Microstructure evolution of an Inconel 718 alloy prepared by electron beam smelting

A new electron beam smelting technology was employed to prepare the Inconel 718 alloy, and the microstructure evolution and nucleation and coarsening mechanisms of gamma', y '' and delta phase of this alloy was investigated. The microstructures can be refined by means of electron beam smelting, and good microstructure stability is observed at 700 degrees C, which is at least 20 degrees C beyond the limiting temperature that Inconel 718 alloy can sustain for prolonged periods. The gamma' and gamma '' precipitates could be formed in less than 1 h when aged at 700 degrees C and 800 degrees C, in which the coarsening of gamma' follows the conventional Lifshitz-Wagner theory, while the gamma '' follows the Lifshitz-Slyozov encounter Modified theory. When thermal aged at 900 degrees C, both gamma' and gamma '' precipitates are absent. The nucleation of delta phase is arised from the stacking faults in gamma '' precipitates induced by formation of a/6 < 211 > Shockley partial dislocations or the lattice distortion when thermal aged at lower temperature. While at higher temperature, the arrangement of a/2 < 110 > matrix dislocations is responsible for the nucleation of delta phase. The coarsening of delta phase is discontinuous during prolonged exposure. The growth rate of the delta lath is controlled by the coarsening in lengthwise direction at first, and then by the intermittent growth in both length and width direction at lower temperature. While for the delta phase nucleated from the matrix, the growth of delta lath is determined by its thickening firstly, and then the coherent growth occurs along the length direction with aging proceeding

Automated summary

The new electron beam smelting technology was used to prepare Inconel 718 alloy and investigate the microstructure evolution and nucleation and coarsening mechanisms of the gamma', gamma'', and delta phases. Good microstructure stability of the alloy was observed at 700 degrees C, with refinement of microstructures achieved. Nucleation and coarsening mechanisms of various phases were found to be influenced by temperature and dislocation arrangements.