Abstract: A superhard construction comprises a substrate and an ultra hard material layer formed over the substrate. One of the interface surface of the substrate or the interface surface of the ultra hard material layer comprises a plurality of spaced-apart projections arranged to project from the interface surface, the interface surface between the spaced-apart projections being uneven. A further superhard construction comprises a plurality of projections arranged to project from the interface surface which abut one or more adjacent projections along an edge thereof on the surface from which the projections project, and extend over all or a majority of the interface surface.

Abstract: A superhard insert for a rotary earth borer tool comprises a cutter end having a peripheral cutter edge, at least part of the peripheral cutter edge being defined by a plurality of edges of a plurality of alternate hard and superhard regions. The edges of the superhard regions are arranged spaced apart from each other and are separated by edges of hard regions. The hardness of each hard region is at most 50% of the hardness of each superhard region.