Microstructural Characteristics of Reaction-Bonded B4C/SiC Composite

Abstract

A detailed microstructural investigation was performed to understand structural characteristics of a reaction-bonded B$_4$C/SiC ceramic composite. The state-of-the-art focused ion beam & scanning electron microscopy (FIB/SEM) and transmission electron microscopy (TEM) revealed that the as-fabricated product consisted of core-rim structures with {\alpha}-SiC and $B_4$C cores surrounded by \beta-SiC and $B_4$C, respectively. In addition, plate-like \beta-SiC was detected within the $B_4$C rim. A phase formation mechanism was proposed and the analytical elucidation is anticipated to shed light on potential fabrication optimization and the property improvement of ceramic composites.Comment: 8 pages, TMS201

Recent progress in B4C–SiC composite ceramics: processing, microstructure, and mechanical properties

“…9c). 85,140 C first dissolves in molten Si and then diffuses to the vicinity of the original a-SiC in the B 4 C-SiC ceramics produced from the preform composed of a mixture of SiC and B 4 C without free C addition (Fig. 10c).…”

“…The Si substitutes for the C atoms on the ends of the linear chain and inserts into the icosahedrons in the B 4 C lattice, and C atoms react with liquid Si, generating SiC. Wang et al 140 mentioned that the B 12 (B, C, Si) 3 rim surrounding B 4 C is generated by Si inward diffusion in B 4 C from a liquid. Sun et al 141 put forward that there are two types of B 12 (B, C, Si) 3 phases in the reaction-bonded B 4 C–SiC ceramics.…”

“…9c). 85,140 C first dissolves in molten Si and then diffuses to the vicinity of the original α-SiC grains, forming supersaturated liquid Si[C]. Compared with the homogeneous nucleation in a liquid phase, the supersaturated liquid Si[C] is more prone to heterogeneously crystallize to form β-SiC attached to the original α-SiC grains because of the relatively lower energy.…”

Effect of Boron Carbide Particle Size Distribution on the Microstructure and Properties of Reaction Bonded Boron Carbide Ceramic Composites by Silicon Infiltration

“…放电等离子烧结 [7][8][9][10][11][12][13][14][15] B4C 颗粒的核-壳结构由 Hayun 等 [18] 首次提出。 该核-壳结构的形成主要基于以下两种不同的机理： (1)Hayun 等 [18] 认为该结构的产生主要基于溶解- B12(C,Si,B)3 壳层； (2)Wang 等 [19] [20] ，在硬度测试中，同样面积的压 痕下界面的总面积越大；然而在陶瓷材料中界面通 常为薄弱带，其抵抗变形的能力差，因而晶粒越细 小，材料的硬度值越小 [21] 。R1、R2、R10 和 R11 中 细颗粒 B4C 的含量逐渐减少(表 1) ，导致复合材料 的硬度值逐渐升高。此外，R1、R2、R10 和 R11 的 坯体密度逐渐升高(如图 2) ，复合材料中 B4C 相的 含量也依次升高(如表 2) ，而 B4C 的硬度高于 SiC 相和游离 Si 相的硬度 [22] (Si： 10 GPa， B4C： 35 GPa， SiC：27~30 GPa),因而材料的维氏硬度逐渐升高。 断裂韧性取决于单位面积的裂纹在增殖时所释 放的应变能 [21] 。裂纹扩展时通常沿着晶界或相界等 薄弱处，穿过的晶粒数量由平均晶粒尺寸决定 [24] ， 晶粒越细小，裂纹扩展时穿过的晶粒数量越多，断 裂时裂纹扩展的路径越长，所释放的应变能越大， 对应的断裂韧性越高 [3] 。在 RBBC 复合材料中，B4C 的平均晶粒尺寸越小，游离 Si 区的平均尺寸也越小， 相界面的面积则越大，裂纹扩展路径越曲折，因而 断裂韧性越高。…”