Effect of Zr addition on the microstructure and intermediate-temperature mechanical performance of a Ni-26W-6Cr based superalloy

In the present work, Zr was added into a Ni-26W-6Cr alloy to improve the intermediate temperature ductility, and the corresponding mechanism was discussed. The enrichment of Zr at the solid-liquid interface during the solidification process causes constitutional undercooling and a decrease of interfacial energy, which can promote the nucleation of the gamma phase. The average gamma grain size after hot rolling and solution treatment is reduced from 41.7 mu m to 20.0 mu m with the addition of Zr from 0 to 0.081 wt%. The Zr-bearing Ni-26W-6Cr alloys with finer as-cast initial grains tend to develop into smaller recrystallized grains after thermal deformation and solution treatment. Besides, the enrichment of Zr and C at the solid-liquid interface increases the number of M6C carbides in the alloys, impeding the grain growth of gamma. The refined grains and the increased M6C carbides effectively hinder the movement of dislocation during tensile. The yield strength and ultimate tensile strength at 650 degrees C are improved from 227 MPa to 274 MPa, 431 MPa to 492 MPa, respectively. The improvement of elongation is attributed to the larger fraction of dynamic recrystallization that releases the local stress caused by dislocation accumulation at the grain boundaries.

Automated summary

In this study, Zr was added to a Ni-26W-6Cr alloy to enhance its intermediate temperature ductility, and the corresponding mechanism was investigated. It was found that the enrichment of Zr at the solid-liquid interface during solidification led to constitutional undercooling and a decrease in interfacial energy, thereby promoting the nucleation of the gamma phase. Additionally, the enrichment of Zr and C increased the number of M6C carbides in the alloys, inhibiting the grain growth of gamma. The refined grains and increased M6C carbides effectively impeded the movement of dislocations during tensile, resulting in improved yield strength and ultimate tensile strength at 650 degrees C.