Study of thermal cycling effects of Al–Ni turbine blades on their lifetime

Five Al–Ni alloys containing 14, 28, 36, 43 and 52 wt.% Ni were melted using an induction furnace in a stream of argon and cast to prismatic-shaped specimens. Thermal fatigue tests were carried out by heating the specimens using an oxyacetylene flame up to the test temperatures ranging from 400 to 700°C and then cooling down to approximately 150°C in an air draft. The heating and cooling cycles were for 25 s. Test results showed that the hardness of the alloys increased with increasing nickel content. The thermal fatigue resistance almost decreases with increasing cyclic temperature range ΔT. The specimens contained different percentages of Al3Ni and Al3Ni2. It is shown that if the material possesses good ductility, failure is governed by the resistance to cyclic plastic strain. This is true for the alloys having a nickel content of up to 36 wt.%. If the material has high strength, failure is governed by the resistance to cyclic elastic strain. This is true for the alloys having a nickel content of greater than 36 wt.%. Increasing the nickel content decreases the thermal fatigue resistance, due to an increase in the percentage of Al3Ni. Further increase in the nickel content (alloy Al–52 Ni) enhances the thermal fatigue resistance due to the higher percentage of Al3Ni2.