Micromanufacturing by severe plastic deformation

Beygelzimer Y., Kulagin R., Estrin Y., Davydenko O., Pylypenko A. Micromanufacturing by severe plastic deformation // Material working by pressure. – 2019. – № 2 (49). - Р. 87-90. The production of precision small-scale objects is now a rapidly expanding industry worldwide. In English literature, it has been named "Micromanufacturing" and covers the production of meso (1-10 mm) and micro size (1-1000 microns) for aerospace, automotive, optical, biomedical and other engineering fields. Features of "Micromanufacturing" poses the following challenges for material science. First, the mechanical properties of materials for small-sized products are significantly different from those of traditional mechanical engineering. This means that micromanufacturing requires new materials, and in very small quantities, for traditional mechanical engineering quantities. Small-scale production of new materials by traditional metallurgical methods is, at least, unprofitable. Thus, the problem arises to create technologies that allow to produce small batches of various metallic materials with specified properties. Secondly, micromanufacturing requires sub-microcrystalline materials. Finally, to produce a series of identical products from the same workpiece, the statistical variation in the material properties in its bulk is as narrow as possible. Metallurgical methods designed to produce large volume blanks may not provide the degree of uniformity of materials required for micro-production. The article shows that the solution of these three problems is possible by applying the methods of severe plastic deformation.

Serial snapshot crystallography for materials science with SwissFEL

New opportunities for studying (sub)microcrystalline materials with small unit cells, both organic and inorganic, will open up when the X-ray free electron laser (XFEL) presently being constructed in Switzerland (SwissFEL) comes online in 2017. Our synchrotron-based experiments mimicking the 4%-energy-bandpass mode of the SwissFEL beam show that it will be possible to record a diffraction pattern of up to 10 randomly oriented crystals in a single snapshot, to index the resulting reflections, and to extract their intensities reliably. The crystals are destroyed with each XFEL pulse, but by combining snapshots from several sets of crystals, a complete set of data can be assembled, and crystal structures of materials that are difficult to analyze otherwise will become accessible. Even with a single shot, at least a partial analysis of the crystal structure will be possible, and with 10–50 femtosecond pulses, this offers tantalizing possibilities for time-resolved studies.

Modeling of the Plastic Deformation of Polycrystalline Materials in Micro and Nano Level Using Finite Element Method

Recent experiments on polycrystalline materials show that nanocrystalline materials have a strong dependency to the strain rate and grain size in contrast to the microcrystalline materials. In this study, mechanical properties of polycrystalline materials in micro and nanolevel were studied and a unified notation for them was presented. To completely understand the rate-dependent stress-strain behavior and size-dependency of polycrystalline materials, a dislocation density based model was presented that can predict the experimentally observed stress-strain relations for these materials. In nanocrystalline materials, crystalline and grain-boundary were considered as two separate phases. The mechanical properties of the crystalline phase were modeled using viscoplastic constitutive equations, which take dislocation density evolution and diffusion creep into account, while an elasto-viscoplastic model based on diffusion mechanism was used for the grain boundary phase. For microcrystalline materials, the surface-to-volume ratio of the grain boundaries is low enough to ignore its contribution to the plastic deformation. Therefore, the grain boundary phase was not considered in microcrystalline materials and the mechanical properties of the crystalline phase were modeled using an appropriate dislocation density based constitutive equation. Finally, the constitutive equations for polycrystalline materials were implemented into a finite-element code and the results obtained from the proposed constitutive equations were compared with the experimental data for polycrystalline copper and good agreement was observed.

A Kinetic Study of the Emerging of Grains and Block of Grains from the Inner Volume to the Free Surface of a Cd-Zn Alloy Superplastically Deformed

A local measurement technique for the study of the kinetic processes of emerging of grains or blocks of grains from the inner volume to the free surface of superplastic materials during deformation is presented and used for the case of the Cd-Zn eutectic alloy deformed at room temperature. This technique could be used to evaluate the approximate time of fracture due to fissure or cavitation growth in samples under superplastic deformation. In principle, this technique will be useful for the development of physical procedures, which allows retarding the process of formation of low mismatch angle, , between neighboring grains, process which gives place to blocks of grains which dynamically behave as units under the shear stress action. For materials with nanocrystalline structures, such processes are expected to be higher than those of the case of microcrystalline materials.