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The Cf/ZrB2-SiC composite was successfully fabricated via brushing nano ZrB2-SiC slurry followed by low-temperature hot pressing technique, in which the UHTC phases were uniformly introduced into intrafascicular space of the subdivided fiber bundles. The fabricated composite exhibited a non-brittle fracture behavior and excellent mechanical properties with a high work of fracture of 1338 J/m2, one order of magnitude higher than that of the ZrB2-SiC ceramic, which was attributed to the hybrid toughening mechanisms such as crack deflection, fiber bridging, fiber pull-out and crack branching. The fiber/matrix interfaces were analyzed by the high resolution transmission electron microscopy, and no obvious chemical reaction was detected, suggesting the degradation of carbon fiber was effectively inhibited. Moreover, the Cf/ZrB2-SiC composite showed a good thermal shock resistance with a thermal shock temperature difference of 764 °C, almost twice those of the ZrB2-SiC ceramic. This work provides a facile and effective approach to fabricate high-performance continuous carbon fiber reinforced ceramic composites with uniform component distribution.

The effects of cooling rate and initial temperature on thermal shock behavior of ZrB2-SiC ceramic were studied by water spraying method with a thermocouple real-time temperature acquisition technique for the first time. It was shown that the cooling rate could be adjusted by changing the water flow rate, and the fracture behavior strongly depended on both the cooling rate and initial temperature. When the extreme value of cooling rate was constant, the decrease of initial temperature would lead to the increase of thermal stress, accompanied by a more serious damage of material, which was mainly because of the nonlinear relationship between thermal expansion coefficient and temperature.

An aqueous polymer quenching technique combing with a thermocouple real-time temperature acquisition technique were adopted to evaluate the thermal shock resistance of a hot-pressed ZrB 2 –SiC–graphite composite. The thermal shock behavior of the composite at different testing temperatures could be controlled and adjusted through varying the polymer concentration in the aqueous quenching solution. Experimental data showed that the critical maximum instantaneous thermal shock cooling rate at different testing temperatures was a constant value of 500 °C s −1 (ν(max) c ), and surface microcracks were assigned to the thermal shock failure. Heat transfer coefficient ( h ) gradient in samples, surface generated under two different quenching media, i.e. water and aqueous silicone oil solution, resulted in different tendency of decrease in strength. Thermal shock failure was presumed to be related to not only the body temperature gradient but also the surface h gradient in samples to produce thermal stress damage. The results indicate a promising method for studying the thermal shock resistance of ceramic materials.

ZrB 2 -SiC-C f composite with carbon coated carbon fibers was successfully prepared by low temperature hot pressing. This composite showed an excellent thermal shock resistance compared with those composites fabricated by hot pressing and spark plasma sintering using as-received carbon fibers. Toughening mechanisms such as crack deflection, crack branching, fibers pull-out and fibers bridging were obviously detected in ZrB 2 -SiC-C f owing to the inhibited degradation of carbon fibers and the relatively weak fiber/matrix interfacial bonding, leading to a non-brittle fracture mode of the composite. Moreover, the composite exhibited an excellent thermal shock resistance with a high critical thermal shock temperature difference of 773 °C which is about twice those of the reported ZrB 2 -based ultra-high temperature ceramics. This work provides valuable guidance in the preparation of ZrB 2 -based ultra-high temperature ceramics with a combination of excellent properties.

ZrB2 grains were prepared on graphite by chemical vapor deposition using a gas mixture of ZrCl4, BCl3, H2 and Ar at 1150 °C. The microstructure and phase composition of the coating were investigated by SEM, XRD, XPS and TEM. The results indicated that ZrB2 grains were deposited and grown directly by a vapor–solid growth mechanism on graphite without intermediate phase. Granulated ZrB2 grains were composed by many sub–grains with different crystal orientation. The rod–like or pagoda–like ZrB2 grains with lamellar structures were grew on the granulated ZrB2 particles and composed of two parts: the internal part with axial stacking faults and annular part with radial stacking faults.

To improve the ablation resistance of graphite, ZrB 2 SiC/SiC coating was prepared by pack cementation. Ablation resistance of the coating was investigated by oxyacetylene torch. After ablation for ∼200 s, the linear and mass ablation rates of ZrB 2 SiC/SiC coated graphite at center area were 4.647 μm/s and 1.216 mg/s, respectively. During ablation process, chemical erosion and particle denudation occurred at the same time were the main factors leading to ablation.

Cu 2 ZnSnS 4 (CZTS) thin films are deposited by spin-coating deposition of sol–gel precursor followed by sulfurization under a sulfur-containing atmosphere. The impact of the sol–gel precursor treatment with preheating temperature on the properties of the CZTS thin films and its photovoltaic solar cell has been investigated. XRD analysis shows that all the deposited CZTS thin films exhibit kesterite crystal structure and own a best crystallinity when the sol–gel precursor is preheated at 300 °C. Raman analysis shows that ZnS as secondary phase has formed on surface of the deposited CZTS thin films and its contents decrease as the preheating temperature increases. Morphological analysis shows that the sol–gel precursor preheated at 300 °C can contribute to the improvement of grain size and crystallinity. Component analysis shows that the higher preheating temperature can contribute to the decrease of tin loss, ZnS content and carbon content but an increase of sodium content. Photoelectric properties analysis shows that the CZTS thin films as a function of preheating temperature at 300 °C have best values with a band gap of 1.45 eV, a resistivity of 8.42 Ω cm, a carrier concentration of 1.26 × 10 17 cm −3 and a mobility of 5.22 cm 2 V −1 s −1 , respectively. Finally, a solar cell device built with the best CZTS thin films exhibits a best efficiency of 1.45%.

The ablation behavior of ZrB 2 –SiC sharp leading edges with different radius ( R ) values of 0.15 ( R 1), 0.5 ( R 2), 1.0 ( R 3) and 1.5 mm ( R 4) was investigated using an oxy-acetylene torch. Under the same ablation condition, sharp leading edge with a lower R value underwent a severer ablation. The surface temperature reached a maximum of ∼2100 °C for R 1, ∼2040 °C for R 2, ∼2000 °C for R 3 and ∼1930 °C for R 4, respectively, and subsequently decreased to a state value of about 1910–1935 °C for all models. R 1 and R 2 underwent intensive mass loss and linear shrinkage, whereas R 3 had only a slight mass loss and linear shrinkage, and R 4 had a slight mass gain and linear expansion. The finite element analysis (FEA) also gave the simulated temperature distributions in the ZrB 2 –SiC sharp leading edge models, which were in good accordance with the experimental results. Considering the surface temperature, shape retention behavior and the lift to drag ratio, R 3 (1.0 mm) was therefore selected as the optimal radius value for ZrB 2 –SiC sharp leading edge. The microstructures of the cross-section and oxidation surface of R 3 were also investigated.

ZrB2–20vol.%SiC containing the various volume fractions of graphite flake (ZSG) composites were investigated to determine the effect of graphite content on the microstructure as well as the mechanical properties and thermal shock resistance. The results revealed that the flexural strength generally decreased as the graphite volume fractions increased. Compared with the fracture toughness of about 4.5 MPa m1/2 for the ZrB2–SiC composites, the toughness of the ZSG composites is essentially higher than that of the ZrB2–SiC composites due to their lower strength relative to the ZrB2–SiC composites. The toughening mechanisms, such as the crack deflection and bridging, were related to the thermal residual stresses, and the thermal residual stresses in interfaces were calculated using Hsueh's formula. Moreover, the critical crack size that represents thermal shock resistance was calculated using the Griffith criterion. It was found that the thermal shock resistance was improved with the increasing graphite volume fractions.

Hot pressed Zr 2 (Al(Si)) 4 C 5 /SiC composites containing 0–30 vol.% silicon carbide (SiC) particles have been investigated to determine the effect of composition (i.e. amount of SiC particles) on the microstructure, mechanical properties, and thermal properties. With increasing SiC volume contents, the Vickers’ hardness, flexural strength, and fracture toughness of the composites were improved. Vickers’ hardness, flexural strength, and fracture toughness increased from 12.2 GPa, 420 MPa and 4.64 MPa m 1/2 for monolithic Zr 2 (Al(Si)) 4 C 5 to 15.4 GPa, 592 MPa and 5.67 MPa m 1/2 for Zr 2 (Al(Si)) 4 C 5 –30 vol.% SiC, respectively. Specific heat capacity increased with SiC addition, while thermal conductivity decreased obviously with increasing SiC volume contents. The results here pointed to a potential method for improving strength and toughness of Zr–Al–C based ceramic composites.

Thermal shock behavior of ZrB 2 –10 vol%SiC ultra-high temperature ceramics with addition of ZrO 2 was investigated by means of water-quenching as well as the finite element analysis. Optimal residual strength and critical temperature difference were obtained from ZrB 2 –10 vol%SiC ceramic added by 10vol%ZrO 2 . Simulated results revealed that ZrB 2 –10 vol%SiC–10 vol%ZrO 2 provided the lowest thermal stress and stress intensity factor during thermal shock, which confirmed the experimental data. Such improvement in thermal shock resistance compared with ZrB 2 –10 vol%SiC was primarily ascribed to the improved toughness by the addition of ZrO 2 . Besides, appropriate phase transformation of ZrO 2 during quenching was further beneficial to resist the thermal shock.

ZrB 2 –20 vol.%SiC–5 vol.%AlN ceramic composites (ZSA) were fabricated by hot pressing sintering under inert gas protected, which mechanical properties were improved obviously by introducing AlN as sintering aid. Ablation tests of ZSA were conducted with different heat flux parameters in high frequency plasma wind tunnel. The results showed that ZSA exhibited excellent ablation resistance at 2000 °C for 300 s in oxidation environment and a dense coherent scale was formed after ablation, whereas a strong degradation and mass loss were observed at 2600 °C for 300 s. The ablation behavior, microstructures evolvement and the effect of AlN were analyzed.

ZrB2-based ceramics containing 20 vol.% SiC and 10 vol.% AlN were prepared by hot pressing two different ZrB2 precursor powders with average particle sizes of 5 μm in ZSA (ZrB2–20 vol.% SiC–10 vol.% AlN) and 2 μm in GZSA (ZrB2–20 vol.% SiC–10 vol.% AlN) ceramics. The microstructures and mechanical properties were investigated. The thermal shock behavior was studied through the methods of retained flexural strength after quenching into water of 20 °C with the temperature differences between 0 and 800 °C. GZSA showed a better resistance to thermal shock in terms of the increased critical temperature difference (ΔTC of GZSA was 408 °C, about 40 °C higher than that of ZSA), since the finer grain size enhanced fracture toughness by promoting crack bridging, which inhibited the propagation of cracks due to thermal stresses. The influence of quenching temperature difference on the fracture toughness was not significant. Comparing with ZSA, the thermal stress fracture resistance parameter, R, and thermal stress damage resistance parameter, R⁗, of GZSA were all increased.

The fully dense HfB 2 –SiC composites with B 4 C addition were hot-pressed at 1850 °C. The effects of B 4 C on densification behavior and thermo-mechanical properties were investigated and compared with B 4 C free composite. Results indicated that B 4 C greatly enhanced the sinterability and refined grains. The highest increase on flexural strength and fracture toughness at room temperature were about 62% and 64%, respectively and the thermal conductivity slightly decreased by the addition of B 4 C.

SiC whisker-reinforced ZrB 2 ultra-high temperature ceramics containing 20 vol.% whisker were prepared in the temperature range of 1750–2000 °C by hot pressing. The microstructure and mechanical properties of ZrB 2 –SiC W ultra-high temperature ceramics were examined. The results showed that SiC whiskers were not stable in the ZrB 2 matrix above 1900 °C and degenerated into particles. The sintering temperature for this material system should be lower than 1800 °C to obtain high performance of ZrB 2 –SiC W . Significant improvement in fracture toughness of the material was obtained at 1800 °C using fine ZrB 2 particles compared to ZrB 2 ceramic. The improvement of toughness was mainly attributed to whisker bridging and cracking deflection around whiskers.

ZrB2–SiC ceramic composites were prepared from commercially available powders by hot-pressing, and aluminum nitride (AlN) was added as a sintering aid. Sinterability, microstructure and mechanical properties were investigated and compared to the composite without AlN. It was shown that the addition of AlN greatly improved the powder sinterability and enabled the production of nearly full dense composite. The flexure strength, hardness and fracture toughness were improved with a small amount (5 vol.%) of AlN due to the improvement in densification and inhibition of grain growth. Meanwhile the sinterability and mechanical properties were greatly enhanced with the introduction of finer starting powders. However, the flexural strength and fracture toughness were not improved much when more AlN was added.

Densified ZrB 2 –SiC-based ultra-high temperature ceramics reinforced with short carbon fibers were prepared by conventional hot-pressing. The microstructure, mechanical and oxidation resistance properties of the composite were investigated. The C sf /ZrB 2 –SiC composite had improved fracture toughness of 6.6 MPa m 1/2 compared to ZrB 2 –SiC composite of 4.3 MPa m 1/2 due to fiber debonding, fiber pull-out and fiber bridging as well as crack deflection. It was found that the low modulus of carbon fiber and a graphitization transition layer between fiber and matrix led to the decreased flexural strength. The oxidation resistance tests were carried out on C sf /ZrB 2 –SiC using an oxyacetylene torch. The temperature of the oxidized specimen exceeded 1800 °C and the surface layer appeared dense and adherent. No macro-cracks or spallation were detected, suggesting that these composites possess a better oxidation resistance than ZrB 2 –SiC. The improved oxidation resistance is attributed to the formation of a coherent SiO 2 rich scale, which acts as an effective barrier against the inward diffusion of oxygen. The results presented here point to a potential way for improving toughness of composite without sacrificing oxidation protection.

Hot-pressed ZrB2–SiC ceramics was hot-pressed at a temperature of 1900 °C, and yttria (Y2O3) was added as a sintering aid. The amount of Y2O3 that was added had a significant influence on the sinterability and mechanical properties of the ZrB2–SiC ceramics. When a small amount (3 vol.%) of Y2O3 was added, the Y2O3 reacted with impurities oxides (ZrO2, B2O3 and SiO2) that were present on the surface of the starting powder. The elimination of impurities oxides suppressed the grain growth effectively, which led to an improvement in the densification of ZrB2–SiC ceramics. The mechanical properties, both the flexural strength and fracture toughness were enhanced through these improvements in the sinterability and microstructure. On the other hand, when a large amount (8 vol.%) of Y2O3 was added, the mechanical properties were not improved much, presumably because the extra additive made redundant liquid phase at the grain boundaries.

Zirconium diboride (ZrB 2 )-based ultra-high temperature ceramics reinforced by SiC whisker were prepared by spark plasma sintering (SPS) and conventional hot pressing (HP). Dense materials were fabricated at 1600 °C by SPS and 1800 °C by HP. The densification behavior was investigated through the analysis of the HP and SPS shrinkage curves. The microstructures and mechanical properties were analyzed and compared in order to understand the influence of the two sintering techniques. The mechanical properties took full advantage of the addition of SiC whisker. Both materials exhibit high flexural strength and fracture toughness of >700 MPa and >6 MPam 1/2 , respectively. The main outcome of the present work is that when the ZrB 2 –SiC W ceramics composite was densified either by SPS or HP, the mechanical properties especially fracture toughness was higher than that of analogous monolithic and composites materials.

TiB 2 /(Cu, Ni) melt-infiltrated composites with high ceramic volume fraction were prepared via powder pre-sintering and melt-infiltration processing in vacuum. Infiltrated TiB 2 /(Cu, Ni) composite shows enhanced damage tolerance and good mechanical properties, i.e., fracture toughness up to 12.5 MPa m 0.5 and bending strength up to 844.7 MPa. The thermal shock and plasma ablation behavior of TiB 2 /(Cu, Ni) composites were conducted by plasma arc heater. The initial microstructure, interfacial bonding and ablated morphology were investigated. The experimental results show that the ablation mechanism of TiB 2 /(Cu, Ni) composites are mainly attributed to the transpiration cooling of metallic phase to bring away inner heat at elevated temperature. The microstructure analysis and properties measurement before and after ablation test reveals a clue of redistribution of infiltrated (Cu, Ni) so as to deduce and explain the functioning of transpiration cooling at ultra-high temperature.