Effect of Al/Ti ratio on γ′ and oxide dispersion strengthening in Ni-based ODS superalloys

Abstract

Oxide dispersion strengthened (ODS) Ni-based superalloys with high Al and Ti content (Ni–20Cr-xAl-yTi-0.6Y2O3-0.6Zr, x/y = ∼1, 1.8 and 16, named ST, SAT and SA alloy, respectively) and reference ODS alloy with low Al and Ti contents were produced by mechanical alloying and spark plasma sintering to investigate effect of Al/Ti atomic ratio on microstructure and Vickers hardness. The results showed that ST, SAT and SA alloys are strengthened by both γ′ phases and nanoscale oxides while the reference alloy is strengthened by only nanoscale oxides. The average size of γ′ increases but volume fraction decreases with decreasing Al/Ti atom ratio. The size and type of nanoscale oxides are different for the alloys with different Al/Ti ratios. The average size of nano-sized oxide is 10.7 nm for ST alloy, 14.7 nm for SAT and 10.2 nm for SA. Y4Zr3O12 and Y2Ti2O7 are identified in ST. Y4Zr3O12, Y2Ti2O7 and YAG(Y3Al5O12) are observed in SAT. Y4Zr3O12, YAM(Y4Al2O9), YAP (orthorhombic YAlO3) and YAH (hexagonal YAlO3) are confirmed in SA. Only Y4Zr3O12 is found in reference alloy. The hardness of ST, SAT and SA alloys is higher than reference alloy and increases with the decreasing Al/Ti ratio. The dependence of γ′ and nanoscale oxides on Al/Ti ratio and their contributions (oxide dispersion strengthening and γ′ precipitation strengthening) to mechanical properties are analyzed.