China's Refractories

Abstract: In order to improve the densification of Si₃N₄ bonded SiC refractories and reduce the nitriding temperature of Si powder, Si₃N₄ bonded SiC refractories were produced by reaction sintering at 1 350 °C for 5 h under a carbon embedded atmosphere, using SiC particles and fine powder, and Si powder as the main raw materials, and introducing Ti-Si-Fe alloy extracted from high-titanium blast furnace slag to partially replace the Si powder. The effects of the Ti-Si-Fe alloy addition (0, 1.8%, 3.6%, 5.4%, and 7.2%, by mass) on the nitriding behavior of Si powder, as well as on the mechanical properties and microstructure of the material were investigated, and the nitriding reaction sintering mechanism was also explored. The results show that: (1) with the increase of the Ti-Si-Fe alloy addition, the cold mechanical properties and the hot modulus of rupture of the refractories are obviously improved, and the refractoriness under load exceeds 1 700 °C; the property enhancement slows down with Ti-Si-Fe alloys addition above 3.6%; (2) Ti-Si-Fe alloy promotes the complete nitridation of Si powder and the reaction sintering of the material at a lower temperature; the volume growth during the nitridation process of the Ti-Si-Fe alloys and Si powder can effectively fill pores, nitriding products improve the bonding state between aggregates and matrix, and that inside matrix, thereby increasing the densification and improving the mechanical properties of the material; (3) after the introduction of Ti-Si-Fe alloys, the liquid phase rich in Ti, Si, N, and Fe components is formed in the reaction system; besides the traditional VS and VLS mechanisms, the dissolution-precipitation mechanism plays a leading role in the formation of short columnar β-Si₃N₄ and granular TiN; and the cross-linked α-Si₃N₄ whisker, short columnar β-Si₃N₄ and granular TiN enhance the mechanical properties of the material.

Key words: Ti-Si-Fe alloy, reaction sintering, Si₃N₄ bonded SiC refractories, densification, dissolution-precipitation