MICROSTRUCTURE, MECHANICAL PROPERTIES AND FRICTION/WEAR BEHAVIOR OF HOT-PRESSED Si₃N₄/ BN CERAMIC COMPOSITES

Abstract

Nano-scale and micro-scale hexagonal boron nitride (hBN) powders, respectively, were added to silicon nitride (Si 3 N 4 ) matrix powder, and Si 3 N 4 /BN ceramic composites with different content of solid-lubrication hBN were produced by hot pressing. The combined effect of starting powder and hBN content on the microstructure, mechanical properties and tribological properties of Si 3 N 4 /BN ceramic composites has been studied. The results showed that the nano-sized starting powder was beneficial to the densification of Si 3 N 4 /BN ceramic composites, and resulted in a Si3N4/BN nano/nano ceramic composite with slightly higher density and improved mechanical properties compared to the corresponding micro/nano ceramic composite. The physical and mechanical properties of Si 3 N 4 -based ceramic composites were found to be affected by addition of BN. Increasing BN content led to a decrease of bulk density, hardness, bending strength and fracture toughness. On the other hand, the starting powder has no significant influence on the tribological properties of Si 3 N 4 /BN ceramic composites. The friction properties and wear resistance continuously improved with increasing BN content up to 20 vol. %, due to the formation of tribochemical film composed of H 3 BO 3 , SiO 2 and metal oxides.

Effect of Mechanical Properties on Wear Resistance of Si3N4 – SiC Ceramic Composite

“…Research in the field of ceramic materials has shown that addition of suitable secondary phase into silicon nitride matrix can significantly influence physical, mechanical and tribological properties of created ceramic composite materials. The secondary phases can be added in form of ceramic micro and nano particles (SiC, Al 2 O 3 , ZrO 2 , TiN, TiC, hBN…), whiskers, or fibres [6,[20][21][22]. Invention of carbon nanomaterials (nanofibers, nanotubes, graphenes) caused progress in composite materials research because of utilising of their progressive properties [23,24].…”

“…The increase of the fracture toughness was caused by the deflection of crack where SiC particles were the obstacles for the propagated cracks. It is supposed that if the particles are adequately small in comparison to the critical length of the cracks, their presence in the matrix does not decrease the fracture toughness of composite [6,31]. For composite samples with addition of 20 vol.% SiC, the decrease of fracture toughness was observed, and this decrease is the consequence of the matrix morphology on the fracture toughness.…”

“…Silicon nitride (Si 3 N 4 ) is an important representative of promising engineering ceramic materials. Si 3 N 4 based ceramics are characterized by high strength, high hardness, excellent wear resistance and corrosion resistance [6][7][8][9]. However, silicon nitride and ceramic materials in general have low fracture toughness compared to metallic materials.…”

Laminated Si3N4-Mo Composites Produced by Hot Pressing

“…However, in Si 3 N 4 -hBN ceramic composites, the binding capacity of hBN and ceramic matrix is poor, and excessive addition of hBN will cause the ceramic composites to lose their original high strength and high hardness. According to existing research findings [11] , the layered ceramic materials made by adding metal Mo as weak surface layer have good corrosion resistance and can achieve toughening effect of ceramic materials. Based on this, we add Mo interface layer to Si 3 N 4 ceramic composites to prepare Si 3 N 4 /Mo layered composites, and explore its physical and mechanical properties.…”

“…Our group has been devoted to the tribological research of Si 3 N 4 ceramic composites in various fields, and the developed Si 3 N 4 -hBN ceramic composites have certain practical functions in many fields [9][10][11][12][13][14][15][16][17] . However, in Si 3 N 4 -hBN ceramic composites, the binding capacity of hBN and ceramic matrix is poor, and excessive addition of hBN will cause the ceramic composites to lose their original high strength and high hardness.…”