Effect of roughness on X-ray diffraction stress analysis with examples for additive manufacturing of metallic alloys

X-ray diffraction is a well-known technique to analyze residual stresses in metallic alloys. For common laboratory conditions, the penetration depth of X-rays is of a comparable order of magnitude as the surface roughness generated by manufacturing processes. In the present paper several models are proposed to evaluate the effect of stress concentration and relaxation due to surface topography on the method. The topography is described as a sine function. It is found that the key parameter to describe this effect is the ratio of the wavelength to the amplitude . A simple analytical model shows that issues may arise when . Numerical simulations exhibit a similar trend. As additive manufacturing processes often lead to rather rough surfaces and to crucial issues linked to residual stresses, an experimental analysis of several examples (Cold Spray, Laser Powder Bed Fusion, Selective Electron Beam Melting and Atomic Diffusion Additive Manufacturing). Although it is difficult to draw general conclusions because surface topography depends on manufacturing parameters and because progress in these techniques is continuous, it is found that, in most, cases, surface roughness is not an issue in 3 of the 4 examples investigated.