查看更多>>摘要：The effects of B addition on microstructure and mechanical properties of a γ'-strengthened CoNi-base superalloy are inves-tigated.The addition of B leads to a substantial increase in the volume fraction of both the eutectic structure and borides.The CoNi-base alloy shows a high solubility limit for the element B.Borides become noticeable in the area surrounding the eutectic structure after the B level exceeds 0.46 at.％ .It is found that the compression property and stress rupture life of the 4W2Ta alloys exhibit an initial rise followed by a subsequent drop as the B content gradually increases from 0.08 to 0.78 at.％ .The 4W2Ta0.46B alloy demonstrates the most excellent high-temperature strength and stress rupture life,revealing that a moderate amount of B in the alloy noticeably enhances its mechanical properties by enhancing the grain boundary cohesion.
查看更多>>摘要：The hot deformation behavior of a newly developed Ni-W-Cr superalloy for use in 800 ℃ molten salt reactors(MSRs)was looked into by isothermal compression tests in the temperature range of 1050-1200 ℃ with a strain rate of 0.001-1 s-1 under a true strain of 0.693.An Arrhenius-type model for the Ni-W-Cr superalloy was constructed by fitting the corrected flow stress data.In this model,the effect of dispersion of solid solution elements during thermal deformation on microstructure evolution was considered,as well as the effects of friction and adiabatic heating on the temperature and strain rate-dependent variation of flow stresses.The hot deformation activation energy of the Ni-W-Cr superalloy was 323 kJ/mol,which was less than that of the Hastelloy N alloy(currently used in MSRs).According to the rectified flow stress data,processing maps were created.In conjunction with the corresponding deformation microstructures,the flow instability domains of the Ni-W-Cr superalloy were determined to be 1050-1160 ℃/0.03-1 s-1 and 1170-1200 ℃/0.001-0.09 s-1.In these deformation con-ditions,a locally inhomogeneous microstructure was caused by flow—i.e.,incomplete dynamic recrystallization and hot working parameters should avoid sliding into these domains.The ideal processing hot deformation domain for the Ni-W-Cr superalloy was determined to be 1170-1200 ℃/0.6-1 s-1.
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