A hybrid ceramic-polymer composite fabricated by co-curing lay-up process for a strong bonding and enhanced transient thermal protection

A hybrid ceramic-polymer composite is fabricated by a co-curing lay-up process by combining a carbon nanotube (CNT) reinforced ceramic composite thin film with a carbon fiber reinforced polymer (CFRP) composite substrate. The ceramic nanocomposite thin film has good flexibility, thermal conductivity and high temperature tolerance. The polymer composite substrate is a carbon fiber reinforced bismaleimide composite that is widely used in aerospace and automotive industries. Finite element analysis (FEA) is used to investigate the maximum survival temperature with different thicknesses of the ceramic nanocomposite. The resultant hybrid composite shows good structural integrity and displays a pull-off bonding strength up to 8.3?MPa. In addition, thermal study illustrates that such a flexible CNT reinforced ceramic composite can effectively protect CFRP in an elevated temperature environment by delaying transient thermal conduction.     

Tough salami-inspired Cf/ZrB2 UHTCMCs produced by electrophoretic deposition

One of the biggest challenges of the materials science is the mutual exclusion of strength and toughness. This issue was minimized by mimicking the natural structural materials. To date, few efforts were done regarding materials that should be used in harsh environments. In this work we present novel continuous carbon fiber reinforced ultra-high-temperature ceramic matrix composites (UHTCMCs) for aerospace featuring optimized fiber/matrix interfaces and fibers distribution. The microstructures – produced by electrophoretic deposition of ZrB₂ on unidirectional carbon fibers followed by ZrB₂ infiltration and hot pressing – show a maximum flexural strength and fracture toughness of 330 MPa and 14 MPa m^1/2, respectively. Fracture surfaces are investigated to understand the mechanisms that affect strength and toughness. The EPD technique allows the achievement of a peculiar salami-inspired architecture alternating strong and weak interfaces.     

Interfacial shear strength of C/C composites

Fiber-bundle push-out, single-fiber push-in, and single-fiber push-out tests were conducted in order to examine the applicability of these methods for determining the interfacial shear strength of carbon-carbon composites. The fiber-bundle push-out test resulted mostly in fractures along the fiber/matrix interface but created a small amount of fractures in the matrix. Hence, the evaluated strength was regarded as an approximate value. In order to precisely evaluate the interfacial strength, push-in and push-out tests for a single fiber were performed using a micro-Vickers indentation tester. In these tests, the load has to be placed within a target fiber, and the indentation should not extend to the matrix. This condition restricted the load that could be applied to a carbon fiber. Within this limit, a single carbon fiber could not be pushed-in. For the sake of load reduction, single-fiber push-out tests were conducted using thin specimens. The thickness appropriate for a single-fiber push-out specimen was estimated based on the interfacial shear strength obtained by the bundle push-out tests. Below this thickness, single-fiber push-out tests could be successfully performed.     

Zirconia ceramic and Nb joints brazed with Mo-particle-reinforced Ag-Cu-Ti composite fillers: Interfacial microstructure and formation mechanism

Zirconia (ZrO₂) ceramic and Nb were successfully brazed using a Mo-particle -reinforced Ag-Cu-Ti composite filler. The effect of the Mo content of the composite filler on the interfacial microstructures and mechanical properties of ZrO₂/Nb-brazed joints was investigated. The calculated Ti activity initially increased and then decreased as the Mo content was increased from 1 to 40 wt%, and played a decisive role in the evolution of interfacial products formed adjacent to the ZrO₂ ceramic. When 40 wt% Mo particles were added to the composite filler, TiO+Ti₃Cu₃O reaction layers formed adjacent to the ceramic substrate. By decreasing the Mo content of the filler, the TiO layer became thinner or even vanished, whereas the thickness of the Ti₃Cu₃O reaction layer increased gradually with decreasing Mo content. Concurrently, a bulky TiCu compound grew near to the ZrO₂ ceramic, and further fine TiCu particles were observed in the brazing seam. This microstructure evolution, as well as the mechanism for the formation of joints brazed with composite fillers of differing Mo content, is discussed based on TEM analyses. The shear strength of the brazed joint is clearly improved when a suitable amount of Mo is added to the Ag-Cu-Ti filler. A maximum shear strength of 370 MPa was obtained when ZrO₂/Nb joints were brazed with Ag-Cu-Ti+5 wt% Mo composite filler.     

Surface microstructure evolution of Cf/SiC ceramic matrix composite microgrooves processed by ultrafast laser

Modern aviation components have higher requirements for high temperature resistance, high strength and lightweight materials, and ceramic matrix composites have superior overall performance. However, its high brittleness and anisotropy lead to a challenge for manufacturing. In order to understand the formation conditions and the evolution of surface microstructures of the C_f/SiC microgrooves processed by ultrafast laser comprehensively, we designed a single-factor experiment and performed sensitivity analysis. The experiment results showed that the pulse energy had great effects on the depth of the microgroove, and the intense ablation caused more active oxidation of SiC to occur, generating more SiO(g). However, too much pulse energy may cause the material removal mechanism to be more due to the photothermal effect rather than the plasma effect. Low repetition frequency caused a large number of laminated connections in the microgroove and the oxide gradually changed from lumpy to flocculent as the repetition frequency increased. The more scanning times, the more ablation products sputtered onto the sample surface, including unablated carbon fibers. Shallow depth and ablation residues remained in the microgroove occurred under few scanning times. Although too fast scanning speed leaded to a rapid decrease in the microgroove depth, too slow scanning speed also generated more unablated carbon fibers sputtering out of the microgrooves. The microgroove depth had the highest sensitivity to the repetition frequency, followed by the pulse energy and scanning speed. The pulse energy and scanning speed had a greater effect on the oxide layer height, the repetition frequency affected the oxide layer width, and the scanning speed affected the microgroove width significantly. According to the processing requirements and the hot spot map, the processing parameters that can be adjusted effectively will be able to be obtained.     

Interfacial microstructure and mechanical properties of ZTA/ZTA joints brazed with Ni-Ti filler metal

The reliable brazing of the ZTA ceramic joints was successfully obtained using Ni-Ti filler metal. The microstructure and mechanical properties of the joints brazed at different temperatures were investigated. During the process of brazing, both Al₂O₃ and ZrO₂ in the ZTA reacted with the Ni-Ti filler, resulting in the formation of the AlNi₂Ti + Ni₂Ti₄O reaction layer adjacent to the ZTA substrate when brazed at 1350 °C for 30 min. NiTi and Ni₃Ti compounds precipitated at the center of brazing seam. When the brazing temperature increased from 1320 °C to 1380 °C, the thickness of AlNi₂Ti + Ni₂Ti₄O layer increased gradually. As the brazing temperature varied from 1400 °C to 1450 °C, TiO was formed adjacent to the ZTA substrate, along with the reduction of Ni₂Ti₄O. AlNi₂Ti distributed at the interface and center of brazing seam. The maximum shear strength of 152 MPa was obtained when brazed at 1420 °C for 30 min.     

Mechanical properties and microstructure evolution of 3D Cf/SiBCN composites at elevated temperatures

3D C_f/SiBCN composites were fabricated by an efficient polymer impregnation and pyrolysis (PIP) method using liquid poly(methylvinyl)borosilazanes as precursor. Mechanical properties and microstructure evolution of the prepared 3D C_f/SiBCN composites at elevated temperatures in the range of 1500‐1700°C were investigated. As temperature increased from room temperature (371 ± 31 MPa, 31 ± 2 GPa) to 1500°C (316 ± 29 MPa, 27 ± 3 GPa), strength and elastic modulus of the composite decreased slightly, which degraded seriously as temperature further increased to 1600°C (92 ± 15 MPa, 12 ± 2 GPa) and 1700°C (84 ± 12 MPa, 11 ± 2GPa). To clarify the conversion of failure mechanisms, interfacial shear strength (IFSS) and microstructure evolution of the 3D C_f/SiBCN composites at different temperatures were investigated in detail. It reveals that the declines of the strength and changes of the IFSS of the composites are strongly related to the defects and SiC nano‐crystals formed in the composites at elevated temperatures.     

Cf/SiC复合材料的制备及性能的研究

采用料浆渗积-有机前躯体裂解工艺制备碳纤维增强碳化硅陶瓷基复合材料.制备材料的抗弯强度达283 MPa,断裂韧性达12.1 MPa·m1/2.     

Enhanced mechanical properties and thermal shock resistance of Cf/ZrB2-SiC composite via an efficient slurry injection combined with vibration-assisted vacuum infiltration

An efficient slurry injection combined with vibration-assisted vacuum infiltration process has been developed to fabricate 3D continuous carbon fiber reinforced ZrB₂-SiC ceramics. Homogenous distribution between carbon fiber and ceramic was achieved successfully, leading to an enhancement in mechanical properties. The C_f-PyC/ZrB₂-SiC composite exhibited a typical non-brittle fracture mode with a superior fracture toughness of 6.72 ± 0.21 MPa·m^1/2 and an extraordinary work of fracture of 2270 J/m², respectively, increasing by nearly 14.8 % and 36 % as compared with those of a parent composite fabricated by only slurry injection and slurry infiltration. The enhancement in fracture toughness and work of fracture were attributed to multiple toughening mechanism including crack deflection, PyC coated fiber bundles pull-out and fiber bridging. Moreover, a critical thermal shock temperature difference of 814 °C was achieved, higher than that of traditional ZrB₂-based ceramics. This work presents an efficient approach to fabricate high-performance C_f/UHTCs with uniform architecture.     

Effects of preform pore structure on infiltration kinetics and microstructure evolution of RMI-derived Cf/ZrC-ZrB2-SiC composite

Reactive melt infiltration (RMI) is often used to fabricate highly dense ceramic matrix composite by infiltration of alloy melt into porous preform. Here, C_f/B₄C-C preforms with various pore structures were prepared, and the effects of pore structure on the ZrSi₂ melt infiltration and the as-received C_f/ZrC-ZrB₂-SiC composites were investigated. Compared with the preform prepared by slurry impregnation (SI), the preform prepared by sol impregnation shows more uniform pore size distribution, which leads to more homogeneous melt infiltration, as well as more uniform formation of ZrC-ZrB₂-SiC and better mechanical properties in the composites. The calculation results of infiltration kinetics indicate that the pore radius decreases quickly during the melt infiltration. As the time needed for pore closure in sol-preform is longer than that in SI-preform, it makes the infiltration kinetics more favorable in the former preform. This study can provide guidance for the pore structure regulation in the fabrication of RMI-composites.     

Comparative investigation of microstructure,mechanical properties and strengthening mechanisms of Al-12Si/TiB2 fabricated by selective laser melting and hot pressing

Near-fully dense Al-12Si matrix composites reinforced with TiB₂ ceramic particles (2?wt%) were successfully fabricated by selective laser melting (SLM) and hot pressing (HP) of powder mixtures. TiB₂ ceramic particles are homogeneously distributed in the Al-12Si matrix at the micrometer-scale owing to a very good wetting between molten Al-12Si alloy and TiB₂ ceramic. The microstructural analysis of the as-fabricated SLM samples show the formation of a supersaturated α-Al phase and the decrease of free residual Si with respect to the hot-pressed ones. Both composites exhibit a fine microstructure with a grain size of ~?5.1?µm and ~?5.8?µm for SLM- and HP-fabricated samples with addition of TiB₂ ceramic particles. The SLM Al-12Si/TiB₂ composite exhibits significantly improved microhardness (~?142?±?6.0 HV_0.05) and yield strength (~247?±?4.0?MPa) compared to the corresponding HP one. Fine cell morphology and nanostructured dispersion strengthening are responsible for the improved mechanical strength of the Al-12Si/TiB₂ composite processed by SLM.     

Study on interfacial debonding stress and damage mechanisms of C/SiC composites using acoustic emission

Among ceramic matrix composites (CMCs), carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are widely used in numerous high-temperature structural applications because of their superior properties. The fiber–matrix (FM) interface is a decisive constituent to ensure material integrity and efficient crack deflection. Therefore, there is a critical need to study the mechanical properties of the FM interface in applications of C/SiC composites. In this study, tensile tests were conducted to evaluate the interfacial debonding stress on unidirectional C/SiC composites with fibers oriented perpendicularly to the loading direction in order to perfectly open the interfaces. The characteristics of the material damage behaviors in the tensile tests were successfully detected and distinguished using the acoustic emission (AE) technique. The relationships between the damage behaviors and features of AE signals were investigated. The results showed that there were obviously three damage stages, including the initiation and growth of cracks, FM interfacial debonding, and large-scale development and bridging of cracks, which finally resulted in material failure in the transverse tensile tests of unidirectional C/SiC composites. The frequency components distributed around 92.5 kHz were dominated by matrix damage and failure, and the high-frequency components distributed around 175.5 kHz were dominated by FM interfacial debonding. Based on the stress and strain versus time curves, the average interfacial debonding stress of the unidirectional C/SiC composites was approximately 1.91 MPa. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to observe the morphologies and analyze the chemical compositions of the fractured surfaces. The results confirmed that the fiber was completely debonded from a matrix on the fractured surface. The damage behaviors of the C/SiC composites were mainly the syntheses of matrix cracking, fiber breakage, and FM interfacial debonding.     

Interfacial microstructure and mechanical properties of TC4/Ti3SiC2 contact-reactive brazed joints using a Cu interlayer

Reliable contact-reactive brazed joints of TC4 alloy and Ti₃SiC₂ ceramic were obtained using a Cu interlayer. The interfacial microstructure of a TC4/Ti₃SiC₂ joint brazed at 920?°C for 10?min was TC4/Ti₂Cu +?α-Ti +?β-Ti/Ti₂Cu +?AlCu₂Ti +?Ti₅Si₃/Ti₅Si₃ +?Ti₅Si₄/Ti₃SiC₂. The interfacial microstructure and mechanical properties of TC4/Ti₃SiC₂ joints brazed at different temperatures were investigated. With increasing temperature, the shear strength of the brazed joints first increased and then decreased. The maximum shear strength was 132?±?8?MPa, and the corresponding fracture occurred along the Ti–Si reaction layer and the Ti₃SiC₂ substrate adjacent to the Ti–Si reaction layer. The microhardness test also demonstrated that the Ti–Si reaction layer possessed the highest microhardness, 812?±?22 HV. The Ti-Si reaction layer was the weakest part of the brazed joints. To eliminate the Ti-Si reaction layer and improve the mechanical properties of TC4/Ti₃SiC₂ brazed joints, a 40-μm Ni layer was plated on the surface of the Ti₃SiC₂ ceramic before brazing. The results showed that the Ti–Si reaction layer that formed adjacent to the Ti₃SiC₂ ceramic was thin and intermittent. Moreover, the interface between the Ti₃SiC₂ ceramic and the TC4 alloy became jagged. The shear strength of the TC4/nickel-plated Ti₃SiC₂ brazed joints improved to 148?±?8?MPa; the corresponding fracture occurred mainly in the Ti₃SiC₂ ceramic and only a small portion of the fracture occurred in the brazing seam.     

Nanoplates forced alignment of multi-walled carbon nanotubes in alumina composite with high strength and toughness

Although the strengthening and toughening effects on ceramic composites are expected to be maximized by alignment of multi-walled carbon nanotubes (MWCNTs) in matrices, this concept has been rarely realized in practice due to the lack of convenient processing strategy. Here, the alignment of MWCNTs in alumina composite can be readily obtained by using α-Al₂O₃ nanoplates as raw powder. With the assistance of vacuum filtration and pressure in sintering, the highly aligned MWCNTs in alumina matrix are formed in in-plane direction. Accordingly, the strength and toughness in 1.5 wt% MWCNTs/alumina composite are improved by 58 % and 66 % with respect to monolithic alumina, respectively. Transmission electron microscopy observation reveals that the MWCNTs under great compressive residual stress are mainly embedded inside the grains, leading to much stronger grain boundaries. Meanwhile, the toughening effect is mainly attributed to the highly energy dissipating bridging and pullout, owing to the very effective load transfer.     

Interfacial adhesion of plasma‐treated carbon fiber/poly(phthalazinone ether sulfone ketone) composite

Interfacial adhesion between fiber and matrix has a strong influence on composite mechanical performance. To exploit the reinforcement potential of the fibers in advance composite, it is necessary to reach a deeper understanding on the relation between fiber surface treatment and interfacial adhesion. In this study, air plasma was applied to modify carbon fiber (CF) surface, and the capability of plasma grafting for improving the interfacial adhesion in CF/thermoplastic composite was discussed and also the mechanism for composite interfacial adhesion was analyzed. Results indicated that air plasma treatment was capable of increasing surface roughness as well as introducing surface polar groups onto CF; both chemical bonding and mechanical interaction were efficient in enhancements of interlaminate shear strength of CF/PPESK composite, while mechanical interaction has a dominant effect on composite interfacial adhesion than chemical bonding interaction. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Oxidation kinetics and mechanisms of a 2D-C/C composite

The isothermal oxidation of a 2D-C/C composite was investigated by thermogravimetric analysis in the temperature range of 745–900 °C and SEM observation. The model-free, model-fitting and reduced-time plot methods were applied to oxidation kinetic analysis. SEM investigation shows that oxidation starts from the fiber/matrix interfaces, and matrix carbon is oxidized much more rapidly than the carbon fibers. According to the model-free curve, the oxidation temperatures are divided into two ranges: lower temperatures (745–800 °C) and higher temperatures (850–900 °C). The apparent activation energy and oxidation controlling mechanisms in different temperature ranges are obtained. Furthermore, the trend of the oxidation rate with weight loss or temperature ranges is discussed by the combination of microstructure and mechanisms of oxidation of 2D-C/C composite.     

Interfacial microstructure and mechanical properties of porous-Si3N4 ceramic and TiAl alloy joints vacuum brazed with AgCu filler

Porous Si₃N₄ ceramic was firstly joined to TiAl alloy using an AgCu filler alloy. The effects of brazing temperature and holding time on the interfacial microstructure and mechanical properties of porous-Si₃N₄/AgCu/TiAl joints were studied. The typical interfacial microstructure of joints brazed at 880 °C for 15 min was TiAl/AlCu₂Ti/Ag-Cu eutectic/penetration layer (Ti₅Si₃+TiN, Si₃N₄, Ag (s, s), Cu (s, s))/porous-Si₃N₄. The penetration layer was formed firstly in the brazing process. With increasing brazing temperature and time, the thickness of the penetration layer increased. A large amount of element Ti was consumed in the penetration layer which suppressed the formation and growth of other intermetallic compounds. The penetration layer led the fracture to propagate in the porous Si₃N₄ ceramic substrate. The maximum shear strength was ~13.56 MPa.