Effects of hot rolling and annealing temperature on microstructure and tensile properties of a Zr-containing Ni-based ODS superalloy

Abstract

A Ni-based ODS superalloy with composition of Ni-20Cr-0.5Ti-0.3Al-0.6Y2O3-0.6Zr (in mass%) was prepared by mechanical alloying and hot isostatic pressing. Hot rolling was carried out at 1100 °C with different reduction ratio (40 %, 50 % and 60 %) and different annealing temperature (1200 °C, 1250 °C and 1300 °C) to investigate their influence on nanoscale oxides, grain and high temperature tensile properties. The results showed that high-density nanoscale oxides Y4Zr3O12 are formed in the Zr-containing Ni-based ODS alloy. Hot rolling and annealing result in the slight increase of oxide size and decrease of oxide density. The growth rate of oxides obeys fifth-law, which is called pipe diffusion along dislocation. The diffusion activity energy is derived as 827 kJ/mol. Average oxide size decreases and number density increases by decreasing rolling reduction ratio or annealing temperature. The size of columnar grain and grain aspect ratio increase with increase of annealing temperature which results into enhanced ultimate tensile strength and improved ductility at 800 °C. In addition, increasing rolling reduction ratio refines grain size and reduces grain aspect ratio in the alloy. The strength of the alloy annealed at 1300 °C with a reduction ratio of 50 % is the highest which is approximately 300 MPa at 800 °C.