Residual stress in polycrystalline diamond Ti-6Al-4V systems

Polycrystalline diamond coatings were deposited on Ti-6Al-4V alloy by I-IF-CVD, at fixed temperature (650 degrees C) for different deposition times. During the process, thick titanium carbide layers were formed at the metal/diamond interface. X-ray diffraction (XRD) methods were used to assess coating quality, phase composition, texture, and residual macrostress of the diamond/TiC/Ti system. For a better evaluation of the residual stress present in each phase, three independent measurements were performed with synchrotron radiation (SR-XRD). The measured residual strain could be interpreted in terms of a simple axially uniform residual stress model: sigma(11) = sigma(22), sigma(33) = 0, sigma(ij) = 0 (i not equal j). Irrespective of film thickness, the residual stress was very intense, compressive both in the diamond layer (approx. -6.5 GPa) and in TiC (approx. -1.4 GPa), and tensile in Ti-6Al-4V (approx. 70 MPa). The high residual strain in the diamond layer affected the results of texture measurements using the traditional pole figure method;more reliable results were obtained by measuring the integrated intensity, rather than peak maximum intensity, as a function of tilting angles. (C) 1997 Elsevier Science S.A.