Features of the Macro-, Micro-, and Fine Structure of the Nickel Superalloy Product Material Formed by the Method of Electron Beam Additive Manufacturing

Abstract

In the present work, the products in the form of vertical walls were made of heat-resistant nickel-based superalloy ZhS32 via the method of electron beam additive technology. Unidirectional printing strategy was applied. The effect of heat input and 3D printing strategy on the macrostructure, dimensions, and morphology of microstructure elements was established. It was shown that the additive product material has a directed macrostructure. The only exclusion was the final layer with a thickness of no more than 3.5 mm. The directed macrostructure consisted of dendrites oriented predominantly along the crystallographic direction {001} of the primary dendrite arms. The misorientation of the dendrite axes did not exceed 9 degrees. The angle between the predominant dendrite growth direction and the normal to the substrate was 23 degrees. The average primary dendrite arms’ spacing increased monotonically from 16 µm at 5 mm from the substrate to 23 µm in the final layers of the product material (the overall height was 41 mm). It was found that the average size of γ’ (Ni3Al)-phase precipitations in the form of nanoscale and submicrocrystalline cuboids varied in the range of 76 to 163 nm depending on the distance from the substrate. The size of γ’-phase precipitations reached a maximum at about 30 mm from the substrate, while in the final layers of the product material, the average cuboid size did not exceed 135 nm. Extreme dependence of the size of γ’-phase precipitations on the height of the product followed from a combination of a given monotonic decrease in heat input and heat accumulation in the product material as it formed, as did additional heat removal by means of radiation during formation of the final layer of the product without re-melting. Chemical elements of the austenitic steel substrate material were not detected in the product material more than 8 mm from the substrate. There were no macrodefects, such as voids, in the entire volume of the product material.