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Fatigue crack propagation behaviors of the as-prepared and thermally exposed (700 °C/196 h, 800 °C/196 h) C/Mo double-coated SiC fiber-reinforced Ti6Al4V composites were investigated. The results show that interfacial microstructure evolution has significant effect on fatigue crack propagation behaviors. As for the as-prepared and 700 °C/196-h thermally exposed composites, fiber-bridging accompanied with interfacial debonding can decrease the crack growth rate significantly, while the latter one has lower crack growth rate at the early fatigue crack propagation stage, as the diffusion of Mo atoms makes the matrix close to the interface have more ductileβ-Ti. However, fiber-bridging phenomena disappeared with the altered interface in the composite after 800 °C/196-h thermal exposure. Fatigue fracture analysis further reveals that multistep deflections of crack in interface contribute to the improvement of interface toughness. The formation of ductileβ-Ti layer resulted from the diffusion of Mo atoms is beneficial to blunt the crack tip. [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]

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: The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites. [Copyright &y& Elsevier]

Abstract: Effect of interfacial shear strength on longitudinal tensile properties for SiCf/Ti–6Al–4V composites is investigated by Monte Carlo finite element method. A two-parameter Weibull function is employed to describe random distribution of fiber strength. Fiber breakage, matrix cracking and interfacial debonding are simulated by killing the element when stress applied to element exceeds corresponding strength and releasing coupled nodes when shear stress exceeds shear strength at interfaces. The results show that tensile strength of SiCf/Ti–6Al–4V composites keeps unchanged for various interfacial shear strengths, but low interfacial shear strength is advantageous to reduce catastrophic failure. Moreover, with low interfacial shear strength, fiber breakage in the composites is more inclined to be non-coplanar. In addition, tensile strength obtained from finite element method is compared with those predicted by global load-sharing model (GLS), local load-sharing model (LLS) and conventional rule of mixtures (ROM) and is identical with that obtained from LLS. [Copyright &y& Elsevier]

Abstract: A two-dimensional finite element model is created to investigate the effects of temperature and residual stress on transverse tensile behaviors for SiC/Ti–6Al–4V composites with square fiber array. The spring elements are used to simulate interfacial debonding when interfacial radial stress, composed of residual radial stress and radial stress introduced by the applied transverse tensile stress, reaches interfacial bonding strength. The results indicate that temperature has an obvious influence on the collapse stress of composites due to the change of matrix strength with temperature. And the higher temperature is, the lower collapse stress is. Residual radial stress can increase the applied stress required to cause interfacial debonding, but has a little influence on the collapse stress of the composites. [Copyright &y& Elsevier]

Abstract: An improved interphase layer model, which combines the interphase layer model and the spring layer model, is presented to describe the interphase of composites. The finite element model consists of the fiber, the matrix, the interphase and the spring element. The finite element model is used to model the push-out test and evaluate interface properties of composites. The results show that the interfacial shear strength of SiC/Timetal-834 is about 500 MPa. Moreover, the effects of the interphase thickness and interfacial shear strength on the peak load of the push-out test are analyzed in detail. Evaluation of interfacial properties in SiC fiber reinforced titanium matrix composites using an improved finite element model [Copyright &y& Elsevier]

Abstract: SiC fiber reinforced copper matrix composites were prepared by foil-fiber-foil method (FFF) and, fiber-coating method (MCF) with and without a Ti6Al4V interlayer, respectively. The copper coating was prepared by different electroplating processes and the Ti6Al4V interlayer by magnetron sputtering. The results show that the tensile strengths of specimens without Ti6Al4V interlayer are nearly identical and poor, between 250 and 290MPa, while the ones of specimen with Ti6Al4V interlayer can be greatly improved, over 500MPa. This great increase attributes to the improvement of the SiC/Cu interfacial bonding strength because the interfacial reactions occur at Cu/Ti6Al4V interface and Ti6Al4V/SiC interface. Additionally, there are generally many micropores produced by hydrogen and oxygen in the electroplated coating, which would influence the density of the matrix. Therefore, the densification of the matrix was worth investigating since it would influence the thermal and electrical conductivity of the composite, though it has only a little contribution to the tensile strength. Experiments indicate that proper heat-treatment before hot pressing could improve the densification of the matrix. [Copyright &y& Elsevier]