Effect of Hf and Zr Contents on Stress-rupture and Fatigue Crack Growth Rate Performances in FGH96 PM Superalloy

Abstract

Four experimental FGH96 alloys with various contents of Hf and Zr (0 and 0.04%, 0.3% and 0.04%, 0.6% and 0.04%, 0.3% and 0.06%, respectively) were produced using PREP (plasma rotating electrode process) + HIP (hot isostatic pressing) route. The unnotched and notched stress-rupture properties and fatigue crack growth rate (FCGR) of all the experimental alloys were investigated to study the effect of Hf and Zr. Relevant fracture morphology and microstructure were observed by scanning electron microscopy and transmission electron microscopy. The results revealed that appropriate content of Hf could lengthen stress-rupture life, eliminate notch sensitivity and slower FCGR. Microstructure analysis showed that the amount of γ′ phase should be increased or decreased by adjusting Hf and Zr contents, and MC carbide and oxide coupled growth should be increased by adding Hf content, which caused oxycarbide to precipitate along grain boundary and strengthen the alloy. It was found that excessive Zr in Hf-containing FGH96 alloy had certain deleterious effects on stress-rupture property because there was strong Zr segregation at prior particle boundary, leaving a long chain of large-size oxides along the boundary. The optimal content of Hf and Zr in FGH96 alloy was 0.6% and 0.04%, respectively.