Analytical Electron Microscopy Investigation of Topologically Close-Packed Phases in CMSX-4 Single Crystal Superalloy

Abstract

In this work the topologically close-packed phases precipitated during annealing of CMSX-4 single-crystal superalloy at temperature 1100• C were investigated. Microstructural analyses were carried out by means of scanningand transmission electron microscopy as well as scanning-transmission electron microscopy in high angle annular dark field mode. Chemical composition in nanoareas was determined using energy dispersive X-ray spectroscopy. Scanning electron microscopy investigation has shown that the topologically close-packed precipitates were formed already after 50 h of annealing at temperature 1000• C. With prolongation of the annealing time up to 2500 h the change of the morphology of topologically close-packed particles from blocky to needle-like occurred. Selected area electron diffraction analysis indicated that the topologically close-packed precipitates are the orthorhombic P phase. Quantitative energy dispersive X-ray spectroscopy analysis revealed that the topologically close-packed precipitates are enriched mostly in Re and W.

Analytical Electron Microscopy Studies of the CMSX-4 Single Crystal Superalloy Subjected to High Temperature Annealing

“…1B,C. The microstructure and chemical composition of TCP phases was the subject of our previous work [12]. We have demonstrated the compositional variations of γ, γ and TCP phases for the as-received condition and annealed at 1100…”

“…Although Ta is γ -forming element, in the present study the increase of its concentration in γ phase was observed with prolongation of the annealing time. Additionally, in our previous work the contribution of Ta to the formation of TCP phases in CMSX-4 was revealed [12]. Therefore it may be suspected that the diffusion of Ta also plays an important role in the microstructural instability of CMSX-4 superalloy at high temperature.…”

“…During prolonged exposure at high temperature the coagulation of γ phase occurs. The evolution of the γ phase in SC nickel-base superalloys was the subject of many studies [4][5][6][7][8][9][10][11][12]. Especially, the directional coagulation under the influence of external stress, generally known as rafting, was studied in detail in many superalloys [4][5][6][7][8].…”

“…Especially, the directional coagulation under the influence of external stress, generally known as rafting, was studied in detail in many superalloys [4][5][6][7][8]. However, reports on the γ evolution during annealing without the external load are very limited [9][10][11][12]. The preferentially-oriented plates of the γ phase formed at high temperature without applied stress was observed first by Hazotte and Lacaze [9].…”

Characterization of the μ and P phase precipitates in the CMSX‐4 single crystal superalloy

“…In our previous works on the chemical composition of the TCP phases in CMSX‐4 subjected to high temperature annealing (Dubiel et al ., ), as well as annealing followed by creep deformation (Dubiel et al ., ), based on STEM‐EDS microanalysis results, it was confirmed that the P and μ phases are rich in W and Re. The differences in the W and Re concentrations in both phases were less than 5 at.…”