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′-Cu4Ti with fine needle-shaped precipitates continuously form in the matrix phase. Cellular discontinuous precipitates composed of the stable β-Cu4Ti 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.
Highlights
Age-hardenable Cu–Ti alloys have gained considerable attention for application in electrical devices such as micro-connecters and relay controls because of their excellent mechanical strength, stiffness, stress-relaxation, and good electrical conductivity
The purpose of this study is to investigate the effects of the distribution of elemental B in the matrix on the microstructural evolution during aging
The microstructural evolution of the quenched Cu–4Ti–0.03B alloys revealed that the B dopant was preferentially located at the grain boundaries of the supersaturated solid-solution phase
Summary
Age-hardenable Cu–Ti alloys have gained considerable attention for application in electrical devices such as micro-connecters and relay controls because of their excellent mechanical strength, stiffness, stress-relaxation, and good electrical conductivity. The disordered Ti-rich region becomes ordered, and continuously transforms to fine, needle-shaped, metastable, and coherent precipitates, which are denoted as β′-Cu4Ti and have a tetragonal structure (prototype: Ni4Mo; space group: I4/m; lattice parameters: a = 0.583 nm, c = 0.362 nm) in the matrix phase. Coarse, cellular, and discontinuous precipitates, which are composed of the stable intermetallic phase and the terminal copper solid-solution, nucleate and grow in the grain boundaries, consuming the finely dispersed, continuous precipitates of β′-Cu4Ti particles [9,10,11,12]. The fine dispersion of fine continuous precipitates (β′-Cu4Ti) contributes to the excellent mechanical properties of age-hardenable Cu–Ti alloys. The formation of cellular discontinuous precipitates should be suppressed in order to improve the mechanical properties and reliability of the age-hardenable Cu–Ti alloys
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