Microstructure And Property Of A Containing 2% Ru Single Crystal Nickel-base Superalloy

In this paper, the containing 2%/free Ru single crystal nickel-base superalloys are designed, prepared, and heat treated under different regimes. By means of creep property tests, microstructure observation and analysis by SEM and TEM, and composition analysis by SEM/EDS, the influence of heat treatment and element Ru on the elements segregation extent of the crystal nickel-base superalloy is investigated. The deformation, damage and fracture mechanism during creep at moderate and high temperature of the 2%Ru single crystal nickel-base superalloy were investigated.The results show that, in the as-cast alloy, the elements segregated greatly in different regions. In the dendrite regions, elements Mo、Cr and W are enriched. While in the inter-dendrite regions, the elements Ru, Ta, Co and Al are enriched. The enhancement of solution temperature may reduce the segregation extent of the elements in the inter-dendrite / dendrite regions of the alloy, which may improve the creep resistance. During long-time aging treatment and creep property tests, a mount of TCP phases precipitated in the free Ru single crystal nickel-base superalloy. However, no TCP phase precipitated when adding 2%Ru to the alloy, and the addition of 2%Ru may greatly improve the creep properties of the alloy. In the temperature ranges of 1070℃ ~ 1100℃, while creep goes into the steady period, the activation energy is measured to be Q = 456.5kJ/mol. During creep at moderate temperature, the slipping of dislocations in the matrix and the shearing of dislocations into cubic γ′ phase are the deformation mechanisms of the alloy. In the latter period of creep under the condition of moderate temperature, the primary slipping system and the secondary slipping system are consecutively activated, which makes the micro-crack initiated and propagated on the interface of the γ′/γ phases, until to the fracture of the alloy, and the direction of γ′/γ phases interface is perpendicular to the stress axis. While creep at high temperature, in the primary period, the morphology of γ′ phase has transformed from cubic structure into rafted structure, and the direction of the rafted structure is vertical to the stress axis. During the steady creep period, the deformation mechanism of the alloy is identified to be the dislocations climbing over the rafted γ′ phase. In the latter period of creep at high temperature, dislocations may shear into the rafted γ′ phase, which is identified to be the principal deformation mechanism.During the latter period of creep, the micro-crack initiated on the interface of rafted γ′/γ phases, which is considered by the alternative slipping of dislocations. The micro-crack propagated along the interface of rafted γ′/γ phases until to the fracture of the alloy, and the direction of the rafted structure is vertical to the stress axis.