Liquid metal infiltration of silicon based alloys into porous carbonaceous materials Part-III: Experimental verification of conversion products and infiltration depth by infiltration of Si-Zr alloy into mixed SiC/graphite preforms

Porous carbonaceous preforms, made from graphite and silicon carbide (SiC) powders, with varying graphite powder mass fractions and particle sizes, were infiltrated at 1500 °C and 1700 °C by Si-8 at. pct Zr alloy to produce dense Si-Zr-SiC composites. The experiments were performed in a graphite chamber vacuum furnace at 10^?2 mbar. The most desirable results were obtained for preforms composed of a mixture of graphite and SiC powders, with preforms containing 15–20 % mass fraction of graphite and infiltrated at 1500 °C. The banding of the Zr-rich phase observed in the cross-sections of SiC-C pre- forms infiltrated by the Si-Zr alloy may help in decoding the reactive infiltration process with binary alloys.     

Effect of pyrolysis temperature on the microstructure and capillary infiltration behavior of carbon/carbon composites

Carbon fiber fabric reinforced plastics were pyrolyzed at temperatures between 900?°C and 1600?°C to convert them into carbon/carbon (C/C) composites. The effects of pyrolysis temperatures on the microstructure, mechanical properties, and especially on the capillary infiltration behavior of C/C composites, suitable for liquid silicon infiltration (LSI), were investigated. The porosity of these C/C composites shows a decreasing trend with increasing pyrolysis temperature. The established model can explains the pyrolysis mechanism and the infiltration behaviors. Within the initial stage, the capillary infiltration rate of C/C composites with the model fluid water increases rapidly. In the second stage, where thermal imaging indicates that water has reached the top area of the plates at the initial stage. Capillary infiltration rate, based on water infiltration experiments mass increase, decreases because the shrinkage of micro-delamination take place at higher pyrolysis temperature. In combination with LSI results, a model for the capillary infiltration behavior of C/C is proposed.     

空间望远镜用C/SiC镜面研制综述

综述了空间望远镜的主镜用高强度、高表面精度、低热膨胀系数的低温（约4K）用镜面的制备和检测过程.日本将Φ710mm的高强度反应烧结SiC材料已用于红外望远镜镜面.在短切炭纤维增强C/C复合材料毛坯的基础上进行液相硅渗透（LSI）而制备的C/SiC复合材料在光学镜面方面具有更大的优势.通过提高C/C复合材料毛坯中沥青基炭纤维体积分数及控制硅化速度,可有效地提高LSI-C/SiC复合材料的机械性能和表面光学精度;通过不同规格的炭纤维的混杂化,可使C/SiC复合材料热膨胀系数的各向异性降低至小于4％的差异.SiC、Si-SiC浆料涂层处理可有效地提高表面精度至2 nm rms的极高要求.     

先驱体转化法制备C/C-SiC复合材料研究

以多孔C/C复合材料为预制型,聚碳硅烷(PCS)为先驱体,制备了C/C-SiC复合材料。研究了浸渍液浓度和不同C/C复合材料预制体密度等级对C/C-SiC复合材料的密度和力学性能的影响。结果表明:当浸渍液浓度为50%时,复合材料的密度均达到最佳值;不同的预制体密度对制得的复合材料性能有很大的影响,其中初始密度为1.2g/cm3试样制得的复合材料性能达到最优,其密度达到1.786g/cm3,弯曲强度达204.1MPa,剪切强度为16.1MPa,断裂韧性为6.83MPa·m1/2。     

Microwave heated chemical vapour infiltration of SiC powder impregnated SiC fibre preforms

Abstract

Abstract

A microwave heated methyl trichlorosilane based chemical vapour infiltration technique has been used to form SiC_f/SiC composites from SiC fibre preforms preimpregnated with SiC powder using two different fabrication techniques. While infiltration rates obtained from samples loaded with powder were generally higher than for preforms without powder, preferential infiltration occurred in regions where the SiC powder was most concentrated as a result of the initial non-uniform distribution of the powder across the preforms. The consequence was density gradients in the final composites. Nevertheless, average densities as high as 75% could be achieved in a 10 h process.     

反应浸渗法制备SiC/FeSix复合材料

研究了在SiC+C坯体中加入Fe粉,用熔融Si进行反应浸渗,以制备不合游离Si的SiC/FeSix复合材料.结果表明:用本实验方法通过调整坯体中Fe含量可以制得不合游离Si的SiC/FeSix复合材料,该材料在室温下的抗弯强度为(220±10)MPa.文中推导了Fe含量与第2相组成的理论模型,同时讨论了热处理工艺对烧结的影响.     

Controllable fabrication and mechanical properties of C/C–SiC composites based on an electromagnetic induction heating reactive melt infiltration

To regulate the microstructures of carbide ceramic-doped C/C (C/C-ceramic) composites using reactive melting infiltration (RMI) in a controlled manner, an electromagnetic induction heating RMI (ERMI) was proposed and used to fabricate typical C/C–SiC composites herein. Because the tedious heating and cooling regions could be bypassed using ERMI, excessive graphitization and ceramic overreactions of the ERMI-C/C-SiC composites were effectively avoided, which made the interfacial bonding strength (τ) of the ERMI-C/C–SiC composites (～25.7 MPa) much lower than that of the CRMI-C/C-SiC composites (～36.1 MPa) (fabricated using conventional RMI (CRMI)). A weaker τ value triggered strengthening/toughening mechanisms such as crack deflection, and crack arrest, which ultimately led to higher flexural strength and displacement of the ERMI-C/C–SiC composites than the CRMI-C/C–SiC composites. The proposed ERMI exhibited relatively good controlling capability to regulate the microstructures of C/C-ceramic composites.     

Thermal stability of CVI and MI SiC/SiC composites with Hi-Nicalon™-S fibers

The influence of high-temperature argon heat-treatment on the microstructure and room- temperature in-plane tensile properties of 2D woven CVI and 2D unidirectional MI SiC/SiC composites with Hi-Nicalon?-S SiC fibers was investigated. The 2D woven CVI SiC/SiC composites were heat-treated between 1200 and 1600 °C for 1- and 100-hr, and the 2D unidirectional MI SiC/SiC composites between 1315 and 1400 °C for up to 2000 hr. In addition, the influence of temperature on fast fracture tensile strengths of these composites was also measured in air. Both composites exhibited different degradation behaviors. In 2D woven CVI SiC/SiC composites, the CVI BN interface coating reacted with Hi-Nicalon?-S SiC fibers causing a loss in fast fracture ultimate tensile strengths between 1200 and 1600 °C as well as after 100-hr isothermal heat treatment at temperatures > 1100 °C. In contrast, 2D unidirectional MI SiC/SiC composites showed no significant loss in in-plane tensile properties after the fast fracture tensile tests at 1315 °C. However, after isothermal exposure conditions from 1315° to 1400°C, the in-plane proportional limit stress decreased, and the ultimate tensile fracture strain increased with an increase in exposure time. The mechanisms of strength degradation in both composites are discussed.     

Tensile creep behavior of three-dimensional four-step braided SiC/SiC composite at elevated temperature

This article presents experimental results for tensile creep deformation and rupture behavior of three-dimensional four-step braided SiC/SiC composites at 1100 °C and 1300 °C in air. The creep behavior at 1300 °C exhibited a long transient creep regime and the creep rate decreased continuously with time. The creep behavior at 1100 °C exhibited an apparent steady-rate regime and the creep deformation was smaller than that at 1300 °C. However, the creep rupture time at both temperatures showed little difference. The mechanisms controlling creep deformation and rupture behavior were analyzed.     

Flexural strength and wear resistance of C/C–SiC brake materials improved by introducing SiC ceramics into carbon fiber bundles

In this work, we adopted PIP technology to introduce SiC ceramics into the carbon fiber bundles of C/C–SiC composites. The obtained C/C–SiC composites containing PIP-SiC exhibited improved flexural strength. Meanwhile, the strength difference was reduced in in-plane and vertical directions. Fracture morphology revealed that the introduction of SiC into the fiber bundles broadened available toughening mechanism of the prepared composites. The braking performance of the materials was tested on an MM-1000 dynamometer. After braking at different speeds, we analyzed wear rates, variations in friction coefficient, and the morphological evolution of the friction surface. The results indicated that the introduction of SiC into the fiber bundles enhanced the abrasive resistance of local C/C regions, which yielded a significant reduction of the wear rates.     

Design of a pilot-scale microwave heated chemical vapor infiltration plant: An innovative approach

A hybrid Microwave-assisted Chemical Vapor Infiltration (MW-CVI) pilot plant to produce silicon carbide-based Ceramic Matrix Composites was designed, built and setup, as a part of the European project HELM. Being different from the existing lab-scale MW-CVI equipment, this pilot plant was designed with the idea of a further industrial scale-up.In order to enable the infiltration of the large samples of interest in industrial applications, the reactor was designed with the internal microwave cavity acting as an overmoded resonator at the frequencies of interest. The designed pilot plant allowed proper microwave heating of cylindrical samples of diameter doubled with respect to typical lab-scale preforms, with reproducible operating conditions in terms of transmitted/reflected power. First infiltration trials resulted in an average reaction efficiency of 25 % with the desired inside-out silicon carbide infiltration. The main steps of the design and the results of the first infiltration tests are discussed in this paper.     

Creep behavior and failure mechanisms of CVI and PIP SiC/SiC composites at temperatures to 1650 °C in air

Creep properties of 2D woven CVI and PIP SiC/SiC composites with Sylramic™-iBN SiC fibers were measured at temperatures to 1650 °C in air and the data was compared with the literature. Batch-to-batch variations in the tensile and creep properties, and thermal treatment effects on creep, creep parameters, damage mechanisms, and failure modes for these composites were studied. Under the test conditions, the CVI SiC/SiC composites exhibited both matrix and fiber-dominated creep depending on stress, whereas the PIP SiC/SiC composites displayed only fiber-dominated creep. Creep durability in both composite systems is controlled by the most creep resistant phase as well as oxidation of the fibers via cracking matrix. Specimen-to- specimen variations in porosity and stress raisers caused significant differences in creep behavior and durability. The Larson-Miller parameter and Monkman-Grant relationship were used wherever applicable for analyzing and predicting creep durability.     

Fabrication of C/SiC composites by siliconizing carbon fiber reinforced nanoporous carbon matrix preforms and their properties

Reactive melt infiltration (RMI) has been proved to be one of the most promising technologies for fabrication of C/SiC composites because of its low cost and short processing cycle. However, the poor mechanical and anti-ablation properties of the RMI-C/SiC composites severely limit their practical use due to an imperfect siliconization of carbon matrixes with thick walls and micron-sized pores. Here, we report a high-performance RMI-C/SiC composite fabricated using a carbon fiber reinforced nanoporous carbon (NC) matrix preform composed of overlapping nanoparticles and abundant nanopores. For comparison, the C/C performs with conventional pyrocarbon (PyC) or resin carbon (ReC) matrixes were also used to explore the effect of carbon matrix on the composition and property of the obtained C/SiC composites. The C/SiC derived from C/NC with a high density of 2.50 g cm^?3 has dense and pure SiC matrix and intact carbon fibers due to the complete ceramization of original carbon matrix and the almost full consumption of inspersed silicon. In contrast, the counterparts based on C/PyC or C/ReC with a low density have a little SiC, much residual silicon and carbon, and many corroded fibers. As a result, the C/SiC from C/NC shows the highest flexural strength of 218.1 MPa and the lowest ablation rate of 0.168 µm s^?1 in an oxyacetylene flame of ～ 2200 °C with a duration time of 500 s. This work opens up a new way for the development of high-performance ceramic matrix composites by siliconizing the C/C preforms with nanoporous carbon matrix.