Effect of laser processing on the structure and properties of surface layers of deformed zirconium doped with Nb, Mo and B

The phase composition and structure of the near-surface layers of zirconium ribbons subjected to laser treatment in the initial state and after alloying with B, Mo, Nb were studied. The distribution of microhardness values on the surface of the coating and changes in microhardness at different distances from the surface were analyzed. X-ray structural analysis of the surface layers was performed, and their phase composition was determined. The influence of β-stabilizing elements on changes in the phase composition was demonstrated. In the Zr—Mo coating, a phase transformation of Zr with bcc modification takes place. It is observed that small intermetallic particles of the ZrMo2 compound are released, which help to increase the hardness in the coating to the values of μ = 1200—1300. The content of niobium in the zirconium matrix in the Zr—Nb coating, calculated according to X-ray analysis, is 29,4% (at.) which is sufficient to stabilize the BCC lattice. The value of microhardness Hμ = 600—700 on the surface of the coating is typical for hardened zirconium with a bcc lattice. The hardness of the Zr—B coating on the surface reaches values of Hμ = 1600—1400, gradually decreases in the depth of the molten layer to Hμ = 1300 and sharply decreases outside the molten zone to Hμ = 300. Significant surface hardening of the coating is associated with a large amount of the strengthening phase ZrB2. As a result of the experiments, it was established that doping with niobium and molybdenum causes fundamental phase changes in the surface layer of coatings due to the stabilization of the β phase. This is important for protecting the surfaces of nuclear power and medical devices. The addition of B significantly increases the hardness due to the mechanism of dispersed strengthening, which contributes to the improvement of the wear resistance of the coatings. Keywords: laser processing, coating, phase composition, dispersed particles, hardness.