Formation of a nanoscale two-phase microstructure in Cu–Zn( Al) samples with macroscopic concentration gradient

Abstract

In binary Cu Zn and ternary Cu–Zn–Al with 1.5 wt% Al, the formation of a nanoscale two-phase α + ordered β 2 microstructure is observed after quenching samples with a macroscopic solute concentration gradient from 875 °C in iced brine. The two-phase microstructure has formed from high temperature β phase and is located at higher Zn contents, after the concentration invariant massive or martensitic transformation, respectively. Its occurrence further substantiates the high competition between different types of solid-state reactions in brass. The nanoscopic α + β 2 microstructure was investigated by a combination of EBSD and TEM. Experimentally measured Kikuchi patterns were correlated with dynamically simulated ones by a pattern deconvolution which compensates the limitation of existing commercial EBSD software. The employed combination of methods revealed changing phase fractions of α and β 2 along the Zn gradient. Cellular reaction, coupled growth and spinodal decomposition were discussed as possible mechanisms for the formation of the nanoscale structure, with coupled growth identified as the most likely. • Combination of state-of-the-art EBSD and (HR)TEM analysis for phase identification • Determination of c-dependent phase fractions by a comparative study of measured and dynamically simulated Kikuchi patterns • Observation of nanoscopic α + β 2 microstructure in α/β brass in direct competition with massive/martensitic transformation • Classification of competitive solid state reactions depending on the level of undercooling classification of competitive solid state reactions depending on the level of undercoolings