The Enhancement Effect of Carbides on the Printability and Mechanical Properties of a Ni–Fe–Cr–Al–Ti Alloy Processed by Electron Beam Freeform Fabrication

The role of carbide in additive manufacturing of nickel-based superalloy is significant and debated. The Ni–Fe–Cr–Al–Ti alloys with different content of carbon were designed and prepared using electron beam freeform fabrication with nickel-based powder-cored wire. The influence of the in-situ forming carbides on the printability, microstructure, and mechanical properties of the alloys was investigated. The role of the in-situ forming carbides in the precipitation of the γ′ phase and its function in suppressing the cracking mechanism was explored. The results showed that the in-situ forming TiC precipitated along the grain boundaries with diverse morphologies including long strips, feathers, and fish bones. With the increase of the proportion of TiC precipitated phase, the distribution of carbides gradually presents a continuous network structure. Moreover, the microhardness and tensile strength of the deposited samples were increased. The alloy with the highest content of in-situ forming TiC shows the highest microhardness (464.9 HV) and tensile strength (967.5 MPa at room temperature, 646.8 MPa at 850 °C). Furthermore, the in-situ forming TiC inhibited the precipitation and growth of γ′ phase by consuming Ti element and reducing the precipitation temperature of γ′ phase. Consequently, the solid-state cracks induced by the γ′ phase transition stress were suppressed effectively, and the printability of the alloy was improved. The above results comprehensively elucidate the roles of the carbide in additive manufacturing of nickel-based superalloy.