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

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 degrees C with different reduction ratio (40 %, 50 % and 60 %) and different annealing temperature (1200 degrees C, 1250 degrees C and 1300 degrees 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 degrees 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 degrees C with a reduction ratio of 50 % is the highest which is approximately 300 MPa at 800 degrees C.

Automated summary

In this study, a Ni-based ODS superalloy was prepared by mechanical alloying and hot isostatic pressing. The influence of hot rolling and annealing on nanoscale oxides, grain, and high temperature tensile properties was investigated. The results showed the formation of high-density nanoscale oxides in the alloy, and the size and density of the oxides were affected by hot rolling and annealing. Decreasing the reduction ratio or annealing temperature resulted in smaller oxide size and higher number density. The grain size and aspect ratio increased with higher annealing temperature, leading to improved ultimate tensile strength and ductility at 800 degrees C. Additionally, increasing the rolling reduction ratio refined the grain size and reduced the grain aspect ratio in the alloy.