Abstract: A coated ceramic silicon nitride cutting tool comprises a substrate having a major portion by volume silicon nitride, a coating of refractory material thereon, and an interfacial layer intermediate between the substrate and the layer of refractory material. The interfacial layer comprises a refractory metal chemically reacted to form a reaction bonded refractory metal nitride for enhancing the adherence of the layer of refractory metal material to the substrate. The interfacial layer is provided by reacting a refractory metal halide with the surface to form a reaction bonded refractory metal nitride.