Study on the Metallurgical Mechanisms of Inclusions in the Fgh4096 Alloy During Electron Beam Smelting

Abstract

In this study, the metallurgical mechanisms of inclusions during electron beam smelting of a FGH4096 powder superalloy was investigated. The macroscopic morphology of electron beam melting ingots and the composition and structure of inclusions, and the effect of melting parameters on the cooling rate, O/N content, number density and size of inclusions have been comprehensively studied and compared. Thermodynamic calculations were done on the mechanism of inclusions removal during melting and the formation of inclusions during solidification. The results show that the final solidification zone accumulates Al2O3, TiN, and CrO2 due to the influence of Marangoni flow, whereas the inclusions in the matrix are mainly multi-layer complex inclusions with Al2O3 core and double-layer carbon nitride with TiN core. Thermodynamic calculations show that Al2O3 precipitates when in the solid-liquid two-phase region. As the temperature decreases, TiN precipitates after solidification of the alloy, which is higher than the precipitation temperature of TiC. It reveals the formation mechanism of multilayer structure of complex inclusions and carbon nitrides. With the increase of melting power and time, the cooling rate and O/N content were decreased, and the smelting power has a greater impact on the cooling rate. With the increase of power, the number density of total inclusions increased, and the sizes of complex inclusions and carbon nitrides increased and then decreased. With the increase of melting time, the number density of total inclusions decreased, and the sizes of complex inclusions and carbon nitrides increased. According to the formula for inclusion growth, this phenomenon can be attributed to the combined influence of cooling rate and O/N content. It provides a theoretical basis for electron beam metallurgy.

Keywords: Electron beam smelting, FGH4096, Inclusions, Oxygen and nitrogen