DEVELOPMENT OF FUNCTIONALLY GRADED SINTERED HARD MATERIALS

Functionally graded materials consisting of two different materials wi th a graded interlayer have attracted much interest for their ability to exhibit the characteristics of the individual materials plus new fu nctionality. This concept was applied to the field of hard materials. The developed material consists of a titanium based ceramic surface la yer, a tough cemented carbonitride core containing B1 type and WC phas es, and an intermediate layer with graded composition. The surface reg ion 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 foun d to have an abrasion resistance and fracture toughness much higher th an those of a conventional cermet of uniform composition. Because of t he graded composition, the ceramic surface layer has high adhesive str ength, providing longer life than coated tools when spalling of the fi lm can occur easily. The new material is produced by controlled sinter ing of a green compact of uniform composition. (C) 1996 EPMA.