It is of great importance to enhance the performance of oxide ceramic composite for fulfilling the increasing requirements from modern society. To this end, graphene is very suitable to be exploited as reinforcement for achieving superior performance in oxide ceramic composites, due to its extraordinary mechanical and electrical properties. In this review, the study of graphene based oxide ceramic composite including the processing, densification, microstructure and properties, based on the reports and researches in the past decade. It can be seen that: (1) the incorporation of graphene can generally improve the strength, fracture toughness and strain tolerance of oxide ceramic composite; (2) for the electrical performance, the graphene/oxide ceramic composites show not only low percolation threshold and high electrical conductivity, but also tunable charge carrier type which can be controlled by the oxygen concentration in oxide matrix. Therefore, it is believed that the graphene based oxide ceramic composites are very promising material for the application requiring both advanced mechanical and functional properties.

Textured ZrB₂-ZrC ceramics sintered by spark plasma sintering were analyzed. The results obtained by SEM and EDS demonstrate the formation of an amount of resultant ZrC phase and trace level of ZrO₂ and BN phases, due to the various reactions between starting powders and impurities. Compared with conventional methods in which TEM was used to analyze the orientation relationship between the phase and the primary phase, EBSD method in SEM can not only study the orientation relationship, but also study a large number of phase boundaries simultaneously to obtain statistical results, so as to avoid artificial selectivity. By using this method, three orientation relationships that may exist between ZrB₂ and ZrC phases, i.e. (011¯0)||(111)&[21¯1¯0]||[101¯], (112¯0)||(2¯02)&[0001]||[111], and (1¯21¯0)|| (2 2¯0)&[0001]||[110] were checked. It is determined that there is no specific orientation relationship between the two phases in this study, inferring that the ZrC phase formed with a homogeneous nucleation mode rather than an epitaxial nucleation.

Dense B₄C ceramic matrix composites were synthesized by reactive hot press sintering at the temperature of 1800℃ and the pressure of 35 MPa using commercial available B₂O₃, Al, graphite, and B₄C as raw materials. Microstructure, phase composition and mechanical properties were observed and tested. The composite ceramics were penetrated by a 7.62 mm calibre armor-piercing bullet at restrained and unrestrained states. Then the protection factor was calculated according to the rules of DOP method. In comparison, the ballistic performances of AZ ceramic and monolithic B₄C were also investigated. The results indicated that the main phase of the as-prepared sample was B₄C (~70wt%) and the secondary phase was Al₂O₃. A complex intermediate phase contained Al-B-O was found filled in the holes between the main phase and the secondary phase. Density, hardness, bending strength and fracture toughness of the composite were 2.82 g/cm³, 41.5 GPa, 380 Mpa, and 3.9 MPa•m^1/2, respectively. The fracture toughness significantly increased by 85.7s% as compared with that of the pure B₄C (2.1 MPa•m^1/2). The protection factor of the composite ceramic gets 11% and 70% increase compared to those of AZ ceramic and monolithic B₄C, respectively. At restrained states, the protection factors of all the samples are further improved by about 10%. These results suggested that B₄C/Al₂O₃ composite ceramic prepared by reactive hot press sintering method might be a good ceramic armor material.

Static tensile test of three dimension needled C/SiC composite material (3D-N C/SiC) was carried out at room temperature and damage processes of the composite was monitored online by an acoustic emission (AE) instrument. Noise information in the AE signals was removed according to Wavelet theory, and K-means clustering was used to analyze the AE signals. Combined with SEM observation, five damage modes were found during the tension: matrix cracking, interfacial debonding, interfacial sliding, individual fiber breakage, and fiber bundle rupture. The damage signal of 3D-N C/SiC composite contained three main frequencies at 240, 370 and 455 kHz, corresponding to interface damage, matrix damage and fiber fracture, respectively. Damage evolutionary mechanism was proposed through AE events and cumulative energy variation with loading time.

Localized mechanical properties of composite components (fiber, matrix, and interface) are critical parameters bridging the composition, microstructure and macro-mechanical performance of continuous fiber-reinforced ceramic matrix composites (CFRCMCs). However, they are difficult to be acquired and decoupled from bulk composites based on the traditional macro-mechanical testing techniques, due to their limited testing volumes and complex heterogeneous composite structures. The above questions has been solved recently by novel nano/micro mechanical testing and focused ion beam milling (FIB) techniques, which provide powerful tools to quantify the micro-mechanical properties of CFRCMCs. In this paper, recent progress in micro-mechanical properties of CFRCMCs was firstly reviewed, with special emphasis on the in-situ modulus and toughness of ceramic fibers and matrix, and the shear property of fiber/matrix interface. Following that, a criterion based on the He-Hutchinson cracking model was proposed to predict the macro mechanical performance of CFRCMCs by using those micro-mechanical parameters.

SiC ceramics have excellent mechanical properties, but its toughness is relatively low. To enhance the fracture toughness of SiC ceramics, graphene is introduced as fillers. In this study, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different contents of rGO were fabricated by hot press sintering (HP). Near fully-dense SiC/rGO composite was obtained after being hot-pressed under 2050℃, 40 MPa for 1 h. In addition, the influences of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites were discussed. The three-point flexural strength of 4wt% rGO/SiC composite reached 564 MPa, and the fracture toughness reached 4.02 MPa•m^1/2, which were 6% and 54% higher than those of hot-pressed SiC ceramics, respectively. The flexural strength of the three points of 6wt% rGO/SiC composite was 420 MPa, which was lower than that of hot-pressed SiC ceramics. While its fracture toughness was up to 4.56 MPa•m^1/2, which was 75% higher than that of hot-pressed SiC ceramics. The results of crack propagation show that the toughening mechanism can be ascribed to crack deflection, crack bridging and rGO pullout.

ZrB₂-SiC ceramics present better oxidation resistance and mechanical properties than monolithic ZrB₂ ceramics. However, the small damage tolerance and poor crack growth resistance, which result in the low fracture toughness, limit the engineering application of ZrB₂-SiC ceramics. Focusing on this issue, microstructure design and introduction of toughening phase are two effective approaches to improve the fracture toughness of ZrB₂-SiC ceramics. In this work, ZrB₂-SiC and C_f/ZrB₂-SiC composites were toughened respectively by interlocking microstructure and chopped carbon fibers via reactive hot pressing. For the ZrB₂-SiC composites, the interlocking microstructure formed by in-situ ZrB₂ platelets presented excellent self-enhancing effect. The ZrB₂-SiC composites had high bending strength and fracture toughness. However, the composite exhibited typical brittle fracture characteristics. Compared with ZrB₂-SiC composite, the flexural strength of C_f/ZrB₂-SiC composite decreased, but the fracture toughness was comparable with the ZrB₂-SiC composite. Furthermore, the critical crack size and the work of fracture of C_f/ZrB₂-SiC composites significantly improved, and the composite presented the non-catastrophic failure mode.

SiC_f/SiC composites modified by layered Y₂Si₂O₇ were presented in this research. Layered Y₂Si₂O₇ was transformed from yttrium oxide by chemical vapor infiltration process in SiC fiber preform, in which yttrium oxide was generated by the solution impregnation and pyrolysis method. Oxidation behavior of the layered-Y₂Si₂O₇ modified SiC_f/SiC composites was studied in the wet oxygen environment at 1400 ℃, showing that Y₂Si₂O₇ can concentrate on the oxidation surface to form a protective layer during the oxidation process. The bending strengths of SiC_f/SiC composites with one layer or three layers of Y₂Si₂O₇ remain 60.38% and 71.93%, respectively, after the oxidation for 80 h. In contrast, it is only 50.11% for SiC_f/SiC composites without Y₂Si₂O₇. Therefore, layered distribution of Y₂Si₂O₇ significantly improves the oxidation resistance of SiC_f/SiC composites in wet oxygen environment.

A modified polymer infiltration and pyrolysis method (PIP) was developed to enhance the densification of C/SiOC composites, using molten MK resin (polymethylsilsesquioxane) as precursor. Organic sulfonic acid was added as cross-linking agent to lower the curing temperature. The cross-linking mechanism and ceramization behavior of MK resin was studied. A high ceramic yield of about 85wt% and low free carbon content below 3wt% are achieved, with excellent high-temperature stability of the derived SiOC. The modified PIP approach presents a high densification efficiency. After only 8 PIP cycles, the final C/SiOC composites possess a density of about 1.81 g/cm ³. Compared with those composites fabricated by conventional PIP process, the C/SiOC composites prepared by modified PIP process show a much denser microstructure with much more improved densification efficiency. Bending strength of the as-fabricated C/SiOC composites is of (312±25) MPa, showing obvious non-brittle fracture behavior.

Cr₂AlC is a representative material in MAX phase family due to its combination of metallic and ceramic properties such as high electrical conductivity, high thermal conductivity, resistance to corrosion, good oxidation resistance. To further improve performance of Cr₂AlC, ZrC as a reinforcement was selected to reinforce Cr₂AlC matrix composites by hot pressing technique. Influence of ZrC content on the mechanical property of ZrC/Cr₂AlC composites has been investigated. The results showed that 10vol% ZrC/Cr₂AlC composite improved flexural strength (715 MPa) and Vickers hardness (7 GPa) by 80% and 106%, respectively, as compared with those of pure Cr₂AlC material. Date from this study indicate that Cr₂AlC MAX possesses broaden application potential.

Ceramic matrix composites (CMCs) are promising candidates for application in aeroengine, aerospace aircraft thermal protection systems, nuclear power system, and other fields. At present, CMCs are developing from structural bearing materials to multi-functional composites. MAX phases are a group of layered ternary ceramics with excellent plastic deformation capacity, high electrical conductivity, good irradiation resistance and ablation resistance. Besides strengthening and toughening CMCs, the introducing MAX phases into CMCs can effectively improve the anti-irradiation, anti-ablation and electromagnetic interference shielding performance, meeting requirements of multi-functional CMCs. This paper reviewed the progress on MAX phases modified CMCs, design mechanism and application prospect.