Enhanced mechanical properties,thermal shock resistance and ablation resistance of Si2BC3N ceramics with nano ZrB2 addition

The mechanical properties, thermal shock resistance, and ablation resistance of nano ZrB₂ modified Si₂BC₃N ceramics were investigated. The results show that ZrB₂ stimulated microstructure evolution obviously. Therefore, the maximum strength and fracture toughness reach 559.6 MPa and 6.77 MPa·m^1/2, which are improved by 61.0% and 29.4%, respectively. Furthermore, the residual strengths of 10 wt% ZrB₂ containing composites tested at 1000 ℃ retain 363.6 MPa, which is much higher than 97.7 MPa of pristine Si₂BC₃N ceramics. Besides, the ablation resistance of ZrB₂ modified Si₂BC₃N ceramics at 3000 ℃ is enhanced remarkably and the linear and mass ablation rates of ZrB₂-10 are only 0.009 mm/s and 1.91 mg/s, respectively. The ablation in the ultra-high temperature zone is totally dominated by the ZrB₂ component, and the thermochemical erosion is determined by the oxidation resistance of ZrB₂ in the thermal affected zone.     

Effect of h-BN on the microstructure and fracture behavior of low carbon Al2O3-C refractories

h-BN is an ideal substitution candidate for graphite due to its similar crystal structure, better oxidation resistance. In this work, the effect of h-BN on microstructure and comprehensive properties of Al₂O₃-C refractories are investigated, and the specimen containing 0.5 wt% h-BN (G0.5N0.5) possesses the best comprehensive properties. The addition of h-BN could reduce the diameter of SiC whiskers, which leads to the highest strength of specimen G0.5N0.5 (42.63 ± 3.10 MPa). Moreover, the fracture behavior of the specimens is demonstrated using wedge splitting test. The results show that the specimen G0.5N0.5 possesses the highest crack initiation and propagation resistance, which could be attributed to the collaborative effect of h-BN and SiC whiskers. Noteworthily, the addition h-BN could improve the thermal shock resistance. The specimens containing h-BN possess the higher residual ratio, compared with the specimen containing no h-BN (G1N0), and the specimen G0.5N0.5 shows the highest residual strength (14.12 ± 0.67 MPa). Furthermore, the oxidation resistance could be enhanced with introducing the h-BN.     

Enhanced ionic conductivity and thermal shock resistance of MgO stabilized ZrO2 doped with Y2O3

The present work focused on the effect of Y₂O₃ co-doping on the phase composition, microstructure, ionic conductivity and thermal shock resistance of 8 mol% MgO stabilized ZrO₂ (Mg-PSZ) electrolyte ceramics for high temperature applications. The addition of Y₂O₃ could promote the process of monoclinic-to-cubic/tetragonal phase transformation and became the metastable phase at room temperature. Meanwhile, the grain size of Mg-PSZ decreased. It was demonstrated that an appreciable increase in the ionic conductivity and compressive strength occurred on substituting MgO with Y₂O₃ in the Mg-PSZ electrolyte ceramics across the measured temperature range. Moreover, the Y₂O₃ addition could restrain the adverse effect of the cyclic thermal shock on the ionic conductivity and compressive strength of Mg-PSZ. The main reason was that the increase of the amount of monoclinic phase caused by cubic/tetragonal-to-monoclinic phase transformation by the cyclic thermal shock was restrained after the Y₂O₃ addition.     

炭/陶复合材料的抗热震性能研究

对含石墨的炭／陶复合材料优良的抗热震性能进行了讨论。这种性质与石墨的导热系数大、断裂功高、热膨胀和弹性模量小密切相关。     

High-temperature mechanical property and thermal shock resistance of Al2O3f/Al2O3 composites

Continuous alumina fiber–reinforced alumina matrix composites (Al₂O_3f/Al₂O₃ composites) were produced via sol–gel process, then the high-temperature mechanical property and thermal shock resistance of Al₂O_3f/Al₂O₃ composites were investigated. The results showed that the composites exhibited excellent high-temperature properties. The mechanical property of the composites was affected by heat treatment (prepared at 1100°C exhibited the most desirable mechanical property). The tensile strength of the composites abruptly decreased at higher temperatures. Although the mechanical property of the composites deteriorated after the thermal shock test was conducted at high temperatures, they exhibited excellent thermal shock resistance. After 50 thermal shock tests conducted at 1300 and 1500°C, the flexural strength of the composites was found to be 124.34 and 93.04 MPa, thus showing a decrease in strength with the increasing temperature.     

Influence of bonding carbon on low carbon Al2O3-C refractory composites

The carbonized behavior of binders (carbores pitch, mesophase pitch, high temperature pitch and phenolic resins) was investigated. Meanwhile, the influence of binders, Ni-catalyst and heat treatment on structure and properties of low carbon Al₂O₃-C materials was researched. Mesophase pitch and high molecular weight resin provided higher carbon yield. The synergistic interaction of pitch and phenolic resin provided the higher carbon yield than that of single component. Ni-catalyst changed structure and morphology of bonded carbon promoting the transition of amorphous carbon to crystalline carbon increasing carbon yield and degree of graphitization. High molecular weight phenolic resins, mesophase or carbores pitch and Ni-catalyst worked together providing low carbon Al₂O₃-C samples of excellent strength performance in a wide temperature range and high resistance of thermal shock. Embedding coke in N₂ could promote the generating of carbon fibers which obviously enhanced thermal shock resistance of low carbon (6% flake graphite) Al₂O₃-C materials after heat treatment.     

Effect of CaF2 on sintering behavior and thermal shock resistance of Y2O3 materials

Y₂O₃ materials have become a popular candidate for preparing refractory crucibles for ultra-pure high-temperature alloy melting in recent years. However, its difficulty in sintering and poor thermal shock resistance limited its industrial application. The effect of CaF₂ on the densification microstructure, mechanical properties, and thermal shock resistance of Y₂O₃ materials was investigated in this paper. The main purpose of this study was to optimize the amount of CaF₂ added in the preparation of Y₂O₃ materials to improve its thermal shock resistance and get better mechanical properties. The mechanism of the densification process of CaF₂-doped Y₂O₃ materials was analyzed by phase analysis and microstructure. The results showed that successive doping of large Ca²⁺ ions caused more lattice distortion in the Y₂O₃ materials, and the diffusion rate of Y³⁺ was increased, thus enhanced grain boundary diffusion and promoted sintering densification in the Y₂O₃ materials. Meanwhile, the addition of CaF₂ also significantly reduced the apparent porosity and enhanced the mechanical properties of the materials. The improvement of these properties was attributed to the increased relative density of CaF₂-doped Y₂O₃ materials and the high sintering activity of CaF₂. In addition, crack deflections effectively improved the thermal shock resistance of the materials. The residual flexural strength ratio of Y₂O₃ materials doped with 1 wt % CaF₂ was increased by 21.2% after thermal shock test compared with undoped specimens.     

Nanoscale toughening of low carbon Al2O3-C refractories by means of SiCnw/Al2O3 composite reinforcement

To improve the thermal shock resistance of low carbon Al₂O₃-C refractories, SiC nanowires (SiC_nw) containing SiC_nw/Al₂O₃ composite reinforcement were introduced. The specific fracture energy of the Al₂O₃-C refractory matrix was obtained by statistical grid nano-indentation. The reinforcement mechanism of SiC_nw/Al₂O₃ on thermal shock resistance of refractories was investigated. The results revealed that the matrix-specific fracture energy of A6 (6 wt% SiC_nw/Al₂O₃ added) was 217 N/m, which was 58.4% higher than reference sample A0 (137 N/m) and 18.6% higher than MA6 (183 N/m, 6 wt% SiC/Al₂O₃ added). A6 showed the highest residual strength ratio of 49.8%, which was 114.7 % higher than A0 (23.2%) and 82.4 % higher than MA6 (27.3%). The components with different morphology in SiC_nw/Al₂O₃ cluster, especially SiC nanowires, promote the generation of microcracks, crack multi-deflection, and branching, which toughen the matrix and improve the thermal shock resistance of refractories. In comparison to the literature, A6 showed a higher rising in residual strength ratio than those with higher graphite content (4 wt% and 20 wt%), which will greatly reduce the consumption of carbon-containing refractories and contribute to the reduction of CO₂ emission.     

合成ZrO2-SiC和工业SiC对Al2O3-C质耐火材料性能影响的对比

为了改善Al2O3-C质耐火材料的抗氧化性和抗热震性,向浇注料中分别添加0、2%、4%、6%的SiC或ZrO2-SiC复合粉,以酚醛树脂为结合剂,在200MPa下制备了2组试样,经250℃充分干燥后,于1400℃下埋炭处理2h,分别检测2组试样的抗氧化性和抗热震性,并采用XRD分析氧化后试样的相组成。结果发现,添加剂中SiC的氧化能有效保护试样中的碳,从而能减少试样的质量损失率和氧化面积,提高其抗氧化性能。由于ZrO2的微裂纹增韧及SiC的颗粒增韧作用,使试样的抗热震性能提高。在试验条件下,添加6%ZrO2-SiC复合粉或工业SiC粉时,试样的抗氧化性和抗热震性最佳。     

Mullite whisker toughened mullite coating to enhance the thermal shock resistance of SiC pre-coated carbon/carbon composites

In order to improve the thermal shock resistance of the coated carbon/carbon (C/C) composites, a mullite whisker toughened mullite coating was fabricated on the surface of SiC pre-coated C/C composites (SiC-C/C) by molten-salt method with a later hot dipping process. The phase compositions, surface and cross-section microstructures, high temperature thermal shock resistance of the as-prepared multi-layer coatings were investigated. Results show that the introduction of mullite whiskers can effectively improve the density of the mullite outer coating and decrease the cracking of the coating during the thermal shock cycle process. After 100 times thermal shock cycles between 1773 K and room temperature, only 1.87 × 10⁻³ g cm⁻² weight loss has been detected, indicating the achievement of the excellent thermal shock resistance.     

ZrO2-莫来石复合耐火材料的反应烧结制备和抗热震性研究

从先进陶瓷精细的制备技术出发 ,以超细ZrSiO4和Al2 O3的反应烧结产物为结合相 ,以粗粒莫来石为骨料 ,制备出ZrO2 -莫来石复合耐火材料。研究了材料的制备工艺、显微结构和力学性能 ,重点探讨了材料的抗热震性。所得ZrO2 -莫来石复合耐火材料同时具有高的致密度 ( >90 % )和优良的抗热震性。     

Study on thermal shock resistance of Sc2O3 and Y2O3 co-stabilized ZrO2 thermal barrier coatings

In order to reveal the effect of Sc₂O₃ and Y₂O₃ co-doping system on the thermal shock resistance of ZrO₂ thermal barrier coatings, Y₂O₃ stabilized ZrO₂ thermal barrier coatings (YSZ TBCs) and Sc₂O₃–Y₂O₃ co-stabilized ZrO₂ thermal barrier coatings (ScYSZ TBCs) were prepared by atmospheric plasma spraying technology. The surface and cross-section micromorphologies of YSZ ceramic coating and ScYSZ ceramic coatings were compared, and their phase composition before and after heat treatment at 1200 °C was analyzed. Whereupon, the thermal shock experiment of the two TBCs at 1100 °C was carried out. The results show that the micromorphologies of YSZ ceramic coating and ScYSZ ceramic coating were not much different, but the porosity of the latter was slightly higher. Before heat treatment, the phase composition of both YSZ ceramic coating and ScYSZ ceramic coating was a single T′ phase. After heat treatment, the phase composition of YSZ ceramic coating was a mixture of M phase, T phase, and C phase, while that of ScYSZ ceramic coating was still a single T′ phase, indicating ScYSZ ceramic coating had better T′ phase stability, which could be attributed to the co-doping system of Sc₂O₃ and Y₂O₃ facilitated the formation of defect clusters. In the thermal shock experiment, the thermal shock life of YSZ TBCs was 310 times, while that of ScYSZ TBCs was 370 times, indicating the latter had better thermal shock resistance. The difference in thermal shock resistance could be attributed to the different sintering resistance of ceramic coatings and the different growth rates of thermally grown oxide in the two TBCs. Furthermore, the thermal shock failure modes of YSZ TBCs and ScYSZ TBCs were different, the former was delamination, while the latter was delamination and shallow spallation.     

Al和Al-Si加入量对Al2O3-C材料高温性能的影响

在板状刚玉颗粒、板状刚玉细粉、α-Al2O3微粉和石墨含量(质量分数,下同)分别为65%、27%、6%和2%的Al2O3-C材料中,分别以5%、8%和11%的Al粉或Al-Si复合粉(8%Al 1.5%Si和8%Al 3%Si)替代等量的板状刚玉细粉,外加3.5%的热固性树脂混练均匀,成型后于800℃埋炭热处理3h。在埋炭条件下检测试样400~1400℃的热态抗折强度、200~1400℃的应力-应变、常温~1500℃的热膨胀率以及试样的抗热震性和抗氧化性,并对部分试样进行了XRD、SEM和EDS分析。结果表明(1)随着温度的升高,试样的热态抗折强度表现出先降低,后快速升高,最后慢速升高的变化趋势;温度≥1000℃时,试样的热态抗折强度随Al粉加入量的增多而提高;在加入Si粉后,试样的热态抗折强度进一步提高。(2)试样在低温时即产生塑性变形,一直到1400℃仍处于塑性变形阶段。(3)试样的抗热震性随Al粉加入量的增多而提高,在加入Si粉后继续小幅提高。(4)试样的抗氧化性随Al粉加入量的增加而提高,加入Si粉后由于形成致密的氧化层结构,抗氧化性进一步提高。     

ZrO_2相变设计改善耐火材料抗热震性的设想

ＺｒＯ２的马氏体相变是陶瓷学界广泛研究的重要课题之一,并在结构陶瓷的增韧和强化中得到成功应用。耐火材料一般在热循环条件下服役,与常温下使用的结构陶瓷不同,其抗热震性是一个重要的性能指标。本文根据ＺｒＯ２的相变特征提出了利用ＺｒＯ２相变改善锆质耐火材料抗热震性的设想。     

Thermal shock resistance of Al2O3/SiO2 composites by sol-gel

In this paper, the SiO₂ ceramic matrix composites were reinforced by the two-dimensional (2D) braided Al₂O₃ fibers by sol-gel. To develop the high performance aeroengine with excellent resistance to thermal shock for advanced aerospace application, two different thermal shock temperatures (1100?°C and 1300?°C) and three different thermal shock cycles (10, 20 and 30 cycles) were tested and compared in this paper; besides, the thermal shock resistance of Al₂O₃/SiO₂ composites was investigated in air. Our results suggested that, the flexural strength of the untreated composites was 78.157?MPa, while the residual strength of Al₂O₃/SiO₂ composites under diverse thermal shock cycles and temperatures had accounted for about 95% and 50% of the untreated composites, respectively. Meanwhile, the density and porosity of the composites were gradually increased with the increase in test temperature. Moreover, the changes in fracture morphology and micro-structural evolution of the composites were also observed. Our observations indicated that, the fracture morphology of the composites mainly exhibited ductile fracture at the thermal shock temperature of 1100?°C, whereas brittle fracture at the thermal shock temperature of 1300?°C. Additionally, Al₂O₃/SiO₂ composites belonged to the Oxide/Oxide CMCs, so no new phase was formed after thermal shock tests. Above all, findings of this paper showed that Al₂O₃/SiO₂ composites had displayed outstanding thermal shock resistance.     

Thermal shock resistance study of stereolithographic additive-manufactured Al2O3 ceramics by in situ digital radiography

Thermal shock resistance is critical to ensure the service safety of ceramic hot-end components. The thermal shock performance of stereolithographic additive-manufactured ceramics has not yet been studied. In this study, a series of thermal shock experiments with various temperature differences was conducted on stereolithographic additive-manufactured Al₂O₃ ceramics. The surface cracks were analysed based on photographs captured before and after the thermal shock experiments. Three-point bending tests with in situ X-ray digital radiography were conducted to determine the thermal shock resistance. Crack initiation, propagation, and coalescence were observed under flexural loads. The critical temperature difference of the stereolithographic additive-manufactured Al₂O₃ ceramics was determined to be 267.22 °C. The crack length increased and residual strength decreased with increasing temperature differences. The layered structure of the stereolithographic additive-manufactured ceramics slowed crack propagation. We expect that this study will serve as a reference for the performance of stereolithographic additive-manufactured Al₂O₃ ceramics in extreme environments.     

Effect of print path process on sintering behavior and thermal shock resistance of Al2O3 ceramics fabricated by 3D inkjet-printing

In this study, Al₂O₃ ceramics parts were printed by inkjet printing technology with different printed paths distributions, such as the spiral printed path, round trip straight printed path and ladder lap printed path. The influences of inkjet printed paths on sintering performance and thermal shock resistance of the Al₂O₃ green bodies were investigated. The sintering performance of the green sample with the ladder lap printed path is the highest among the three samples. Sintered at 1550?℃, its bulk density and porosity reached 3.73?g/cm³ and 10.80%, respectively. In addition, the thermal shock resistance of the sample with the step print path reached 11 times. The results suggest that the optimization of the printed path provides an effective way to print 3D ceramics with good performances through 3D inkjet-printing technology.     

镁铝钛耐火材料的Al2O3含量与其性能的关系

分别以79.3%~85.3%(质量分数,下同)的电熔镁砂、10%的电熔尖晶石、电熔白刚玉(2.5%~8.5%)和钛白粉(2.2%和5.5%)为原料制备了2组镁铝钛试样,研究了镁铝钛材料中Al2O3含量(分别约为7%、10%和13%)对其烧结、抗热震性以及抗炉外精炼渣侵蚀性的影响,并借助SEM、EDS分析了侵蚀后试样的显微结构。结果表明:随着镁铝钛试样中Al2O3含量的增加,试样更易烧结,烧后显气孔率降低,体积密度升高,抗渣性能提高;Al2O3含量的增加,使试样中的尖晶石数量增多,而尖晶石和方镁石热膨胀系数的差异形成的微裂纹,使试样的耐压强度降低,抗热震性提高;显微结构分析显示,随着Al2O3含量的增加,试样中析出的晶间尖晶石增多,有助于提高试样中的固-固结合率,从而增强其抗侵蚀能力。     

MgO-SiC-C复合材料力学性能和抗热震性能研究

对MgO-SiC-C复合材料的力学性能和抗热震性能的研究结果表明SiC含量增加,材料的强度和抗热震性能提高。升温过程中结合剂结构的变化对MgO-SiC-C复合材料强度变化起重要作用。     

纳米ZrO2对MgO-CaO材料烧结及抗热震性的影响

在≤0.1mm的MgO-CaO砂中分别加入占其总质量2%、4%、6%和8%的纳米ZrO2,分别经干混、压制成型,1600℃3h煅烧后,检测其体积密度和抗热震性,并进行XRD和SEM分析,以研究添加纳米ZrO2对MgO-CaO材料烧结和抗热震性能的影响及其作用机理。结果表明:添加2%的纳米ZrO2即可显著提高MgO-CaO材料的烧结程度和抗热震性;综合考虑MgO-CaO材料的烧结程度和抗热震性认为,添加6%的纳米ZrO2可使材料获得良好的性能。