| 摘要 |
A preform element comprises a substrate having an outer peripheral surface and at least one end surface. At least a portion of the peripheral surface of the substrate has bonded thereto an inner surface of a peripherally extending facing layer of superhard material, such as polycrystalline diamond. The portion of the peripheral surface of the substrate and the inner surface of the peripheral facing layer are provided with inter-engaging formations, such as ribs and grooves, whereby the peripheral facing layer is keyed to the substrate.
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