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Description
To implement a soft stress state scheme used to obtain high quasi-hydrostatic pressure and large plastic deformations, Bridgman type static anvils and anvils with mutual axial rotation - shear under pressure - are most suitable. The last technique has been given the name high pressure torsion (HPT). This method is widely used to study the features of phase transitions under pressure and also to obtain and study bulk nanocrystalline materials. Depending on the task, anvil punches are used with different bandwidths of x-rays and gamma rays. To study the kinetics, degree, and hysteresis of baric phase transformations, superhard materials with a relatively high permeability of gamma and X-rays are used: cubic boron nitride (c-NB), synthetic sapphire, and also the skeleton - artificial finely dispersed diamond with SiC binder. A vacuum pumping or an inert gas medium is used to create a chemical inert medium. To produce nanocrystalline structures of metals and alloys, the anvil punches made of tungsten carbide with a cobalt binder are mainly used: WC-6.
To solve a number of spectroscopy tasks under conditions of high static compression and deformation of materials, a set of HPT methods was created on the basis of hydraulic presses with an effort of 106 and 5 * 10^6 N and also portable cameras for studying in situ phase transitions. Operating ranges of varied parameters: pressure 1.0 - 18 GPa, temperature 20 - 800 K, true logarithmic deformation up to (e ≤ 7). A device for measuring the moment of the resistance force of samples to deformation by torsion was created with conversion to the resistance to torsion. The device is based on a strain gauge and an electronic dynamometer with data transfer and recording to a computer. To avoid the influence of low and high temperatures, the strain gauge is moved away from the anvil block on the lever 0.52 m from the axis of rotation of the anvils.
The portable chamber for compression and HPT with anvils made of cubic boron nitride is made of stainless steel. The supporting parts for the c-NB anvils are made of WC -6, the rotating anvil is supported by a thrust bearing. The camera is used in situ for two methods: Mössbauer spectroscopy with E = 14.4 eV and also for X-ray diffractometry, mainly on synchrotron radiation (SI) λ = 3685 nm at the SR beamline №4 of the VEPP-3 storage ring of BINP SB RAS. In the portable chamber, the features and hysteresis of the baric phase bcc-hcp direct and reverse transition both in single-crystal and nanocrystalline samples of pure iron were studied. The exposure time of the spectra using the SI and Mössbauer spectroscopy methods was 1 hour and 60 hours, respectively.
The experiments of the samples produced by mechanical alloying by HPT of non-soluble elemental powder mixtures of Fe-Cu, Ag-Cu, Au-Co were carried out. It is found that non-equilibrium nanostructured solid solutions were obtained in all concentrations of powder mixtures.
The research was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme Рressure No. АААА-А18-118020190104-3), supported in part by RFBR (project No. 19-32-60039).
