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• The decoupling model of three-dimensional crystal orientation is invented in this paper, which is an effective tool for crystal orientation research in the industry. • A large amount of orientation deviation data and its distribution pattern for single crystal turbine blades are presented for the first time. • The reliability analysis system for the orientation-dependent fatigue life of single-crystal blades is developed by the GRNNs-MCS method. • The fatigue lifetime reliability of single-crystal blades has been significantly improved by crystal orientation design technology. The uncertainty in the casting orientation of single-crystal aeroengine turbine blades is an intractable engineering problem, and breaking through the crystal orientation design technology is vitally important to enhance the fatigue lifetime reliability of the blade. In this paper, a three-dimensional decoupling model for casting orientation is established according to the crystallographic characteristics of single-crystal blade, and the distribution information and statistical features of the orientation deviation angle of single-crystal turbine blades are obtained for the first time according to this decoupling model. Subsequently, the orientation-dependent models and generalized regression neural networks (GRNNs) analysis system of reliability are established, and the analysis of fatigue life response for single-crystal blades in four quadrants is carried out based on the neural network analysis system. Finally, three orientation design schemes are developed, and the improvement effect of each scheme on lifetime reliability are investigated. For the secondary orientation design scheme, the lifetime reliability is improved from 62 % to more than 95 % at the design life of 15,000 cycles; For the integrated orientation design scheme, the life reliability is improved from 50 % to more than 95 % at the design life of 20,000 cycles. The results show that the orientation design can effectively improve the fatigue life reliability of the product, especially in the long-life design interval of 10,000 to 20,000 cycles. Therefore, the orientation design should be highly emphasized in the design of single-crystal turbine blades for aeroengine. [ABSTRACT FROM AUTHOR]

• Thermal fatigue behavior of Ni-based single crystal superalloy at 25–900 °C are investigated. • The cracks only initiate at the direction of 45° from [0 0 1] direction in hot corrosion environment, which is different from the multi-point initiation of cracks in air environment. • The invisibility of crack morphology in hot corrosion environment deserves to be highlighted. • The influence mechanism of hot corrosion on the thermal fatigue behavior of Ni-based single crystal superalloy is proposed. As an important failure model for single crystal materials in service, with the increasing complexity of working environments, the thermal corrosion fatigue failure needs to be studied urgently. In this study, the thermal corrosion fatigue crack initiation and propagation behaviors of an Ni-based single crystal superalloy in both air and hot corrosion environments at 25–900 °C were studied by using a designed precise thermal fatigue test device. The microstructure characteristics and crack composition were analyzed by SEM, TEM and EDS, and the internal stress and recrystallization during thermal fatigue were characterized by EBSD. Moreover, the detailed and comprehensive crack morphology was characterized with different surface treatments. The results showed that the crack morphology was invisible in the hot corrosion environment, which is worthy of being highlighted. The initiation and propagation of thermal fatigue cracks were also accelerated in the hot corrosion environment, which contributed to the sufficient thermal stress, the accelerated material degradation of the inner/outer layers in the crack region, and the rapid forward diffusion of O 2 in the inner crack layer. Finally, the influence mechanism of hot corrosion on the thermal fatigue behavior of the Ni-based single crystal superalloy is proposed. [ABSTRACT FROM AUTHOR]

Hot corrosion behaviour of Ni-base single crystal at 900 ℃ is investigated under three different mixed salts. The result shows that hot corrosion degree in Na 2 SO 4 +NaCl+NaVO 3 is the most serious, followed by Na 2 SO 4 + NaVO 3 , and Na 2 SO 4 +NaCl is the least. The hot corrosion mechanism of superalloy in Na 2 SO 4 +NaCl+NaVO 3 salts is proposed. More importantly, the interaction of Na 2 SO 4 , NaCl and NaVO 3 is a synergistic relationship in which Na 2 SO 4 causes a basic corrosion attack, and NaCl with NaVO 3 strengthen this attack. Therefore, in hot corrosion protection, the type of corrosive salt should be reduced to avoid the synergistic effect caused by multiple salts. [Display omitted] • Hot corrosion behavior of Ni-based single crystal superalloys at 900 ℃ under three different mixed salts was investigated. • Sulfides in γ′-depleted layer are mainly affected by critical oxygen partial pressure and standard free energy of sulfide. • NaCl and NaVO 3 consume the protective oxides and prolong the time of internal sulfidation-oxidation cycle reaction. • There is a synergistic relationship between the corrosion salts of Na 2 SO 4 , NaCl and NaVO 3. [ABSTRACT FROM AUTHOR]

The twin relationships of the A–C type non-modulated martensitic variant pair in Ni 54 Mn 25 Ga 21 ferromagnetic shape memory alloy were investigated in detail through experimental observations and theoretical calculations. Variants A and C are microtwins connected by intervariant interface, while the lamellae in each variant are nanotwins separated by twin boundaries. The nanotwins with different thicknesses in each variant have two types: the major lamella and the minor lamella. The orientation relationships between the lamellae across an intervariant interface vary with the volume fraction of the minor lamella. The twin relationships between the nanotwins were identified experimentally and theoretically. Specifically, the lamellae in a variant have a {1 1 2} compound twin relationship, the major lamellae (or minor lamellae) are twin related with a twinning plane of high indices, but the major and minor lamellae across the A–C interface are not twin related. The mobility of various interfaces, such as the twin boundary in a variant and intervariant interface is discussed, based on the identified twin relationships. [ABSTRACT FROM AUTHOR]

A sodium ion conducting gel polymer electrolyte based on poly(vinylidene difluoride-co-hexafluoropropylene) porous membrane is reported, which is prepared through a simple phase separation process. It exhibits high safety, good mechanical properties and good electrochemical stability. The gel polymer electrolyte provides the sodium ionic conductivity of 0.60 mS cm − 1 at ambient temperature, while the commercial separator (Celgard 2730) offers only 0.16 mS cm − 1 . The temperature dependence of the ionic conductivity from 25 to 75 °C is consistent with an Arrhenius-behavior. The ionic transference number of sodium ion (t Na + ) in the gel polymer electrolyte is 0.30, higher than that (0.17) in the commercial separator. This provides a new direction to improve the safety of sodium ion batteries. [ABSTRACT FROM AUTHOR]

Tension–tension fatigue properties of SiC fiber reinforced Ti–6Al–4V matrix composite (SiC f /Ti–6Al–4V) at room temperature were investigated. Fatigue tests were conducted under a load-controlled mode with a stress ratio 0.1 and a frequency 10 Hz under a maximum applied stress ranging from 600 to 1200 MPa. The relationship between the applied stress and fatigue life was determined and fracture surfaces were examined to study the fatigue damage and fracture failure mechanisms using SEM. The results show that, the fatigue life of the SiC f /Ti–6Al–4V composite decreases substantially in proportion to the increase in maximum applied stress. Moreover, in the medium and high life range, the relationship between the maximum applied stress and cycles to failure in the semi-logarithmic system could be fitted as a linear equation: S max / μ = 1.381 − 0.152 × lgN f . Fractographic analysis revealed that fatigue fracture surfaces consist of a fatigued region and a fast fracture region. The fraction of the fatigued region with respect to the total fracture surface decreases with the increase of the applied maximum stresses. [ABSTRACT FROM AUTHOR]

A composite polymer membrane is prepared by coating poly(vinylidene fluoride) (PVDF) on the surface of a membrane based on methyl cellulose (MC) which is environmentally friendly and cheap. Its characteristics are investigated by scanning electron microscopy, FT-IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The outer PVDF layers are porous which results in high electrolyte uptake and the lithium ion transference number is much larger than that of the pure MC. Moreover, the cell based on Li//LiFePO 4 delivers high discharge capacity and good rate behavior in the range of 4.2–2.5 V when the composite membrane is used as the separator and the host of a gel polymer electrolyte, lithium as the counter and reference electrode, and LiFePO 4 as cathode. The obtained results suggest that this unique composite membrane shows great attraction in the lithium ion batteries with high safety and low cost. [ABSTRACT FROM AUTHOR]

7050 Al alloy was successfully processed by equal-channel angular pressing (ECAP) at room temperature (RT). The effect of ECAP on the subsequent aging precipitation behavior was investigated by using transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The results reveal that the kinds, spatial distribution and sizes of precipitates in the unECAPed and the ECAPed samples are different. ECAP accelerates the process of aging precipitation and results in the broadening of precipitate size distribution. ECAP can produce not only deformation heat but also internal defects such as excess vacancies and high density of dislocations when the sample passes through the main deformation zone. Deformation heat can lead to pre-precipitation, forming a small amount of GPII zones during ECAP processing. Strain-induced excess vacancies make solute segregation along dislocations by the mechanism of nonequilibrium segregation. High density dislocations mainly accelerate the process of aging precipitation. Besides, dislocations also induce the competition between homogeneous precipitation and heterogeneous precipitation on dislocations due to the flow of solutes and vacancies towards dislocations. [ABSTRACT FROM AUTHOR]

Abstract: The interfacial reactions of B4C-coated and C-coated SiC fiber reinforced Ti–43Al–9V composites were investigated by scanning electron microscope and transmission electron microscope. The detailed microstructures as well as the chemical composition throughout the reaction zone were identified. For SiCf/B4C/TiAl composite, the reaction zone from B4C coating to TiAl matrix is composed of 4 layers, namely, a carbon-rich layer, a mixed layer of TiB2 + amorphous carbon, a TiC layer and a mixed layer of TiB + Ti2AlC. For SiCf/C/TiAl composite, the reaction zone from C coating to TiAl matrix is composed of 3 layers, namely, a fine-grained TiC layer, a coarse-grained TiC layer and a thick Ti2AlC layer. For both kinds of composites, the reaction mechanisms of the interfacial reactions were analyzed, and the corresponding reaction kinetics were calculated. The activation energies of interfacial reaction in SiCf/B4C/TiAl composite and SiCf/B4C/TiAl composite are 308.1 kJ/mol and 230.7 kJ/mol, respectively. [Copyright &y& Elsevier]

Highlights: [•] The substructures in rotation-twinned T (Al20Cu2Mn3) particles were investigated. [•] A flattened hexagonal structural subunit with 20 atomic columns was proposed. [•] The stacking mode of these subunits at APB and TB were revealed. [•] The transition structures at twin domain junctions were unraveled. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural characteristics in the matrix of SiCf/Ti–6Al–4V composites prepared by consolidation of the matrix-coated fibers in the high-temperature β single-phase field were investigated using both experimental and modelling methods. Some of the critical microstructure features, like volume fraction of component phases, composition of matrix alloys and matrix morphology were systematically studied, providing valuable insight into the microstructural characteristics in the matrix of SiCf/Ti–6Al–4V composites. In order to assist in understanding the grain growth occurred in the matrix during consolidation processing, a theoretical model was developed. Excellent agreement between theoretical and experimental results was achieved. [Copyright &y& Elsevier]

Abstract: The microstructures of titanium aluminides matrix based on TiAl both in matrix-coated fiber and in fiber-reinforced composites were studied in this paper. The titanium aluminides matrix was examined by means of scanning electron microscope, X-ray diffractometer and transmission electron microscope. The results show that, in sputtering process, amorphous phase forms firstly, and α-Ti(Al) + TiAl3 form later. Subsequently, during hot isostatic pressing, the amorphous phase, α-Ti(Al) and TiAl3 in the matrix-coated fibers transform into γ-TiAl and α2-Ti3Al in the composites. [Copyright &y& Elsevier]

Abstract: Ti-43Al-9V/Ti-6Al-4V joints were fabricated by vacuum hot pressing under 920 °C/45 MPa/2 h. After fabrication the joints were thermally exposed in vacuum at 920 °C for 5 h and 17 h, and at 1100 °C for 1 h. The interfaces of both the as-prepared and the thermally exposed joints were analyzed by means of optical microscope, scanning electron microscope, electron backscatter diffraction system and energy dispersive spectrometer. The results indicate that sound joints can be achieved under 920 °C/45 MPa/2 h, and the interfacial phase sequence of the as-prepared joints was identified as Ti-43Al-9V/γ(TiAl)/B2 (the ordered form of β-Ti phase)/α 2(Ti3Al)/α(Ti)/Ti-6Al-4V. The thickness of the interfacial zone increased with the duration of thermal exposure at 920 °C. Furthermore, the interfacial zone thickened rapidly when the joints were thermally exposed at temperature above the phase transformation point (α-Ti → β-Ti) of Ti-6Al-4V. In this paper, the interface growth way was also discussed based on the locations of the refractory phase YAl2 and microvoids. The analysis of the thermally exposed joints confirmed the correctness of the interface growth way. Moreover, elemental diffusion mechanism was discussed in this paper. [Copyright &y& Elsevier]

Abstract: SiC fiber reinforced titanium aluminides matrix composites based on TiAl (Ti–43Al–9V) were fabricated by means of matrix-coated fiber method through hot isostatic pressing. Microstructure of the SiCf/Ti–43Al–9V interfacial reaction zone in the composites was identified by means of scanning electron microscopy and transmission electron microscopy. The results show that three types of reaction products TiC, Ti2AlC and (Ti,V)5(Si,Al)3 are formed between carbon coating of SiC fiber and the matrix. TiC is adjacent to the carbon coating of the SiC fiber, and (Ti,V)5(Si,Al)3 is close to the matrix. Ti2AlC layer exists as columnar grains between TiC and (Ti,V)5(Si,Al)3 layers. The TiC layer can be divided into fine-grained layer and coarse-grained layer. The fine-grained TiC layer contains amorphous carbon, and the coarse-grained TiC layer is separated from fine-grained TiC by an intermittent carbon layer. In addition, TiC particles are also formed between carbon coating and SiC. Furthermore, the formation mechanism of the interfacial reaction products was discussed. [Copyright &y& Elsevier]