Xian Luo

Finite element analysis of pressure on 2024 aluminum alloy created during restricting expansion-deformation heat-treatment

Abstract Metals heat-treated under high pressure can exhibit different properties. The heat-induced pressure on 2024 aluminum alloy during restricting expansion-deformation heat-treatment was calculated by using the ABAQUS finite element software, and the effects of the mould material properties, such as coefficient of thermal expansion (CTE), elastic modulus and yield strength, on the pressure were discussed. The simulated results show that the relatively uniform heat-induced pressure, approximately 503 MPa at 500°C, appears on 2024 alloy when 42CrMo steel is as the mould material. The heat-induced pressure increases with decreasing the CTE and the increases of elastic modulus and yield strength of the mould material. The influences of the CTE and elastic modulus on the heat-induced pressure are more notable.

Effect of properties of SiC fibers on longitudinal tensile behavior of SiCf/Ti-6Al-4V composites

Three types of SiC fibers with different tensile strength were employed to prepare unidirectional titanium matrix composites. The strengths of the original SiC fibers and extracted fibers from the composites were measured. The results show that the mechanical properties of fibers are greatly damaged by the consolidation processing of the composite. The strength data of the extracted fibers are used to predict the strength of the composites according to two theoretic models. The Globe Load-Sharing(GLS) model overestimates the strength of the composites. If the Local Load-Sharing(LLS) model assumes that failure occurs after the formation of a cluster with three broken fibers, the model can predict the strength of the composites exactly.

HRTEM and HAADF-STEM tomography investigation of the heterogeneously formed S (Al2CuMg) precipitates in Al–Cu–Mg alloy

The distribution of variants and three-dimensional (3D) configurations of the heterogeneously formed S (Al2CuMg) precipitates at dislocations, grain boundaries and the Al20Cu2Mn3 dispersoid/Al interfaces were studied in this research. By means of high resolution transmission electron microscopy, we systematically investigated the orientation relationships (ORs) between these heterogeneously formed S precipitates and the Al matrix, and further unraveled that the preferred orientation of S variants at grain boundaries and at dispersoid/Al interfaces are respectively associated with the OR between the precipitate habit plane and the grain boundary plane, and the OR between the precipitate habit plane and the interface plane. The inherent characteristic of the crystal structure of the S phase, i.e. the symmetry of the pentagonal subunit, was considered to be the fundamental factor determining the preference of the variant pair. By using high angle annular dark field scanning transmission electron microscopy tomography, we successively obtained the 3D reconstruction of the S precipitates at these defects. Both the morphology of an individual S precipitate and the overall configuration of the S precipitates nucleated at these defects can be clearly observed without misunderstandings induced by the overlap and projection effects of the conventional two-dimensional methods.

Reaction diffusion in continuous SiC fiber reinforced Ti matrix composite

Abstract SiC continuous fiber-reinforced pure Ti(TAI) matrix composites were fabricated by a vacuum hot pressing(VHP) method and then heat-treated in vacuum under different conditions. The interfacial reaction and the formation of interfacial phases were studied by using SEM, EDS and XRD. The results show that there exists reaction diffusion at the interface of SiC fibers and Ti matrix, and the concentration fluctuation of reaction elements such as C, Ti and Si appears in interfacial reaction layer. The interfacial reaction products are identified as Ti 3 SiC 2 , TiC, and Ti 5 Si 3 C x. At the beginning of interfacial reaction, the interfacial reaction products are TiC x and Ti 5 Si 3 C x. Along with the interfacial reaction diffusion, Ti 3 SiC 2 and Ti 5 Si 3 C x single-phase zones come forth in turn adjacent to SiC fibers, and the TiC+Ti 5 Si 3 C x double-phase zone appears adjacent to Ti matrix, which forms discontinuous concentric rings by turns around the fibers. The formed interfacial phases are to be Ti 3 SiC 2 , Ti 5 Si 3 C x and TiC x +Ti 5 Si 3 C x , from SiC fiber to Ti matrix. The interfacial reaction layer growth is controlled by diffusion and follows a role of parabolic rate, and the activation energy (Q k ) and (k o ) of SiC/TAI are 252.163 kJ/mol and 7.34 × 10 −3 m/s 1/2 , respectively.

A review on the research progress of push-out method in testing interfacial properties of SiC fiber-reinforced titanium matrix composites

Experimental analysis of single-fiber push-out for SiC fiber-reinforced titanium matrix composites (TMCs) is complicated by the incorporation of large thermal residual stresses, strong chemical bond of the fiber/matrix interface and matrix plastic deformation. This paper summarizes the development of push-out test and the characteristics of push-out test for TMCs such as crack initiating at the bottom face and theoretical analysis of the test. Moreover, it deeply analyzes the progresses of interfacial shear strength and fracture toughness, and work focus is pointed out in future.

Evaluation on the interfacial fracture toughness of fiber-reinforced titanium matrix composites by push out test

Abstract The models for single-fiber push out test are developed to evaluate the fracture toughness GIIc of the fiber/matrix interface in titanium alloys reinforced by SiC monofilaments. The models are based on fracture mechanics, taking into consideration of the free-end surface and Poisson expansion. Theoretical solutions to GIIc are obtained, and the effects of several key factors such as the initial crack length, crack length, friction coefficient, and interfacial frictional shear stress are discussed. The predictions by the models are compared with the previous finite element analysis results for the interfacial toughness of the composites including Sigma1240/Ti-6-4, SCS/Ti-6-4, SCS/Timetal 834, and SCS/Timetal 21s. The results show that the models can reliably predict the interfacial toughness of the titanium matrix composites, in which interfacial debonding usually occurs at the bottom of the samples.

Influence of CH3SiCl3 consistency on growth process of SiC film by kinetic monte carlo method

CH3SiCl3 (MTS)-H2-Ar system has been applied to prepare SiC film with chemical vapor deposition (CVD) method in this paper. For three facets of SiC film, some significant influence on growth rate, surface roughness, thickness and relative density brought by MTS consistency has been mainly discussed with kinetic monte carlo (KMC) method. The simulation results show that there is a certain scale for mol ratio of H2 to MTS (H2/MTS) with different deposition temperature. When MTS consistency increases, growth rate and surface roughness of three facets all increase, which manifests approximate linearity relationship. Thickness of three facets also increases while increasing trend of three facets thickness is different obviously. Although relative density of three facets all increases, increasing trend shows a little difference with MTS consistency increasing.

Microstructure of SiC Fiber Fabricated by Three-stage Chemical Vapor Deposition: Microstructure of SiC Fiber Fabricated by Three-stage Chemical Vapor Deposition

Continuous silicon carbide(SiC) fiber with carbon coating was fabricated by three-stage chemical vapor deposition(CVD) on tungsten filament heated by direct current(DC),using CH_3SiCl_3 +H_2 as gaseous reactant for SiC sheath and C_2H_2 for the outmost carbon coating,respectively.Microstructure of the SiC fiber was examined by X-ray diffraction(XRD),scanning electron microscope(SEM),Raman spectroscope and transmission electron microscope (TEM).The results show that the SiC fiber consists of tungsten core,a W/SiC interfacial reaction zone, two layers of SiC with total thickness of 41μm and an outermost carbon coating of about 2 urn in thick.The deposited SiC is mainly composed of P-SiC,and exhibits strong〈111〉fiber texture with abundant growth defects,such as co-deposit of free silicon and stacking faults,leading to the lattice imperfection of the SiC sheath.Raman spectrum indicates that the outmost carbon coating decomposed from C_2H_2 involves a mixture of amorphous carbon and graphite crystallite.

Effect of Carbon Coating on Tensile Strength of SiC Filament by Chemical Vapor Deposition

The tensile strengths of carbon-coated and non carbon-coated SiC filament by Chemical Vapor Deposition were tested, respectively, which were analyzed according to double-parameter Weibull distribution. Various techniques including XRD and SEM were also used to study the phase composition and microstructure of SiC filament. The result shows that carbon coating plays a very important role on increasing the tensile strength.

The influence of interface reaction zone on interfacial fracture toughness of SiC fiber reinforced titanium matrix composites

Abstract A fiber-reaction zone-matrix three-phase model is developed to evaluate the interfacial fracture toughness of titanium alloys reinforced by SiC monofilaments. Based on fracture mechanics, theoretical equations of GIIc are presented, and the effects of several key factors such as crack length and the interface reaction zone thickness on the critical applied stress necessary for crack growth and interfacial fracture toughness are discussed. Finally, the interfacial fracture toughness of typical composites including Sigma1240/Ti-6Al-4V, SCS-6/Ti-6Al-4V, SCS-6/Timetal 834, SCS-6/Timetal 21s, SCS-6/Ti-24Al-11Nb and SCS-6/Ti-15V-3Cr are predicted by the model. The results show that the model can reliably predict the interfacial fracture toughness of the titanium matrix composites. dA is the incremental increase in crack surface area, and dUex is the work done by the loading system, and dUse is the change in strain energy of the system due to crack advance, dUfr is the work done in frictional sliding at the interface.