氧化锆纤维对纳米SiO2复合绝热材料性能的影响

针对纳米二氧化硅复合绝热材料强度不高、高温环境下收缩严重的问题,采用氧化钇稳定的氧化锆纤维作为功能性添加材料,研究了不同煅烧温度下氧化锆纤维的添加量对绝热材料线收缩率的影响,以及引入氧化锆纤维对绝热材料耐压强度的影响,结合SEM等表征方法及固体烧结动力学理论阐释了氧化锆纤维的增强和抑制绝热材料高温收缩的机理。结果表明:煅烧温度高时,绝热材料线收缩率大。氧化锆纤维的添加能有效降低绝热材料的高温线收缩率。当添加量为6%(质量分数)时,1 000℃下线收缩率从13.3%降至2.6%。随着氧化锆纤维添加量的增加,绝热材料的耐压强度先增大后减小。     

Y—TZP陶瓷的蠕变活化能

本文研究了一种氧化钇稳定四方氧化锆多晶体陶瓷的高温蠕变活有以及应变速率、晶粒大小和致密度等因素对其蠕变活化能的影响，讨论了材料的形变机理。     

ZrO2连续纤维研究进展

耐高温、高强度ZrO2连续纤维在工业及航空、航天领域中有着重要的用途。本文总结了近年来国际上对氧化锆连续纤维的研究成果。系统介绍了ZrO2连续纤维的制备方法以及对纤维性质的研究。     

氧化锆纤维布的研究

氧化锆纤维布是大容量碱性电池的理想隔膜材料.本文研究了氧化锆纤维布的制备工艺,原料纤维、浸渍工艺参数、热处理工艺等对氧化锆纤维布性能的影响.所研制的氧化锆纤维布在大容量镍氢电池中作为隔膜得到了应用,电性能及吸碱速率和吸碱量优于美国产品,但强度低于美国产品.     

氧化锆纤维增强超薄陶瓷板的制备及力学性能研究

建筑陶瓷薄板作为一种轻薄、低能耗的家装产品而逐渐成为市场的发展潮流,如何进一步对其实现减薄和增强也成为研究的热点。本文以建筑陶瓷高铝粉料为基体,设计二次球磨法并引入长径比为70~82的氧化锆纤维作为增强相,借助KH570表面改性剂改善纤维/基体(F/M)的界面结合,制备了氧化锆纤维增强超薄陶瓷板。研究表明,采用二次球磨工艺可以有效实现纤维在基体中的分散,当氧化锆纤维的掺杂量为3%(质量分数)时,超薄陶瓷板的弯曲强度可达到106.4 MPa,相较于空白样(96.8 MPa)提升了9.92%。在高温固相反应中,陶瓷熔融相的Na⁺、K⁺对氧化锆晶格的渗透作用会引起四方晶系氧化锆相向锆英石相的转变,四方晶系氧化锆相内部存在微裂纹拓展、颗粒弥漫增强、“纤维桥联-断裂拔出”等多种良性增强机制。     

发动机悬置用低蠕变配方的研究

研究了生胶、炭黑及硫化体系对橡胶材料蠕变性能的影响,蠕变对发动机悬置刚度的影响;同时研究开发了高温低蠕变天然橡胶配方,以改善发动机悬置高温低蠕变性能。结果表明,烟片胶、恒黏胶及脱蛋白天然橡胶中,脱蛋白天然橡胶蠕变性能最佳,而烟片胶蠕变性能最差。橡胶蠕变后,发动机悬置刚度增加。高温低蠕变天然橡胶配方可大大改善发动机悬置蠕变性能。     

晶须/纤维增强3D打印氧化锆多孔陶瓷制备及性能研究

钇稳定氧化锆（YSZ）是一种抗氧化性和耐久性优异的陶瓷,够承受高温,非常适合作热防护材料。采用乳液/泡沫模板法将其制成具有微米级孔的多孔结构,再以氧化铝晶须或氧化锆纤维作为增强相,然后结合直写成型这种3D打印成型技术,又可在毫米级孔尺度上获得设计的自由。由此制备的梯度多孔结构,不仅可以增大材料的比表面积,减小体积密度,更能大大提高多孔YSZ的力学性能。研究增强体的类型、加入量及烧结温度对多孔氧化锆陶瓷微观形貌结构的影响,分析其与抗压强度的相互作用关系。结果表明,氧化铝晶须和氧化锆纤维的加入,均能有效提高多孔氧化锆陶瓷孔的抗压强度,晶须的增强效果更好。氧化锆纤维加入量为4wt%的多孔氧化锆陶瓷孔隙率最高,抗压强度提升最小,为166.6MPa。在1500℃烧结温度下,当氧化锆纤维加入量为8wt%时,抗压强度最大,达到269.36MPa。     

镁基复合材料高温蠕变研究进展

综述了目前镁基复合材料的高温蠕变研究现状,介绍了镁基复合材料的制备方法及高温蠕变机理,同时阐述了镁基复合材料门槛应力、蠕变断裂机制及界面反应规律等方面的研究进展,并展望了镁基复合材料的应用前景和研究方向。     

氧化锆-碳化硅复合材料性能研究

从稀土氧化物、氧化锆含量、碳化硅含量、温度及制备工艺方面对氧化锆-碳化硅复合材料电阻率的影响进行了讨论,同时探讨了氧化锆-碳化硅复合材料的高温氧化性能,为氧化锆-碳化硅复合材料的制备及其电性能研究提供了依据。     

钇铝石榴石纤维的应用与制备

钇铝石榴石纤维具有抗氧化、耐高温、抗高温蠕变等特点,可作为高温耐火材料,也可作为高温复合材料的增强材料。本文对钇铝石榴石的晶体结构、应用和制备方法进行了介绍,并展望了钇铝石榴石纤维的发展趋势。     

Oxidation resistance and thermal stability of the SiC-ZrB2 composite ceramic fibers

In this study, continuous SiC-ZrB₂ composite ceramic fibers were synthesized from a novel pre-ceramic polymer of polyzirconocenecarbosilane (PZCS) via melt spinning, electron beam cross-linking, pyrolysis, and finally sintering at 1800°C under argon. The ZrB₂ particles with an average grain size of 30.7 nm were found to be uniformly dispersed in the SiC with a mean size of 59.7 nm, as calculated using the Scherrer equation. The polycrystalline fibers exhibit dense morphologies without any obvious holes or cracks. The tensile strength of the fibers was greater than 2.0 GPa, and their elastic modulus was ~380 GPa. After oxidation at 1200°C for 1 hour, the strength of the fibers did not decrease despite a small loss of elastic modulus. Compared to the advanced commercial SiC fibers of Tyranno SA, the fibers exhibited improved high-temperature creep resistance in the temperature range 1300-1500°C.     

Tensile creep properties and damage mechanisms of 2D-woven C/HfC–SiC composites in high temperature

2D-C/HfC–SiC composites were prepared by a combination of precursor infiltration and pyrolysis (PIP) and chemical vapor infiltration (CVI). Creep tests were performed at 1100°C in air under different stress conditions. Unlike most, C/SiC and SiC/SiC ceramic matrix composites only underwent primary and secondary creep stages, and the C/HfC–SiC composites underwent tertiary creep stage in the creep process. The reason was that the mechanical properties of C/HfC–SiC materials prepared by PIP + CVI methods were different from those prepared by traditional methods. The microscopic morphological analysis of the sample fracture showed that the oxidation products SiO₂ and Hf–Si–O glass phases of the HfC–SiC matrix played a crack filling role in the sample during creep. In turn, it provided effective protection to the internal fibers of the sample. The creep failure of C/HfC–SiC composites in a high-temperature oxidizing atmosphere was caused by the oxidation of the fibers. The total creep process was dominated by the oxidation of carbon fibers. It is noteworthy that there was the generation of Hf_xSi_yO_z nanowires in the samples after high-temperature creep. The analysis of the experimental data showed that the creep stress had a linear negative correlation with the creep life.     

Creep-Crack Growth by Damage Accumulation in a Glass-Ceramic

The growth rate, near-tip creep response, and damage processes of creep cracks in a pyroceram glass-ceramic were studied under tensile loading at elevated temperatures. The rates of crack extension were characterized as a function of the applied stress intensity factor. The damage processes which occurred near the crack tip and led to creep crack extension were identified using a replica technique and by direct observations in a scanning electron microscope equipped with a high-temperature loading stage. The accumulated creep strains near the crack tip were measured via the stereoimaging technique. The results indicate that creep-crack growth in the pyroceram glass-ceramic occurs in both continuous and discontinuous manners, with the damage processes manifested as the nucleation, growth, and coalescence of inhomogeneously distributed cavities and microcracks. Measurements of the total accumulated creep strain near the crack tip suggest that crack extension follows a critical strain criterion. Both the microcrack density and the total accumulated creep strain show similar dependence with distance from the crack tip. These observations suggest that damage accumulation and crack extension in the glass-ceramic are controlled by the near-tip creep rates.     

聚四氟乙烯高温蠕变性能表征方法的研究

采用自制的高温蠕变仪来测试聚四氟乙烯( PTFE)材料的高温压缩蠕变行为。以6 mm x 6 mm x 50.8 mm的纯PTFE试样为例,在250℃, 5.226 kg载荷的环境中进行测试。结果表明:表征材料高温蠕变性能的要素主要有试验温度、载荷应力、最后的应变及试样具体的蠕变曲线。并通过计算得出试样所受应力为1.452 MPa.蠕变量为0.56 mm,应变为0.011。最后,通过自制的高温蠕变仪绘制出PTFE的蠕变曲线,该曲线与典型蠕变曲线基本吻合。     

Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperature

The behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high‐temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high‐temperature X‐ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as‐received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina‐rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.     

A first study of the high-temperature plasticity of ceria-doped zirconia polycrystals

Ceria–zirconia ceramic alloys were sintered by high-temperature annealing, considering several synthesis temperatures to obtain a full-dense ceria–zirconia ceramic material using a temperature as low as possible. It was found that fully density is achieved at temperatures of 1450 °C.Monolithic specimens were crept under compression at high temperatures. The creep results fitted an empirical constitutive equation consistent with a classical Ratchinger mechanism for grain switching. This result was confirmed through microstructural characterization of as-received and post-mortem specimens. Since the conventional Ashby–Verrall model is contrary to the mechanism controlling creep in other zirconia alloys, the results are considered in the framework of a new grain boundary sliding model, with particular discussion of the validity of that model for the ceria–zirconia case.     

Effect of creep strain on the optomechanical properties and some structural properties of terylene fibers

This article sheds light on the effect of creep strain [?(t); %] on the optomechanical properties and some structure properties of terylene fibers at several constant applied loads. Automated multiple‐beam Fizeau fringes in transmission were used with a mechanical creep device attached to a wedge interferometer where the fiber was subjected to a constant load. This technique was used to determine the mean refractive indices and the mean birefringence values of terylene fibers under different conditions of ?(t). The obtained optical results were used to evaluate the optical orientation function, optical stress coefficient, density, crystallinity, and mean‐square density fluctuation with ?(t). The obtained results show that, under a constant load, the terylene fibers extended with time, the rate of which decreased with time. An empirical formula is suggested to represent the variation of ?(t) of terylene fibers with time, and the constants of this formula were determined. A mechanical model is proposed to represent ?(t) of terylene fibers, which consists of two Kelvin elements combined in series, which were used to provide an accurate fit to the experimental creep curve. The stress–strain curve via creep was studied to determine some mechanical parameters of the investigated fibers: Young's modulus, yield stress, and yield strain. Illustrations with microinterferograms, graphs, and tables are given. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

To drill or not to drill? Creep of an oxide-oxide composite with diamond-drilled effusion holes at elevated temperature

Ceramic matrix composites (CMCs) are prime candidates for use in aircraft engines. Yet even with their high-temperature capabilities, many CMC components will need cooling. Film cooling technique requires rows of small holes through the component surface. Effects of multiple small holes on tensile stress-strain and tensile creep performance of an oxide-oxide CMC consisting of Nextel 720 alumina-mullite fibers in a porous alumina matrix were evaluated at 1200°C. Test specimens included 17 holes with a .5 mm diameter in the gage section. The holes were precision drilled using diamond coated drill bits. The presence of diamond-drilled holes noticeably lowered tensile properties and degraded creep performance of the CMC. Our earlier study considered the effects of small holes drilled using a CO₂ laser on the tensile properties and tensile creep resistance of this composite. The presence of laser-drilled holes also considerably lowered the creep resistance of the Nextel 720/alumina CMC. In both cases the reductions in tensile strength and creep resistance are due to damage caused to composite microstructure by hole drilling. However, different drilling techniques result in different microstructure degradation mechanisms. Damage to the CMC microstructure caused by these two drilling techniques and implications for mechanical performance and durability are discussed.     

Tensile creep behavior of SiCf/SiC ceramic matrix minicomposites

Single fiber-tow minicomposites represent the major load-bearing element of woven and laminate ceramic matrix composites (CMCs). To understand the effects of fiber type, fiber content, and matrix cracking on tensile creep in SiC_f/SiC CMCs, single-tow SiC_f/SiC minicomposites with different fiber types and contents were investigated. The minicomposites studied contained either Hi-Nicalon™ or Hi-Nicalon™ Type S SiC fibers with a boron nitride (BN) interphase and a chemical-vapor-infiltrated-silicon-carbide (CVI-SiC) matrix. Tensile creep was performed at 1200 °C in air. A bottom-up creep modeling approach was applied where creep parameters of the fibers and matrix were obtained separately at 1200 °C. Next, a theoretical model based on the rule of mixtures was derived to model the fiber and matrix creep-time-dependent stress redistribution. Fiber and matrix creep parameters, load transfer model results, and numerical modeling were used to construct a creep strain model to predict creep damage evolution of minicomposites with different fiber types and contents.     

复合钢板焊接接头处高温蠕变特性及安全评定

从蠕变机理、试验研究和有限元数值分析3个方面着手,综述了当前国内外对金属焊接接头的高温蠕变特性研究现状。对复合钢板焊接接头高温蠕变的检测与安全评定方法进行了探究。