Oxidation behavior of a single-crystal Ni-base superalloy between 900 and 1000 °C in air

Influence of micro-structure on corrosion behavior of a Ni-based superalloy in 3.5% NaCl

Thermal exposure specimens of K465 superalloy are carried out at 850, 950, 1000, 1050 and 1100 degrees C in order to investigate the stability of carbides. MC carbide is stable from 850 to 950 degrees C; M6C carbide is most stable above 1000 degrees C; M23C6 carbide appears in the 950-1000 degrees C temperature range. The rate of MC decomposition increases with the rise of thermal exposure temperature. Some M6C carbide particles, which are transformed from MC carbide, have irregular morphology and adhere to the original MC carbide; the other M6C carbide particles are precipitated in the forms of needle and tiny block. Furthermore, needle-shaped M6C carbide is the most prevalent and has the coherent relationship with the matrix. M6C and script-like MC carbide particles are detrimental to room temperature tensile and stress rupture properties of the alloy. M23C6 particles are precipitated in grain boundaries, but have little effect on the properties of the alloy because of their small amount. (c) 2006 Elsevier B.V All rights reserved.

Relative stability of carbides and their effects on the properties of K465 superalloy

This study investigates how carbon content affects the microstructure and elevated temperature tensile strength of fine-grain CM-681LC superalloy. Experimental results indicate that increasing the carbon content from 0.11 to 0.15 wt% increases the total area fraction of carbides considerably. However, the two alloys exhibit similar carbide shapes and sizes, probably because the short solidification time in the fine-grain process limits the growth of carbides. Besides, carbon addition significantly reduces the area fraction of γ–γ′ eutectic phases from 8.6 to 5.3% because the eutectic phase forming elements are consumed by (Ta, Hf)C carbides and the carbides occupy the position of γ–γ′ eutectic phases during the solidification. Further, the carbon addition improves the mechanical strength by about 6% and the elongation by about 50% in tensile tests at 760 °C and yields favorable tensile performance at elevated temperature.

https://ir.nctu.edu.tw:443/bitstream/11536/5248/1/000278766800016.pdf

The effects of carbon content on the microstructure and elevated temperature tensile strength of a nickel-base superalloy

Nickel-based superalloy Nimonic 80A with various carbon contents has been developed. Various strengthening mechanisms of carbon were analyzed by optical microscope, X-ray diffraction, scanning electron microscope equipped with energy dispersive spectroscopy and transmission electron microscope. Detailed microstructural analysis revealed that with the increase of carbon content from 0.01% to 0.10%, both the lattice parameters of γ′ and γ phases decreased, and the misfit δ between the coherent γ′ and γ phases increased slightly from 0.289% to 0.317% after full heat treatment at 1070 °C/8 h, A.C. + 700 °C/16 h, A.C. The diameter of spherical γ′ phase decreased from 22.24 nm of 0.01%C alloy to less than 15.76 nm of 0.06%C and 0.10%C alloys. Cr23C6 carbide precipitated at the grain boundary in the alloys with carbon content higher than 0.06%, and when carbon content increased to 0.10%, Cr23C6 carbide had an orientation relationship with the γ matrix: [ 00 1 ¯ ] Cr23C6 [ 00 1 ¯ ] γ matrix and ( 100 ) C r 23 C 6 (1 0 0) γ matrix, which can enforce the grain boundary strength. The growth of room temperature tensile strength with the increase of carbon content was primarily due to the coherent strain strengthening and the precipitate strengthening of Cr23C6 carbide. After stress-rupture test at 750 °C/310 MPa, the misfit δ increased from 0.182% to 0.237% with the increase of carbon content, but the values were lower than those after full heat treatment. The precipitate of blocky Cr23C6 in 0.10%C alloy tended to become spherical and dislocation lines were found in the γ matrix channels between γ′ phases, the combination of the dislocation strengthening and precipitate strengthening of Cr23C6 carbide at grain boundary was beneficial to the stress-rupture properties.

C.Y Jo

Papers

Formation of MC-γ/γ' eutectic fibers and their effect on stress rupture behavior in D/S Mar-M247LC superalloy