Fiber Reinforced Titanium Matrix Composites Research Articles

Solidification behavior of SiCf/Ti17 induced by fixed-point laser surface remelting

Taking advantage of laser additive manufacturing, continuous SiC fiber reinforced titanium matrix composites (SiCf/TMCs) with low density and excellent mechanical properties can be used to hybrid-fabricate large components with complex shape for aerospace applications. However, due to the anisotropy in both microstructure and heat transfer ability, the high-density and rapid heat input from laser during hybrid manufacturing process will cause the non-uniform damage of fibers and various solidification microstructure in the molten pool. In order to understand the solidification behavior of molten pool in SiCf/Ti17 composites, the fixed-point laser surface remelting was used to bring in rapid and symmetrical heat input. With the decrease of temperature from center to edge of the molten pool, both fiber damage degree and the contents of Si and C elements in melt decreased. The solidification microstructure contains TiCx, Ti5Si3 and β-Ti, and their morphology varies according to the melt composition. SiC fibers act as heterogeneous nucleation sites for first solidified phases and promote their preference growth along the radial direction of fibers resulting from the excellent heat transfer ability. The faceted Ti5Si3 grains solidified through peritectic reaction L+TiCx→Ti5Si3 exhibit strong <0001> texture.

Micron-sized SiC particles reinforced TC4 composites: Mechanical properties and strengthening mechanisms

SiC fiber, W fiber, C fiber and other continuous fiber-reinforced titanium matrix composites (TMCs) have limited their application prospects due to their anisotropy, interface reaction, and high costs. In contrast, the SiC particles (SiCp) reinforced TMCs are of particular interests due to their ease of fabrication, lower costs, and isotropic properties. Micron-sized SiCp reinforced TC4 (Ti-6Al-4V) composites (SiCp/TC4) were synthesized via spark plasma sintering (SPS). The microstructure and mechanical properties of SiCp/TC4 composites have been investigated. The results showed that SiCp/TC4 composites exhibite a typical Widmanstatten structure composed of plate α, grain boundary α phase, and intercrystalline β phase. TiC particles formed via the reaction of SiCp with the TC4 matrix distributed at grain boundaries. In the meanwhile, a small amount of Ti5Si3 have been observed around the β phase. The strength of the composites increased continuously with the increase of SiCp contents. Due to effects of grain refinement and load transfer strengthening and solution strengthening from C, O and Si elements, the composites of 0.5 wt% SiCp/TC4 has achieved a high yield strength and an ultimate tensile strength of 1053 MPa and 1144 Mpa, which are higher than TC4 matrix for 33.5% and 27.1%. SiCp/TC4 composites have widespread application prospects in aerospace, military and automotive industries.

Effect of Sintering Temperature on Properties of Carbon Fiber-Reinforced Titanium Matrix Composites.

Carbon fiber-reinforced titanium matrix composites were prepared by powder metallurgy. Carbon fiber (CF) powder and titanium (Ti) powder are mixed, pressed, and then sintered at a high temperature of 1300–1500 °C. The morphology and conductivity of carbon fiber-reinforced titanium matrix (Ti-CF) composites were studied. When the temperature range of the Ti-CF composites was from 1300 to 1500 °C, the porosity and resistivity first decreased and then increased. When the sintering temperature was 1350 °C, the diffraction peak of the sample was the strongest, the porosity was the smallest (4.16%), and the resistivity was the smallest (2.7 MΩ·mm). CFs have a very good strengthening effect on titanium-based composite materials.

The Constitutive Model of a Unidirectional SiC Fiber-Reinforced Titanium Matrix Composite During Spectrum Loading

An approach to simulate the constitutive model of a unidirectionally SiC fiber-reinforced titanium matrix composite during spectrum loading was developed in this paper. Based on the assumption that there is a microcrack in the matrix and the maximum shear stress criterion, the debonding length and the distribution of interfacial slip zone under spectrum loading were derived. The stress at a loading point was divided into four stages including crack opening section, positive slip zone, reverse slip zone, and bond zone. Based on the partial crack shear-lag model, the stress of fiber and matrix in the four stages was derived, and the constitutive model of the composite under spectrum loading was established. At last, the effects of different damages on the constitutive model and interfacial debonding zone of a unidirectionally SiC fiber-reinforced titanium matrix composite were investigated.

Low-cycle fatigue behavior and damage progression of a fiber reinforced titanium matrix composite

The low-cycle fatigue behavior and damage progression of a SiC fiber reinforced Ti–6Al–2Sn–4Zr–2Mo-0.1Si matrix composite was investigated systematically. The fatigue life increased from 4 to 52388 cycles when the maximum stress decreased from 1500 MPa to 1100 MPa. The modulus calculated from the stress-strain response exhibited little variation for all the specimens during the fatigue process. Fractographic observations showed that the fatigue cracks initiated internally and propagated preferentially in the internal sputtered matrix instead of the unreinforced matrix in the external layer for the cylindrical specimen. The proportion of the fatigue region in the fracture surface increased as the applied stress level decreased. The internally-progressed damage, especially breaks of bridging fibers, was well characterized in situ by the acoustic emission system.

Damage identification in fiber reinforced titanium matrix composites using acoustic emission

The fundamentals of acoustic emission behavior in SiC fiber reinforced titanium matrix composites were investigated. In order to obtain preferred damage modes and provide insight into damage identification, the acoustic emission responses in the fiber tensile test, the matrix tensile test, the longitudinal tensile test and the transverse tensile test for the single fiber composite were studied respectively. Extracted signals of fiber fracture, matrix deformation, matrix fracture, fiber fragmentation, fracture of the fiber-matrix reaction layer and interface debonding were analyzed by waveform pattern, frequency contents and time-frequency distribution. The signal characteristics with respect to amplitude, waveform shape, frequency centroid and wave modes were given for different damage modes. Furthermore, the generation and propagation mechanisms of multiple signals were also discussed with the assistance of theoretical models.

Simulation of tension-compression hysteresis loop of an unidirectionally SiC fiber-reinforced titanium matrix composite

ABSTRACT An approach to simulate the hysteresis loops of an unidirectionally SiC fiber-reinforced titanium matrix composite during tension-compression(T-C) fatigue loading has been developed in this paper. The T-C fatigue process of one cycle was divided into four stages of tension loading (TL), tension unloading (TU), compression loading (CL) and compression unloading (CU). It is assumed that fiber sliding relative to matrix occurs in the whole interfacial debonding area during TL. And there exists a closure stage of matrix crack during CL. Based on the BHE model, the stress–strain relationships during four stages have been derived. By combining the experimental normalized stiffness with the stress–strain relationship during TL, the average matrix crack spacing during various cycles are obtained. Combining the matrix cracking evolution law with another two damage evolution laws, the fatigue hysteresis loops of various cycles under T-C fatigue loading have been acquired. The theoretical results have been compared with experimental data of an unidirectionally SiC fiber-reinforced titanium matrix composite. And the effects of different damages on the hysteresis loops of TMCs have been investigated.

Interfacial reactions and matrix microstructure evolution in SiCf/Ti composites dominated by primary structure of Ti matrix

Abstract High-performance continuous SiC fiber reinforced titanium matrix composites (SiCf/Ti) are strongly required by aerospace vehicles, and their properties strongly depend on the microstructure of the interfacial reaction layer and the matrix. Thus, it is important to explore new routes to regulate these two SiCf/Ti components. In this work, α-phase-dominated and β-phase-dominated primary PVD Ti17 coatings were fabricated by controlling the bias voltage during physical vapor deposition (PVD). Their effects on the matrix microstructure evolution and interfacial reactions in SiCf/Ti after consolidation were further explored. It was found that compared with a primary α-Ti PVD Ti17 coating, a primary β-Ti PVD coating induced competitive growth between α-Ti and β-Ti grains in SiCf/Ti17 during consolidation. This yielded a smaller grain size and more β phase in the SiCf/Ti17 evolved from the primary β-Ti coating. In addition, a thicker reaction layer formed, as well as a lower interface strength and tensile strength in the SiCf/Ti17 evolved from a primary β-Ti coating, compared with the SiCf/Ti17 evolved from a primary α-Ti PVD Ti17 coating.

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

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.

Microstructure and interfacial strength of SiC fiber-reinforced Ti17 alloy composites with different consolidation temperatures

The interfacial reaction and titanium matrix microstructure in continuous SiC fiber-reinforced titanium matrix composite were investigated. By comparison of two samples actuated by 800 °C (in α + β dual-phase field) and 920 °C (in β single-phase field) consolidation, it can be concluded that tri-layer interfacial reaction regions consisting of fine TiCx/transition TiCx/coarse TiCx are formed in both two samples. In addition, the total thickness of reaction layer for composites prepared at 920 °C is thicker than that consolidated at 800 °C, while fine TiCx layer of 920 °C sample is thinner than that of 800 °C sample, which may be ascribed to the quick growth of PVD-Ti17 grain manufactured at 920 °C. In addition, lower interfacial shear strength is obtained in 920 °C sample, which can be ascribed to the formation of too thick brittle TiC layer. The research in the work is expected to motivate further exploration for interface adjustment of titanium matrix composites.

Comparison between axial residual stresses measured by Raman spectroscopy and X-ray diffraction in SiC fiber reinforced titanium matrix composite

Accurate measurement and analysis of residual stress state in the SiCf/Ti composites are crucial to optimizing their fabrication process and to understanding their failure mode, but they are still a challenge. In this work, SiCf/C/Ti17 composites with~48% fiber volume fraction, consisting of W-core SiC fibers (~100 m in diameter), turbostratic C coating (~2.5 m in thickness) and Ti17 matrix, are prepared by consolidating precursor wires fabricated by matrix-coated fiber method through hot isostatic pressing at 920℃/120 MPa/2 h; these samples are used for measuring their stresses. It is noted that turbostratic C coating, a necessary diffusion barrier layer between SiC fiber and Ti17 alloy matrix, bears the residual stress caused by the mismatch of thermal expansion coefficients between fiber and matrix during consolidation. It is found that the graphene planes are almost parallel to the axial direction of SiC fibers in the turbostratic C coating revealed by high magnification transmission electron microscope, and thus G peak position of C coating would be sensitive to stress state. Accordingly, micro-Raman spectroscopy is first used to measure the G peak positions of C coating under stress and stress-free state in the SiCf/C/Ti17 composite, respectively. Based on the position shift of G band caused by residual stress, the axial residual compressive stress of SiC fiber in SiCf/C/Ti17 composite is calculated to be~705.0 MPa. For comparison, X-ray diffraction method is also adopted to measure the interplanar spacing values of the Ti17 alloy matrix in different directions to obtain the spatial strains. During measurement, -Ti (213) high-angle diffraction peak is chosen to reduce test error, and then the different interplanar spacing values of -Ti (213) are obtained by varying the values of in three different directions at =0, 45 and 90. As three-axis-stress model is employed, the residual tensile stress of Ti17 alloy matrix in the axial direction of SiCf/C/Ti17 composite is~701.3 MPa, which is transformed through linear elastic theory into the residual compressive stress of SiC fiber of~759.4 MPa. The similar results confirm that it is reliable to characterize the residual stress in the SiCf/C/Ti17 composite with high-texture turbostratic carbon by both the Raman spectroscopy and the X-ray diffraction method.

Interfacial Fracture Toughness of Fiber Reinforced Titanium Matrix Composites by Push out Test

Abstract The model for single fiber push-out test was developed to evaluate the fracture toughness GIIc of the fiber/matrix interface in titanium alloys reinforced by SiC monofilaments. Theoretical solution to GIIc was obtained from fracture mechanics, and the effects of several key factors such as the applied stress needed for crack advance, crack length, and interfacial frictional shear stress were discussed. The predictions by the model were 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 model can reliably predict the interfacial toughness of the titanium matrix composites, in which interfacial debonding usually occurs at the bottom of the samples.

Spark plasma consolidation of continuous fiber reinforced titanium matrix composites

An attempt was made to produce continuous fiber reinforced titanium matrix composites using spark plasma sintering machine from foils and fibers. The materials used were metastable beta titanium alloy Ti-15V-3Cr-3Al-3Sn foils (125µm thick) and silicon carbide fibers (100µm in diameter). The method involved consolidating foils with fibers placed in between them at regular intervals. After a series of trials, the feasibility of the process was established. Spark plasma consolidation enabled satisfactory foil bonding and fiber embedment at a significantly lower temperature and time compared to conventional diffusion bonding or vacuum hot pressing. The composite samples consolidated above the beta-transus temperature of the titanium alloy were found to develop satisfactory strengthening precipitation upon direct aging. The current study shows that spark plasma consolidation is an excellent alternative to conventional diffusion bonding for producing continuous fiber reinforced titanium matrix composites.

Comparison of Residual Stress Measured by Diffraction Method and Matrix Etching Method in SiC Fiber Reinforced Titanium Matrix Composites

Measurement and modeling of residual stresses in SiC fiber reinforced titanium matrix composites (SiCf/Ti) are still a challenge. Diffraction method and matrix etching method can characterize the strains of matrix and fiber, respectively. A In this work, SiCf/Ti samples with perpendicular and parallel cross-sections to the fibers have been fabricated, and the residual stresses were measured by X-ray diffraction and matrix etching. The results showed that the axial matrix stress in sample with perpendicular cross-sections to the fibers was larger than that in sample with parallel cross-sections to the fibers, while the axial matrix stress calculated from etching was consistent with that from X-ray diffractions based on triaxle stress model, confirming the reliability of triaxle stress model.

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

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.

Analysis on the interfacial shear strength of fiber reinforced titanium matrix composites by shear lag method

Based on shear-lag method, two models for a single fiber push-out test are proposed to evaluate the interfacial shear strength of SiC fiber-reinforced titanium-matrix composites (TMCs). In the models, the effects of specimen parameters (such as specimen thickness and fiber volume fraction) on the interfacial shear strength are considered. The interfacial shear strengths of SCS-6/Ti-24-11 and SCS-6/Ti-15-3 composites are predicted using the model. The predicted results indicate that the models can be reliably used to predict interfacial shear stress of TMCs.

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.

Finite element modeling of consolidation process of SiC fiber-reinforced titanium matrix composites via matrix-coated fiber method

The consolidation process of SiCf/Ti-6Al-4 V composites by matrix-coated fiber (MCF) method via hot pressing was investigated using finite element modeling (FEM). By analyzing the elastic–plastic contact deformation of the representative aligned coated fibers, the consolidation maps delineating the time–temperature–pressure relationship for full densification were constructed. Both the flow coefficient and the contact area coefficient used to describe the contact deformation were calculated according to the model. In addition, the effect of fiber content on matrix stress distribution was analyzed. The results show that fiber content is a significant factor that influences the densification process. Higher fiber content will lower the consolidation rate.

Research on residual stress in SiCfreinforced titanium matrix composites

This study aimed to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites. The analytical solution of residual stress field distribution was obtained by using coaxial cylinder model, and the numerical solution was obtained by using finite element model (FEM). Both of the above models were compared and the thermal residual stress was analyzed in the axial, hoop, radial direction. The results indicated that both the two models were feasible to theoretical calculate the thermal residual stress in continuous SiC fiber reinforced titanium matrix composites, because the deviations between the theoretical calculation results and the test results were less than 8%. In the titanium matrix composites, along with the increment of the SiC fiber volume fraction, the longitudinal property was improved, while the equivalent residual stress was not significantly changed, keeping the intensity around 600 MPa. There was a pronounced reduction of the radial residual stress in the titanium matrix composites when there was carbon coating on the surface of the SiC fiber, because carbon coating could effectively reduce the coefficient of thermal expansion mismatch between the fiber and the titanium matrix, meanwhile, the consumption of carbon coating could protect SiC fibers effectively, so as to ensure the high-performance of the composites. The support of design and optimization of composites was provided though theoretical calculation and analysis of residual stress.

Interfacial Behaviors in SiC Fiber Reinforced Titanium Matrix Composites during Thermal Exposure

Interfacial behaviors of SiC fiber reinforced titanium matrix composites during thermal exposure were investigated by SEM, EDS and XRD. The effect of C coating was mainly analyzed. The results showed that C coating can be an effective barrier of the diffusion of Si element. And the C coating of SCS-6 SiC reinforced Ti6Al4V will be almost completely consumed after thermal exposure for 25 hours at 925°C. TiC will be found in the interface when the C coating exists. After C coating is completely consumed, there is Ti3SiC2 occurring besides TiC and the interfacial debonding strength is high. However, without the protection of C coating, the fibers will be consumed and their longitudinal tensile strength will be decreased, and this will affect the service performance of the composites.