Hot Workability of NiW Medium/Heavy Alloys with Ultra-high W Content
The flow behavior and microstructural evolution of a high-density Ni-42W-10Co-1Mo(wt％)alloy were investigated at 1150-1300 ℃ under strain rates of 0.001-1 s-1 using a Gleeble-1500D.The results show that the initial microstructure is composed of face-centered cubic matrix and σ phase.The flow stress is sensitive to the deformation temperature and strain rate,and the stress-strain curve shows typical dynamic revertive softening characteristics when deformed at 1 s-1,while typical dynamic recrystallization softening characteristics are observed when deformed at 0.1-0.001 s-1.The Arrhenius equation was established based on the stress-strain curves,and the hot deformation activation energy of the Ni-42W-10Co-1Mo alloy was calculated to be 446.2 kJ/mol.The thermal processing map was constructed based on the dynamic material model to evaluate the thermal processing performance,and the instable zone was located at 1300 ℃ under high strain rate.The deformation microstructural evolution reveals that the dynamic recrystallization mechanism is discontinuous dynamic recrystallization,which preferentially nucleates around the σ phase.Finally,the optimized hot working window for Ni-42W-10Co-1Mo alloy was obtained at 1250-1300 ℃ under strain rate of 0.1-0.01 s-1.
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