Effect of Al/Ti Ratio on Γ′ And Oxide Dispersion Strengthening in Ni-Based Ods Superalloys

Oxide dispersion strengthened (ODS) Ni-based superalloys with high Al/Ti content (Ni-20Cr- x Al- y Ti-0.6Y 2 O 3 -0.6Zr, x / y =~1, 1.8 and 16, named SA, SAT and ST 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 different Al/Ti atomic ratios on microstructure and Vickers hardness. The results showed that the ODS alloys are strengthened by both γ′ phases and nanoscale oxides while the reference alloy is strengthened only by nanoscale oxides. The average size of γ′ increases with decreasing Al/Ti atom ratio. The size and type of nanoscale oxides also depend on Al/Ti atom ratio. The average size of nano-sized oxide particles is 10.7nm for ST alloy, 14.7nm for SAT and 10.2nm for SA. Y 4 Zr 3 O 12 and Y 2 Ti 2 O 7 are identified in ST. Y 4 Zr 3 O 12 , Y 2 Ti 2 O 7 and YAG(Y 3 Al 5 O 12 ) are observed in SAT. Y 4 Zr 3 O 12 , YAM(Y 4 Al 2 O 9 ), YAH (orthorhombic YAlO 3 ) and YAP (hexagonal YAlO 3 ) are confirmed in SA. Only Y 4 Zr 3 O 12 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 atom ratio and their contributions (oxide dispersion strengthening and γ′ precipitation strengthening) to mechanical properties are analyzed