On the Evolution of Primary Gamma Prime Precipitates During High Temperature and High Strain Rate Deformation and Subsequent Heat Treatment in the Ni-Based Superalloy, RR1000

Abstract

The microstructural evolution following compression and subsequent sub-solvus and supersolvus heat treatment was studied in the Ni-based superalloy, RR1000, typically used for rotor disc applications in aero-engines. For a low strain rate of 0.1 s À1 at close to solvus temperature, 1413 K (1140°C), the flow stress is constant. For larger strain rates of 1 and 10 s À1 at sub-solvus temperature, 1373 K (1100°C) dynamic re-crystallization (DRX) of c grains occurs during forging with accompanying stress decay. Incoherent primary c¢ precipitates form mainly via meta-dynamic re-crystallization (MDRX) at 1 s À1 and are as intergranular. For 10 s À1 , the coherently nucleated or existing precipitates present in the initial as-HIP condition become incoherent when the grain boundary sweeps past them during DRX and subsequent grain growth. The incoherent primary c¢ precipitates are mainly intragranular. During sub-solvus heat treatment at 1373 K (1100°C), dissolution of the incoherent precipitates occurs through coarsening of the coherent intragranular population with only sporadic incoherent precipitates remaining. The prior induced deformation (strain and strain rate) influences the evolution of precipitate morphologies during cooling following heating to super-solvus temperature. Using numerical simulations, a quantitative calculation of the different precipitate morphologies was carried out during slow cooling from super-solvus temperature, 1443 K to 1373 K (1170°C to 1100°C).

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

“…An additional important aspect to consider, which will be discussed more in detail later, is the occurrence of adiabatic heating during deformation which is important in terms of thermal activation. Due to the larger strains in the central region of the samples, the temperature at the center will be even higher than what was measured by the thermocouple at the surface, but according to finite element simulations for similar set-ups the difference is expected to be in the order of 10 • C [31,32].…”

Thermoelastic properties and γ’-solvus temperatures of single-crystal Ni-base superalloys

“…While in the literature there are disagreements as far as specific aspects of this cutting process are concerned, SX researchers from academia and industry believe that it is desirable to design alloys with a high c& -volume fraction, a high c& -solvus temperature and a chemical composition, which gives rise to high planar fault energies which affect the physical nature of APBs and stacking faults. The c&solvus temperature has been considered as especially important and has been highlighted as a reference temperature in many scientific and technological SX publications, e.g., [24][25][26][27][28][29][30][31].…”

Solving Recent Challenges for Wrought Ni-Base Superalloys

“…They precipitate preferentially at grain boundaries as a result of incomplete dynamic or meta-dynamic recrystallization of c grains during relatively high strain rate deformation on compacted powder at temperatures below T solvus . [19] In addition to billet grain size, it is necessary that forging temperatures (below the T solvus ) and strain rates are deployed that promote super plastic forming as a result of grain boundary sliding and recrystallization. As a general rule, the appropriate forging conditions are those that give rise to a strain rate sensitivity index m greater than 0.3 in the equation below, which correlates flow stress (r) as a function of strain rate (de/dt), in which K is a material constant.…”