Non-destructive determination of residual strains/stresses and microstresses in polycrystalline materials by means of neutron diffraction

High penetrability of neutrons into the majority of materials enables to study non-destructively the elastic strain/stress state deep under the surface (mm-cm, depending on particular material). This can become important after technological treatment of components, e.g. after welding. In multiphase materials, neutron diffraction can provide information about the strain/stress behaviour of individual phases (phase-specific strains). Phase-specific strains then can be studied in the dependence on phase compositions, thermal treatment, deformation degree or other technological treatment, e.g. ECAP (Equal Channel Angular Pressing). Strain/stress investigations by the non-destructive neutron diffraction technique can be carried out for strain/stress mapping in raw materials, industrial components, in the vicinity of welds and weld-repairs, to assess aging and fatigue effect, in the components after service, etc. A wide variety of polycrystalline materials can by investigated - metallic materials (steels, non-ferrous alloys), ceramics, hybrid composites, carbon composites, plasma sprayed materials etc. Currently used competing non-destructive techniques are mainly based on X-rays diffraction technique. Disadvantages of using X-rays are getting only surface information. The neutron diffraction technique can, on the contrary, provide information on both macro- and micro-strains even in multi-component materials in the depth of several centimetres. The determination of macrostrains is based on the measurement of small angular shifts of diffraction peaks caused by small lattice-parameter variations in the gauge volume brought about by the stress with respect to the stress-free lattice spacing. The strain tensor can be determined by combining the results of a set of measurements for different orientation of the sample relative to the scattering vector. Dedicated strain scanner provides sufficiently high flux to study residual stresses efficiently. The microstrains, which are related to stress fields resulting from microstructural defects (dislocations, stacking faults, etc.), cause broadening of the diffraction peaks. The microstrain evaluation is based on the profile analysis of the broadened diffraction maxima. A high instrumental resolution is necessary for the measurement of broadening of diffraction profiles. The Czech research institute offers its capacity in non-destructive neutron diffraction technique for determination of residual elastic lattice strains/stresses as well as microstrains/microstresses in polycrystalline materials to study e.g. deformation mechanisms or degradation processes after mechanical, thermal or cyclic loading. In the case of commercial agreement with technical assistance: The partner sought is industrial companies from metallurgy, engineering, welding industry, partner developing new materials, nuclear power plant industry, automotive, railway or aerospace industry etc. looking for an experienced partner for a specific expertise including measured data interpretation. In the case of technical cooperation agreement: The partner sought is industrial company from metallurgy, engineering, welding industry, partner developing new materials, nuclear power plant industry, automotive, railway or aerospace industry etc. looking for an experienced partner for joint development cooperation. In the case of research cooperation agreement: The partner sought is industrial company from metallurgy, engineering, welding industry, partner wishing ro develop new material, nuclear power plant industry, automotive, railway or aerospace industry etc. looking for an experienced partner for joint research project (e.g. Horizon 2020).