Yafang Han

Thermal cycling behaviors of thermal barrier coatings on intermetallic Ni3Al based superalloy

Ni3Al based alloy IC6, a high performance cast alloy with approximately 14 wt.% Mo addition, has been developed for turbine blades and vanes of advanced aero-engines and other high temperature structural components. However, because of the high Mo content, during high temperature use, Mo will diffuse into the protective coating layer, which will affect the thermal cycling performance directly. In order to block the diffusion and improve the thermal cycling behavior of thermal barrier coatings (TBCs), a Si chemical gradient MCrAlY-Si bond coat was prepared by changing the Si content from 0.35 wt.% at the interface of substrate and bond coat to almost 0 near to the surface of the bond coat. For comparison, conventional two-layered structural TBCs with MCrAlY as bond coat were also prepared. The fabricated coatings were evaluated for the microstructures and the composition distribution properties, such as thermal stability and resistance to oxidation. For the bond coat without Si addition, Mo, content near the surface was higher than 7 wt.% after isothermal oxidation at 1373 K for 60 h and 12.5 wt.% after thermal cycling tested at 1373 K for 300 It (600 cycles). However, in the Si chemical gradient bond coat, only 0.4 wt.% Mo was detectable after isothermal oxidation at 1373 K for 100 h and approximately 0.66 wt.% after thermal cycling tested at 1373 K for 340 h (680 cycles)

Surface recrystallization of a Ni3Al based single crystal superalloy at different annealing temperature and blasting pressure

The effects of annealing temperature and grit blasting pressure on the recrystallization behavior of a Ni3Al based single crystal superalloy were studied in this work. The results show that the precipitation of the Y-NiMo phase occurs at 900 and 1000 °C, which precedes recrystallization. The initial recrystallization temperature was between 1000 and 1100 °C. Cellular recrystallization was formed at 1100 and 1200 °C, which consisted of large columnar γ′ and fine γ + γ′. The dendrite arm closed to the interdendritic region may act as nucleation sites during initial recrystallization by a particle simulated nucleation mechanism at 1280 °C. The size of the grains first turned large and then became small upon the pressure while the recrystallization depth increased all the time.

Rotating bending fatigue property of the Ni3Al-based single crystal superalloy IC6SX at 900°C

The high cycle fatigue behavior of a Ni3Al base single crystal superalloy IC6SX has been investigated at 900°C in this work. The specimens used for the fatigue tests were prepared by screw selection crystal method in a directional solidification furnace. The rotating bending fatigue tests were carried out at 900°Cin air, the stress ratio of R(σmax/σmin) was -1, and the rotating speed of the fatigue tests was 6500r/min(108Hz). The stress-fatigue cycle life (S-Nf) curve was obtained based on the fatigue tests, and the fracture surfaces were examined using scanning electron microscopy (SEM). It has been found that the median fatigue strength is 457.5MPa and the safety fatigue strength is 413.93MPa. And the fatigue fracture was composed of three different characteristic regions.

Research on the creep mechanism of a Ni3Al-based single crystal superalloy IC6SX under 980°C/205MPa

The Ni3Al-base single crystal superalloy IC6SX used in this work was prepared by spiral grain selection method. And the creep behaviors of the IC6SX alloys was studied systematically under 980°C/205MPa. The microstructure evolution, movement of dislocations, formation of the dislocation networks and dislocation configuration for the alloy during the creep process were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It has been found that the creep performance of the single crystal alloy IC6SX is excellent under the condition of 980°C/205MPa. The results showed the creep mechanism included dislocation slipping and diffusion for Ni3Al-based Single Crystal Superalloy IC6SX under 980°C/205MPa.