Hot deformation characterisation of Haynes-242

Ni-based superalloys are metallic materials with exceptional combinations of creep and oxidation resistance at high temperatures. Wrought alloys are hot formed at high temperatures and subsequently annealed and aged. The final mechanical properties of the alloys are a combination of the grain size generated during the process and the precipitation state after aging. In fact, precipitation phenomena are complex for these alloys, which contain up to 12 different elements in their compositions. This study will deal with the forming characteristics of Haynes 242. Prior to forming, usually by forging, the material has to be reheated and this initial thermal treatment can affect grain size. The reheating stage is defined by the temperature and soaking time at the selected temperature. The best combination of these two parameters has to warranty that forging will be performed above the solvus temperature of precipitates without promoting excessive grain growth. The initial part of the study will analyse the effect of different temperatures and soaking times on the grain size and precipitates. After reheating, forging operations are performed at different forming temperatures and strain rates. Forging conditions will be simulated by means of hot compression testing. Compression samples will be first reheated according to the optimal conditions defined in the first part of the study, and then compressed at different temperatures and strain rates. Hot flow curves will be obtained which will be used for the analysis of the hot flow behaviour of the alloy. Metallographic evaluation of the compressed samples will assess the evolution of the grain size during forming and the mechanisms taking place, i.e. dynamic recrystallization or dynamic recovery, according to the deformation parameters. These results will be useful for the assessment of hot deformation operations (reheating and forging conditions) for Haynes 242, leading to fine and homogeneous microstructures