ZrB_2-SiC复相陶瓷的制备及其力学性能研究

本文以ZrB_2和SiC粉为原料,采用Si_3N_4球为球磨介质,通过等静压成型及无压烧结制备了ZrB_2-SiC复相陶瓷,并对ZrB_2-SiC复相陶瓷进行了体积密度、力学性能检测和微观结构分析。结果表明:随着ZrB_2球磨时间的增加,ZrB_2颗粒粒径逐渐减小,复相陶瓷的体积密度逐渐增加;随着SiC含量的增加,复相陶瓷体积密度先增加后略有降低。ZrB_2最佳球磨时间为6 h,SiC最佳含量为20 vol%。ZrB_2-SiC 20 vol%复相陶瓷体积密度达到4.98 g/cm~3,抗弯强度达到331 MPa,断裂韧性达到6.8 MPa/m~2。     

锆英石碳热还原制备ZrB2-ZrO2-SiC复合粉体

以锆英石、硼酸和炭黑为原料,在流通氩气气氛中于1 500℃煅烧制备ZrB₂-ZrO₂-SiC复合粉体,研究了保温时间（分别为3、6和9 h）和添加剂AlF₃添加量（质量分数分别为0、0.5%、1.0%、1.5%、2.0%和2.5%）对合成产物物相组成和显微结构的影响。结果表明：1)将锆英石在流通氩气气氛中于1 500℃碳热还原可制备ZrB₂-ZrO₂-SiC复合粉体;ZrB₂、ZrO₂呈粒状,SiC呈纤维状。2)随着保温时间的延长,ZrB₂的量逐渐增多,m-ZrO₂和SiC的量均逐渐减少,非氧化物ZrB₂、SiC、ZrC的总量逐渐增多。3)与未添加AlF₃的试样相比,添加0.5%（w）AlF₃的试样中m-ZrO₂量显著减少,ZrB₂的量显著增多,SiC的量有所减少;但随着AlF     

热压烧结Al2O3-ZrB2-SiC复相陶瓷的高温力学性能研究

为提高Al2O3陶瓷的高温力学性能,采用热压烧结工艺(烧结温度1 800℃,烧结压力20 MPa,保温1 h)制备了Al2O3-ZrB2-SiC复相陶瓷(简称AZS),并研究了ZrB2含量对Al2O3基陶瓷高温抗折强度和抗热震性的影响。结果表明:1)在Al2O3基陶瓷中加入第二相ZrB2能有效改善材料的高温抗折强度和高温强度保持率,在1 000和1 200℃时,加入20%体积分数ZrB2的AZS陶瓷试样具有最高的高温抗折强度,而加入24%体积分数ZrB2的AZS陶瓷试样具有最高的高温强度保持率。2)AZS陶瓷的抗热震性能优于纯Al2O3陶瓷。经100℃温差急冷后,加入20%体积分数ZrB2的AZS陶瓷具有最高的残余强度,比纯Al2O3陶瓷提高了17.2%;经300和500℃温差急冷后,加入24%体积分数ZrB2的AZS陶瓷都具有最高的残余强度,比Al2O3陶瓷分别提高了35.3%和20.9%。     

无压烧结硼化锆基ZrB2-SiC复相陶瓷的结构与性能

以钇铝石榴石-YAG为烧结助剂,通过无压烧结制备了ZrB2-SiC复相陶瓷。研究了烧结助剂含量对烧结材料力学性能和显微结构的影响,材料的显微结构由扫描电镜SEM及其能谱分析EDS测定。研究结果表明,烧结助剂(YAG)和原料中的杂质形成玻璃相填充在晶界上,显著促进了硼化锆基ZrB2-SiC复相陶瓷的致密化。     

ZrB2陶瓷制备研究进展

航天航空、新兵器、新能源等高科技领域的快速发展对超高温陶瓷材料提出了迫切的需求,ZrB2陶瓷材料是最重要的超高温陶瓷材料之一。本文阐明了ZrB2陶瓷拥有优异性能的原因,综述了ZrB2陶瓷材料的制备研究进展,介绍了固相法、气相法、前体法制备ZrB2陶瓷材料的机理,对比了各种ZrB2陶瓷材料制备方法的优缺点,并指出了有机前体转化法具有可设计性好、不含杂质元素、成型可控、陶瓷转化温度低等优点。本文总结得出有机前体转化法是制备ZrB2超高温陶瓷复合材料较理想的方法,以及基于有机聚合物的ZrB2陶瓷前体是未来重要的发展方向之一。     

O’-Sialon-ZrO2-SiC复合材料的抗氧化性能研究

研究了O’-Sialon-ZrO2-SiC复合材料的氧化过程。结果表明,材料的氧化过程呈保护型氧化,材料最终的氧化产物为α-方石英、ZrSiO4、ZrO2,且其氧化动力学过程符合氧化前期、中期、后期三段模型。     

SiO2-SiC棚板的性能优化研究

为改善SiO2-SiC棚板的性能,特别是高温性能,以SiC、SiO2为主要原料,黏土粉、Al2O3和CaO微粉为添加剂,羧甲基纤维素为临时结合剂,研究了SiO2加入质量分数(2%、5%、8%、10%),热处理温度(分别为1 380、1 400、1 420、1 440、1 460和1 480℃),添加剂(分别为质量分数0.3%的黏土、Al2O3和CaO微粉)对试样性能的影响,并进行了生产应用。结果表明:1)SiO2加入量提高有利于常温强度的改善,但过高时对高温强度无益,SiO2的最佳加入质量分数为5%。2)提高热处理温度会明显改善SiO2-SiC材料的高温强度,但温度过高时,高温强度反而略有下降,较适宜的热处理温度为1 440℃左右。3)添加黏土、Al2O3和CaO微粉均能使SiO2-SiC材料的常温和高温强度有所提高;添加CaO微粉促进了SiO2的鳞石英化,试样的综合性能最好。4)生产试用结果表明,本研究中最佳试样的使用性能超过其他厂家的。     

浅谈ZrB2陶瓷的制备

综述了硼化锆的基本性质、粉体的制备、成型方法、烧结方法,并对当前硼化锆陶瓷的研究所存在的问题,如高温易氧化、韧度低、难烧结等提出几点可能的解决方法。     

SPS制备MgO-Y2O3复相陶瓷及其性能研究

与单相的MgO和Y2 O3陶瓷相比,MgO-Y2 O3复相陶瓷具有更高力学性能的同时兼具良好的红外透过性,可以满足在极端条件下使用红外窗口材料的要求.本文分别采用沉淀法和软模板法制备了高比表面积的MgO和Y2 O3粉体,通过球磨将两种粉体混合均匀,利用SPS制备得到了复相陶瓷.主要探索了不同烧结温度对陶瓷微观结构、致密度、力学、热学及光学性能的影响.研究结果表明,复相陶瓷的最佳烧结温度为1200℃,密度达到完全致密,透过率最高为51％(4.17μm),硬度为10.31 GPa,断裂韧性为2.54 MPa·m1/2,杨氏模量为248 GPa,MSP强度为129 MPa以及室温热导率为15.57 W/(m·K).     

Mechanical properties of sintered ZrB2-SiC ceramics

ZrB₂ ceramics containing 10-30 vol% SiC were pressurelessly sintered to near full density (relative density >97%). The effects of carbon content, SiC volume fraction and SiC starting particle size on the mechanical properties were evaluated. Microstructure analysis indicated that higher levels of carbon additions (10 wt% based on SiC content) resulted in excess carbon at the grain boundaries, which decreased flexure strength. Elastic modulus, hardness, flexure strength and fracture toughness values all increased with increasing SiC content for compositions with 5 wt% carbon. Reducing the size of the starting SiC particles decreased the ZrB₂ grain size and changed the morphology of the final SiC grains from equiaxed to whisker-like, also affecting the flexure strength. The ceramics prepared from middle starting powder with an equiaxed SiC grain morphology had the highest flexure strength (600 MPa) compared with ceramics prepared from finer or coarser SiC powders.     

Study of tribological properties of polymer derived ZrB2-SiC ceramics

ZrB₂–SiC composite ceramics with different compositions (20 and 60?vol% ZrB₂–SiC, 20ZS and 60 ZS, respectively) were prepared. Wear tests were conducted on the obtained ceramics in multiple distances using ball-on-flat tribotester. Volume loss and cross-sectional profiles of samples were measured by three–dimensional (3D) profilometer to study the onset of track wear damages. Pressure–depth curves and hardness were measured by indentation to investigate defects produced in the tribo-film by the debris. The debris of 20ZS was found to be joined to the tribo-film and accumulated with distance, shifting from microcrack (＜10,000 cycles) to abrasive wear (50,000 cycles). Compared to 20ZS, lower debris accumulation of 60ZS resulted in better wear resistance, leading to thinner and more stable non-substrate regions for this sample. These differences between both samples basically resulted from different particle sizes. Fine grains were easily pulled out in the experiment, resulting in abrasive wear of the specimen. While transgranular fracture of grains and the pinning led to larger grains with less debris, the damage mode remained transgranular fracture.     

Pressureless sintered in situ toughened ZrB2-SiC platelets ceramics

ZrB₂-SiC composite ceramics were densified by pressureless sintering with addition of Si₃N₄ or MoSi₂ at temperatures that induced SiC anisotropic growth from particles to platelets, within a ZrB₂ matrix with rounded grains. Si₃N₄ addition resulted in the formation of large amounts of liquid phase which enhanced mass transfer mechanisms in terms of matrix grain growth and homogeneous distribution of SiC platelets having an aspect ratio of 3. On the contrary, MoSi₂ helped the densification with local formation of liquid phases leading to a finer matrix with finer SiC platelets, though more agglomerated and with a lower aspect ratio (about 2). These different microstructures had very different fracture properties values, namely a toughness of 3.8 MPa m^1/2 and a strength of 300 MPa for the Si₃N₄-doped composite; toughness of 5 MPa m^1/2 and strength of 410 MPa for the MoSi₂-doped one.     

Toughening of laminated ZrB2-SiC ceramics with residual surface compression

Laminated ZrB₂-SiC ceramics with residual surface compression were prepared by stacking layers with different SiC contents. The maximum apparent fracture toughness of these laminated ZrB₂-SiC ceramics was 10.4 MPam^1/2, which was much higher than that of monolithic ZrB₂-SiC ceramics. The theoretical predictions showed that the apparent fracture toughness was strongly dependent on the position of the notch tip, which was confirmed by the SENB tests. Moreover, laminated ceramics showed a higher fracture load when the notch tip located in the compressive layer, whereas showed a lower fracture load as the notch tip within the tensile layer. The toughening effect of residual compressive stresses was verified by the appearance of crack deflection and pop-in event. The influence of geometrical parameters on the apparent fracture toughness and residual stresses was analyzed. The results of theoretical calculation indicated that the highest residual compressive stress did not correspond to the highest apparent fracture toughness.     

High temperature oxidation behavior of ZrB2-SiC added MoSi2 ceramics

In this paper, MoSi₂, MoSi₂-20?vol% (ZrB₂-20?vol% SiC) and MoSi₂-40?vol% (ZrB₂-20?vol% SiC) ceramics were prepared using pressureless sintering. The oxidation behaviors of these MoSi₂-(ZrB₂-SiC) ceramics were investigated at 1600?°C for different soaking time of 60, 180 and 300?min, respectively. The oxidation behaviors of the MoSi₂-(ZrB₂-SiC) ceramics were studied through weight change test, oxide layer thickness measurement, and microstructure analysis. Further investigation of the oxidation behaviors of the MoSi₂-(ZrB₂-SiC) ceramics was conducted at a higher temperature of 1800?°C for 10?min. The microstructure evolution of the ceramics was also analyzed. It was finally found that the oxidation resistance of MoSi₂ was improved by adding ZrB₂-SiC additives, and the MoSi₂-20?vol% (ZrB₂-20?vol% SiC) ceramic exhibited the optimal oxidation resistance behavior at elevated temperatures. From this study, it is believe that it can give some fundamental understanding and promote the engineering application of MoSi₂-based ceramics at high temperatures.     

Temperature-dependent fracture strength and the effect of oxidation for ZrB2-SiC ceramics

Using the stress distribution of the body containing a spherical inclusion, the stress intensity factor at the tip of the annular flaw emanating from the inclusion is formulized. Since the thermal expansion coefficient of matrix and inclusion is not matched, the residual stress is also taken into account. Introducing into the proposed temperature-dependent fracture surface energy or fracture toughness, the temperature-dependent fracture strength for ZrB₂-SiC is obtained. The influence of oxidation on the fracture strength is also discussed and the analysis reveals that the oxidation has significant effect on the fracture strength under some circumstances. The calculated results are compared with the experimental data and they have very good consistency.     

Ablation behavior of laminated Graphite/ZrB2-SiC ceramics in two different directions

Laminated Graphite/ZrB₂-SiC ceramics were fabricated by tape casting and hot pressing. The ablation properties of the ceramics in the parallel and the perpendicular directions were studied using an oxyacetylene torch. The mass ablation rates were 8.1?±?0.4?mg/s in the parallel direction and 0.2?±?0.1?mg/s in the perpendicular direction. The linear ablation rates were 3.1?±?0.2?µm/s in the parallel direction and 1.2?±?0.1?µm/s in the perpendicular direction. Thus, the ablation resistance of the laminated Graphite/ZrB₂-SiC ceramics in the perpendicular direction was higher than that in the parallel direction. This anisotropy was mainly attributed to the lower surface temperature in the perpendicular direction resulted from higher thermal conductivity, as well as the orientation of the weak graphite interface layer perpendicular to the ablation surface.     

Thermophysical and radiative properties of pressureless sintered SiC and ZrB2-SiC laminates

The evaluation of thermal and radiative properties of materials to be used as a hot part of thermal protection systems is a key issue for the design process of the HTC and UHTC components. Ceramic laminates with composition 100?vol%SiC and 80?vol%ZrB₂-20?vol%SiC were prepared by the tape casting technique and pressureless sintered. Thermal properties such as the thermal expansion coefficient, specific heat, thermal diffusivity and conductivity were measured; in addition the total emissivity was evaluated. A comparison of the thermal behavior of these two kinds of laminates is made. Moreover their possible integration in a unique structure is discussed.     

ZrB_2-SiC复相陶瓷的注浆成形与无压烧结

研究了ZrB2-SiC复相陶瓷的注浆成形技术,着重讨论了pH值和固相体积含量对料浆粘度的影响;分析了注浆成形后,生坯断面的显微结构以及相对应的烧结体的显微结构。结果表明:ZrB2原始粉料的研磨处理有利于复相陶瓷制品的烧结致密化。当pH值为11时,可制得固相体积含量为50%,粘度为660mPa.s的ZrB2-SiC浆料。     

Measurement of thermal residual stresses in ZrB2-SiC composites

Neutron diffraction, Raman spectroscopy, and x-ray diffraction were employed to measure the stresses generated in the ZrB₂ matrix and SiC dispersed particulate phase in ZrB₂-30 vol% SiC composites produced by hot pressing at 1900 °C. Neutron diffraction measurements indicated that stresses begin to accumulate at ∼1400 °C during cooling from the processing temperature and increased to 880 MPa compressive in the SiC phase and 450 MPa tensile in the ZrB₂ phase at room temperature. Stresses measured via Raman spectroscopy revealed the stress in SiC particles on the surface of the composite was ∼390 MPa compressive, which is ∼40% of that measured in the bulk by neutron diffraction. Grazing incidence x-ray diffraction was performed to further characterize the stress state in SiC particles near the surface. Using this technique, an average compressive stress of 350 MPa was measured in the SiC phase, which is in good agreement with that measured by Raman spectroscopy.