Yefimov M. The physical principles of surface strengthening of materials by the formation of metastable structure states

The dissertation work is devoted to the investigation of the influence of the pulse laser radiation with the pulse duration 20-30 ns and the pulse plasma treatment on the surface of steels and to the problems of formation of the coating applied by the gas thermal evaporation method. For the first time it was shown that the new metastable FCC-solid solution was formed in surface layer of the austenitic steels under influence of the ns-laser radiation. This solution has increased lattice parameter and exists simultaneously with base FCC-solid solution, having practically invariable lattice parameter. This state of the irradiation surface layer is defined by the cellular dislocation structure without redistribution of alloyed elements between the boundary regions and all volume. In the carbon steels the metastable austenitic lattice parameter is by 0,5-0,9 % increased after pulse ns-laser radiation then after ms-laser one. It is supposed that the appearance of the new solid solution with a elevated latti ce parameter is connected with the increasing of the concentration of the interstitial atoms in the FCC-solid solution. It is found that hardened surface layers with fine martensite-austenite structure form in carbon steels under the influence of plasma-detonation working. The hardening of surface layer is explained by strong thermal influence of plasma pulses and alloying of the surface by elements composing plasma. In hardened layer with the fine structure melting and quenching from liquid state and deformation hardening have been occurred. It is shown that only partially amorphous powder coating containing boron has high hardness (about 5-7 GPa) up to 650-700C.