Study of high-temperature behavior of a heat-protective coating of zirconium dioxide by laser heating

Abstract

When studying the high-temperature behavior of the heat-protective coating of zirconium dioxide, the method of laser heating has been tested. The coating was applied by the method of high-energy plasma spraying on the intermetallic sublayer of the Ni–Co–Cr–Al–Y system made of a powder material of the composition (ZrO2 + 7% Y2O3) of spherical morphology.The aim of this work was to study the processes of structural-phase transformations, melting and crystallization occurring in a ceramic coating material under the action of a single laser pulse with a duration of 14 ms with different energies (5, 10, 15, and 20 J). It was found that after spraying, the coating in the initial state has a two-phase composition (T-ZrO2 + K-ZrO2), and a layered microstructure with a columnar structure of zirconium dioxide grains. Laser heating with a pulse energy of 5 J stimulates the phase transformation T-ZrO2 → K-ZrO2, the appearance of porosity and microcracks. With an increase in the pulse energy to 10 and 15 J, the processes of melting and ultrafast crystallization, accompanied by grain refinement, intensively occur on the coating surface. According to the theoretical estimates, the reflow processes affect surface layers with a thickness of 2.2 to 6.6 μm, and phase transformations take place at a depth of ~11 μm. With an increase in the laser pulse energy to E = 20 J, the process of destruction of the coating was initiated by the mechanism of cracking with delamination of fragments of the surface layer 5–10 μm thick.The laser heating method is recommended as an express diagnostics for comparative tests of the heat resistance of ceramic coatings obtained by different methods and from different starting materials.