The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to hig...The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.展开更多
Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation,thus potentially causing unanticipated catastrophic fractures.The underlying mechanism of microstructural ev...Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation,thus potentially causing unanticipated catastrophic fractures.The underlying mechanism of microstructural evolutions caused by fretting wear is ambiguous,which obstructs the understanding of fretting fatigue issues,and is unable to guarantee the reliability of structures for long-term operation.Here,fretting wear studies were performed to understand the microstructural evolution and oxidation behavior of anα/βtitanium alloy up to 108 cycles.Contact surface degradation is mainly caused by surface oxidation and the generation of wear debris during fretting wear within the slip zone.The grain size in the topmost nanostructured layer could be refined to~40 nm.The grain refinement process involves the initial grain rotation,the formation of low angle grain boundary(LAGB;2°–5°),the in-situ increments of the misorientation angle,and the final subdivision,which have been unraveled to feature the evolution in dislocation morphologies from slip lines to tangles and arrays.The formation of hetero microstructures regarding the nonequilibrium high angle grain boundary(HAGB)and dislocation arrays gives rise to more oxygen diffusion pathways in the topmost nanostructured layer,thus resulting in the formation of cracking interface to separate the oxidation zone and the adjoining nanostructured domain driven by tribological fatigue stress.Eventually,it facilitates surface degradation and the formation of catastrophic fractures.展开更多
基金This research was financially supported by the National Nat-ural Science Foundation of China(Grant No.52171088)the Young Elite Scientists Sponsorship Program by CAST(grant No.2022QNRC001).We thank X.Si for assistance in sample prepara-tion.
文摘The strength of traditional Al-Mg alloys is relatively low because it mainly relies on solid solution strengthening.Adding a third component to form precipitation can improve their strength,but it usually leads to high-stress corrosion cracking(SCC)sensitivity due to the formation of high-density precipitates at grain boundaries(GBs).So far,it is still challenging to improve the strength of Al-Mg alloys without re-ducing SCC resistance.Herein,a nanostructured Al-5Mg-3 Zn alloy with a good yield strength of 336 MPa and good elongation was successfully produced.By dynamic plastic deformation and appropriate anneal-ing treatment,near-equiaxed nanograins were introduced in the nanostructured Al-5Mg-3 Zn alloy with a high proportion(71%)of the low-angle grain boundary.TEM statistical investigations show that the pre-cipitation of active T’phase at GBs has been greatly suppressed in the nanostructured Al-5Mg-3 Zn alloy at sensitized conditions,and the area fraction of GB precipitates is reduced from 72%to 21%,which sig-nificantly decreases the SCC susceptibility.This study provides guidance for developing advanced Al-Mg alloy with high SCC resistance.
基金supported by the National Natural Science Foundation of China(Nos.11802145 and 12002226)Hanqing LIU acknowledges the support of JSPS Postdoctoral Fellowship(No.P20737)from the Japan Society for the Promotion of Science and 2021 Open Project of Failure Mechanics and Engineering Disaster Prevention,Key Lab of Sichuan Province(No.FMEDP202106),China.
文摘Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation,thus potentially causing unanticipated catastrophic fractures.The underlying mechanism of microstructural evolutions caused by fretting wear is ambiguous,which obstructs the understanding of fretting fatigue issues,and is unable to guarantee the reliability of structures for long-term operation.Here,fretting wear studies were performed to understand the microstructural evolution and oxidation behavior of anα/βtitanium alloy up to 108 cycles.Contact surface degradation is mainly caused by surface oxidation and the generation of wear debris during fretting wear within the slip zone.The grain size in the topmost nanostructured layer could be refined to~40 nm.The grain refinement process involves the initial grain rotation,the formation of low angle grain boundary(LAGB;2°–5°),the in-situ increments of the misorientation angle,and the final subdivision,which have been unraveled to feature the evolution in dislocation morphologies from slip lines to tangles and arrays.The formation of hetero microstructures regarding the nonequilibrium high angle grain boundary(HAGB)and dislocation arrays gives rise to more oxygen diffusion pathways in the topmost nanostructured layer,thus resulting in the formation of cracking interface to separate the oxidation zone and the adjoining nanostructured domain driven by tribological fatigue stress.Eventually,it facilitates surface degradation and the formation of catastrophic fractures.
