Discontinuous Precipitation and Phase Stability In Re- and Ru-Containing Nickel-Base Superalloys

Abstract

The phase stability of nickel-base superalloys has been investigated using a new in-housedesigned alloy series with stepwise increased additions of Re and Ru at otherwise fixed atomic fractions of alloying elements. Results presented in this study are focused on the lesser-known topologically closed packed (TCP) formation of columnar colonies or so-called discontinuous precipitation. A detailed investigation of these colonies allowed for identifying compositional changes during the growth process and for providing a three-dimensional (3-D) illustration of the TCP phases within these colonies. The results were used to compare the colony growth process with existing growth models. Furthermore, the influence of Re and Ru on the appearance of discontinuous precipitation has been investigated by means of colony width and the effect on creep properties. Larson-Miller plots are given to illustrate the creep strength of directionally solidified samples with and without TCP colonies compared with single crystalline samples free from TCP colonies.

Formation of an Intermediate Layer Between Grains in Nickel-Based Superalloy Turbine Blades

“…[39][40][41] To reduce the energy of the grain boundary, the DP reaction can easily occur from the following reaction [22][23][24]42] :…”

Discontinuous Precipitation in Ni-Base Superalloys During Solution Heat Treatment

“…[2] It has been observed in the substrate beneath coatings [3][4][5] or on grain boundaries. [6][7][8] In all cases, there is the requirement of a super-saturated matrix, which provides the driving force for growth. [2] In multi-component Ni-base superalloys, DP morphology constitutes a polycrystalline colony comprising of c¢ matrix with/without c-lamellae and needle-like tetragonal close-packed (TCP) phases segregated in Cr, W, and Re, which constitute the precipitate.…”

“…[2] In multi-component Ni-base superalloys, DP morphology constitutes a polycrystalline colony comprising of c¢ matrix with/without c-lamellae and needle-like tetragonal close-packed (TCP) phases segregated in Cr, W, and Re, which constitute the precipitate. [3][4][5][6][7][8] The advancement of the DP zone occurs by partitioning of Cr, W, and Re to the growing tips of the precipitates along the grain boundary.…”

“…[6][7][8] (ii) Beneath an aluminized or Pt-aluminized surface coating-the reaction can be written as c + Al fi c¢ + TCP and in this case the DP zone is also referred to as the ''secondary reaction zone'' or SRZ. [3][4][5] It should be pointed out that DP is also referred to as ''Type II'' re-crystallization.…”

Misorientation effect of grain boundary on the formation of discontinuous precipitation in second and third generation single crystal superalloys

“…DP transformation is one type of microstructural instability of a grain boundary, it transforms γ -γ two-phase microstructure into γ -γ +TCP lamellar structure in Ni-based superalloys. The occurrence of DP on grain boundaries in Re-containing single crystal superalloys were reported in several studies [9][10][11][12][13][14]. DP transformation depletes the strengthening elements Re a Corresponding author: qfeng@skl.ustb.edu.cn and W in the γ matrix, resulting in microstructural and property degradation.…”