Revealing intermetallic strengthening in bainitic steel designed for nickel aluminide formation

BainNiAlCu steel was designed to achieve a cementite-free bainitic structure and susceptibility to the formation of intermetallic phases at elevated temperatures. Based on Transmission Electron Microscopy (TEM) observations, the intermetallic strengthening occurring in the bainitic ferrite matrix was revealed. The B2-ordered phase are rich in Ni, Al, and Cu, which indicates the growth of NiAl/Cu co-precipitates. The intermetallic phase was characterized by a spherical morphology and nanometer size. The micro-segregation of Ni, Al and Cu was observed at the boundaries of cementite particles and the bainitic matrix. The redistribution of atoms during the growth of carbides forms a heterogeneous nickel aluminide nucleation site. Intermetallic strengthening is a promising strategy for controlling the thermal stability of bainitic structures. The results of this research constitute fundamental knowledge regarding the design of ultra-fine, cementite-free bainitic steels subjected to intermetallic strengthening.