Structural design and high temperature tribological behavior of a new turbine blade tip protective coating

Severe damage to the blade tip usually occurs when the turbine blade tip scratches against the abradable coating. Therefore, blade tip strengthening is a hot research topic. To improve the wear resistance of turbine blade tips, NiAlTa coatings were prepared on K417G superalloy by electro spark deposition. The microstructure and phase composition of the coating were analyzed by scanning electron microscope and X-ray diffraction. Microhardness tester and scratch method were used to test the microhardness and bonding strength of the coating. Using ZrO2 balls as friction pair, the tribological behavior and wear mechanism of the coating were investigated by a self-developed tribometer at 25 °C and 800 °C. The NiAlTa coating mainly consists of the β phase NiAl and the laves phase NiTaAl. The laves phase NiTaAl encapsulates the NiAl phase, and this plant-like "cell wall" structure endows the coating with excellent mechanical properties, wear resistance, and cutting performance. Compared with the substrate, NiAlTa coating has higher microhardness (~797.18 HV0.2) and lower wear rate (~10−6 mm3·N−1·m−1). The wear process of NiAlTa coatings is dominated by plastic deformation, with little evidence of material loss from the brittle fracture. The competition between the anti-wear lubricating effect of the "glaze" layer and the plowing effect of oxides and ZrO2 debris affects the tribological behavior of the coating. The cutting performance of the NiAlTa coating can be attributed to the two-body or three-body abrasive wear caused by the oxides and ZrO2 debris embedded in the "glaze" layer.