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

Abstract

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 (Laughlin and Cahn, 1975; Han et al., 2016; Datta and Soffa, 1976; Han et al., 2020; Huang et al., 2023; Soffa and Laughlin, 2004; Wang et al., 2021; Si et al., 2016; Markandeya et al., 2004; Nagarjuna et al., 2001) [1-10]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.