Effects of heat treatment on the microstructure evolution and the high-temperature tensile properties of Haynes 282 superalloy

The effects of heat treatment conditions on the microstructure and the deformation behavior of Haynes 282 superalloy in tension at 750 °C were investigated. The standard 2-step aging heat treatment (1010 °C/2 h + 788 °C/8 h) was compared to alternative, more economical, 1-step aging treatment (800 °C/4 h). Moreover, three different cooling rates from the solution temperature of 1135 °C were studied to represent the effective cooling rates that large-scale components may experience. Regardless of the heat treatment conditions, as much as about 20% of fine spherical intragranular γ' particles were successfully precipitated with an average size between 12 nm and 39 nm. The average γ' particles size increased as the cooling rate from the solution temperature decreased. All four heat-treated alloys exhibited good mechanical properties at the high temperature of 750 °C with a yield strength in particular well over 620 MPa. As it could be expected, the yield strength increased and the ductility decreased as the average γ' particles size decreased. The alloys exhibited a mixed mode of deformation characterized by shearing and bypassing. However, the dominant deformation mechanism depended on the γ' characteristics resulting from different heat treatment conditions: only 1-step aged specimens with the largest γ' particles of 39 nm size, which was furnace-cooled from solution temperature, exhibited a plastic behavior typical of a dislocations shearing mechanism while the other alloys showed primarily an Orowan dislocations bowing and looping mechanism behavior. The major operative deformation mechanism could be well predicted by strength increment calculations based on the precipitation strengthening model. Our results suggest that wrought Haynes 282 produced by a more economical 1-step aging treatment may be a reliable candidate for high temperature applications under advanced ultra-super-critical (A-USC) conditions.