Crystallography and diffraction patterns of the precipitates in Cu-3 wt% Ti alloy

Cu-Ti alloys are candidates for replacing Cu-Be alloys owing to their excellent mechanical properties, bending properties, and stress relaxation resistance. However, the precipitation behavior of Cu-Ti alloys remains poorly understood. In this study, diffraction patterns, orientations, and morphologies of continuous and discontinuous precipitates in a Cu–3 wt% Ti (Cu-3Ti) alloy are investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). In the peak-aging condition, numerous rod-like nanosized continuous precipitates (CP) of β′-Cu4Ti are uniformly distributed in the Cu–3Ti alloy. The CP retain their tetragonal structure, and their orientation relationships with the matrix are determined as [001]Cu//[001]β' and (010)Cu//(310)β', exhibiting six variants. With increasing aging time, discontinuous precipitates (DP) of β-Cu4Ti grow at the grain boundaries, displaying an orthorhombic structure (a = 0.453 nm, b = 0.4342 nm, and c = 1.293 nm). The orientation relationships between the DP and the Cu-matrix are determined as [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]Cu//[501]β and (111)Cu//(010)β. Typical diffraction pattern models of the CP and DP in different directions were simulated, and the simulations were in good agreement with the experimental data.