反应烧结SiC陶瓷的研究进展

反应烧结是SiC陶瓷的一种重要制备工艺.本文分析了传统反应烧结工艺制备SiC陶瓷的不足,介绍了一些新型制备工艺;讨论了其烧结机理.并提出一些相关思考及展望.     

醇–水混合溶剂凝胶注模制备SiC多孔陶瓷的工艺与性能

将SiC陶瓷粉末、醇-水混合溶剂、丙烯酰胺-亚甲基双丙烯酰胺凝胶体系以及堇青石-锂辉石复合烧结助剂配制成料浆,采用凝胶注模成型–烧结工艺制备SiC多孔陶瓷,研究烧结助剂用量和烧结温度对多孔SiC陶瓷的形貌与显微结构、物相组成以及强度、孔径、开孔率与渗透率等性能的影响。结果表明:温度高于1 300℃时,复合烧结助剂熔融形成固溶体,从而实现SiC多孔陶瓷的低温烧结;随烧结助剂用量增加或烧结温度升高,SiC多孔陶瓷的开孔率和气体渗透速率均下降。在料浆中SiC陶瓷粉体体积分数为20%、烧结助剂质量分数为10%、醇水体积比为7:3、锂辉石与堇青石质量比为2:1的条件下,于1 370℃烧结后得到的SiC多孔陶瓷,孔隙率高、孔径分布集中(4~15μm),孔形貌呈均匀的三维无规则贯通结构,抗弯强度为8.5 MPa,开孔率达到67.9%,透气率为280.5 m~3/(m~2·Pa·h)。     

真空烧结温度对铜基减磨材料性能的影响

以铜粉、锡粉、铅粉等为原料,采用“压制-烧结”工艺制备了铜基减磨材料,烧结采用真空无压烧结和还原气氛保护烧结两种工艺方法.运用对比试验的方法,探讨了真空无压烧结工艺中不同烧结温度对铜基减磨材料烧结体性能的影响.结果表明:真空烧结工艺与还原气氛保护烧结工艺相比,相同的烧结温度下材料的孔隙度、抗拉强度、抗压强度和硬度变化不...     

钇稳定二氧化锆流延成型薄膜的无压烧结研究

讨论了流延法制备的钇稳定氧化锆(YSZ)陶瓷薄膜的无压烧结过程.通过SEM、TG-DTA和XRD等手段对素坯和烧结过程进行微观检测和表征.结果表明,固体含量为55%(质量分数)的素坯薄膜,在75℃～1000℃温度区间,有机添加剂的烧除对最终烧结体的致密化贡献不大,但对陶瓷薄膜的形变影响很大,YSZ素坯薄膜内有机添加剂的匀速烧除,能够有效控制流延法制备陶瓷薄膜的起翘开裂,且能够有效抑制最终烧结体内气孔的数量,对最终致密化起促进作用;在1000℃～1450℃的温度区间,陶瓷薄膜的晶粒生长和致密化主要以表面物质扩散机制进行,且晶粒的生长和致密化同步进行.在最佳烧结温度1500℃时相对密度达到最大值98%左右,随后,晶粒的尺寸随温度及保温时间的增加而增大,而密度有所下降.     

热等静压原位合成SiC–TiC复相陶瓷的微观组织与性能研究

采用纳米级β-SiC粉末、Si粉末、C粉末以及微米级TiH_2粉末为原料,利用热等静压原位合成工艺制备了SiC–TiC复相陶瓷,研究了不同原位合成反应和烧结工艺对复相陶瓷微观组织及力学性能的影响。结果表明:以SiC、TiH_2、C粉末为原料的原位合成反应,无明显副反应发生,更有益于制备成分符合预期、致密度良好且性能优秀的SiC–TiC复相陶瓷。在1600℃,120 MPa,4 h等静压烧结工艺下原位合成得到的体积分数为SiC–32%TiC复相陶瓷具有最好的致密度、硬度、三点弯曲强度以及良好的断裂韧性,分别达到98.7%、21.2 GPa、428 MPa和5.5 MPa·m1/2。提高热等静压压力有助于提高材料的烧结扩散活性,从而提高材料的致密度,有益于力学性能的提升。     

TiB2/SiC陶瓷复合材料制备工艺的研究

以TiO2、B4C和C为原料,基于原位合成法在SiC基体中生成TiB2颗粒,并采用无压烧结法制备出TiB2/SiC复合陶瓷.通过对复合材料制备工艺的研究,发现:高于1 300℃的预烧结能形成TiB2/SiC复合陶瓷坯体.C含量、烧结温度和保温时间对复合材料的相对密度均有影响.当C含量(质量分数)为4%时、在1 400℃...     

用Ni＋Ti粉坯热压反应烧结连接SiC

用Ni＋Ti粉坯作为焊料，采用热压反应烧结连接法连接SiC陶瓷，研究了焊接温度、保温时间、连接压力和压坯厚度对试样连接强度的影响规律。在本文所述试验范围内，确定的最佳工艺为：连接温度1100℃，保温时间20min，焊接压力12．7MPa，焊料压坯厚度0．3mm，所得连接件的相对抗弯强度为53％。微观结构和XRD物相分析表明：在Ni＋Ti粉坯与sic陶瓷接合界面处，发生了元素的互扩散和界面反应，在适当的工艺条件下，接头界面具有在NiTi、Ni3C、Ni16Ti6Si7混合物的基体中弥散分布TiC相的微观组织，借助于主要基体相NiTi的韧性和与母材SiC晶格匹配良好的TiC可以实现有效的界面结合。     

常压烧结SiC超光滑抛光性能研究

采用常压烧结的方法制备了反射镜用SiC陶瓷材料。研究了金刚石、氧化铬(Cr_2O_3)和二氧化硅(SiO_2)_3种磨料对常压烧结SiC陶瓷抛光性能的影响。结果表明,常压烧结SiC的各项物理性能满足反射镜基底材料的基本要求;金刚石磨料与常压烧结SiC陶瓷的硬度差最小,且超顺滑抛光过程中金刚石磨粒形状在SiC陶瓷表面产生的位错、空位等缺陷最少,因此采用金刚石磨料时,常压烧结SiC陶瓷的表面质量最好,其表面粗糙度值(RMS)为0.789 nm,面形精度为0.007λ(λ=0.632 8μm),满足反射镜的使用要求。     

烧结温度对反应烧结碳化硅组织与性能的影响

本文研究了1450、1550、1650℃不同烧结温度制备的反应烧结SiC材料的密度、硬度、抗弯强度、显微组织、显微硬度及断裂行为。结果表明:烧结温度对材料密度影响较小。低温反应烧结的SiC晶粒的晶体结构不够完整,存在亚晶界等缺陷,晶粒强度较低,烧结材料的硬度和抗弯强度较低。高温反应烧结的SiC晶粒的晶体结构完整性增加,晶粒强度较高,烧结材料的硬度和抗弯强度较高。因此为了提高反应烧结碳化硅的力学性能,应该适当提高烧结温度或延长烧结时间。     

烧结温度对碳化硅陶瓷力学性能的影响

采用硼、碳助剂无压烧结制备碳化硅陶瓷。针对烧结温度与碳化硅烧结体密度、抗弯强度以及硬度之间的关系进行了试验研究,并对不同温度下制备的烧结体进行了显微结构形貌观察和XRD图谱分析。结果表明,烧结温度在2190～2220℃范围内可以制备密度高、力学性能好的碳化硅陶瓷。其相对密度超过96%;抗弯强度接近400MPa;维氏硬度23GPa以上。在试验温度范围内,密度与抗弯强度之间的关系近似为线性关系,密度越高抗弯强度和硬度性能越好。     

Wettability of silicon carbide ceramic by Al2O3/Dy2O3 and Al2O3/Yb2O3 systems

Wettability is an important phenomenon in the liquid phase sintering of silicon carbide (SiC) ceramics. This work involved a study of the wetting of SiC ceramics by two oxide systems, Al₂O₃ /Dy₂O₃ and Al₂O₃ /Yb₂O₃, which have so far not been studied for application in the sintering of SiC ceramics. Five mixtures of each system were prepared, with different compositions close to their respective eutectic ones. Samples of the mixtures were pressed into cylindrical specimens, which were placed on a SiC plate and subjected to temperatures above their melting points using a graphite resistance furnace. The behavior of the melted mixtures on the SiC plate was observed by means of an imaging system using a CCD camera and the sessile drop method was employed to determine the contact angle, the parameter that measures the degree of wettability. The results of variation in the contact angle as a function of temperature were plotted in graphic form which showed that the curves displayed a fast decline and good spreading. All the samples of the two systems presented final contact angles of 40° to 10° indicating their good wetting on SiC in the argon atmosphere. The melted/solidified area and interface between SiC and melted/solidified phase were evaluated by scanning electron microscopy (SEM) and their crystalline phases were identified by X-ray diffraction (DRX). The DRX analysis showed that Al₂O₃ and RE₂O₃ reacted and formed the Dy₃Al₅O₁₂ (DyAg) and Yb₃Al₅O₁₂ (YbAg) phases. The results indicated that the two systems had a promising potential as additives for the sintering of SiC ceramics.     

Fabrication,microstructures and properties of 50 vol.-% SiCp/6061Al composites via a pressureless sintering technique

Commercial F500 SiC powder and 6061 Al powder were chosen to fabricate the 50?vol.-% SiCp/6061Al composites via pressureless sintering. Effects of pre-treatment of the SiC powder and sintering temperature on the microstructures and properties of the composites were studied. Densification mechanism and interfacial reaction of the composites were also investigated. The results show that the composites have a high sintering ability and a low interfacial reaction activity. The density, bending strength and thermal conductivity of the composites are all sensitive to the sintering temperature. The composites sintered at 680°C are nearly fully dense and have the following optimal properties: the relative density of 98.5%, the bending strength of 495?MPa, the TC of 153?W/(m?K) and the coefficient of thermal expansion of 8.1?×?10^?6/°C (50–100°C), which are superior to most of the SiCp/Al composites of the similar composition reported previously.     

Synthesis and properties of ceramics in the SiC — B4C — MeB2 system

The effect of impurities and additives of titanium and zirconium borides on the structure and mechanical properties of SiC — B₄C ceramics over a broad temperature range has been investigated. The ceramics was fabricated by hot pressing without a protective medium. Introduction of borides is accompanied by improvement in all the studied mechanical properties at room temperature, and the nature of hardening of the ceramics is practically independent of the type of SiC powders used. At high temperatures, the mechanical behavior of the ceramics is determined by the impurity composition: the ceramics obtained using abrasive powders loses strength beginning at 600°C, while using powders with decreased impurity content makes it possible to preserve the strength of the material up to a temperature of 1400°C. Translated from Poroshkovaya Metallurgiya, Nos. 5–6(413), pp. 29–42, May–June, 2000.     

添加剂对多孔陶瓷显气孔率的影响

采用硅粉,碳粉,尿素以及氧化铝,氧化钇为原料,利用常压烧结法制备了氮化硅多孔陶瓷,并着重研究了添加剂对氮化硅多孔陶瓷显气孔率的影响,得出氮化硅多孔陶瓷的显气孔率随着碳粉或尿素含量的增加而增大,且碳粉的造孔作用优于尿素。     

纳米SiC增强纯Al基复合材料的微观组织和力学性能

与采用微米尺度SiC颗粒为增强相制备的Al基复合材料相比,以纳米SiC颗粒为增强相制备的Al基复合材料具有更加优异的力学性能,可极大提高SiC增强Al基复合材料的服役可靠性及应用范围。采用传统粉末冶金方法制备纳米SiC颗粒增强纯Al基复合材料,研究烧结温度和增强相体积分数对复合材料微观结构和力学性能的影响。研究表明,烧结温度和增强相体积分数均对复合材料的微观结构和力学性能有重要影响。随烧结温度升高,复合材料中的残留微孔减少,密度和强度均得到显著提高。含体积分数为3%纳米SiC颗粒的复合材料在610℃具有最高的强度,进一步提高纳米SiC颗粒的含量并不能提高材料的力学性能,这主要是由于当纳米SiC颗粒的体积分数超过3%时将出现明显的团聚,从而降低强化效应。     

Toward Oxidation-Resistant ZrB<Subscript>2</Subscript>-SiC Ultra High Temperature Ceramics

Ultra high temperature ceramics (UHTCs), including ZrB₂-SiC, are designed for extreme environment applications in which temperatures exceed 2273 K (2000 °C). A key material property of UHTCs in many applications is their resistance to oxidation. Recent research into UHTCs is described, revealing a variety of different methods for improving the oxidation performance, which include control of starting powders, composition and size distribution, mixing, and densification techniques. The use of additives has also been researched widely, for example, to increase the viscosity of any liquid phase formed or provide protective refractory phases at high temperatures. SiC additions are effective in forming protective silica but only in static environments and to ~1873 K (1600 °C). For higher temperature applications, additions of La lead to the formation of a dense ZrO₂ scale probably via liquid phase sintering. Such ceramic systems, which produce self-generating refractory oxidation barriers or dense ZrO₂ scales, show the greatest promise in providing oxidation-resistant UHTCs.     

烧结温度对NiFe2O4/TiN复合陶瓷惰性阳极材料性能的影响

采用两步烧结法制备了掺杂质量分数为7%TiN的NiFe₂O₄/TiN复合陶瓷惰性阳极材料,重点研究了烧结温度对NiFe₂O₄/TiN复合陶瓷惰性阳极材料的微观结构及性能的影响.研究结果表明:随着烧结温度的升高,惰性阳极材料的晶粒间隙变小,气孔逐渐减少,晶粒间结合度提高,体积密度呈先升高后降低趋势,在1325℃时达到最大值5.20g/cm³,但材料内部存在微裂纹;烧结温度为1300℃时,材料表现出较好的综合性能,抗弯强度达到最大值66.77MPa,一次热震强度剩余率为95.54%,表现出良好的耐高温冰晶石熔盐腐蚀能力;烧结温度超过1300℃时,材料内部缺陷尺寸增加,电解质成分更容易渗入到阳极材料中,耐腐蚀性能下降.     

莫来石/SiC复相材料的烧结工艺和成分优化

利用工业氧化铝和超细氧化硅合成莫来石，并结合SiC制备出了莫莱石／SiC复相材料。研究了烧结工艺及氧化铝和氧化硅的摩尔比对复相材料密度和强度的影响，并以材料的热震残余强度为指标、利用正交设计法研究了微量添加剂的影响效果。结果表明，复相材料的体积密度随烧结温度的升高和烧结时间的延均出现先升高后降低的规律，而开口气孔率的变化规律则相反；随结合相中Al2O3与SiO2的摩尔比的提高，复相材料的密度增加、气孔密度降低，而强度则先增后减，通过烧结工艺与结合相和添加剂成分的优化，材料密度最高可达2．5g/cm^2，抗折强度达34．5MPa，耐压强度可达90MPa，热震后的残余强度率为67．2％。     

B4C含量对ZrB2陶瓷微观结构及力学性能的影响

针对ZrB₂陶瓷粉末在球磨时易掺入ZrO2,影响ZrB₂陶瓷烧结致密化的问题,添加B₄C作为烧结助剂,采用无压烧结法制备ZrB₂陶瓷材料,研究B₄C含量(w(B₄C),下同)对材料微观形貌、硬度与抗弯强度的影响。结果表明,B₄C通过与晶粒表面的ZrO2发生反应,抑制ZrB₂晶粒粗化,减小晶粒尺寸,从而提高烧结致密度。随B₄C含量增加,ZrB₂陶瓷的晶粒尺寸和相对密度逐渐增大,抗弯强度和硬度先升高后降低。当w(B₄C)为7%时,ZrB₂晶粒细小,材料的抗弯强度和硬度(HV)达到最大,分别为242 MPa和12.65 GPa。w(B₄C)增加至9%时,出现晶粒异常长大,材料力学性能下降。