The Ni-based single crystal superalloy has an excellent performance derive for high temperature fatigue strength. So, the expansion of application has been expected mainly in advanced gas turbine parts. However, it is known that the γ′ microstructure changes inside the material by plastic strain processing and heat-treatment. As a result, the fatigue strength was remarkably reduced. The new phenomenon was found that the B containing alloy coatings formed by thermal spraying restore high temperature fatigue strength of the weakened single crystal superalloy. We introduce the improvement effect of high temperature fatigue strength achieved by means of spraying the B containing alloy to CMSX-4 Ni base alloy substrate produced alterated layer.

The high temperature oxidation resistance behavior of atmospheric plasma sprayed CoNiCrAlY coating with a thin layer of Cr 2 O 3 employing chromate treatment was investigated. The high-temperature oxidation test was performed at 1423K for 7.2, 14.4 and 32.4ks, respectively. The formation of the oxide layer on the CoNiCrAlY coatings with Cr 2 O 3 thin layer by chromate treatment was compared with that of the non-Cr 2 O 3 thin layer. The oxide layer formed on the both types of MCrAlY coatings grows with increasing the elevated temperature and the holding time. Also, the thickness of the oxide layers was proportional to the square root of time. The thickness of the oxide layer on CoNiCrAlY coatings with the thin layer of Cr 2 O 3 was only 60% as compared with that of the non-Cr 2 O 3 thin layer in high temperature oxidation tests at 1423K.

The gas turbine blades in a severe environment are overlaid with MCrAlY coatings by Low Pressure Plasma Spray (LPS) process for protection against hot corrosion. However, the service life of each blade is limited by damage due to embrittlement layer, which is formed by reaction diffusion at the interface between the coating and the substrate. Reaction diffusion behavior between the CoNiCrAlY coatings and substrates was investigated. In addition, high-temperature oxidation behavior of the CoNiCrAlY coating by LPS was evaluated. The CoNiCrAlY coatings for reaction diffusion test were carried out by 3 kinds of spray process (LPS, High Velocity Oxygen Fuel Spray: HVOF, Atmospheric Plasma Spray: APS) on 2 kinds of substrate (Directional Solidification and Single Crystal Ni-based super alloys). It has been found that the CoNiCrAlY coating by APS inhibited the reaction diffusion at the boundary of the coating and the base material as compared with LPS coating. It was also confirmed that the protective dense layer of aluminum oxide against hot corrosion was formed in the surface of the CoNiCrAlY coatings by LPS.