar to those in the case of the single LTA, but the tensile fracture at the segregation bands in the NZ was inhibited. Consequently, the elongation of the joints improved along with an increase in tensile strength. The possible mechanisms related to the improvement of tensile properties of the joints were discussed. [Copyright &y& Elsevier]

In this paper, the safe sealing temperature range of tempered glass was determined to be no more than 300 °C by experiments. On this basis, the feasibility of silver oxide system low melting solder (SOSLMS) used in tempered vacuum glazing (TVG) sealing was explored by sealing strength experiment, scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and other test methods. The results of sealing strength experiment showed that the bonding strength of the sealing layer was inversely proportional to the sealing temperature. The bonding strength of the sealing layer in the range of 260 °C–290 °C met the standard requirements (not less than 0.6 MPa) except for the failure of the sample sealing at 300 °C. The observation results of SEM showed that when the sealing temperature was 260 °C and 270 °C, the solder layer had uniform fusion and dense structure, and the sealing layer was tightly bonded. With the increase of sealing temperature, the solder layer began to produce large holes, and there was obvious open gap between solder layer and glass substrate after stretching. The analysis results of EDS showed that the Ag and V elements all diffused into the glass at each sealing temperature, the difference of diffusion concentration and distribution was not significant. The analysis results of XRD showed that when the sealing temperature was in the range of 260 °C–270 °C, there was no crystallization phenomenon in the SOSLMS. When the sealing temperature was in the range of 280 °C–300 °C, Ag 2 VO 2 PO 4 crystals began to precipitate, and with the increase of temperature, the higher the crystallinity was, the greater the crystal content was. In conclusion, in the range of 260 °C–270 °C, the SOSLMS showed good sealing performance, which was suitable for TVG sealing. • A kind of silver oxide system low melting solder was considered to be suitable for tempered vacuum glazing sealing. • The optimal sealing temperature range of silver oxide system low melting solder was 260 °C–270 °C. • The bonding strength of the sealing layer was inversely proportional to the sealing temperature. • The precipitation of Ag 2 VO 2 PO 4 crystals was considered to be the fundamental reason of the reduction of bonding strength. [ABSTRACT FROM AUTHOR]