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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 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: 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]

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: 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]

Most laser clad surface layers on aluminium alloys consist of a hard carbide phase and an aluminium alloy matrix phase. The distribution of the carbide phase and the strength of the matrix phase are not always satisfactory. The paper describes a method to fabricate a metal matrix composite layer on Al 6061 by adopting the laser induced reaction synthesis technique. Powder of pure titanium, pure carbon, pure tungsten or tungsten carbide are mixed at various proportions and then pasted on an Al 6061 surface. Laser cladding with Ni–Al powders delivered by a coaxial nozzle onto the above pasted surface using a 2 kW Nd:YAG laser was carried out. During laser cladding, exothermic reactions of Ti–C, W–C and Ni–Al expedite the melting and alloying of the coatings. X-Ray diffraction and scanning electronic microscopy results show that TiC and WC phases were in situ synthesized during the cladding process and they appear in a Ni–Al matrix. The microstructure, hardness and pin-on-disk wear of the coatings are investigated and discussed. [Copyright &y& Elsevier]

In this study, novel CrCoNi–Al 2 O 3 composites with 2.5–7.5 wt% Al 2 O 3 were prepared by mechanical alloying (MA) plus rapid spark plasma sintering (SPS) method, and their microstructure and mechanical properties were systematically investigated. The results demonstrate that the Al 2 O 3 nanoparticles are distributed homogeneously in the CrCoNi medium entropy alloy (MEA) matrix with ultra-fine grain size (≤0.37 μm). Moreover, the composites have clean, regular and well bonded matrix/α-Al 2 O 3 interfaces. Interestingly, a large number of nano twin bundles, large-scale 9R phase and geometrically necessary dislocations (GNDs) were formed near the matrix/α-Al 2 O 3 interfaces. The Vickers hardnesses of the 2.5–7.5 wt% Al 2 O 3 composites reach 521–603 HV 0.3 , and the compressive yield strength is 1877–2359 MPa with fracture strains of 9.3–31.6%. The yield strength of the composites is by 65.4–107.8% higher than that of the pure CrCoNi matrix, meanwhile they still have considerable ductility, which indicates composite strengthening is a feasible method to improve mechanical properties of high/medium entropy alloys. The composite includes multiply strengthening mechanisms, namely grain refinement strengthening, twin strengthening, Orowan strengthening and dislocation strengthening. The contributions of various strengthening mechanisms were quantitatively analyzed, which were well consistent with the experimental values. • CrCoNi–Al 2 O 3 composites with different Al 2 O 3 contents were successfully prepared via powder metallurgy route. • The grain size of CrCoNi-matrix was effectively refined by Al 2 O 3 nanoparticles uniformly distributed in the matrix. • Nano twin bundles, broad 9R phase and geometrically necessary dislocations were formed near CrCoNi/α-Al 2 O 3 interfaces. • CrCoNi–Al 2 O 3 composites possess remarkable strength due to the synergy of multiply strengthening mechanisms. [ABSTRACT FROM AUTHOR]