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Abstract Multiscale graphene/carbon fiber (G/CF) reinforcements were developed for copper matrix hybrid composites. The homegenious G/CF/Cu mixture powders were firstly prepared by the simple wet-mixing process, and then densified by hot-pressed sintering to obtain bulk composites. Microstructure, electrical conductivity and mechanical properties of such composites were investigated. In the sintered compacts, the hybrid G and CF reinforcements distributed randomly in Cu matrix. CF presented the various space orientations, and G nanosheets exhibited the interconnected network distribution. Hardness and tensile yield strength of composites were improved evidently by hybrid G/CF addition, which increased with G increasing. However, the ultimate tensile strength were firstly enhanced and then deteriorated by increasing G content. The lower electrical conductivity showed in the more G-added composite, but still reached more than 80.0% IACS. These performance change could be sought in the spatially geometrical distribution and characteristic of hybrid CF/G additions, and the relevant mechanisms were discussed. [ABSTRACT FROM AUTHOR]

Abstract Microstructure and mechanical properties of the as-annealed Ti-stabilized Fe-17Cr ferritic stainless steel were investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and tensile tests. Experimental results show that the size of the ferrite grain in the Fe-17Cr stainless steel is about 40 µm after rolling and annealing. Orientation distribution function (ODF) by EBSD indicates that nearly homogeneous {111} annealing texture is produced in the annealed sheets. Pole figures (PF) by EBSD show that Kurdjumov–Sachs orientation relationship between the TiN particles and ferrite grains is established in the as-annealed microstructure. Tensile tests demonstrate that the yield strength (YS), ultimate tensile strength (UTS), and elongation (EL) of the as-annealed Ti-stabilized Fe-17Cr ferritic stainless steel are 319 MPa, 626 MPa, and 36.5%, respectively. In the SEM micrograph of the fracture, deep dimples can be observed and TiN particles can be found in the core of the dimples, which indicates that the samples undergo large deformation before fracture. [ABSTRACT FROM AUTHOR]

This paper investigated the relationship between crystallographic-orientation and micro-cracks of Ti-47Al-2Cr-2Nb alloy. Results show that the crystallographic-orientation is adverse in the nearly γ microstructure and becomes advantageous in the fully lamellar microstructure. Therefore, micro-cracks largely generate in the nearly γ microstructure and much decrease in the fully lamellar microstructure. [ABSTRACT FROM AUTHOR]

This research proposed an in situ casting method for preparing Al 3 Ti p /A356 composites with high strength and good ductility by adding Ti powders into molten A356 at 800 °C. A sampling experiment was firstly carried out to explore the evolution process of Ti powders in the A356 melt. Based on which in situ Al 3 Ti p /A356 composites with 1.5 and 3.0 wt% Ti additions were fabricated respectively. Both the microstructures and tensile properties of samples after T6 heat treatment were investigated. The results showed that blocky Si-substituted Al 3 Ti particulates were synthesized in the in situ reaction and the formation of which followed a reaction-peeling model. The utilization ratio of Ti powders in the fabricating process could research 70%. In situ Al 3 Ti particulates existed inside the α-Al crystals of A356 alloy, with the size smaller than 10 µm. Both the equiaxed transition from long columnar dendrite structure and refining of α-Al crystals occurred due to the nucleating effect of Al 3 Ti. Compared with T6-A356, the yield strength, ultimate tensile strength, and percent elongation of the T6-A356/3.0Ti were improved by 29.2%, 36.0% and 143.6%, respectively. The mechanisms of the improved tensile properties, including the strength and ductility, of the composites were also discussed in this research. [ABSTRACT FROM AUTHOR]

The fatigue crack growth (FCG) behavior and microstructure of Ni-based alloy welded joint, fabricated by narrow gap tungsten inert gas welding (NG-TIG), were systematically investigated in this paper. The microstructure of weld metal (WM) and base metal (BM) are columnar grains and equiaxed grains respectively, plentiful irregular carbides aggregate at grain boundaries and the number of twin crystals decreases distinctly in HAZ due to the thermal input. The FCG tests results indicated that a higher FCG rate (d a /d N ) as well as a lower FCG threshold (Δ K th ) for WM were obtained compared to BM and HAZ. It was found that crack deflection and branching in the whole welded joint occurred at FCG path in near-threshold regime. The misorientation of grain boundaries is considered as the main factor to account for the deceleration and retardation behavior revealed by electron back-scattered diffraction (EBSD) analysis. EBSD results also indicate that the misorientation of 20–30° is a critical value from a tortuous path to a relative straight path. A contrasting morphology of Paris regime and near-threshold regime showed the fracture mode transition from tensile mode to intense shear mode. [ABSTRACT FROM AUTHOR]

The mechanical behavior of single crystal Al sample with different sizes in mini-, micro- and nano-scales and different loading directions along [111] and [110] have been systematically investigated. The sample size and orientation effects are examined. The results are compared with previously reported data on other face-centered cubic Ni, Cu, Au and Ag, establishing an interesting trend for sample size effect with respect to stacking fault energy. With higher stacking fault energy and thus higher dislocation mobility such as Al, the sample size dependence would be lower. [ABSTRACT FROM AUTHOR]

The resolution dependence of orientation gradients was studied in a well-annealed 99.9995% pure polycrystalline copper pulled to failure in tension. Owing to the well developed neck, different regions in the sample correspond to different tensile strains. Post-mortem characterization was performed using EBSD on cross-sections containing the tensile axis. Kernel average misorientation (KAM) was calculated as a metric to establish correlation between defect accumulation and microstructural features, with a threshold of 5° to focus on intra-granular gradients. The region with the lowest strain (2%) showed high KAM values adjacent to grain boundaries compared to the grain interior, regardless of the point spacing, i.e. the spatial resolution. However, in the region with the highest strain (13%) a strong dependence on resolution was found. For point spacings of 0.5 μm or smaller, the same correlation of high KAM with locations near boundaries was found. At coarse spacings i.e. low spatial resolution, by contrast, the reverse was found in that the highest KAM values appear in the grain interiors, as previously observed in X-ray microscopy on the same sample which had a similar coarse resolution. An analysis of orientation gradients parallel to, and perpendicular to boundaries suggested that the latter tend to be the larger of the two. This helps to explain why boundary-adjacent points have low KAM values. The conclusion is that measurement of local orientation gradient requires a resolution that is comparable to the dislocation substructure. [ABSTRACT FROM AUTHOR]

Tensile behavior of the nickel-base single-crystal superalloy DD6 was studied from room temperature to 1020 °C. The plate specimens were along [001] orientation parallel to the loading axis in tension. The microstructures on the surface and fracture morphology were investigated after tensile test to rupture by scanning electron microscopy (SEM). The results of the present investigation indicate that the yield strength at 650 °C is superior to that at room temperature, 850 °C and 1020 °C. Low ductility and serrated flow in stress–strain curves were also observed at 650 °C. The microstructures on the surface of the plate specimens and fracture morphology observation indicated that localized slip which resulted in glide plane decohesion caused the low ductility of DD6 alloy. [ABSTRACT FROM AUTHOR]

Highly bimodal pore size distributions are found in ceramic scaffolds prepared by freeze casting (ice templating). The scaffolds, with preferred orientation in the ice crystal growth direction, have large interlamellar pores between the scaffold walls and small intergranular pores within the walls. The constitutive equations based on a continuum theory of sintering are used in a finite element analysis of the sintered scaffolds. The calculations employed a model of large isolated pores surrounded by a shell containing small pores. During sintering at 1173 to 1773 K the scaffold walls densified first, followed by wall closure at higher temperatures. Excellent agreement is found between the predicted and measured porosity. The compressive strength and elastic modulus depend on the fraction of interlamellar porosity, not the total porosity, indicating that the scaffold wall strength does not affect these properties. [ABSTRACT FROM AUTHOR]

The microstructural and textural evolutions together with the orientation dependencies of mechanical properties of the extruded Mg–6Li–1Zn (LZ61), Mg–8Li–1Zn (LZ81) and Mg–12Li–1Zn (LZ121) alloys were investigated. The shear punch testing (SPT) method was employed to evaluate the room- and high-temperature (200–300 °C) mechanical anisotropy of the extruded materials. Microstructural analysis revealed that, despite a great discontinuous dynamic recrystallization (DDRX) occurred in the extrusion direction (ED) and normal direction (ND), the microstructural anisotropy was observed in all extruded materials, the effect which was more pronounced in the LZ81 alloy by developing banded structure in the ND condition. Textural studies in both hcp LZ61 and LZ81-α phase showed a fiber-type texture with the basal planes being parallel to the ED after extrusion. For the LZ81 alloy, however, the interfering presence of β phase affects the LZ81-α-phase texture by reducing the intensity of the maximum orientations of the basal and prismatic planes. Similar weakened bimodal type texture was formed in the bcc-structured LZ81-β phase, where some <110> poles were located parallel to the ED along with developing some other poles of a fiber-type character. It was also found that the abnormal grain growth might have been encouraged by the strong texture developed in the extruded LZ121 alloy. The SPT results indicated that the texture-dependent hcp LZ61 alloy showed higher shear strength in the ND condition than the ED condition, caused by the texture strengthening effect. As the Li content and deformation temperature increase, the texture dependence of strength properties, and thus, the mechanical anisotropy, decrease so that the LZ121-ND sample showed lower shear strength than the ED specimen due to the greater grain sizes achieved in the ND condition. [ABSTRACT FROM AUTHOR]

Due to their remarkable mechanical properties, carbon nanotube (CNT) reinforced aluminum (Al) matrix composites have attracted a wide range of research interests. This work attempts to experimentally and numerically investigate the relationship between the micro-structures and mechanical behavior of CNT/Al composites. Three-dimensional (3D) computational structural modeling of CNT/Al composites is performed, in which the size, morphology, orientation, location and volume fraction of CNTs are reproduced to be similar to those of the actual micro-structures of CNT/Al composites. The strengthening of the mechanical properties of the constituent materials of CNT/Al composites and reasonable load and boundary conditions are studied based on the models of CNT/Al composites developed. The tensile mechanical behavior of CNT/Al composites is numerically evaluated and experimentally verified. Results show that the enhanced mechanical properties of CNT/Al composites can be attributed to three factors: CNT reinforcements, matrix grain refinement and layered architectures. Through the microscopic structural modeling methods presented herein, the effects of model size, interfacial behavior, volume fraction of CNTs and layered structures on the mechanical behaviors of CNT/Al composites can be reproduced to understand the strengthening and deformation mechanisms of CNT/Al composites. [ABSTRACT FROM AUTHOR]

Abstract: The rotary bending high cycle fatigue properties of a single crystal superalloy in three orientations were tested at 700°C in ambient atmosphere. The [011] orientation shows the highest fatigue strength. Moreover, the fatigue strength with 〈111〉 orientation is obviously higher than that with 〈001〉 orientation. There are two types of fracture modes, one is cleavage fracture for the [001] orientation, the other is the mixed fracture of cleavage and tearing for the [011] orientation. The 〈011〉 orientation shows more pronounced crystal lattice rotation than the 〈111〉 orientation. Nevertheless, lattice rotation does not occur in the crystals with [001] orientation. Fatigue steps of the [001] and [111] orientated crystals propagate along different {111} glide planes, which means that the slip in 〈111〉 orientation moves more easily than in 〈011〉 orientation. The typical deformation mode of [001], [011] or [111] orientation is respectively slip bands running through γ and γ′ phases, dislocation pairs shearing γ′ particles, or superlattice stacking faults besides high-density dislocation shearing γ′ particles. [Copyright &y& Elsevier]

Abstract: Microstructural evolution was studied in a near-lamellar two phase (α2+γ) Ti–47Al–2Cr–2Nb alloy under high temperature creep and exposure conditions. The aim of this study was to probe the role of stress orientation, with respect to lamellar plates, on microstructural changes during primary creep. Creep testing was complemented with SEM and TEM based microstructural characterization. It was observed that retention of excess α2 resulted in an unstable microstructure. Under stress and temperature, excess α2 was lost and Cr-rich precipitates formed. Depending on stress orientation, the sequence of precipitates formed was different. α2 loss was accompanied by formation of the non-equilibrium C14 Laves phase when lamellar plates were oriented parallel to the stress axis. In contrast, α2 loss did not result in formation of the C14 phase in perpendicular samples. It was concluded that C14 formed preferentially in certain test orientations because of its effectiveness in relieving residual stresses in α2 that arose from lattice misfit and modulus mismatch. [Copyright &y& Elsevier]