Influence of Carbide Distribution on Ductility of Haynes®282® Forgings

Abstract

Haynes ® 282 ® , a relatively new superalloy is used in gas turbines in form of sheets, plates and forgings. Forgings undergo a series of deformation steps at high temperatures to form complex shapes of components. The deformation on forgings, changes the microstructural features and their distribution, and any change in distribution of microstructural features can affect the mechanical properties of the material. The present study is undertaken to investigate the possible causes of anisotropy in mechanical properties of a Haynes ® 282 ® forging through optical and electron microscopy. Microscopic investigations show that ductility is anisotropic and changes from 15% to 21%. The electron backscattered diffraction (EBSD) investigation reveals that the presence of carbide stringers (banding of MC and M6C carbides) is associated with fine grains, thereby giving a bimodal distribution of grain size. Carbide stringers follow the complexity of forgings and are identified as the primary cause for the anisotropic behavior in ductility. Furthermore, micromechanical simulations of carbide stringers in association with a bimodal grain structure was seen to qualitatively correspond to the experimental observation indicating improved ductility with banding along the tensile axis

Dynamic and Post-Dynamic Recrystallization of Haynes 282 below the Secondary Carbide Solvus

“…One should also note that larger second phase particles may act to limit grain growth by grain boundary pinning [39], but due to the very sparse distribution of primary carbides in the present alloy this would only be effective much later, in the grain growth stage. At that point, however, it can have a large impact on the spatial grain size distribution, and if there are process related orientation of carbides (stringers) this may also affect the mechanical anisotropy of the final component [20,21].…”

“…Limited efforts have been made towards understanding the effects of prior thermomechanical processing steps, i.e., forging. Joseph et al [20,21] showed that alignment of primary carbides from forging can lead to inhomogeneous grain size distributions and anisotropy in the ductility. Gardner et al [22] applied multistep processing, and showed that SRX during interpass annealing is an important factor, but also that the effects of previous steps on the final microstructure is negligible if the processing conditions during the final step allows sufficient DRX.…”

Review of Microstructure–Mechanical Property Relationships in Cast and Wrought Ni‐Based Superalloys with Boron, Carbon, and Zirconium Microalloying Additions

“…The formation from refractory metals, such as Ti, Mo, and W, imparts their high thermal stability, while the NaCl or hexagonal crystal structure is embrittling. During hot deformation, various phenomena around MC carbides including fragmentation, [ 27,124,125 ] nucleation of recrystallized grains, [ 126,127 ] and Zener–Smith pinning [ 45,46 ] have been observed. M 6 C and M 23 C 6 are secondary carbides formed primarily via solid‐state phase transformations during thermo‐mechanical processing.…”

“…Preferences for carbide and boride formation, depending on a) C and B, b) Zr and B, and c) C and Zr contents. [ 12,26–28,40,47,48,54,56,57,63–65,80,81,104,106,108,111,137,143,221–224 ] For a more intuitive representation and a table of the used references, readers are referred to the supporting information.…”

Aging behavior of Haynes® 282® wrought nickel superalloy subjected to a cold pre-deformation by differential speed rolling

“…The effect of varying heat treatment parameters on the alloy's mechanical properties have been explored in numerous recent works (e.g. [5][6][7][8][9]). On the other hand, a very low attention has been given so far to the impact of a cold-straining processing [10] on structural and mechanical properties evolution upon the further aging treatment of nickel superalloys.…”