№74-13
Characteristics of changes in microstructure and mechanical characteristics under high energy load
V. Kozechko1, V. Kozechko1
1Dnipro University of Technology, Dnipro, Ukraine
Coll.res.pap.nat.min.univ. 2023, 74:154-162
https://doi.org/10.33271/crpnmu/74.154
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ABSTRACT
Purpose. Verification of the hypothesis about the possibility of obtaining a fine-grained structure of a metal as a result of processing with high-density energies.
The methods. The research was carried out on cylindrical samples with a diameter of 50 mm and a length of 300 mm, which were made of structural steel 45 in a normalized state. The thickness of the inner coaxial layer BP1 with a detonation speed D=7.5 km/s was 3 mm, the thickness of the outer layer BP2 with a detonation speed D=3.5 km/s was 40 mm. The two-layer BP charge used in the experiment increases the duration of the shock wave and at the same time protects the samples from destruction.
Findings. The mechanism of nanostructuring, in general terms, consists in the accumulation of the degree of deformation without destruction, which leads to the defragmentation of the structure with a significant increase in the density of dislocations.
One of the methods that allows you to achieve a high density of dislocations, comparable to IPD, is treatment with shock waves.
The change in the grain structure in the places of the pores indicates extremely high degrees of inhomogeneous deformation in these areas. During the passage of the shock wave in the middle of the sample, at the boundaries of the interface of phases with different densities, diffraction wave effects occur, which lead to the occurrence of shear deformations. It can be assumed that in the area of pores and microcracks, the deformation conditions are similar to those realized by some methods of intensive plastic deformation. This leads to a sharp grinding of the grain structure and a corresponding change in mechanical properties.
The originality. The paper found that the processing of steel parts with the help of high-density energy leads to a sharp grinding of the grain to the nanostructure size and, as a result, to an increase in mechanical properties. The revealed regularities make it possible to obtain optimal parameters of high-energy processing, which lead to an increase in hardness, a redistribution of internal stresses and a decrease in surface roughness.
Practical implementation. Obtaining grains with nanostructural characteristics in the structure of the material will allow to create fundamentally new devices and materials. Such materials will have properties significantly exceeding their achieved level – which is important for many fields of engineering, medicine, biotechnology, environmental protection, defense, etc.
Keywords: nanostructure, microhardness, high density energy, shock wave load.
References
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