X-Ray Determination of Texture and Residual Stress in Low Contraction Electrolytic Chromium Deposition

摘要

Residual stresses are believed to be responsible for the intrinsic cracks observed in electrolytic chromium coatings. The cracks directly affect the wear and erosion behavior of the coating and substrate. Crystalline orientation significantly influences the elastic-plastic properties of materials. It also affects the method by which residual stress can be determined using x-ray diffraction. For this study, we investigated texture and residual stress analysis for two low contraction (LC) chromium coating specimens and compared the results with a high contraction (HC) chromium specimen. High- resolution pole figure analysis and x-ray diffraction were used to characterize the texture in the coatings. Randomly oriented materials allow the application of the x-ray diffraction squared sin(psi) stress measurement method. For highly textured body-centered-cubic crystals, the squared sin(psi) method failed, so a Matlab matrix inversion method was used to determine residual stress. One of the LC chromium specimens exhibited near random orientation with very weak fiber texture, and the other specimen exhibited intermediate mixed <111> and <211> fiber texture. The HC chromium specimen exhibited strong predominately <111> fiber texture. A correlation between residual stress and texture was found. The HC chromium specimen with high fiber texture showed higher surface tensile stresses, while the LC chromium specimens with more randomly oriented crystallites showed lower residual stresses.