Sialon tool materials

Abstract

Sialons are phases in the Si–Al–Q–N and related systems that are built up of (Si, Al)(O, N)₄ tetrahedra in the same way that the structural unit in the silicates is the (Si, Al)O₄ tetrahedron. These new materials include nitrogen-containing ceramics, glasses, and glass-ceramics but only β’-sialon, the silicon-aluminium oxynitride isostructural with β-silicon nitride, Si₃N₄, has so far been commercially developed for engineering applications. Fully dense shapes are fabricated by pressureless sintering with additions of yttrium oxide to give the strongest ceramic yet known and the product holds great promise as a cutting tool for machining metals. Because of its high hardness, impact strength, and fracture toughness yttrium-sialon tool tips are superior to cobalt-bonded tungsten carbide (hardmetal) for many cutting applications.