Polycrystalline diamond body and process

A process for preparing a polycrystalline diamond body which consists essentially of confining within a reaction chamber a charge composed of solid eutectiferous silicon-rich alloy, or solid components for providing eutectiferous silicon-rich alloy, and a mass of diamond crystals in contact with said mass of solid eutectiferous silicon-rich alloy, or with at least one of said components for providing eutectiferous silicon-rich alloy, and hexagonal boron nitride in contact or in association with said alloy or with at least one of its components, said eutectiferous silicon-rich alloy consists essentially of silicon and a metal which forms a silicide with said silicon and which is selected from the group consisting of cobalt, chromium, iron, hafnium, manganese, molybdenum, niobium, nickel, palladium, platinum, rhenium, rhodium, ruthenium, tantalum, thorium, titanium, uranium, vanadium, tungsten, yttrium, zirconium and alloys thereof, said hexagonal boron nitride being present in an amount of at least about 5% by weight of the mass of diamonds, applying a pressure of at least about 25 kilobars to said confined charge compressing the mass of diamond crystals to a density higher than 90% by volume of the resulting compressed means of diamond crystals, maintaining said applied pressure, heating the pressure-maintained charge to an infiltration temperature sufficient to melt said alloy and at which no significant graphitization of the diamond occurs whereby said alloy is infiltrated through the interstices between said compressed means of diamond crystals, said alloy being used in an amount sufficient to fill the interstices of said compressed mass of diamond crystals, said infiltrating silicon-rich alloy encapsulating the surfaces of the compressed diamond crystals reacting with diamond surfaces or any non-diamond elemental carbon producing a carbide which at least in major amount is silicon carbide, ceasing the input of heat into the resulting infiltrated diamond mass, removing said pressure and recovering the resulting polycrystalline diamond body comprised of diamond crystals bonded together by a silicon atom-rich bonding medium wherein the diamond crystals are present in an amount ranging from at least 90% by volume up to about 95% by volume of the total volume of said body.