A method for forming a diamond body includes placing a thermally stable polycrystalline diamond body and a first substrate into an enclosure, the thermally stable polycrystalline diamond body comprising a plurality of bonded diamond crystals and a plurality of interstitial regions between the bonded diamond crystals, the interstitial regions being substantially free of a catalyst material, heating the thermally stable polycrystalline diamond body and the first substrate to remove residual materials from the thermally stable polycrystalline diamond body, subjecting the thermally stable polycrystalline diamond body and the first substrate to a vacuum for evacuating such residual material, and pressing under high temperature the enclosure, the thermally stable polycrystalline diamond body and the first substrate while maintaining a vacuum in the enclosure to bond the thermally stable polycrystalline diamond body to the substrate.