The The effect of iron on precipitation hardening in the Cu-Ni-Mn alloys

Abstract

The peculiarities in the structure and properties formation of precipitation-hardened Сu–Ni–Mn–Fe alloys within the concentration range of Ni (19.3–21.0 %), Mn (19.5–20.5 %), Fe (0.6–2.7 %), Cu – balance (in wt. %) were investigated in this work. The methods of quantitative metallography, X-ray analysis, scanning electron microscopy, energy-dispersive spectroscopy and differential thermal analysis were applied. Two solid solutions based on a-Cu differing in composition and hardness were found in the structure of the cast Сu–Ni–Mn–Fe alloys. The temperature ranges of solutions’ formation were determined as (1010±10) °С and (890±10) °С, correspondingly. NiMn phase was also formed at (405±15) °С due to precipitation hardening. In the Сu–Ni–Mn–Fe alloys annealed at 500 and 900 °С for 60–750 hours, the volume fraction and size of NiMn precipitates increased with prolonging annealing time and lowering annealing temperature. As iron content was raised up to 2.7 wt. %, the density of NiMn precipitates increased, especially during first 60 hours of annealing at 900 °С. By adding iron, oxidation resistance was improved, but melting temperature and fluidity did not yield any significant change. Hardness of the Сu–Ni–Mn–Fe alloys with higher iron contents increased by 10 НRB on average. However, when test temperature was raised up to 400 °С, tensile strength decreased (by ~1.3 times) and elongation dropped markedly (by ~10 times).

Structure and properties of precipitation-hardened Сu–Ni–Mn–Fe binders for composite coatings

“…%) (Fig. 1, a) [3]. After that, at 880-900 С secondary solid solution based on alpha-copper (referred as -Сu( 2)) is formed.…”

“…Commercially fabricated Cu-20Ni-20Mn alloy contains foreign additives of up to 2.7 wt. % of Fe [3]. But the conducted research of the iron effect on precipitation hardening of the Cu-Ni-Mn alloys was concentrated basically on the alloys doped with more than 2.7 wt.…”

Physical-and-chemical processes at the interfaces of (Cu–Ni–Mn–Fe)/ (W–C) composites

“…In terms of high-temperature strength properties, copper-matrix composites are superior compared with other MMCs [29][30][31][32]. Commercial copper alloys usually contain manganese, nickel and iron to improve performance characteristics [33][34][35][36][37]. The cast materials have a high fluidity and can reproduce fine details in master patterns during infiltration, while their good corrosion and oxidation resistance promotes longer service life.…”

“…The cast materials have a high fluidity and can reproduce fine details in master patterns during infiltration, while their good corrosion and oxidation resistance promotes longer service life. The high strength of the Cu-Ni-Mn-Fe alloys is attained by precipitation hardening [37][38][39][40][41][42]. This process involves the formation of θ-NiMn phase from a supersaturated solid solution of alpha-copper.…”

“…This process involves the formation of θ-NiMn phase from a supersaturated solid solution of alpha-copper. The evolution of NiMn precipitates dispersed in the α-Cu matrix affects the achievement of the material's final strength [37,40].…”