The effect of heat treatment on the microstructure and mechanical properties of Ni-base superalloy Haynes 282 was investigated. Applying a standard two-step ageing (1010 °C/2 h + 788 °C/8 h) to the as-received, mill-annealed, material resulted in a the presence of discrete grain boundary carbides and finely dispersed intragranular g´, with an average size of 43 nm. This condition showed excellent room temperature strength and ductility. The introduction of an additional solution treatment at 1120 °C resulted in grain growth, interconnected grain boundary carbides and coarse (100 nm) intragranular g´. The coarser g´ led to a significant reduction in the strength level, and the interconnected carbides resulted in quasi-brittle fracture with a 50 % reduction in ductility. Reducing the temperature of the stabilization step to 996 °C during ageing of the mill-annealed material produced a bi-modal g´ distribution, and grain boundaries decorated by discrete carbides accompanied by g´. This condition showed very similar strength and ductility levels as the standard ageing of mill-annealed material. This is promising since both grain boundary g´ and a bi-modal intragranular g´ distribution can be used to tailor the mechanical properties to suit specific applications. The yield strength of all three conditions could be accurately predicted by a unified precipitation strengthening model.

Precipitation of grain boundary carbides in a mill-annealed Haynes 282 in the temperature range 650 °C to 1120 °C was investigated. The kinetics of M23C6 was significantly faster than that of M6C. With increasing aging temperature, the morphology changes from continuous film to an interconnected brick wall structure and finally to discrete particles. No morphological changes were observed with aging time. Serrated grain boundaries formed during aging around 750 °C. The solvus temperature for both M23C6 and M6C was approximately 1100 °C.

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

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