Creation of an intermediate layer, or interlayer, between the substrate and the diamond film is a common approach for surmounting the aforementioned problems. The choice of an interlayer is governed by several conditions. It should be a sufficient barrier to the mutual NSC 405020 of iron and carbon as well as have an intermediate coefficient of thermal expansion between that of the steel and diamond to offset thermally induced stresses. Additionally, it should be able to accommodate the CVD processing conditions used for diamond deposition and adhere well to the substrate . Many interlayers have been explored including CrN  and , TiN  and , Ni  and , and Ti . Additionally, more exotic systems of materials, such as a dual metal interlayer of W-Al , have also been investigated. Most of these interlayers have been met with limited success. One such problem is the sharp change in material properties at the interface, with locally high stress providing a driving force for delamination. With the addition of an interlayer, multiple interfaces are present, which can increase potential for interfacial fracture/delamination. One such solution is to create a gradual transition in surface composition/structure via thermal diffusion such as seen via nitriding  or boriding .