Effect of Melt Superheating Temperature on Stress-Rupture Properties and Microstructure of a Hot Corrosion Resistant Nickel-Based Superalloy
摘要
The stress-rupture behavior and microstructural evolution of a hot corrosion-resistant superalloy were systematically investigated after melt superheating treatment at temperatures ranging from 1525 to 1675 °C. In the as-cast condition, increasing the melt superheating temperature initially resulted in a reduction in grain size, a reduction in porosity, a decrease in secondary dendrite arm spacing, and diminished dendritic segregation, with optimal refinement achieved at 1625 °C. However, further temperature increases beyond 1625 °C reversed these trends. In the heat-treated state, the area fraction and size of the γ′ precipitates exhibited a similar trend, reaching their maxima at 1625 °C, with an area fraction of 41.39% and an average size of 0.321 μm. Beyond this critical temperature, both parameters declined. Additionally, an increasing proportion of MC carbides underwent transformation into M6C and M23C6 carbides as the melt superheating temperature rose. Stress-rupture tests at 900 °C /270 MPa demonstrate that, the stress-rupture life extends by 54.9% as the melt superheating temperature increases from 1525 to 1625 °C, but subsequently declines at 1675 °C. This behavior is attributed to the enhanced undercooling effect induced by elevated superheating temperatures, which promotes grain refinement, reduces SDAS, and mitigates elemental segregation. According to the Hall-Petch relationship, refined grains enhance grain boundary strength, thereby enhancing stress-rupture property. Additionally, dendrite arm spacing affects the characteristics of precipitates in the alloy, ultimately extending its stress-rupture life. Beyond 1625 °C, grain coarsening occurs, and the size and area fraction of the γ′ phase decrease, leading to a reduction in the alloy’s creep life.