Pressureless Sintering of Hafnium Carbide–Silicon Carbide Ceramics

Abstract

HfC-30 vol%SiC ceramics with a relative density of 99.7% was obtained by pressureless sintering at 2300°C for 0.5 h. The resultant ceramics showed fine microstructure with HfC grain size around 1 lm. The hardness (20.5 ± 0.2 GPa), bending strength (396 ± 56 MPa), and fracture toughness (2.81 ± 0.18 MPaÁm 1/2 ) of HfC-30 vol%SiC ceramics were at least 20% higher than those of monolithic HfC ceramics. The influences of SiC particle size, volume fraction, and the oxide impurity on the microstructure evolution of HfC-based ceramics were examined. The results indicate that SiC addition and the oxygen impurity introduced by ball milling play opposite roles in the HfC grain growth during sintering. The oxide impurity introduced by ball milling caused the HfC grain coarsening, whereas SiC particles inhibited the grain growth of HfC significantly.

Laminated HfC–SiC ceramics produced by aqueous tape casting and hot pressing

“…It has attracted considerable attention as potential candidate material for a variety of ultra-high temperature applications, including atmospheric re-entry, hypersonic flight, and hightemperature electrodes, nozzles and armor, because of its high melting point, high thermal and electrical conductivity and excellent chemical and physical stability at high temperatures [4][5][6][7][8][9]. However, the low fracture toughness and poor thermal shock resistance limit its use in structural applications to date [10,11].…”

Microstructure, mechanical properties and oxidation behavior of TaC- and HfC-based materials containing short SiC fiber

“…On the contrary for HfC, addition of SiC particles resulted in toughness values of 2.2-2.8 MPa m 1/2 (i.e. even lower than upon addition of fibers) and similar 4-pt bending strength values (396 MPa) [39]. A significant contribution from SiC fiber mainly invested the densification behavior, especially in the case of HfC.…”

“…Hot pressing, spark plasma sintering and pressureless sintering have been often associated to the use of additives to improve densification and mitigate the severe sintering temperatures [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Small amounts of metals such as Fe, Mn, Co, and Ni, lower the temperature needed for densification [5][6][7]; alternative sintering additives such as B, C, and B 4 C, remove surface oxides on the starting particles enabling densification at 1900-2300 1C [8,9].…”

Polymer precursor‐derived HfC–SiC ultrahigh‐temperature ceramic nanocomposites

“…The HfC–SiC composite ceramics are commonly synthesized by milling and sintering of HfC and SiC powder mixtures . However, due to the difficulties in dispersing of raw powders, it is hard to get products with uniform microstructure and distribution .…”