Creep of Directionally Solidified Eutectics Ni/Ni3 Al-NbC under Thermal Cycling

A nickel-based eutectic alloy with a gamma/gamma'-NbC structure was directionally solidified with a planar front. The specimens were tested for creep under sawtooth thermal cycling in the temperature range from 600 to 1100 degrees C. It has been established that the lifetime under the conditions of thermal cycling is about five times shorter than it is predicted by the linear damage accumulation rule on the basis of results of isothermal creep tests. Faster creep under thermal cycling is caused by the rapid coarsening of the gamma/gamma' microstructure due to the periodic partial dissolution and reprecipitation of the gamma' phase in heating and cooling half-cycles.