Abstract
Leaded brass alloys with high zinc content are classified as dual-phase (α-β′) brass alloys. For these alloys, α-β′ phase transformation induced by thermomechanical processing (TMP) is expected to play a significant role not only in the formation of α and β′ phases and uniformity of lead particles but also in the development of Σ3 boundaries and their variants in the α phase. To assess such impact, the current study has employed two TMP schemes, with each scheme consisting of four cycles of compression and annealing. Samples of the first scheme (TMP-1) were annealed at 670 °C to promote phase transformation from α to β′, as compared to the second scheme (TMP-2) samples annealed at 525 °C. Microstructure examination indicated that TMP-1 scheme fostered a remarkable growth in the area fraction of β′ phase, accompanied by grain coarsening of α and β′ phases. This resulted in the isolation of α grains and less interaction of Σ3 boundaries at trip junctions, and therefore, a reduction in the fraction of Σ3 boundaries occurred in the α phase. On the other hand, the TMP-2 scheme successfully enhanced cluster formation of α grains, enabling further generation of Σ3 boundaries via strain-induced boundary migration mechanism and ultimately leading to breakup of the random boundary network. In addition, the two schemes resulted in limited coarsening of lead particles. Most lead particles were located at the α-βʹ interfaces, which suppressed grain boundary migration via the particle-dragging effect. For both TMP schemes, the initial texture of tension fibers was largely preserved after four cycles for both α and βʹ phases. Nevertheless, the TMP-2 scheme produced texture randomization of the α phase due to increasing the fraction of Σ3 boundaries.
Highlights
Thermomechanical processing (TMP) has been effectively applied for the production of grain boundary engineering (GBE) structure in fcc metals of low stacking fault energy (SFE)
The current study aims to examine the microstructure development in leaded brass alloys, α-β brass alloys, using repetitive TMP
From the works mentioned above, it can be deduced that the random distribution of β grains and the formation of lead particles at grain/interphase boundaries in the initial structure of the leaded brass rationalize the slight grain coarsening in the α phase for samples processed by TMP-2 scheme
Summary
Thermomechanical processing (TMP) has been effectively applied for the production of grain boundary engineering (GBE) structure in fcc metals of low stacking fault energy (SFE). A study by Lee et al [16] examined the grain boundary characteristics in a two-phase (α + β ) brass alloy using repetitive TMP of cold rolling (20%) and annealing (680 ◦C), indicating an increase in the fraction of Σ3n boundaries in the α phase to a maximum of 78%. The increase in TMP cycles promoted the formation of new grains of α phase, annealing twinning in the newly formed α phase, and coarsening of microstructure This was found to increase the fraction of Σ3n boundaries in the α phase. Increasing the area fraction of β phase and refining α grains can create more prolonged interphase boundaries, significantly expanding the formation of lead particles at these high-energy interfacial sites. The formation of CSL boundaries in α and β phases was evaluated using electron backscattered diffraction (EBSD)
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