The Stress of Diamond Films on the Surface of the First Wall Material

This paper proposes to deposit a diamond films on the surface of the first wall material (W mono-blocks), and through numerical simulation and experimental characterization, the effect of diamond films thickness on stress is systematically studied. In this paper, the finite element software ANSYS workbench is first used to simulate the thermal residual stress of the diamond films on the tungsten surface, and the influence of the films thickness on the size and distribution of the thermal residual stress is studied, and the optimal deposition thickness range of the diamond films is confirmed. High-performance first wall materials are particularly important for the operation of fusion reactors. The finite element simulation results obtained the diamond films thickness range with low thermal residual stress value. The diamond films was prepared on the surface of the tungsten pipe through the microwave plasma chemical vapor deposition (MPCVD) method to match the thickness of the simulation result. The total stress of the films and the adhesion to the substrate are characterized the key to investigating whether the diamond films can be applied on the surface of the first wall material is the key. A MPCVD method was used to prepare a diamond films with a thickness matching the simulation result on the surface of the tungsten pipe component. Raman spectroscopy and indentation were used to study the thickness of the films and its total stress and its correlation with the simulation results. The influence of substrate adhesion. The simulation results show that as the thickness of the diamond films increases, the maximum principal stress and maximum shear stress of the films first decrease and then increase, from 75-100 μm to the lowest, which is less than the normal fracture strength of the diamond films, and the maximum stress reduction area appears at the edge of the films. Diamond films with thicknesses of (55.48±0.5), (80.86±0.5), (103.56±0.5) μm, and (123.84±0.5) μm were prepared on the surface of the substrate by the MPCVD method. Through Raman characterization, the first-order characteristic peaks of the four samples were all lower than 1 332 cm–1, the surface has tensile stress. At the same time, among the Raman peak positions of the four collection points of the diamond films with a films thickness of (103.56 ±0.5) μm, the Raman peak position in the middle region of the films is 1 331.75 cm–1, which is closer to 1 332 cm–1, which is substituted into the Raman stress formula. The tensile stress is 141.75 MPa, and the maximum tensile stress at the corresponding corners is 635.04 MPa, so excessively high tensile stress at the corners will cause cracks to appear. The center positions of the four thickness diamond films were indented by Rockwell hardness tester. It can be seen that the indentation test results and the Raman spectrum characterization results are mutually verified. Therefore, the diamond films with a thickness of (103.56±0.5) μm is not easy to be damaged, showing the best performance. Comparing with the VDI3198 standard, the indentation pits can reach the HF1 and HF2 level, indicating that the diamond films with a thickness of (103.56±0.5) μm has a high adhesion to the substrate, which provides a theoretical basis for the application of the diamond films on the surface of the first wall material. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.