Search

NiAl alloy sheet was successfully prepared using current-assisted sintering, thus verifying the possibility of preparing a NiAl thin-wall component by current-assisted sintering and foil/foil reaction synthesis. Ni/Al laminated sheets were obtained by annealing at 550 °C at 5 MPa for 0.5 h; uniform NiAl alloy sheets were fabricated by annealing at 1150 °C at 15 MPa for 20 min. The experimental results showed that current-assisted sintering significantly reduced the reaction temperature and reaction time. Microstructural characterization revealed that the inter-diffusion ability of Al atoms is considerably weaker than that of Ni atoms. Molecular dynamics simulation confirmed these experimental results and showed that this difference becomes significant under the action of an electric field. The mechanism of synthesis of Ni/Al laminated sheets using current sintering is mainly determined by the diffusion behavior of Ni atoms. [ABSTRACT FROM AUTHOR]

By applying the TC4-Ti2AlC composite coatings to the Ti6Al4V substrate by laser, the wear resistance of the Ti6Al4V alloy was improved. Analysis was done on the composite coatings' microstructure, phase composition, microhardness, and tribological characteristics. According to the findings, coatings without defects can be created when Ti2AlC content ranges between 5 and 15 wt.%. Furthermore, the coating without Ti2AlC consisted of a α-Ti solid solution while coatings with Ti2AlC included a α-Ti solid solution, hard phases of TiC and Ti3Al, as well as a Ti2AlC ceramic phase. During laser cladding, Ti2AlC partially dissolved and turned into TiC and Ti3Al, resulting in an average hardness of 371.61 ± 3.95 HV0.5, 382.92 ± 3.61 HV0.5, 388.91 ± 3.29 HV0.5 for the coatings with Ti2AlC weight fractions of 5, 10, and 15%, respectively. These numbers were about 1.16 ~ 1.22 times the hardness of the titanium alloy matrix (320 ± 3.12 HV0.5). Besides, the Ti2AlC lubricant and hard phases act synergistically to bring composite coatings better performances in wear resistance and friction reduction compared to the pure TC4 coating. The lowest coefficient of friction (0.382) (COF) and the greatest wear resistance (8.87 × 10−5 mm3/N m) were obtained at the composition of TC4-10wt.%Ti2AlC; more particularly, the wear resistance at TC4-10wt.%Ti2AlC was 1.2–2.1 times that of pure TC4 coating. The principal causes of wear in a pure TC4 coating are adhesive wear and oxidation, however, these wear processes shift to minor abrasive wear and oxidation when assisted by oxide coatings, Ti2AlC lubricant, and TiC, Ti3Al hard phases. [ABSTRACT FROM AUTHOR]

Turbine blades are the most demanding components in aircraft engines, and their performance is related to the safety of the whole engine. Due to the complex service environment and harsh service conditions of blades, various types of damage cannot be prevented in service. Therefore, it is of great engineering and economic significance to study the service damage of blades. In this paper, the directional solidification alloy turbine blade after actual service was selected as the research object. The cross section position of 80% upper height of the blade was intercepted, and the qualitative and quantitative microstructure analysis was carried out by SEM and EDS analysis. The results show that there are two different types of γ' phases in this leaf. One kind of γ' phase has small size and regular shape, the other has large size and irregular shape. The degree of microscopic damage among different parts of the blade is characterized with the help of dimensional distribution characterization of the γ' phase of each part, combined with the analysis of hardness testing of each part of the cross-section.The results show that the service conditions of different parts are different, and the degree of microstructure damage is different. In addition, matrix crack and coating crack in some parts of blade are summarized and analyzed. [ABSTRACT FROM AUTHOR]

High-borated stainless steels prepared via ingot casting and hot rolling have a relatively low ductility, which limits their use as structural and functional materials in fuel reprocessing systems. In this study, 2.1 wt.% B stainless steel composites were prepared by a novel method of hot-roll bonding and solution treatment using an ingot casting slab and two layers of boron-free stainless steel. The aim of this study was to determine the effect of solution treatment on the interfacial microstructure and mechanical properties of high-borated stainless steel composites. As expected, a high-borated stainless steel slab containing many brittle ceramic (Cr, Fe)2 B-type particles was successfully hot-rolled and bonded with boron-free stainless steel slabs. Furthermore, metallurgical bonding was realized via the formation of ~ 50 μm wide transition regions by solution treatment, for which the mechanism was found to consist of recrystallization and diffusion-controlled reactions. The formation of transition regions enhanced the geometrical restriction effect. Neither delamination nor cracking was observed along the interfaces during a bending test of the composite plates. [ABSTRACT FROM AUTHOR]

Various constraints exist in bipedal movement. Due to the natural ability of effectively handling constraints, trajectory optimization has become one of the mainstream methods in biped gait planning, especially when constraints become much more complex on non-flat terrain. In this paper, we propose a multi-modal biped gait planner based on DIRCON, which can generate different gaits for multiple, non-flat terrains. Firstly, a virtual knot is designed to model the state transitions when the swing foot contacts terrain and is inserted as the first knot of the target trajectory of the current support phase. Thus, a complete gait or multi-modal gaits sequence can be generated at one time. Then, slacked complementary constraints, which can avoid undesired trajectories, are elaborated to describe the coupling relationships between terrain information and bipedal motion for trajectory optimization based gait planning. The concrete form of the gait planner is also delivered. Finally, we verify the performance of the planner, as well as the structural design of our newly designed biped robot in CoppeliaSim through flat terrain walking, stairs terrain walking and quincuncial piles walking. The three experiments show that the gaits planned by the proposed planner can enable the robot to walk stably over non-flat terrains, even through simple PD control. [ABSTRACT FROM AUTHOR]

The compromise between strength and plasticity has greatly limited the potential application of particles reinforced magnesium matrix composites (MMCs). In this work, the Ti particles reinforced AZ31 magnesium (Mg) matrix composites achieved simultaneous improvement in strength, elongation and wear resistance. The Ti particles reinforced AZ31 composites were fabricated by ultrasonic-assisted stir casting with hot extrusion. The results showed that a strong interfacial bonding was obtained at Ti/Mg interface because of the formation of semi-coherent orientation relationship of TiAl/Mg, TiAl/Al 2 Ti and Al 2 Ti/Mg interfaces. The as-extruded 6 wt.%Ti/AZ31 composite presented the best compressive mechanical properties and wear resistance with ultimate tensile strength, elongation and wear rate of 327 MPa, 20.4% and 9.026 × 10−3 mm3/m, obviously higher than those of AZ31 alloys. The enhanced mechanical properties were attributed to the grain refinement and strong interfacial bonding. The improved wear resistance was closely related to the increased hardness of composites and the formation of protective oxidation films. • Ti particles refine the grain size of Ti/AZ31 composites. • A strong interfacial bonding forms at Ti/Mg interface. • Ti/AZ31 composites get an increase in strength, elongation and wear resistance. [ABSTRACT FROM AUTHOR]

Abstract Mo–MoSi 2 high temperature structural materials were obtained by hot-dip siliconizing method. The results show that the silicon melt and molybdenum substrate have good wettability, molten silicon reacts with molybdenum substrate to form a molybdenum silicide phase with a columnar structure, and a strong MoSi 2 crystallographic preferred orientation (CPO) on the (110) crystal face is characterized. While, the Mo–MoSi 2 high temperature structural materials consist mainly of silicon rich layer, MoSi 2 layer, interface layer and molybdenum substrate. The coating surfaces contain a high silicon concentration (55–65 wt%) than the MoSi 2 layer (30–35 wt%). Moreover, the thicknesses and the average grain sizes of siliconized coatings increase sharply with increasing siliconizing time. The coatings thicknesses are 20, 25, 30, and 50 µm, respectively. And the average grain sizes are 6.9, 9.3, 11.7, and 11.8 µm, respectively. [ABSTRACT FROM AUTHOR]

Abstract: Effect of zinc addition on the shear property evolution between Sn-0.7Cu solder alloy and their joints reflowed at 250°C was investigated. The shear strength of Sn-0.7Cu/Cu joint was found to be higher than of Sn-0.7Cu solder alloy. Although a small addition of zinc element strengthened Sn-0.7Cu solder alloy, it decreased the shear strength of Sn- 0.7Cu solder joints. Based on the fractography analysis and interfacial microstructure observation, it is proposed that the deposition of Cu-Zn intermetallic toward the interface during reflowing is largely responsible for the shear property evolution between the Sn-0.7Cu solder alloy and their joints. [Copyright &y& Elsevier]

High-efficiency and low-cost hot forming technologies for titanium alloys have been developed for producing complex-shaped, thin-walled tubular components under non-superplastic forming conditions. Under these forming conditions, there exist complex and highly integrated material evolution processes including microscopic heterogeneous deformation, microstructure evolution and damage behaviour. This paper presents an integrated crystal plasticity finite element model of near-α titanium alloys during non-superplastic hot deformation conditions considering grain boundary sliding (GBS), dynamic recrystallisation (DRX), as well as void evolution. The polycrystalline model of a near-α TA15 titanium alloy was established, containing α phase, β phase and grain boundary (GB) regions, in which the GB region was a visualised representation of GBS. The quantitative strength ratio between the GB regions and α phase was calculated according to the Zener–Holloman parameter Z and grain size, which determined the microscopic deformation behaviour. There were found to be two high microscopic strain regions in the α phase: intragranular deformation bands through the most favourable slipping and near the GBs through multiple slipping, which promoted continuous and discontinuous DRX, respectively. With the decrease in parameter Z or grain size, the activated dislocations accommodating GBS were found to no longer pile up inside the grain, but instead travel across the grain interior. Finally, methods to improve the macroscopic plastic formability were proposed for the difficult-to-form titanium alloys experiencing non-superplastic hot deformation. [ABSTRACT FROM AUTHOR]

A Z-parameter method based on the Larson–Miller relationship is proposed to assess the remaining life of a CrMoV steel. It is found that the non-linear master curve of stress σ vs Larson–Miller parameter P of the steel can be expressed as: P=26.68-2.49 log σ-0.01σ. A family of curves parallel to the master curve can be expressed as: P=Z-2.49 log σ-0.01σ, where the value of Z represents the deviation from the master curve which corresponds with the deterioration in rupture properties. The deterioration in rupture properties is connected with the degradation of microstructure, namely the spheroidization of carbides in the pearlitic steel. A relationship between the value of the Z-parameter and the level of spheroidization E can be expressed as: Z=27.32-0.54E. A normal distribution is supported for the value of the Z-parameter by both normal probability plotting paper and Shapiro–Wilk normality tests. [Copyright &y& Elsevier]

Sn–Ag–Cu–Bi solders, which have high quality and performance that can meet the requirement of electronic packaging, have been investigated in this paper. The research was focused on the influence of aging on the microstructural evolution and mechanical properties in Sn–3Ag–0.5Cu–xBi (x=0–3 wt.%) solders. The effect of Bi was discussed based on the experimental results. The experimental results indicated that the addition of Bi enhanced the tensile strength of the solders but decreased their elongation. After aging treatment, Sn–3Ag–0.5Cu solder showed significant change in strength and elongation which resulted from the obvious coarsening of Ag3Sn and Cu6Sn5 intermetallics. As for Bi-bearing solders, Bi precipitation in Sn matrix was only observed in Sn–3Ag–0.5Cu–3Bi solder after being aged at 120 °C for 100 h, while all the Bi-bearing solders exhibited relatively stable mechanical properties with aging time which can be attributed to the strengthening effect of Bi from solid solution strengthening to precipitating strengthening. [Copyright &y& Elsevier]

ZrO 2 –Al 2 O 3 (ATZ) ceramics are attracting high interest in biomedical applications because of their desirable mechanical performance and biocompatibility. However, strength and toughness are mutually exclusive in structural ceramics. In this paper, based on digital light processing, novel textured ATZ ceramics with obvious crystallographic orientations were fabricated by incorporating Al 2 O 3 platelets with a high aspect ratio and equiaxed particles into the ZrO 2 matrix. The optimized fracture toughness of 16.9 ± 0.8 MPa m1/2 was achieved in the textured ATZ ceramic, which was about 67.3 % higher than non-textured ZrO 2 ceramics, without sacrificing strength. The coupling toughening effects of macrolayer structure, equiaxed and platelet-shaped Al 2 O 3 particles, and ZrO 2 particles were responsible for the enhanced mechanical performance. The macroscale toughening of 3D-printed lamellar architecture led to effective energy dissipation. Additionally, the crack deflection and crack branching induced by dual-morphology Al 2 O 3 particles, accompanied by the phase transformation of the ZrO 2 matrix, were significant microscopic toughening mechanisms. [ABSTRACT FROM AUTHOR]

In order to further improve the hot gas bulging formability of laser-welded TA15 titanium alloy tube, studies about the effects of initial microstructures on the formability were carried out at 800 °C. Vacuum annealing procedures were performed to obtain different microstructures. The formability of these TA15 titanium alloy sheets with different microstructures was subsequently investigated by hot tensile tests and hot gas free bulging. A unified physically based material model considering dislocation density, work hardening, recrystallization, grain size and damage was built to analyze the deformation process. Results show that a good agreement was achieved between the unified material model and experiment results. The evolution of physical variables such as recrystallization fraction, and grain size can be predicted properly by the model. In the unified material model, the initial dislocation density would affect the dynamic recrystallization (DRX) rate. The DRX rate would increase with the increasing dislocation density. Therefore more DRX occurred at the early stage of deformation of initial material with higher dislocation density, while most of the DRX occurred at the middle-late stage of deformation of the annealed material with lower dislocation density. The initial material demonstrated the best formability due to the wide occurrence of DRX at the early stage of deformation, which increased the fraction of high angle grain boundaries, refined the microstructure, promoted the occurrence of grain boundary sliding and enhanced the formability of the material. However, most of the DRX occurred at middle-late stage of deformation of annealed material, which may increase the softening rate and lower the formability. Hence increasing the occurrence of DRX at the early stage of deformation by increasing the initial dislocation density in the material is an efficient approach to improve the gas bulging formability. [ABSTRACT FROM AUTHOR]

Abstract: High temperature corrosion and microstructure deterioration phenomenon of KHR35H radiant tubes had been investigated after a service life of approximately 2years in annealing process. Analyses revealed that deterioration in mechanical properties of the radiant tube was caused primarily by significant growth of precipitates during high temperature service. Internal oxidation and simultaneously in situ carbides dissolution were responsible for the formation of large number of voids and microcracks at the inner wall of the tubes, which brought the reduction of effective thickness of the tube wall and may act as crack sources under either thermal shock or creep deformation. [Copyright &y& Elsevier]

In an artificial island construction project based on the large-scale marine reclamation land, the soil settlement is a key to affect the late safe operation of the whole field. To analyze the factors of the soil settlement in a marine reclamation project, the SEM method in the soil micro-structural analysis method is used to test and study six soil samples such as the representative silt, mucky silty clay, silty clay and clay in the area. The structural characteristics that affect the soil settlement are obtained by observing the SEM charts at different depths. By combining numerical calculation method of Terzaghi’s one-dimensional and Biot’s two-dimensional consolidation theory, the one-dimensional and two-dimensional creep models are established and the numerical calculation results of two consolidation theories are compared in order to predict the maximum settlement of the soils 100 years after completion. The analysis results indicate that the micro-structural characteristics are the essential factor to affect the settlement in this area. Based on numerical analysis of one-dimensional and two-dimensional settlement, the settlement law and trend obtained by two numerical analysis method is similar. The analysis of this paper can provide reference and guidance to the project related to the marine reclamation land.

MoS 2 three dimensional (3D) architectures with various subunits were synthesized using glycerol to mediate the growth of MoS 2 crystals though a CS 2 -assisted hydrothermal approach. It has been found that the thickness and lateral size of subunits can be distinctly reduced by increasing glycerol content in the mixture solvent. A stable porous MoS 2 architecture, composed of nanosheets with a tiny size, ∼3 layers and expanded interlayer distance, namely MoS 2 -15, was obtained when the volume proportion of glycerol reaches 15%. The sample MoS 2 -15 exhibits superior electrochemical performance in lithium ion storage, due to reasonable design as well as smart organization of MoS 2 subunits, featured by a capacity of 1027 mAh g −1 at 0.1 A g −1 after 100 cycles and 738 mAh g −1 at 5 A g −1 after 300 cycles, exceeding other MoS 2 nanostructured materials in this work. More importantly, the as-prepared various architectures exhibit tunable electrochemical behaviors depending on structure and morphology evolution, which truly reflects the potential to optimize the microstructure for lithium-ion host materials. [ABSTRACT FROM AUTHOR]

To analyze the microstructure across thickness exposed to various environment of the pyrolysis furnace tubes, the sample of Cr35Ni45Nb heat-resistant steel from a five-year service tube was sliced into slices from inner to outer wall. Moreover, microhardness was examined to investigate the influence of the microstructure on the property of the heat-resistant steel. The results show that the primary carbides Cr 7 C 3 and NbC have transformed into chromium-rich Cr 23 C 6 and niobium-rich carbides G phase in the middle section of the aged pyrolysis furnace tube. The Cr 2 O 3 and SiO 2 layer covered the outer and inner surfaces, and the Cr-depleted zones were formed under the oxide layer of the inner and outer walls. The carbides of M 23 C 6 were transformed into M 7 C 3 type carbides in the carburization zone under the Cr-depleted zone of inner surface, while the M 7 C 3 type carbides also existed under the Cr-depleted zone of outer wall. [ABSTRACT FROM AUTHOR]

• The paramagnetic structure of HPNb alloy change into ferromagnetic after carburization. • The M 23 C 6 carbides are replaced by carbon-rich M 7 C 3 carbides in carburization zone. • The carburized tube furnace tubes become brittle after carburization. • Carburization reduced the high temperature creep strength of HPNb alloy tube. The structure characteristics and mechanical properties of as-cast and carburized HPNb alloy tubes were investigated in this paper. Through magnetism test by the vibrating sample magnetometer, we find that the paramagnetic structure of as-cast HPNb alloy tubes has changed into ferromagnetic structure after carburization. Electron back-scattered diffraction (EBSD) and X-ray diffraction (XRD) analyses show that the M 23 C 6 type carbide transformed into M 7 C 3 type carbide in carburization zone. Due to the coarser primary carbides and blocky-shaped secondary carbides after carburization, the ductility and toughness of the ethylene cracking furnace tubes are very low and become brittle. At high temperature, the tensile strength and yield strength of carburized tube are higher than those of as-cast tube, but the tensile elongation is lower. Owing to the microstructure degradation, the creep strength of HPNb alloy decreased after carburization. Hence, the carburization also could lead to the decrease of the remnant life of the pyrolysis furnace tubes. [ABSTRACT FROM AUTHOR]