Precipitation and tensile behaviors of Allvac 718Plus superalloy during long-term thermal exposure

Allvac 718Plus alloy is a promising Ni-based superalloy with excellent thermal stability and mechanical properties up to 704 degrees C. The gamma ' coarsening, a precipitation and the resulting degraded tensile properties at room and elevated (704 degrees C) temperatures during long-term thermal exposure at 704 and 760 degrees C are systematically investigated in this work. The results showed that a higher exposure temperature and a longer exposure time significantly accelerate the gamma ' coarsening and a precipitation. The a particles were detrimental to the alloy by acting as the preferential nucleation sites for cracks, and the reduction in tensile strengths was mainly caused by the increasing size of gamma ' precipitates during thermal exposure. Furthermore, there were significant differences between the deformation mechanisms of room-temperature and elevated-temperature (760 degrees C) tensile tests. Concerning the deformation mechanism of gamma-matrix, planar slipping dominates during tensile testing at room temperature, while the formation of stacking faults and microtwinning are primary during tensile testing at elevated temperature (760 degrees C). The dominant precipitation strengthening mechanism depended on the gamma ' characteristics of different thermal exposure conditions and the tensile temperature. The 704 degrees C/100 h exposure sample shows a dislocation shearing mechanism when tested at room or elevated (760 degrees C) temperature. Notably, the 760 degrees C/1000 h exposure sample exhibits a mixed precipitation strengthening mechanism of Orowan bypassing and superlattice stacking faults shearing when tensile tested at room temperature while showing a dislocation and superlattice stacking faults shearing mechanism when tensile tested at elevated (760 degrees C) temperature.