Thickness-dependent creep rate caused by climbing control of a superdislocation in a Ni-based single crystal superalloy

Abstract

Creep tests are carried out on Ni-based single crystal superalloy sheet samples with different thicknesses at 1100 °C/130 MPa. The results indicate that the secondary creep rate at constant stress exhibits a strong thickness dependence and increases with the decrease in sample thickness. Under load in [001] direction, two types of a<100> family superdislocations with Burgers vectors a[100] and a[010] enter γ′ rafts in thin samples, whereas only the type of a[100] superdislocation enter γ′ rafts in thicker samples. The density of a<100> superdislocations is higher in thin sheets than in thick ones. It is proved that the movement mode of a<100> superdislocations in γ′ rafts is pure climb according to non-compact dislocation core structure. In addition, the climb velocity of the a<100> superdislocations in thin samples is determined to be greater than that in thick ones caused by the fact that the a<100> superdislocations in thin samples experience a higher driving force. On these bases, it is revealed that more types of Burgers vectors, higher density and greater climb velocity of a<100> superdislocations in γ′ rafts contributes to higher secondary creep rate in thinner samples.