Fabrication of Boron Nitride Dispersed Nanocomposites by Chemical Processing and Their Mechanical Properties

Abstract

‫ك‬કɟɵɃɁȡ᧸ǓǮᳶ‫ك‬ɣȮảոᄃɒɖ⓹۰ቦᄦǽΰ⓯ǷǬǽᣀමᏙ៙ଯ۠ গРগક᧳Ꮱᲇકᮾ᳣ཀࢫ567-0047 গРಊ⇹ቆలῡ᳇ȹˎ 8-1Hexagonal boron nitride h-BN dispersed nanocomposites were fabricated through a chemical process involving sintering of matrix ceramic powders covered partly with turbostratic BN t-BN, which was synthesized by the reduction of a mixture of boric acid and urea precipitating on the matrix ceramic powder during drying after wet-ball milling. Silicon carbide SiC, silicon nitride Si 3 N 4 , alumina Al 2 O 3 and aluminum nitride AlN were employed as matrix for h-BN dispersed nanocomposites. The nano-sized h-BN particles were found to be homogeneously dispersed within the matrix grains as well as at grain boundaries, which is typical of nanocomposite structures. As a result, the present nanocomposites showed unique and excellent properties such as high strength, low Young's modulus, high thermal shock resistance, and good machinability.

Electrical and thermal properties of silicon carbide–boron nitride composites prepared without sintering additives

“…In contrast, a gradual increase of the fracture toughness from 3.12 MPa m 1/2 to 3.79 MPa m 1/2 with increasing the BN content from 0 to 30 wt% was observed in chemically-processed SiC-BN composites [13]. However, the fracture toughness of monolithic and chemically-processed SiC-BN composites, which contained 5-30 vol% BN and which were hot-pressed with 7 wt% Al 2 O 3 and 2 wt% Y 2 O 3 , were both about 4 MPa m 1/2 [21].…”

“…[21]. In contrast, the flexural strength of powder-processed SiC-30 vol% BN composites was 390 MPa at room temperature [21].…”

“…[21]. In contrast, the flexural strength of powder-processed SiC-30 vol% BN composites was 390 MPa at room temperature [21]. The fracture toughness of SiC-BN composites showed quite different behavior depending on both the microstructure and additive composition [22,24].…”

“…Previous works concerning SiC-BN composites [12][13][14][15][16][17][18][19][20][21][22][23][24][25] have focused on their mechanical properties and processing methods. Chemical processing routes to synthesize BN or both SiC and BN generally lead to a finer and more homogeneous microstructure than conventional powder processing routes.…”

“…Chemical processing routes to synthesize BN or both SiC and BN generally lead to a finer and more homogeneous microstructure than conventional powder processing routes. The finer and homogeneous microstructure of chemically-processed SiC-BN composites results in a higher strength than conventionally powder-processed SiC-BN composites [12,13,21]. In contrast, the fracture toughness of the chemically-processed SiC-BN composites is lower than that of conventionally powder-processed SiC-BN composites because of the finer microstructure [22].…”