Vztah mezi mikrostrukturou a otěruvzdornosti Si3N4/SiC nanokompozitu s přídavkev oxidů kovů vzácných zemin

Abstract

Ceramic materials on the base of Si3N4 are recently one of the best candidates for tribological application owing to the combination of their good thermal and mechanical properties, chemical resistance and high hardness. The aim of this work was the preparation of Si3N4/SiC nanocomposites with different rare earth oxide sintering aids (La2O3, Sm2O3, Yb2O3 a Lu2O3) and the evaluation of their hardness, indentation fracture toughness and wear resistance at room temperature. The sintering conditions for the preparation of dense Si3N4/SiC nanocomposites have been optimised and the materials exhibited high hardness in the range of 16 – 17 GPa and fracture toughness 6 – 8 MPam1/2. Both the hardness and fracture toughness increased with decreasing ionic radius RE3+ of added lanthanoid (RE = La, Sm, Yb, Lu). The friction coefficient of Si3N4/SiC nanocomposites was in the range 0.63 – 0.75. The friction coefficient of composites was always lower in comparison with that of reference Si3N4 monoliths. Similarly, the specific wear rate of composites was lower in comparison to reference Si3N4 materials prepared with the same additives. The friction coefficient significantly decreased with a decreasing ionic radius RE3+ of rare-earths either in monolithic or composite materials most probably due to the higher rigidity and better high-temperature properties of amorphous grain boundary phase containing Lu and Yb compared to Sm and La-based glasses. The nanocomposites always exhibited lower specific wear rate compared to Si3N4 monoliths.