Microstructure evolution and phase transformation of TiB2/SiC/B4C composites synthesized from Ti‐SiC‐B4C ternary system

Bulk TiB₂/SiC/B₄C composites have been synthesized from Ti‐SiC‐B₄C ternary system with different Ti weight percentages via reactive hot pressing at 1800°C under an applied pressure of 30 MPa for 1.5 h. By Ti amount increasing, the flexural strength curve exhibited an “M‐like” tendency reaching the maximum value of 512.36 MPa for 30 wt.% Ti. Microstructural evolution of the composites from conterminously large matrix grains to finely clear‐edged particles was observed by scanning electron microscopy. The phase transformation and element diffusion were analyzed by XRD and Energy Disperse Spectroscopy. A hybrid reinforcing mechanism of fracture and crack deflection is proposed to illustrate the change in flexural strength.     

A Si–SiC Oxidation‐resistant Coating for Carbon/Carbon Composites by Hot‐pressing Reaction Technique

A Si–SiC coating was prepared by hot‐pressing reactive sintering (HPRS) technique for protecting carbon/carbon (C/C) composites against oxidation. The Si–SiC coating has a dense and crack‐free structure with a thickness of 70–90 μm. The Si–SiC coating by HPRS has a higher SiC content and lower Si content than the coating by pressure‐less reactive sintering (PRS). It also exhibits better oxidation‐protective ability than that prepared by PRS. With hot‐pressing, the flexural strength of the Si–SiC coated C/C composites decreases from 121 MPa to 99 MPa, and the interface bonding strength increases from 6 MPa to 10 MPa.     

Fabrication and Properties of Ti3SiC2/SiC Composites

Ti3SiC2/SiC composites were fabricated by reactive hot pressing method. Effects of hot pressing temperature, the content and particle size of SiC on phase composition, densification, mechanical properties and behavior of stress-strain of the composites were investigated. The results showed that ： （ 1 ） Hot-pressing temperature influenced the phase composition of Ti3SiC2/SiC composites. The flexural strength and fracture toughness of composites increased with hot pressing temperature. （2） It became more difficult for the composites to densify when the content of SiC in composites increased. It need be sintered at higher temperature to get denser composite. The flexural strength and fracture toughness of composites increased when the content of SiC added in composites increased. However, when the content of SiC reached 50 wt%, the flexural strength and fracture toughness of composites decreased due to high content of pore in composites. （3） When the content of SiC was same, Ti3SiC2/SiC composites were denser while the particle size of SiC added in composites is 12. 8 μm compared with the composites that the particle size of SiC added is 3 μm. The flexural strength and fracture toughness of composites increased with the increase of particle size of SiC added in composites. （4） Ti3SiC2/SiC composites were non-brittle fracture at room temperature.     

Preparation and properties of poly(ε‐caprolactone) self‐reinforced composites based on fibers/matrix structure

Self‐reinforced poly(ε‐caprolactone) (PCL) composites were prepared from bi‐component PCL yarns composed of PCL drawn fibers and PCL matrix by a combined process of yarns winding and hot‐pressing. Series of PCL polymers with different melting points were synthesized and used as matrix. PCL melt‐spun fibers were subject to different draw ratios and functioned as reinforcement. During the process of hot‐pressing, the matrix with low melting points melted and bonded the unmelted drawn fibers together creating self‐reinforced composites, the morphologies of which were examined by scanning electron microscope. Tensile testing of the composites was performed along the longitudinal and transverse directions separately. The longitudinal tensile test results showed that the Young's modulus and strength at break of the self‐reinforced composites were 59% and 250% higher than that of pure PCL. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44673.     

High‐temperature mechanical behavior of ZrB2‐based composites with micrometer‐ and nano‐sized SiC particles

Using micrometer‐ and nano‐sized SiC particles as reinforcement phase, two ZrB₂‐SiC composites with high strength up to 1600°C were prepared using high‐energy ball milling, followed by hot pressing. The composite microstructure comprised finer equiaxed ZrB₂ and SiC grains and intergranular amorphous phase. The temperature dependency of flexure strength related to the initial particle size of SiC. In the case of micrometer‐sized SiC, the high‐temperature strength was improved up to 1500°C compared to room‐temperature strength, but the strength degraded at 1600°C, with strength values of 600‐770 MPa. In the case of nano‐sized SiC, the enhanced high‐temperature strength was observed up to 1600°C, with strength values of 680‐840 MPa.     

Fabrication and properties of Cf/ZrC‐SiC‐based composites by an improved reactive melt infiltration

C_f/ZrC‐SiC composites with a density of 2.52 g/cm³ and a porosity of 1.68% were fabricated via reactive melt infiltration (RMI) of Si into nano‐porous C_f/ZrC‐C preforms. The nano‐porous C_f/ZrC‐C preforms were prepared through a colloid process, with a ZrC “protective coating” formed surrounding the carbon fibers. Consequently, highly dense C_f/ZrC‐SiC composites without evident fiber/interphase degradation were obtained. Moreover, abundant needle‐shaped ZrSi₂ grains were formed in the composites. Benefiting from this unique microstructure, flexural strength, and elastic modulus of the composites are as high as 380 MPa and 61 GPa, respectively, which are much higher than C_f/ZrC‐SiC composites prepared by conventional RMI.     

Three-dimensional carbon fiber-reinforced silicon carbide matrix composites by vapor silicon infiltration

Three-dimensional carbon fiber-reinforced SiC matrix composites (C_f/SiC) were fabricated by vapor silicon infiltration (VSI) successfully. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and wavelength dispersive spectrometer (WDS) analysis revealed that the microstructure and composition of constituent phases are strongly dependent on temperature. At 1973 K, the obtained C_f/SiC composite mainly consists of SiC, carbon fiber and residual Si, and shows a densified microstructure. The flexural tests show non-catastrophic fracture behavior for composites fabricated by VSI process, and the ultimate flexural stress is comparable to those of composites fabricated by other processing techniques, demonstrating VSI is an effective way to fabricate the dense C_f/SiC composites with good mechanical properties.     

Microstructure and mechanical properties of hot-pressed SiC nanofiber reinforced SiC composites

This study reports on the preparation and mechanical properties of a novel SiC_nf/SiC composite. The single crystal SiC nanofiber(SiC_nf) reinforced SiC ceramic matrix composites (CMC) were successfully fabricated by hot pressing the mixture of β-SiC powders, SiC_nf and Al–B–C powder. The effects of SiC_nf mass fraction as well as the hot-pressing temperature on the microstructure and mechanical properties of SiC_nf/SiC CMC were systematically investigated. The results demonstrated that the 15 wt% SiC_nf/SiC CMC obtained by hot pressing (HP) at 1850 °C with 30 MPa for 60 min possessed the maximum flexural strength and fracture toughness of 678.2 MPa and 8.33 MPa m^1/2, respectively. The nanofibers pull out, nanofibers bridging and cracks deflection were found by scanning electron microscopy, which are believed can strengthen and toughen the SiC_nf/SiC CMC via consuming plenty of the fracture energy. Besides, although the relative density of the prepared SiC_nf/SiC CMC further increased with the sintering temperature rose to 1900 °C, the further coarsend composites grains results in the deterioration of the mechanical properties for the obtained composites compared to 1850 °C.     

Microstructure and mechanical properties of hot-pressed SiC/(W,Ti)C ceramic composites

SiC/(W, Ti)C ceramic composites with different content of (W, Ti)C solid-solution were produced by hot pressing. The effect of (W, Ti)C content on the microstructure and mechanical properties of SiC/(W, Ti)C ceramic composites has been studied. Densification rates of the SiC/(W, Ti)C ceramic composites were found to be affected by addition of (W, Ti)C. Increasing (W, Ti)C content led to increase the densification rates of the composites. The sintering temperature was lowered from 2100 °C for monolithic SiC to 1900 °C for the SiC/(W, Ti)C composites. Results show that additions of (W, Ti)C to SiC matrix resulted in improved mechanical properties compared to pure SiC ceramic. The fracture toughness and flexural strength continuously increased with increasing (W, Ti)C content up to 60 vol.%, while the hardness decreased with increasing (W, Ti)C content.     

Microstructure and ablation behavior of SiC coated C/C–SiC–ZrC composites prepared by a hybrid infiltration process

In this study, C/C–SiC–ZrC composites coated with SiC were prepared by precursor infiltration pyrolysis combined with reactive melt infiltration. The pyrolysis behavior of the hybrid precursor was investigated using thermal gravimetric analysis-differential scanning calorimetry, X-ray diffraction, and scanning electron microscopy techniques. The microstructure and ablation behavior of the composites were also investigated. The results indicate that the composites exhibit an interesting structure, wherein a ceramic coating composed of SiC and a small quantity of ZrC covers the exterior of the composites, and the SiC–ZrC hybrid ceramics are partially embedded in the matrix pores and distributed around the carbon fibers as well. The composites exhibit good ablation resistance with a surface temperature of over 2300 °C during ablation. After ablation for 120 s, the mass and linear ablation rates of the composites are 0.0026 g/s and 0.0037 mm/s, respectively. The great ablation resistance of the composites is attributed to the formation of a continuous phase of molten SiO₂ containing SiC and ZrO₂, which seals the pores of the composites during ablation.     

Strength improvement and purification of Yb2Si2O7‐SiC nanocomposites by surface oxidation treatment

A two‐step processing was developed to prepare Yb₂Si₂O₇‐SiC nanocomposites. Yb₂Si₂O₇‐Yb₂SiO₅‐SiC composites were first fabricated by a solid‐state reaction/hot‐pressing method. The composites were then annealed at 1250°C in air for 2 hours to activate the oxidation of SiC, which effectively transformed the Yb₂SiO₅ into Yb₂Si₂O₇. The surface cracks purposely induced can be fully healed during the oxidation treatment. The treated composites have improved flexural strength compared to their pristine composites. The mechanism for crack healing and silicate transformation have been proposed and discussed in detail.     

Mechanical properties of talc‐ and (calcium carbonate)‐filled poly(vinyl chloride) hybrid composites

The main objective of this study was to investigate and compare the mechanical properties of poly(vinyl chloride) (PVC) composites filled with calcium carbonate (CaCO₃), talc, and talc/CaCO₃. Talc and CaCO₃ with different grades were incorporated into the PVC matrix. To produce the composites, the PVC resin, fillers, and other additives were first dry‐blended by using a laboratory mixer before being milled into sheets in a two‐roll mill. Test specimens were prepared by compression molding, after which the mechanical properties of the composites were determined. Single and hybrid filler loadings used were fixed at 30 phr (parts per hundred parts of resin). Talc‐filled composite showed the highest flexural modulus and the lowest impact strength, whereas uncoated, ground, 1‐μm CaCO₃ (SM 90) showed optimum properties in terms of impact strength and flexural modulus among all grades of CaCO₃. It was selected to combine with talc at different ratios in the hybrid composites. The impact strength of the hybrid composites gradually increased with increasing SM 90 content, but the flexural and tensile properties showed an opposite behavior. Hybrid (10 phr talc):(20 phr SM 90)‐filled PVC composite reached a synergistic hybridization with balanced properties in impact strength, as well as flexural and tensile properties. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Mechanical and Dielectric Properties of Mullite Fiber‐Reinforced Mullite Matrix Composites with Single Layer CVD SiC Interphases

Mullite fiber‐reinforced mullite matrix (Mu_f/Mu) composites were fabricated via the solgel process. Prior to the solgel process, SiC coatings were deposited on the fibers by the chemical vapor deposition (CVD) process. Effects of the SiC coatings on the mechanical and dielectric properties of the composites were investigated. The results show that the composites with SiC interphases exhibit evident toughened fracture behavior, and their flexural strength is about 2.37 times that of the as‐received composites. Besides, the complex permittivity of the composites with SiC interphases at X‐band is also increased remarkably due to the existence of carbon in the SiC interphases.     

Ni‐Coated SiC Particles: Synthesis and Densification

The mechanofusion process, a dry particle coating route, has been successfully applied to coat micrometric SiC particles with submicrometric Ni filaments. In a first step, the mechanofusion parameters were optimized to form a continuous Ni coating onto SiC particles. In a second step, the Ni‐coated SiC particles were sintered by hot isostatic pressing. The temperature and pressure cycles were determined to ensure a good densification of the material. Such a densification process leads to the formation of a δ‐Ni₂Si bilayer at the SiC/Ni interface; the inner δ‐Ni₂Si layer in contact with SiC being more rich in carbon than the one in contact with the matrix. From X‐ray diffraction, wavelength‐dispersive X‐ray spectrometry and scanning electron microscopy characterizations, a mechanism is proposed to explain the microstructure of the end‐product.     

Influence of precursor concentration on the densification efficiency and properties of SiC/SiC composites

The SiC/SiC composites were manufactured by polymer precursor impregnation pyrolysis process with near stoichiometric SiC fiber 2D preform as the reinforcing phase, the mixed solution of polycarbosilane (PCS), and xylene as impregnant. The effects of PCS concentration on the densification process, microstructure, and mechanical behavior of SiC/SiC composites were investigated using mechanical property testing, scanning electron microscopy, and other characterization techniques. Results showed the porosity and flexural strength of SiC/SiC composites increased first and then decreased with the increase of PCS concentration. When the concentration of PCS was 55% and 60%, the flexural strength of SiC/SiC composites reached 565.77 and 573.02 MPa, respectively. The mechanical behavior of SiC/SiC composites presented typical pseudoplastic characteristics such as fiber pulling-out, fiber bridging, and interface layer peeling, which would meet the dual requirements of optimizing the matrix and interface structure.     

Effect of the dissolution time on the structure and properties of lyocell‐fabric‐based all‐cellulose composite laminates

In this study, all‐cellulose composite laminates were prepared from lyocell fabric with ionic liquid (1‐butyl‐3‐methyl imidazolium chloride), a conventional hand layup method, and compression molding. Eight layers of lyocell fabric, which were impregnated with ionic liquid, were stacked symmetrically and hot‐pressed under compression molding for various times; this resulted in the partial dissolution of the surface of the lyocell fibers. The dissolved cellulose held the laminas together and resulted in a consolidated laminate. Finally, the prepared laminate was impregnated in water to remove the ionic liquid and to regenerate a matrix phase in situ; this was followed by hot‐press drying. Optical microscopy and scanning electron microscopy studies were used to analyze composite structures. With increasing dissolution time, the void content in the composites decreased, and the interlaminar adhesion improved. For LC‐2h and LC‐3h, the highest tensile strength and modulus values obtained were 48.2 MPa and 1.78 GPa, respectively. For LC‐4h, the highest flexural strength and modulus values obtained were 53.96 MPa and 1.2 GPa, respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43398.     

Tensile Properties of Ceramic Matrix Fiber Composites

The mechanical properties of various 2D ceramic matrix fiber composites were characterized by tension testing, using the gripping and alignment techniques development in this work. The woven fabric composites used for the test had the basic combinations of Al₂O₃ Fabric/Al₂O₃, SiC fabric/SiC, and SiC minofilament uniweave fabric/SiC. Tension testing was performed with strain gauge and acoustic emission instrumentation to identify the first-matrix cracking stress and assure a valid alignment. The peak tensile stresses of these laminate composites were about one-third of the flexural strengts. The SiC monofilament uniweave fabric (14 vol%)/SiC composites showed a relatively high peak stress of 370 MPa in tension testing.     

A novel method of hyperbranched poly(amide‐ester) modifying nano‐SiO2 and study of mechanical properties of PVC/nano‐SiO2 composites

A new method of surface chemical modification of nano‐SiO₂ was proposed in the paper. In the presence of catalyst, the active hydroxyl groups on the surface of nano‐SiO₂ reacted with AB₂‐type monomer (N,N‐dihydroxyethyl‐3‐amino methyl propionate) by one‐step polycondensation. And the product's Fourier transform infrared graphs and transmission electron microscopy (TEM) images proved that hyperbranched poly(amine‐ester) (HPAE) was grafted from nano‐SiO₂ surface successfully. Moreover, polyvinyl chloride (PVC)/modified nano‐SiO₂ composites were made by melt‐blending. The composites' structures and mechanical properties were characterized by TEM, scanning electron microscopy, and electronic universal testing machine. The results showed that nano‐SiO₂ grafted by HPAE increased obviously in dispersion in PVC matrix, and mechanical properties of PVC were effectively improved. Additionally, it was found that mechanical properties of PVC/nano‐SiO₂ composites reached the best when weight percent of nano‐SiO₂ in PVC matrix was 1%. Compared with crude PVC, the tensile strength of HPAE grafted nano‐SiO₂/PVC composite increased by 24.68% and its break elongation, flexural strength, and impact strength increased by 15.73, 4.07, and 184.84%, respectively. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Comparative study of aluminum diethylphosphinate and aluminum methylethylphosphinate‐filled epoxy flame‐retardant composites

Epoxy resin (EP) is one of the main polymers in electrical and electronic applications. In this work, flame‐retardant epoxy resin composites based on aluminum diethylphosphinate (Al(DEP)) and aluminum methylethylphosphinate (Al(MEP) were prepared using aromatic amine 4, 4‐diaminodiphenylmethane as curing agent. The flammability, thermal degradation, flexural properties, and morphologies of composites were investigated with respect to the filler loading and filler type. Results showed that both Al(MEP) and Al(DEP) were efficient flame retardants for EP and a low dosage (15 wt%) is enough to achieve the important criterion UL 94 V‐0. Limiting oxygen index (LOI) of composites is increased with filler loading (phosphorus content) and reached of 32.2% for 15 wt% of Al(MEP) and 29.8 for 15 wt% of Al(DEP). The char formation and flexural modulus of composites are also improved by adding the two fillers. However, the flexural strength of all the composites decreased with increasing filler loading. In comparison with Al(DEP)/EP, Al(MEP)/EP provides a higher flammability, better thermal stability and char formation but inferior flexural properties. Scanning electron microscopy revealed that the dispersion of Al(DEP) filler in the EP matrix is more uniform and exhibits better compatibility with EP matrix, which in turn generates better flexural strength and higher modulus when compared with Al(MEP)‐filled EP composites. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Oxidation Behavior of Hot Pressed ZrB2‐ZrC‐SiC Ceramic Composites

Dense ZrB₂‐SiC ceramics containing 40 vol% ZrC particles are fabricated via hot pressing method. Then the sintered ceramics are oxidized in air up to 1500°C, and the oxidation kinetics of the ceramic composites is deduced in combination with the reacted fraction curves. As indicated by the experimental results, the oxidation kinetics changes from reaction‐controlled process to diffusion‐controlled one with increasing of oxidation temperature. In addition, the oxidation kinetics parameters are obtained, which indicates that the oxidation resistance decays at elevated temperatures. Furthermore, the evolution of surface morphology and oxide scale during oxidation process is clarified.