Development of Functionally Graded Sintered Hard Materials

Abstract

Functionally graded materials consisting of two different materials with a graded interlayer have attracted much interest for their ability to exhibit the characteristics of the individual materials plus new functionality. This concept was applied to the field of hard materials. The developed material consists of a titanium based ceramic surface layer, a tough cemented carbonitride core containing Bl type and WC phases, and an intermediate layer with graded composition. The surface region is characterised by a high compressive residual stress of 0·8 GN m⁻². When applied in the form of cutting tools, the material was found to have an abrasion resistance and fracture toughness much higher than those of a conventional cermet of uniform composition. Because of the graded composition, the ceramic surface layer has high adhesive strength, providing longer life than coated tools when spalling of the film can occur easily. The new material is produced by controlled sintering of a green compact of uniform composition. PM/0743