Interfacial stress evolution simulation on the graphite substrate/interlayer/diamond film during the cooling process

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films. The evolution of interfacial stress during the cooling process is critical for the fabrication of large-area crack-free diamond films, so it is very worthy of further study. Variable-temperature X-ray diffraction (XRD) tests and finite element simulation were performed to evaluate the stress evolution of a diamond film. The film (with diameter of 150 mm) was prepared on a graphite substrate with Ti interlayer using DC arc plasma jet. Residual compressive stress in the diamond film is gradually increased during the cooling process. Moreover, the value and growth rate of the residual stress from the XRD tests are significantly lower than the finite element simulation results. All XRD peaks of diamond, graphite, and titanium carbide (TiC) generated on both sides of the Ti interlayer shift to a larger angle. By contrast, several XRD peaks of Ti deviate to a low angle. Elastic deformation of the Ti layer may offset the lattice contraction caused by the cooling effect. Elasticity modulus of TiC is significantly greater than that of Ti, which is more inclined to release the stress of the diamond film by self-fracturing. After the variable-temperature tests, residual compressive stress of the diamond film at room temperature is 1.1 GPa, whereas that before the tests is 1.4 GPa. These values are significantly lower than the finite element simulation results (3.05 GPa). (C) 2016 Elsevier B.V. All rights reserved.