Microstructural evolutions and fracture behaviors of a newly developed nickel-base superalloy during creep deformation

The creep behaviors of the newly designed nickel-base superalloy M951G have been studied over a stress range of 120-760 MPa and a temperature range of 700 degrees C-1000 degrees C, and the corresponding relationship among testing conditions-microstructural evolutions and fracture characteristics-creep properties has been established. Results show that both the microstructural evolutions and fracture characteristics are dependent on testing temperatures and applied stresses. According to X-ray diffraction (XRD) examinations, creep deformations at 700-800 degrees C and high temperatures low stresses have not any distinctive effect on the acquired patterns. However, deformations at high temperatures relatively higher stresses have significantly highlighted the (220)(gamma &') planes, which may enhance the creep strength and lead to a better plasticity for M951G alloy. Furthermore, precipitate dimensional changes and their effects on creep properties also have been widely discussed. At the same testing temperature, creep life of M951G alloy decreases with applied stress increasing, which has been analyzed in detail. Fracture behaviors of M951G alloy are observed by using optical microscope (OM) and scanning electron microscope (SEM), which change from a mixed type of transgranular and intergranular to pure intergranular cracking with the variation of creep conditions. The values of apparent stress exponents at 700 degrees C and 1000 degrees C are calculated to be about 11.5 and 6.4 respectively, the difference of which is due to the changes of the deformation mechanisms, fracture modes and the degeneration of microstructures. (c) 2018 Published by Elsevier B.V.