Creep mechanism of a Ni-Co base wrought superalloy

Abstract

Ni-based wrought superalloys are widely used in the hot section of aircraft gas turbine engines for their capability in retaining strength and resisting creep, fatigue, and oxidation at elevated temperature. With the development of the newer generation turbine disk alloys, it is highly imperative for aircraft engine manufacturers to substantiate the use of the materials by conducting a thorough examination of their mechanical properties. As these components are subjected to elevated temperatures and complex stress state in the service process where time dependent creep is the primary deformation failure mechanism and life-limiting factor for the component, it is of great importance to evaluate the relationship between microstructure, creep behavior and the underlying creep deformation mechanism. Therefore, the main objective of the present research aims at investigating the fundamental relationship between external creep condition and internal creep deformation mechanism in a new wrought superalloy with low stacking fault energy (SFE). In order to study the influences of the loading stress level and temperature on the creep deformation mechanism, stress range of 345-840 MPa and temperature range of 650-815°C were selected to carry out the creep experiment. The results show that two kinds of γ' with different diameters distributed in the matrix and the larger one began to coarsen when the creep temperature increased to 725°C. Under creep temperature of 650°C, the formation of SF resulted from the shearing of γ' by dislocations dominated the creep deformation. When the temperature range was raised up to 725-760°C, SF and microtwins were the main microstructures after creep deformation. With further increasing the temperature and load, instead of accommodating only in the γ', the SF and microtwins penetrated the whole γ' and matrix area. When the temperature was increased to 815°C, the climb/bypass mechanism controlled the creep process. © right.