Ageing behaviour of an Fe–20Ni–1.8Mn–1.6Ti–0.59Al (wt%) maraging alloy: clustering, precipitation and hardening Original Research Article

Changes in the solute distribution as well as the evolution of precipitation, microstructure and mechanical properties have been studied in an experimental maraging Fe–20Ni–1.8Mn–1.5Ti–0.59Al (wt%) alloy during ageing at 550 °C. An initial hardening reaction within 5 s is reported, which is remarkable in terms of extent and rapidity. This strengthening was caused by the formation of complex multi-component atomic co-clusters containing primarily Ni–Ti–Al as well as some Mn. This cluster strengthened condition produced the optimum toughness observed throughout the ageing sequence. After 60 s ageing, the appearance of discrete precipitation of needle-shaped η-Ni3Ti particles was associated with a second rise in hardness towards an eventual peak at 600 s. This precipitation hardening was accompanied by an increase in tensile strength and a decrease in ductility. A reverse transformation of martensite to austenite occurs progressively during ageing and this contributes to the initial and secondary softening.