Microstructure and mechanical properties of self-Reinforced alpha–Silicon carbide

Two-stage sintering inhibits abnormal grain growth during β to α transformation in SiC

“…the deeply probing work of Heuer and co-workers. [1][2][3] Previous work has investigated means of manipulating the ␤ to ␣ transformation, including applied pressure, 4-7 starting powder polytype composition, [8][9][10] sintering aids, [11][12][13][14][15][16][17] and sintering atmosphere. [18][19][20][21][22] For example, in the work by Zhang et al 17 it was shown that the composition of a Al metal-B-C liquid phase forming additive significantly affected the resulting grain morphology, particularly depending on the Al content; the ␣ SiC aspect ratio was reduced with decreasing Al content when hot-pressed in an Ar atmosphere.…”

Relationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide Ceramics

“…A fracture toughness of ϳ8 MPa⅐m 1/2 has been reported in toughened SiC ceramics with yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) as a grain-boundary phase, 1 and a higher fracture toughness of ϳ9 MPa⅐m 1/2 is reported in toughened SiC ceramics with Al-B-C. 4 Attempts to introduce the elongated SiC grains into the microstructure involve the following two strategies: (i) taking advantage of the ␤ 3 ␣ phase transformation at high temperatures, which usually accelerates grain growth, [1][2][3][4][5][6] and (ii) using the solutionreprecipitation process. [7][8][9][10] The latter efforts include seeding to promote preferential grain growth without phase transformation 7,8 and using fine ␣-SiC starting powders to trigger abnormal grain growth. 10 These elongated grains can act as a reinforcing phase that promotes crack bridging and deflection, resulting in improved toughness.…”

Fine‐Grained Silicon Carbide Ceramics with Oxynitride Glass

“…Clear examples are SiC nanoceramics for superplasticity 1,2 and in situ-toughened SiC ceramics for improved toughness. [3][4][5][6][7][8] Several attempts to control the microstructure of SiC have been reported, including control of the initial ␣-SiC content in the starting powder, 9 seeding for favored preferential grain growth, 10,11 the incorporation of ␣-SiC platelets, 12 the addition of liquid-forming additives such as AlN-Y 2 O 3 13 and Al-B-C, 14 and heat treatment for controlled grain growth. 15,16 A fracture toughness of ∼8 MPaиm 1/2 has been reported in SiC ceramics with yttrium aluminum garnet (Y 3 Al 5 O 12 , YAG) 3 as a grain-boundary phase, and a higher fracture toughness (∼9 MPaиm 1/2 ) has been reported in SiC ceramics with Al-B-C. 14 However, the correlation between the chemistry of the glassy phase and the properties of the resulting ceramics is not well established.…”