Microstructural Subsequence and Phase Equilibria in an Age-Hardenable Cu-Ni-Si Alloy

Abstract

We investigated the microstructural subsequence and phase equilibrium of Cu-4.3 at% Ni-2.2 at% Si alloy specimens during isothermal aging over a temperature range of 698 K to 873 K. During aging in this temperature range, the microstructure of the specimens evolved in the following sequence; continuous precipitation of ne disk-shaped δ-Ni 2 Si in the matrix, discontinuous precipitation of cellular components containing coarse ber-shaped δ-Ni 2 Si at grain boundaries, and then occupation of the specimen with cellular components. By analyzing the variations in the hardness and electrical conductivity with aging time as well as temperature, we described the kinetics of the highest number density of ne δ-Ni 2 Si continuous precipitates. Based on the chemical analyses of the specimen in a phase equilibrium state using an extraction procedure, we proposed a revised solvus of solutes Ni and Si in the Cu solid solution phase, as well as Cu in the δ-Ni 2 Si intermetallic phase in a Cu-δ-Ni 2 Si pseudo-binary system. [

Aging Behavior and Precipitation Analysis of Cu-Ni-Co-Si Alloy

“…The strengthening mechanism of Cu-Ni-Si alloys includes solid solution strengthening, aging strengthening, and work hardening [12][13][14][15]. Since the strengthening power of this alloy is mainly due to the fine, dispersed Ni 2 Si that precipitated during the aging treatment, the strength and electrical conductivity are closely related to the distribution, number, and size of the precipitated phases.…”