New insights into the formation mechanism of the multicomponent carbides (Nb, M)C (M = Ti, Cr and Mn)

Abstract

Combining first-principles calculations and classical nucleation theory, the results of elemental doping on the structure, electrons and stability of niobium carbides are investigated. Ti, Cr and Mn doping altered the physical characteristics of the carbides, resulting in lower mismatch strains and interfacial energies between the carbide and the substrate. Elemental doping reduced the critical nucleation size of carbides and contributed to the promotion of carbide nucleation. However, excessive doping with Cr and Mn increases the formation energy of carbides and unfavorable to carbide stabilization. Therefore, Cr and Mn are involved in the early elemental aggregation of carbides, while Ti and Nb are the main carbide-forming elements. The nano-precipitated phases of various compositions produced in niobium microalloyed steel were experimentally validated utilizing transmission electron microscopy (TEM) and three-dimensional atom probe tomography (3D-APT). The carbides primarily composed of Nb, Ti and C elements, with the presence of Cr and Mn in the core region leading to the formation of a core-shell structure, which is consistent with theoretical calculations.

Keywords

• Carbides
• First-principles calculation
• Core-shell structure
• Nucleation