Hardening mechanisms in stainless steel/aluminum bronze composite fabricated using electron beam additive manufacturing

Abstract

The authors investigated the features of structural-phase state of a composite based on stainless austenitic steel with addition of 25 % (vol.) aluminum bronze. The composite was obtained by electron beam additive technology with simultaneous feeding of two wires. The paper considers analysis of the structural-phase state and mechanical characteristics. The contributions of various mechanisms to the composite hardening were evaluated. It was established that a multiphase structure is formed in the steel – 25 % bronze composite, which consists of 43.9 % austenite, 32.0 % ferrite and 24.2 % bronze. Dispersion-hardened copper particles are isolated in austenite grains, volume fraction of which counts 47 %. Dispersion-hardened NiAl particles with a volume fraction of 20 % are isolated in ferrite grains. Transmission electron microscopy data indicate a coherent conjugation of arrays of dispersion-hardened particles with the matrix. Such a composite structure provides an increase in the tensile strength by an average of 50 % compared to austenitic steel obtained by electron beam additive technology without the addition of aluminum bronze. It was found that the contributions of various hardening mechanisms to yield strength of austenite, ferrite and bronze amounted to 959.3, 972.7 and 408.7 MPa, respectively. Bronze grains do not make a significant contribution to increase in yield strength of the composite, except for its increase due to dislocation hardening. The main contributions to increase in the composite yield strength are made by austenite grains due to grain-boundary, dispersion and dislocation hardening and by ferrite grains due to grain-boundary, solid-solution and dislocation hardening.