Cubic boron nitride/diamond (cBND) composite films with excellent adherence to various substrates and their fabrication method are disclosed. The cBND composite confining cBN can be prepared without any amorphous/turbostratic BN (aBN/tBN) incubation layers. The cBND composite is established on the compatibility of structural and physical properties of two superior materials: cBN on top and diamond beneath. The underlying diamond is adapted to the substrate of choice using a variety of methods which may include prescratching the substrates, bias enhanced nucleation, etching for depleting undesirable chemical elements, construction of buffer layers and gradient buffer layers for the isolation of undesirable chemical elements or/and adaptation of physical properties. The diamond nuclei are preferably formed either by bias-enhanced nucleation or by pre-scratching the substrate prior to nucleation. The cBN films in cBND composites of the present invention can grow directly on the underlaying diamond films in heteroepitaxial relationships.