The regularities of changes in the structure and phase composition of the thermal protective aluminide-nickel coating (Ni — 45 %; Al — 14 %; Co — 22 %; Cr — 18.9 %; Fe — 0.15 %; Nb — 0.14 %; Y — 0.09 %; Ca — 0.06 %; Mn — 0.01 %; C — 0.15 %; Si — 0.15 %; S — 0.006 %) after exposure to short-term pulsed heat fluxes of various power, created by the radiation of a pulse-periodic laser LRS-150A with a radiation wavelength λ = 1.06 µm and a pulse duration τ = 12·10–3 s. The radiation energy was E = 5, 10, and 15 J. Microstructural analysis and the elemental composition of the resulting coating were carried out as well as analysis of the phase composition. X-ray microanalysis of the coating was also carried out. In the initial state and after irradiation of the coating with a heat flux of power P = 7·103 W/cm2, light microregions are observed in the micrographs of the surface. These regions do not have clearly defined external boundaries and consist of the NiAl phase and a small amount of the Ni3Al phase with the presence of inclusions of particles containing a solid solution of Ni – Co – Cr. After irradiation of the coating with heat fluxes of higher power (P = 1.7·104 W/cm2 and P = 2.2·104 W/cm2), large convex formations appeared on its surface, consisting mainly of Ni3Al and NiAl phases. On micrographs of the surface, they appear as white areas with well-defined outer boundaries. The content of the Ni3Al phase in them in comparison with the initial state increased, and the content of the NiAl phase decreased, while the particles of inclusions of Ni, Co, and Cr disappeared. It can be assumed that an increase in the Ni3Al content is associated with the dissolution of particles of a solid solution of Ni – Co and Cr in the melt and the subsequent diffusion of nickel into the NiAl phase. When exposed to a heat flux of power P = 2.2·104 W/cm2, microcracks appear on the areas of the coating surface covered with aluminum oxide.
Formation of β-NiAl Phase During Casting of a Ni-Based Superalloy
