Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance a...Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.展开更多
High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. An...High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. And low ductility restricts engineering applications of the bcc-structured HEAs. In engineering materials, improvement in ductility usually results in deduction of mechanical strength. A method to improve both mechanical strength and ductility in a bcc-structured HEA was proposed by adding interstitial carbon. Experimental results showed that replacement of 5 at.% Cr with 5 at.% C in a bcc-structured Fe35Mn25Al15Cr10Ni15 HEA resulted in an increase in fcc phase from 0.3 to 93.7 vol.%. Strength and ductility increased at the same time. The transition of bcc-structure to fcc-structure along with a remaining small amount of bcc phase improved mechanical properties. This work indicates that interstitial carbon can be employed to modulate the fraction of constituent phases in a bcc-structured HEA to enhance engineering mechanical properties.展开更多
基金Foundation item： National Natural Science Foundation of China （50671081）
文摘Nb-Ti-Si-based ultrahigh-temperature alloys concocted with boron ranging from 0 to 2 at% are prepared by arc-melting technology. The effects of adding boron on their as-melted microstructure and oxidation resistance are analyzed. The （Nb,Ti）ss, β-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 exist in Nb-22Ti-16Si-6Cr-3Al-4Hf alloy, while （Nb,Ti）ss, α-（Nb,Ti）5Si3 and γ-（Nb,Ti）5Si3 are present in Nb-22Ti-16Si-6Cr-3Al-4Hf-lB and Nb-22Ti-16Si-6Cr-3Al-4Hf-2B alloys. The oxidation of Nb-Ti-Si-based ultrahigh-temperature alloys is dominated by the diffusion of oxygen through （Nb,Ti）ss. Compared to boron-free alloys, the boron-containing alloys have significantly lower oxidation rate when oxidized at 1 200 ℃ for less than 50 h, but, for more than 50 h, their oxidation resistance deteriorates.
基金Acknowledgements This work was financially supported by the Joint Fund of Iron and Steel Research （No.U1660103） and National Natural Science Foundation of China （No. 51574162）. XRD, SEM and EBSD tests were conducted in the Instrumental Analysis ＆ Research Center at Shanghai University. The authors would like to express sincere thanks to the staff support at the Center. We thank Dr. Tyler for editing. Part of the work was undertaken in the US National High Magnetic Field Laboratory, which is supported by NSF DMR- 1157490, the State of Florida, and DOE.
文摘High-entropy alloys （HEAs） usually contain more than five alloying elements. The ductility of a body-centered cubic （bcc）- type HEA typically is lower than that of their face-centered cubic （fcc） counterpart. And low ductility restricts engineering applications of the bcc-structured HEAs. In engineering materials, improvement in ductility usually results in deduction of mechanical strength. A method to improve both mechanical strength and ductility in a bcc-structured HEA was proposed by adding interstitial carbon. Experimental results showed that replacement of 5 at.% Cr with 5 at.% C in a bcc-structured Fe35Mn25Al15Cr10Ni15 HEA resulted in an increase in fcc phase from 0.3 to 93.7 vol.%. Strength and ductility increased at the same time. The transition of bcc-structure to fcc-structure along with a remaining small amount of bcc phase improved mechanical properties. This work indicates that interstitial carbon can be employed to modulate the fraction of constituent phases in a bcc-structured HEA to enhance engineering mechanical properties.
