Multiple cycles of combined cold rolling and short-time annealing on the microstructure and properties evolution of NiAl bronze

Abstract

In this study, three cycles of combined cold rolling and annealing (CRA) were applied to study the mechanical behavior of NiAl bronze (NAB) alloy. The underlying mechanisms for microstructure and mechanical properties were elucidated. Microstructure characterization and quantitative analysis demonstrated significant morphology changes by CRA. The results showed that large α-Cu phase is compressed, lamellar κIII phase is broken and sphericalized, and κII phase accumulates and forms a hard phase band skeleton. Finally, the microstructure with spheroidized κIII phase embedded in the skeleton of the κII phase is obtained. The optimal ultimate tensile strength of 903 MPa and yield strength of 596 MPa are obtained after one cycle of CRA, which exhibits an improvement of about 40 % and 130 % compared to the as-cast samples, respectively. The best ductility of 18.0 % is obtained after three cycles of CRA, with an improvement of about 75 % over the as-cast samples. The high strength is mainly attributed to the grain refinement and high density of dislocations. Additionally, the higher density of low-angle grain boundaries can promote the formation and growth of twins. The saturation fraction of twin boundaries in experimental alloys of about 66 % is achieved after two cycles of CRA.