Microstructural evolution and microhardness variations in a Cu–36Zn–2Pb alloy processed by high-pressure torsion

A coarse-grained Cu–36Zn–2Pb alloy with an initial grain size of ~54 μm was processed by high-pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa through 1–10 turns, and the evolution of microstructure and microhardness was investigated. Analysis by X-ray diffraction (XRD) showed that in HPT processing the β′-phase transforms to an α-phase and a {111} texture is formed. Microscopic examination showed that dislocations were first formed at equivalent strains of not more than ~25 and when the equivalent strain increased to ~40 there was evidence for twins and secondary twinning. Fine grains were formed with an increase in equivalent strain to ~100 and with further straining these refined grains acted as precursors for additional grain refinement. The refined equiaxed grain size was ~250 nm after HPT through an equivalent strain of ~100 and the results show the microhardness reached a saturation value of ~220 Hv.