Investigation of metastable γ′ precipitate using HRTEM in aged Cu–Be alloy

Plate-like precipitates in Cu–1.9Be alloy have been studied using high-resolution transmission electron microscopy (HRTEM). The metastable γ′ phase and its matrix orientation were determined in samples which were solutionized, after aging at 320 °C for 2, 6 and 72 h. The relationships were determined as follows: [0 1 1] Cu-matrix (α)//[0 0 1] precipitate (γ′) and (1 0 0)α//(1 0 0)γ′. The habit planes were determined to be the ( 3   1   1 ¯ ) and ( 2 ¯   1   1 ¯ ) planes of α for the γ′ phase. The angle between [1 0 0]γ′ and [2 0 0]α was found to be 6° and 6.5° for aging times of 6 h and 72 h, respectively. As the aging time increased, the length and width of the Cu–Be precipitates increased from 10–20 nm to 50–100 nm and 2–5 nm to 10 nm, respectively, along the trace of the habit planes.