High-Temperature Dislocation Climb in the γ′ Rafts of Single-Crystal Superalloys: The Hypothesis of a Control by Dislocation Entry into the Rafts

Abstract

The good mechanical resistance to high temperature creep of [001] oriented single crystal superalloys is due to the properties of the rafts, i.e. platelets of the L12 γ' phase embedded in a γ matrix. At temperatures higher than 900°C, the plastic strain of the rafts results from the climb of dislocation pairs with a total. < 100 > Burgers vector and/or from the climb at the γ/γ' interfaces of 2 ⁄. < 110 > dislocation segments. This climb motion involves the exchange of vacancies between these dislocations and vacancy sinks such as pores and the specimens' surfaces. In this paper we suggest that the entry of. < 100 > into the rafts requires the overcoming of a threshold stress and show that this hypothesis gives a natural explanation to some of the most salient aspects of their mechanical behavior.

Defect Creation in the Root of Single-Crystalline Turbine Blades Made of Ni-Based Superalloy

“…The mono-vacancy concentration determined by the PALS method applied to both equilibrium vacancies and non-equilibrium vacancies. Non-equilibrium vacancies may be related to the heterogeneity of chemical composition and occurrence of pores or dislocations [31]. The differences in the concentration of mono-vacancies in areas 1, 2, and 3 were related to the change of non-equilibrium defects only, assuming that in the macroscopic areas of 1, 2, and 3, where the positron source was active, the average macroscopic chemical composition and temperature were the same.…”

“…The dendritic segregation of alloying elements is one of the reasons for the heterogeneity concentration of vacancy-type defects. The heterogeneity of vacancy-type defects concentration, especially the vacancy clusters, may be related to the pore distribution in as-cast blades [31]. Exceeding the critical concentration of the vacancies in the γ phase may cause creation of undesirable TCP phases [30,32].…”

Dislocation Densities and Velocities within the γ Channels of an SX Superalloy during In Situ High-Temperature Creep Tests

“…At high temperatures the hard phase deforms by dislocation climb [ 7 , 8 , 9 ], while the softer channels are plastically deformed by a glide of the usual fcc <110> {111} dislocations [ 10 ]. The high symmetry of the [001] tensile axis results in eight of the 12 available slip systems being equally active.…”