Gayvoronsky I. Structural and phase state of aluminum, titanium and zirconium surface layers after pulse laser alloying with transition metals

The paper is devoted to the research of structural formation peculiarities in surface layers of aluminum, titanium and zirconium after laser alloying with the mixtures of transition metal powders. It was studied thermal stability of the phase composition of surface layers of aluminum after laser alloying by the mixture of copper and iron powders. It was found that heterogeneous structure of alloying zone contains intermetallic phases including quasicrystalline ψ phase. Annealing of laser alloying zone of the samples caused the formation of intermetallic approximant and the alignment of microhardness average values in zone depth. It was shown that ψ phase remains thermally stable at a temperature which was close to the melting point of the aluminum matrix. It was shown that high cooling rate during pulse laser treatment of cast alloy with quasicrystalline composition of the Al-Cu-Fe system caused increasing in the quantity of ψ phase in the structure of laser treatment zone which was accompanied by increasing in the values of integral microhardness. Research of phase composition of the surface layers of titanium and zirconium after laser alloying with mixtures of transition metal powders (Zr + Ni and Ti + Ni respectively) revealed that pulse laser alloying in the Ti-Ni-Zr alloy system did not lead to formation of icosahedral ψ phase at all applied processing modes. It was proposed the method of laser reinforcement of surface layers in titanium alloys which consists in covering the sample by alloying organic mixtures and in subsequent pulse laser treatment in the mode of surface melting. Active interaction of titanium matrix with the substances of the alloying mixture is accompanied by the formation in the structure of its surface layers of titanium carbides and nitrides which in its turn leads to increasing of average microhardness values of the laser treatment zone structure in comparison with the initial microhardness of titanium in several times. The method of modeling the reciprocal lattice of a quasicrystalline icosahedral structure which was based on the interpretation of Fibonacci sequence was proposed and used. The specified method consists in the reproduction of the base group of nodes which were located at the ends of icosahedron vectors according to one of the recursive algorithms. The cross sections of the model which were oriented perpendicular to the symmetry axis of the II, III and V order, were coexisted with the corresponding experimental diffraction patterns of icosahedral phases. It was found that the quantity of nodes self-assemblies in the model correlated with the intensities of the corresponding experimental reflexes. The results of the research can be used in engineering (aviation and automobile industry) when creating wear-resistant coatings on parts of tools which affected by frictional wear in contact areas during the operation and in nuclear power engineering (construction of reactors) during production of constructive fuel cells in the active zone of nuclear reactors.