Influence of direction of notch on thermal fatigue property of a directionally solidified nickel base superalloy

Thermal fatigue property of a directionally solidified nickel base superalloy at the condition of different notched orientation and upper temperatures was investigated. The results show that cycle numbers of crack initiation decrease, propagation rate of crack increases and resistance of thermal fatigue reduces with the rise of upper temperature. Thermal fatigue property of the specimen with the notched direction vertical to orientation of dendrite growth (DZ319T) is superior to that of the specimen with the notched direction parallel to orientation of dendrite growth (DZ319L). DZ319L alloy initiates thermal fatigue crack by carbide and propagates along the direction of carbide distribution, which resultes in big propagation rate and poor thermal fatigue property. Crack initiation of DZ319T alloy is mainly by oxidized cavity. The join of oxidized cavity makes crack propagate. There are two cracks in DZ319T alloy, which greatly drops the stress concentration near the notch and decreases the propagation rate of crack. DZ319T alloy has excellent thermal fatigue property.