Machining processes require tool materials with properties such as high hardness at elevated temperature, high fracture toughness and chemical stability with the workpiece. Advances in science and industry, as well as the development of harder materials have permitted cutting tool technology to evolve. In cutting processes, the contribution of different wear mechanisms to total wear is related to the mechanical and chemical properties of the two materials in contact. The high temperatures at tool-workpiece contact zones often result in diffusion of material from the workpiece to the cutting tool. Diffusion experiments were carried out to understand wear mechanisms involved at cutting edges of ceramic tools and the influence of microstructure on diffusion without the interference of mechanical wear processes. The chemical stability was analyzed from static interaction couple experiments at 1100°C with ceramic composite materials and gray cast iron. To investigate the influence of grain size on diffusion, sub-micrometric and nanometric alumina based composites with NbC as the second phase were used. These experiments showed that the influence of grain size on diffusion and the relative inertness of the composites in the presence of gray cast iron.