Effect of boron doping on cellular discontinuous precipitation for age-hardenable Cu-Ti alloys

Abstract

The effects of boron doping on the microstructural evolution and mechanical and electrical properties of age-hardenable Cu-4Ti (at.%) alloys are investigated. In the quenched Cu-4Ti-0.03B (at.%) alloy, elemental B (boron) is preferentially segregated at the grain boundaries of the supersaturated solid-solution phase. The aging behavior of the B-doped alloy is mostly similar to that of conventional age-hardenable Cu-Ti alloys. In the early stage of aging at 450 °C, metastable β'-Cu 4 Ti with fine needle-shaped precipitates continuously form in the matrix phase. Cellular discontinuous precipitates composed of the stable β-Cu 4 Ti and solid-solution laminates are then formed and grown at the grain boundaries. However, the volume fraction of the discontinuous precipitates is lower in the Cu-4Ti-0.03B alloy than the Cu-4Ti alloy, particularly in the over-aging period of 72-120 h. The suppression of the formation of discontinuous precipitates eventually results in improvement of the hardness and tensile strength. It should be noted that minor B doping of Cu-Ti alloys also effectively enhances the elongation to fracture, which should be attributed to segregation of B at the grain boundaries.