Effect of High Undercooling on Dendritic Morphology and Mechanical Properties of Rapidly Solidified Inconel X750 Alloy

The rapid dendrite growth kinetics of Inconel X750 alloy was explored under electromagnetic levitation and free fall conditions. The dendrite growth velocity of the primary γ phase varies as a double exponential function with undercooling (ΔT). The critical undercooling for the transformation of the primary γ phase from dendrites to equiaxed grains in electromagnetic levitation (EML) and drop tube (DT) experiments is similar. With comparable undercoolings, the grain size of γ phase solidified in the DT is much smaller than that in the EML owing to the effect of large cooling rate. As the undercooling continuously increases to 230 K, the phase constitution changes from γ and precipitated phases to single γ phase. Based on EDS and TEM results, the precipitated phase is confirmed as (Ti, Nb)C phase, and the γ/(Ti, Nb)C interface is semicoherent. The compressive and nanomechanical properties of Inconel X750 alloy solidified in EML experiments were also investigated. The results show that the elastic modulus of γ phase is smaller than that of (Ti, Nb)C phase. According to the compression tests, the elastic modulus of Inconel X750 alloy is improved by high undercooling. Interestingly, the elastic modulus decreases when the undercooling is larger than 230 K, which is attributed to the increasing solubility of Ti and Nb in γ phase and the disappearance of (Ti, Nb)C phase.