Subsurface gradient of residual stress and lattice parameter in mechanically polished tungsten measured using classical X-rays and synchrotron radiation

Data obtained for tungsten sample using MGIXD method (Cu Kalfa radiation, 4 different incident angles)) and ED diffraction with synchrotron radiation. In the used MMXD method [28], the residual stress analysis is based on the ED synchrotron X-ray diffraction measurement performed for multiple hkl reflections. To do this, data were collected for one constant 2θ angle with the white synchrotron beam. Next, data were grouped for strictly chosen penetration depths in order to perform the residual stress analysis layer by layer in the sample and to get much deeper profile than in the case of the MGIXD method. 1. The complementary MGIXD and MMXD methods reveal a significant residual stress gradient present in the subsurface volume of a polished tungsten sample. The compressive stress of about -1000 MPa was determined very close to the polished surface (MGIXD method). Going deeper in the subsurface volume the residual stresses gradually decrease down to zero value at the depth of about 10 μm (MMXD method). 2. The value of lattice parameter remains constant (in the margin of 0.001Å) up to 9-10 μm of the depth, regardless the method used to determine it. 3. The results obtained using classical MGIXD for sample surface are continued by the MMXD results. High energy synchrotron radiation allowed measurements for significantly larger subsurface depths in comparison with a classical laboratory X-rays. 4. The MMXD with synchrotron radiation allowed to determine depth-dependent stress profile with spatial resolution of 1 µm, which is much better than in the case of standard ED measurements. 5. Almost isotropic elastic properties of tungsten crystallites simplifies analysis of the residual stress state