EFFECT OF ALLOYING ON SUPERPLASTICITY OF TWO PHASE BRASSES – DIFFUSION
Superplasticity is an ability of fine-grained materials (usually, with grain size less than 10 µm) to show large neck-free elongations during deformation at high temperatures (usually T=0.5 T melt) prior to failure due to high strain rate sensitivity of flow stress.
However, in the process of superplastic deformation (SPD) of two component brass intense grain growth occurs and considerable porosity develops. The porosity can be a consequence of grain boundary sliding (GBS), which is the main deformation mechanism for most alloys. In this case, pores arise in triple junctions and at shelves of grain boundaries because of growth in places where applied stresses concentrate and dynamic grain growth occurs; features of accommodation processes include diffusion and dislocation creep.
Superplastic deformation parameters of the brasses with different compositions were compared. It was shown that alloying by Aluminium and Tin increases the superplastic elongations and decrease cavitations.
Superplastic deformation mechanisms and diffusion characteristics of two components and multi-components brasses have been investigated in the current study. Effect of additional alloying elements on superplastic deformation behaviour and diffusion parameters was analysed. Diffusion characteristics were investigated by creating two diffusion couples using bars of brasses as the cores, with tungsten wires stretched along the lengths, and then a layer of pure copper. Samples were annealed at 550°С in a carbon rich atmosphere and quenched with microstructure analysis done at varying intervals of time.