Thermal stability of Ni-Mn electrodeposits

Abstract

The effect of Mn additions on the structural stability of electrodeposited Ni is investigated by comparing the microstructure evolution of Ni and Ni-Mn specimens with similar crystallographic initial textures. As deposited, Ni-Mn electrodeposits have a smaller crystallite size and substantially higher yield strength than Ni deposits, in agreement with the Hall-Petch relationship. Moreover, dilute Ni-Mn electrodeposits exhibit a thermal stability that significantly exceeds that of pure Ni. Indeed, Ni-Mn retains its texture, fine-grain microstructure, and strength above 500°C (for 1 h anneal), and does not recrystallize up to 800°C. In contrast, pure Ni with larger average grain size and similar preferred orientation shows abnormal grain growth at 300°C and recrystallization at 600°C. This study suggests two distinct temperature regimes. Below 600°C, grain boundary segregation appears as a plausible mechanism for the thermal stability of Ni-Mn electrodeposits, whereas grain boundary pinning by precipitation contributes to the improved microstructural stability of Ni-Mn above 600°C. © 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.