Study of Mechanical Behaviour of Polycrystalline Materials at the Mesoscale Using High Energy X-Ray Diffraction

International audienceOwing to its selectivity, diffraction is a powerful tool for analysing the mechanical behaviour of polycrystalline materials at the mesoscale, i.e. phase and grain scale. In situ synchrotron diffraction (transmission mode) during tensile tests and modified self-consistent elastoplastic model were used to study elastic and plastic phenomena occurring in polycrystalline specimens during deformation. The evolution of stress for grains which belong to different phases of duplex stainless steel and pearlitic steel was analyzed

Application of Laboratory Diffraction Methods in Characterization of Elements Made By Additive SLM Methods - State of the Art

The greatest challenge of widely developed incremental manufacturing methods today is to obtain, as a result of the manufacturing process, such components that will have acceptable strength properties from the point of view of a given application. These properties are indirectly determined by three key characteristics: the level of surface residual stress, the roughness of the component and its porosity. Currently, the efforts of many research groups are focused on the problem of optimizing the parameters of incremental manufacturing so as to achieve the appropriate level of compressive residual stress, the lowest possible porosity and the lowest possible roughness of parts obtained by 3D methods. It is now recognized that determining the level of these three parameters is potentially possible using experimental X-ray diffraction methods. The use of this type of radiation, admittedly, is only used to characterize the surface layer of elements, but its undoubted advantage is its easy availability and relatively low cost compared to experiments carried out using synchrotron or neutron radiation

Laser Powder Bed Fusion and Selective Laser Melted Components Investigated with Highly Penetrating Radiation

Methods of incremental manufacturing, i.e. 3D printing, have been experiencing significant growth in recent years, both in terms of the development of modern technologies dedicated to various applications, and in terms of optimizing the parameters of the process itself so as to ensure the desired mechanical and strength properties of the parts produced in this way. High hopes are currently being pinned on the use of highly penetrating types of radiation, i.e. synchrotron and/or neutron radiation, for quantitative identification of parameters characterizing objects produced by means of 3D printing. Thanks to diffraction methodologies, it is feasible to obtain input information to optimize 3D printing procedures not only for finished prints but also to monitor in situ printing processes. Thanks to these methodologies, it is possible to obtain information on parameters that are critical from the perspective of application of such obtained elements as stresses generated during the printing procedure itself as well as residual stresses after printing. This parameter, from the point of view of tensile strength, compression strength as well as fatigue strength, is crucial and determines the possibility of introducing elements produced by incremental methods into widespread industrial use

Determination of Stress Values in the Surface Layer of Inconel 718 Samples Dedicated to Fatigue Tests

This work deals with the problem of X-ray stress determination on the samples dedicated to fatigue tests. A number of research studies point out the fact that the processing of hard, difficult to machine materials like nickel superalloys, reveals more than one trend of residual stress versus working parameters of behaviour (Lavella and Berruti, 2010). Many papers have shown that the residual stresses are dependent on a combination of a number of factors. When the above is taken into account simultaneously with the requirements of the internal General Electric specification for the fatigue tests samples preparation (Metallic test specimen preparation, low stress, 2017) the problem of turning and grinding parameters gathers significance. It is well known that the quality of the surface layer, produced during machining, is of vital importance for the fatigue life specially for the components of aircraft produced form nickel superalloys e.g. Inconel 718 (Kortabarri et al., 2011). That is why the surface layer’s properties are described in detail by the standards. The aim of the work is to determine one of the most influential features from the point of view of fatigue life, i.e. the stress state on the surface layer with one non-destructive method – the diffraction analysis

Study of Stresses in Texture Components Using Neutron Diffraction

International audienceIn this work a new method for analysis of neutron diffraction results obtained during “in situ” tensile load is proposed and tested. The methodology is based on the measurements of lattice strains during “in situ” tensile test for several hkl reflections and for different orientations of the sample with respect to the scattering vector. As the result the full stress tensor for preferred texture orientations in function of applied stress can be determined with help of crystallite group method. The experimental data are presented and compared with self-consistent model calculations performed for groups of grains corresponding to the measured hkl reflections

Intergranular Stresses and Micro-damage Process in Two-phase Materials Studied Using Diffraction and Self-consistent Model

International audienceAs a selective and non-destructive method, the diffraction method applied for in-situ tensile test is particularly useful in analysing the evolution of phase behaviour during elastic and elasto-plastic deformation of polycrystalline materials. This experimental technique enables determination of the mechanical properties for group of grains inside the gauge volume defined by diffraction condition. The measurements are carried out using selected hkl reflections during tensile/compression tests. In the case of multiphase polycrystalline materials, the measurement of separate diffraction peaks enables independent investigations of the mechanical behaviour of each phase.In this work, a methodology combining diffraction experiments and self-consistent calculations was used to study behaviour of phases within two-phase polycrystalline materials (Al/SiCp composite and duplex austenitic-ferritic steel). Special attention was paid to the role of first and second order stresses on the yield stresses of the phases, as well as on the evolution of these stresses during the deformation process. The stresses were determined from lattice strains measured in situ during tensile tests and after sample unloading using neutron diffraction (JINR, Dubna, Russia and ISIS, RAL, UK) and diffraction of X-ray synchrotron radiation (ID15B, ESRF, Grenoble, France).Comparison of the elasto-plastic self-consistent model with measured lattice strains allowed the determination of micro-mechanical properties of each phase in two-phase polycrystalline materials. The partitioning of the load between phases were correctly predicted by the self-consistent model. It was shown that the developed version of this model can be used to predict the consequences of damage processes occurring in a given phase.The experimental and model results obtained in this work were used to study slip on crystallographic planes, localisation of stresses in polycrystalline grains and initiation of micro-damage occurring during plastic deformation