Nanoscale oxide and γ' phase synergistically strengthened nickel-based alloys with varying Al/Ti ratios produced by HIP

Abstract

In this paper, three nickel-based superalloys with different Al/Ti atomic ratios (1, 1.8 and 16), designated as ODS-1, ODS-1.8 and ODS-16, respectively, were prepared by mechanical alloying (MA) followed by hot isostatic pressing (HIP). The evolution of microstructure and tensile properties of the alloys under varying Al/Ti ratio was analyzed and discussed. The result showed that the size, type and constitution of oxides change with variation of Al/Ti ratio. The average size of the oxides decreases with increasing Al/Ti ratio, which is 15.8 nm for ODS-1, 13.8 nm for ODS-1.8 and 11.8 nm for ODS-16, respectively. The oxides in ODS-1 contain 21.4% Y4Zr3O12, 42.9% Y2TiO5, 21.4% YAM and 14.3% YAP. The oxides in ODS-1.8 consist of 23.5% Y4Zr3O12, 35.3% Y2TiO5, 17.6% YAM and 23.5% YAP. In contrast, only two types of oxides are formed in ODS-16, including 50% Y4Zr3O12 and 50% YAP. As the Al/Ti ratio is increased from 1 to 16, the percentage of Y-Al-O phase increases from 35.7% to 50%, while the proportion of Y-Ti-O phase decreases from 42.9% to 0%. Increasing Al/Ti ratio inhibits the formation of Y-Ti-O phase while promoting the generation of Y-Al-O particles. The finer oxide distribution in ODS-16 is considered to be the main reason for its finer grain size distribution. The bimodal distribution of the γ' phase can be found in all three alloys, but the bimodal distribution feature of the γ' phase in ODS-1 and ODS-1.8 is more significant than that in ODS-16. The average grain size decreases with increasing Al/Ti ratio. The tensile strength at 700 °C is reduced, but the ductility is improved with the increase of Al/Ti ratio. The influence of Al/Ti ratio on the formation of nanoscale oxides and γ' phases are revealed.