Electron beam additive manufacturing of composite alloy from stainless steel and aluminum bronze: Microstructure and mechanical properties

Abstract

The authors investigated the microstructure, phase composition and mechanical properties of the steel-bronze composite obtained by electron beam additive manufacturing with simultaneous supply of aluminum bronze wires BrAMc9-2 and stainless steel 06Kh18N9T. X-ray diffraction analysis revealed that the composite contains 25 % (vol.) of aluminum bronze, which leads to the formation of a three-phase structure consisting of γ-Fe, α-Fe and α-Cu grains. According to scanning electron microscopy, the volume fraction of austenite, ferrite and bronze in the steel – 25 % bronze composite is 40.7, 35.7 and 23.6 %, respectively. Unstable conditions of the electron beam additive manufacturing process lead to the release of dispersed particles in austenite and ferrite grains. Dispersion-hardened copper particles with an average particle size of 40 nm, the volume fraction of which is 47 %, are isolated in austenite grains. Dispersion-hardened NiAl particles with a volume fraction of 20 % are isolated in ferrite grains, the average size of which is 44 nm. Transmission electron microscopy data indicate the coherent conjugation of arrays of dispersion-hardened particles with the matrix. Such a composite structure provides an increase in yield strength and tensile strength by an average of 400 and 600 MPa compared with yield strength and tensile strength of 06Kh18N9T steel obtained by electron beam additive manufacturing without bronze addition. Microhardness of the composite is on average 2.2 GPa, which is 0.4 GPa higher than that of 06Kh18N9T steel obtained by electron beam additive manufacturing without bronze addition.