The mechanical properties of C/C-ZrC-SiC composites after laser ablation

Considering practical environment, the bending property of C/C-ZrC-SiC, C/C-SiC and C/C composites after ablation was worthily studied. Results revealed that C/C-ZrC-SiC composites had a better laser ablation resistance and higher bending strength retention compared with C/C-SiC and C/C composites. The mass loss rate and ablated depth of C/C-ZrC-SiC composites was − 0.09% and 190.377 μm, respectively. The retention of bending strength of C/C-ZrC-SiC composites was 217.67 ± 44.12 MPa, whose strength decreased by 3.57% compared with that of as-prepared C/C-ZrC-SiC composites. The excellent anti-ablation property and residual bending strength of C/C-ZrC-SiC composites were attributed to the lowest ablative temperature and the effective protection of the ZrO₂ grain and ZrO₂-SiO₂ layer, which were formed by oxidation of ZrC-SiC, evaporation of SiO₂, migration of liquid ZrO₂-SiO₂ and the infiltrated as well as grown ZrO₂. However, the fracture behavior transformation of composites from pseudo-plastic rupture to brittle rupture was induced by the ablation damage.     

二次烧结温度对牙科氧化锆陶瓷组织和力学性能的影响

研究二次烧结温度对氧化锆牙科陶瓷微观组织和力学性能的影响。方法：氧化锆亚微米粉经过干压、冷等静压成型后在1050ºC预烧结,然后将预烧结牙科氧化锆瓷块在1300ºC-1600ºC进行二次烧结。对不同二次烧结温度下材料的线收缩率、烧结密度、物相、三点抗弯强度进行测量分析,并通过扫描电镜观察试样的断面形貌。结果：结果表明随着二次烧结温度提高,氧化锆的密度、弯曲强度呈上升趋势。在1350ºC时体积密度达到6.10g/cm³,1500ºC时的机械性能最优,三点弯曲强度为852MPa,主晶相为四方相。结论：亚微米氧化锆粉体烧结活性高,力学性能优良,能够满足口腔全瓷修复材料的要求。     

Ablation behavior of a novel HfC-SiC gradient coating fabricated by a facile one-step chemical vapor co-deposition

To protect carbon/carbon composites against ablation at ultra-high temperature, a novel HfC-SiC gradient coating was fabricated by a facile one-step chemical vapor co-deposition. The phase composition, microstructure, bonding strength and ablation behaviour were investigated, and the mechanical properties of ablated coatings were characterized as well. The bonding strength of HfC-SiC gradient coating is 19.6?±?0.5?N (176% higher than that of HfC coating). HfC-SiC gradient coating shows excellent ablation resistance under oxyacetylene flame. The mass and linear ablation rate of HfC-SiC coating were only 0.153?±?0.02?mg·s^?1 and ?0.998?±?0.08?μm·s^?1, respectively. After ablation for 60?s, the hardness and elastic modulus of ablated HfC-SiC gradient coating are higher than those of ablated HfC coating. The excellent ablation resistance of HfC-SiC gradient coating results from its high bonding strength and the adhesion effect of Hf-Si-O sticky glass phase.     

Large-scale and ultra-low thermal conductivity of ZrO2 fibrofelt/ZrO2-SiO2 aerogels composites for thermal insulation

The large-scale fibrous/aerogels composites are prepared by using zirconia fibrofelt (ZFF) as skeleton to give high strength and ZrO₂-SiO₂ aerogels (ZSA) as filler to give excellent thermal insulation through vacuum impregnation. The ZFF/ZSA with a low density of 0.302?g/cm³ and a high porosity (89%) exhibits large size of 180?mm in length, 180?mm in width and 25?mm in height which is larger than other fibrous aerogels. Meanwhile, the ZFF/ZSA exhibits high compressive strength of up to 0.17?MPa which is approximately six times higher than that of ZFF (0.028?MPa). The ZFF/ZSA shows a much lower thermal conductivity of 0.0341?W?m^?1 K^?1 at room temperature and 0.0460–0.096?m^?1 K^?1 during 500?°C and 1100?°C which are lower than that of conventional fibrous materials, indicating its excellent thermal insulation property in a wide temperature range, and the thermal insulation mechanism is analyzed. Thus, the large-scale, low density, high strength, and low thermal conductivity of ZFF/ZSA composites show enormous potential application in the fields of architecture, engineering pipes and aerospace for thermal insulation and protection.     

Fire reactions of ceramic and polymer moulding composites

Abstract

Abstract

Low cost ceramic dough moulding compounds/composites (CDMC) are composed of inorganic metal silicates and chopped fibre reinforcements. This paper investigates the fire reactions of these materials under severe thermal and heat conditions. This research is targeted to potential applications in the replacement of glass fibre reinforced polymeric insulation materials such as phenolic composites as engine heat shields which experience high temperature and heat transmission. The materials developed can provide good properties, including heat insulation with high thermal stability for engine drafts, where traditional glass/phenolic composites were used and gave a very short life cycle. This work compares the thermal properties of the glass fibre reinforced phenolic composites and metal silicate composites produced under the same processing conditions. The results show that CDMC possesses significantly better thermal stability and heat resistance in comparison with phenolic moulding composite (phenolic dough moulding composites). The indication was that under the testing condition of heat flux of 75?kW?m^?2 intended for materials used for applications in marine, transport and possibly nuclear waste immobilisation, the integration of the CDMC was kept intact and survived as a high temperature insulation material.     

Mechanical properties of ceria-calcia stabilized zirconia ceramics with alumina additions

Ceria-stabilized zirconia-based composites have been developed aiming to obtain ceramic materials with enhanced hardness, strength, fracture toughness, and resistance to low temperature degradation. These composites are based on ceria-calcia stabilized zirconia (10 mol% CeO₂-1 mol% CaO TZP) and α-alumina (0?15 wt%) as a second phase. Raw materials in the form of powders were dispersed through ball milling, dried by slip casting, and subsequently grounded before being pressed and conventionally sintered at 1450 °C. Compared to the strength and hardness of 10Ce-TZP ceramics (typically 500 MPa and 6 GPa), an increase was observed for all compositions, especially for 10Ce-1CaO-5Al₂O₃ (739 MPa and 10.2 GPa). Single Edge V-Notched Beam fracture toughness values ranged from 5.1 to 6.6 MPa?√m, indicating a loss of transformability for all compositions. As in 10Ce-1CaO-TZP co-doped ceramics, the aging resistance of all alumina-containing composites was also excellent.     

ZrO2f-coated Cf hybrid fibrous reinforcements and properties of their reinforced ceramicizable phenolic resin matrix composites

Carbon fiber-reinforced ceramicizable phenolic resin matrix composites have been widely used in the field of thermal protection materials. In this paper, the ZrO_2f-coated C_f (ZrO_2f/C_f) hybrid fibrous reinforcements were designed to improve oxidation resistance of carbon fiber and ceramicizable composites reinforced by ZrO_2f/C_f hybrid fibrous reinforcements were prepared to investigated oxidation resistance and mechanical properties of the composites at high temperature. The results show that ZrO_2f/C_f hybrid fibrous reinforcements have good thermal stability and high oxidation resistance, and its ceramicizable composites have good bending strength at high temperature. Weight loss rate of the composites is only 21 %, and bending strength can be as high as 39 MPa when ablation time was 12 min at 1400 °C.     

A novel quartz fibre reinforced dense polyimide matrix composite: effect of preform stitching

ABSTRACT

A dense polyimide (PI) composite reinforced by quartz fibres (QFs), was prepared by vacuum assisted polymer infiltration and hot-pressing in this work. The microstructures and the mechanical properties of the as-fabricated composites were investigated. The results show a high flexural strength (≈686?MPa) of the composite, due to its dense nature. Moreover, there was no significant change in the bending strength of the stitched composites. The laminates mainly suffered delaminations and fracture of the QFs. The intralaminar bonding of the composite was enhanced by a novel stitching technique (all 28 layers stitched together by untwisted quartz filament tows in the plain stitch). As a result, the interlaminar fracture energy with 1 stitches?cm^?2 stitch density was increased by 87.1%, compared to that of the unstitched composite. In the case of stitched specimens, stitching plays an important role in improving the G_c and suppresses the influence of in-plane fibre orientation.     

Preparation of porous spodumene/zircon composite ceramics and its thermal and mechanical properties

Abstract

Porous β-spodumene/zircon (ZrSiO₄) composite ceramics were prepared by addition of zirconia to spodumene mineral using conventional solid reaction methods. The formation of the zircon was investigated by means of the differential scan calorimetry measurements and an X-Ray diffractometer. The microstructure of the composite ceramics was observed through a scanning electron microscope. The results show that the presence of zircon benefited the formation and stability of the porous structure and improved significantly the thermal endurance and mechanical properties of the spodumene matrix. The composites with 10–15% porosity exhibit an excellent thermal shock resistance, a low thermal expansion coefficient of approximately 1·4 × 10^?6 K^?1 in the range of 200–800°C and a high flexural strength about 100 MPa. It is found that the spodumene/zircon composites, widely used as a high temperature structure material, can be synthesised by a cost effective method.     

Fabrication and properties of 2D C/C–ZrB2–ZrC–SiC composites by hybrid precursor infiltration and pyrolysis

Abstract

Two dimensional C/C–ZrB₂–ZrC–SiC composites were fabricated through precursor infiltration and pyrolysis process using a mixture of polycarbosilane and ZrB₂ precursor and ZrC precursor as the impregnant. The microstructures, mechanical properties and ablation properties of the composites were investigated. The results showed that the homogeneity of the composite improved on using novel precursors that can dissolve with polycarbosilane through the formation of nanocomposite matrix. The flexural strength and fracture toughness first increased and then decreased on increasing the pyrocarbon content in the composite. Compared with the C/C–SiC composite, the ablation resistance of C/C–ZrB₂–ZrC–SiC composite was greatly enhanced. The mass loss rate and linear recession rate exposed to the plasma torch were 1?7 mg/s and 1?8 μm/s, respectively. The formation of a ZrO₂–SiO₂ glassy layer on the surface significantly contributed to the excellent ablative property of the composite.     

Alumina toughened zirconia from yttria coated powders

Alumina toughened zirconia (ATZ) ceramics are attractive materials for biomedical implants and other engineering applications requiring high strength and abrasion resistance at ambient temperature. As the toughness of conventional ATZ composites is moderate it was tried to improve the mechanical properties by starting from a very tough and transformable 2.5Y-TZP powder derived from powder coating. 2.5Y-TZP and ATZ materials with 20–40 vol% of alumina were produced and tested with respect to mechanical properties, microstructure and phase composition. ATZ materials with a bending strength of up to 1900 MPa and a fracture toughness of 4.8–5.5 MPa √m were obtained. Transformability of the TZP distinctly declines with rising alumina content. Calculation of cooling and transformation stresses of the materials qualitatively confirms the measured toughness values. Alumina addition initially induces tensile residual cooling stress in the zirconia matrix which facilitates phase transformation. Formation of compressive stresses during transformation limits the transformability and toughness.     

Fabrication of composites with excellent mechanical properties based on cubic boron nitride reinforced with carbon nanotubes

Composites consisting of cubic boron nitride (cBN) as a matrix and carbon nanotubes (CNTs) as reinforcing additives were fabricated by high-temperature and high-pressure sintering (HTHP). Microstructures, mechanical properties, fracture modes and toughening mechanisms of these composites were investigated. Composites exhibited excellent bending strength, wear resistance, and fracture toughness. Fracture toughness of composites reached 7.02 MPa·m^1/2. Comparing to pure cBN matrix, bending strength improved from 475.27 to 600.15 MPa, and wear resistance increased by 43.23%. Such improvements of mechanical properties were mainly attributed to pullout and bridging reinforcements by CNTs. CNTs incorporation also changed fracture mode from inter-to trans-granular.     

Obtaining complex-shaped oxide ceramic composites via ionotropic gelation

In this communication, we present a new processing method for obtaining oxide ceramic composites based on the ionotropic gelation technique. Nextel 610 fiber fabrics were infiltrated by an alumina-zirconia suspension with a total solid content of 50 vol% and alginate as the binder. Subsequently, the suspension was slowly cross-linked by adding Al³⁺ cations and transferred to a gel state. The gelled fabric layers could be easily cut, stacked and shaped, as well as joined to other ceramic materials and composites. Furthermore, the fiber content could be adjusted by pressing the layers together. In summary, the composites produced with this technique presented a very good fiber bundle infiltration, matrix with fine porosity and excellent mechanical properties. Nextel 610/alumina-zirconia composites sintered at 1200°C for 1 hour showed bending strength of 306 MPa, interlaminar shear strength of 9.8 MPa and nominal fracture toughness of 13.6 MPa m^0.5.     

Microstructure,high-temperature mechanical and dielectric properties of novel Si3N4 f/SiNO wave-transparent composites

Continuous Si₃N₄ fiber reinforced SiNO matrix composites (Si₃N_4 f/SiNO composites) were innovatively prepared for long-time high-temperature resistant wave-transparent materials of hypersonic aircraft. The microstructure, high-temperature mechanical and dielectric properties of Si₃N_4 f/SiNO composites were investigated in detail. The as-fabricated Si₃N_4 f/SiNO composites have homogeneous SiNO matrix distribution for the special winding process, which is beneficial for the mechanical strength and wave-transparent properties. The average tensile strength and flexural strength at room temperature is 87.8 MPa and 171.2 MPa respectively, which suggests Si₃N_4 f/SiNO composites have excellent mechanical strength. The tensile strength value decreases to 54.6 MPa after heat-treated at 1000 ℃ for the surface reactions between the SiNO matrix and Si₃N₄ fibers. After heat-treated at 1550 ℃, the composites have the tensile strength value of 24.2 MPa for the high strength retention rate of Si₃N₄ fibers at this temperature. Si₃N_4 f/SiNO composites have excellent room temperature dielectric properties and excellent dielectric stability in different frequency bands (7–18 GHz). The dielectric constant values vary from 3.69 to 3.75 while the dielectric loss attains the order of 10^?3. The dielectric constants and dielectric loss of Si₃N_4 f/SiNO composites are relatively stable from RT to 800 ℃. The as-fabricated Si₃N_4 f/SiNO composites that have excellent high temperature resistance and dielectric properties are the ideal high temperature wave-transparent composites.     

Simultaneous enhancement of mechanical and ablation properties of C/C composites modified by (Hf-Ta-Zr)C solid solution ceramics

In order to improve the mechanical and ablative resistance of C/C composites, (Hf-Ta-Zr)C single-phase solid solution ceramics were introduced into C/C composites by polymer infiltration and pyrolysis (PIP) to fabricate (Hf-Ta-Zr)C modified C/C composites (HTZ). Their mechanical property and ablation resistance were studied. The results showed that HTZ achieved simultaneous enhancement of mechanical property and ablative resistance. Their flexural strength and modulus could reach 219.34 MPa and 24.82 GPa, respectively. In addition, the mass and linear ablation rate of HTZ were 0.379 mg/s and 0.667 µm/s, respectively after the 90 s oxyacetylene ablation. A dense Hf-Ta-Zr-O multiphase oxide layer was formed on the surface of the HTZ during ablation process, which protected the interior modified C/C composites from ablation. Our work expands a rational design of modified C/C composites and broaden the application of solid solution ceramic in the field of ultra-high temperature ablation resistance for carbon or ceramic-based composites.     

Dense and strong ZrO2 ceramics fully densified in <15 min

ABSTRACT

Crack-free zirconia ceramics were consolidated via sintering by intense thermal radiation (SITR) approach at 1600–1700°C for 3–5?min. The resulted ceramic bulks can achieve a relative density up to 99.6% with a grain size of 300–1200?nm. Their bending strength, Vickers hardness and indentation toughness values are up to 1244?±?139?MPa, 13.3?±?0.3?GPa and 5.5?±?0.1?MPa?m^1/2, respectively. Quantitative Raman and XRD analysis show the presence of minor m phase on the natural surface (<7%), fracture surface (<10%) and indentation areas (<15%). It reveals that the SITR method is efficient for rapidly manufacturing zirconia ceramics with desired density, fine grained microstructure and good mechanical properties that are strongly demanded in dental applications.     

Microstructure and Mechanical Properties of Three-Dimensional Textile Hi-Nicalon SiC/SiC Composites by Chemical Vapor Infiltration

Three-dimensional textile Hi-Nicalon SiC-fiber-reinforced SiC composites were fabricated using chemical vapor infiltration. The microstructure and mechanical properties of the composite materials were investigated under bending, shear, and impact loading. The density of the composites was 2.5 g·cm⁻³ after the three-dimensional SiC perform was infiltrated for 30 h. The values of flexural strength were 860 MPa at room temperature and 1010 MPa at 1300°C under vacuum. Above the infiltration temperature, the failure behavior of the composites became brittle because of the strong interfacial bonding and the mismatch of thermal expansion coefficients between fiber and matrix. The fracture toughness was 30.2 MPa·m^1/2. The obtained value of shear strength was 67.5 MPa. The composites exhibited excellent impact resistance, and the dynamic fracture toughness of 36.0 kJ·m⁻² was measured using Charpy impact tests.     

Preparation and corrosion resistance of cordierite–spodumene composite ceramics using zircon as a modifying agent

To prolong the service life of cordierite–spodumene composite ceramics applied to the solar heat transmission pipeline, the zircon modifier was introduced to improve the corrosion resistance of the ceramics. The effects of zircon on the density, bending strength, crystalline phase, microstructure and chemical stability were studied. The results showed that the sintering temperature range of the composite ceramics was broadened to 40–60?°C with the introduction of 5–15?wt% zircon. Moreover, the mechanical strength and corrosion resistance of the ceramic materials were improved with the zircon introduction. In particular, sample C3 containing 15?wt% of zircon and sintered at 1360?°C exhibited the best performance, which had the 0.03% Wa, 0.07% Pa, 2.34?g?cm^?3 Db and 100.17?MPa bending strength. After acid and alkali corrosion, the water absorption was still less than 0.5% and the strength loss rate decreased to less than 5.3%. The XRD and SEM analyses demonstrated that the ZrSiO₄ grains dispersed at the grain boundaries could enhance the mechanical properties. Furthermore, the existence of the Zr⁴⁺ ions not only reduced the cationic solubility of the glassy phases but also led to a reaction with OH^? to form Zr(OH)₄ on the surfaces. This improved the corrosion resistance of the composite ceramics and endowed it with a high residual strength after the acid and alkali corrosion.     

Preparation of carbon/carbon‐ultra high temperature ceramics composites with ultra high temperature ceramics coating

In order to increase the oxidation resistance of carbon/carbon (C/C) composites at long‐term high temperature, C/C‐Ultra High Temperature Ceramics composites (UHTCs) with a dual‐layer UHTCs oxidation coating was successfully designed and fabricated. The microstructure and ablation resistance were investigated and discussed. After ablation in arc‐heated wind tunnel with temperature being 2200°C for 1000s, the mass ablation rate and linear ablation rate were ?1.9 × 10^?2 mg/cm²s and 2.9 × 10^?5 mm/s, respectively. The formation of thermodynamically compatible oxide scale including ZrO₂ skeleton and SiO₂ or Zr–Si–O glass on the surface were mainly contributed to the excellent ablation resistance of the composite.     

Ablative properties and mechanisms of hot vulcanised silicone rubber (HVSR) composites containing different fillers

Hot vulcanised silicone rubber (HVSR) composites were prepared using silicon carbide (SiC), hafnium oxide (HfO₂), zirconium oxide (ZrO₂) and zirconium boride (ZrB₂) as fillers, respectively. The tensile properties and the ablative response of the composites were examined. Tensile tests indicated that the tensile strength of HVSR was increased by the incorporation of ZrB₂. The linear ablation rate of the composites increased in the order HVSR/ZrB₂?2?2?2 and HVSR/ZrO₂, respectively, compared to that of 333?K for the blank HVSR. Scanning electron microscopy and X-ray diffraction results showed that the dense and rigid ceramic layer was hard to peel off under the high pressure and shearing forces of ablative gases. The HVSR/ZrB₂ specimens exhibited the best ablation resistance among all the composites involved in this work.