This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-...This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.展开更多
In this study,based on two attractive energetic compounds pentazole(PZ) and tetraazacubane(TAC),a new family of high energy and high nitrogen compounds pentazolyltetraazacubanes were designed.Then,a different number o...In this study,based on two attractive energetic compounds pentazole(PZ) and tetraazacubane(TAC),a new family of high energy and high nitrogen compounds pentazolyltetraazacubanes were designed.Then,a different number of NH2 or NO2 groups were introduced into the system to further adjust the property.The structures,properties,and the structure-property relationship of designed molecules were investigated theoretically.The results showed that all nine designed compounds have extremely high heat of formation(HOF,1226-2734 kJ/mol),good density(1,73-1.88 g/cm3),high detonation velocity(8.30-9.35 km/s),high detonation pressure(29.8-39.7 GPa) and acceptable sensitivity(△V:41-87 A3).These properties could be effectively positive adjusted by replacing one or two PZ rings by NH2 or/and NO2 groups,especially for the energy and sensitivity performance,which were increased and decreased obviously,respectively.As a result,two designed pentazolyltetraazacubanes were predicted to have higher energy and lower sensitivity than the famous high energy compound in use 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane,while two others have better co mbination property than 1,3,5-Trinitro-1,3,5-triazacyclohexane.In all,four new pentazolyltetraazacubanes with good combination performance were successfully designed by combining PZ with TAC,and the further property adjustment strategy of introducing a suitable amount of NH2/NO2 groups into the system.This work may help develop new cage energetic compounds.展开更多
文摘This study examines the effects of friction stir welding(FSW)and post-weld heat treatment(PWHT)on the grain boundary character distribution and corrosion resistance of cross sectional(top and bottom)regions of nickel-and molybdenum-free high-nitrogen austenitic stainless steel(HNASS).FSW at 400 rpm and 30 mm/min resulted in finer grains(4.18μm)and higher coincident site lattice(CSL)boundaries(32.3%)at the top of the stir zone(SZ)due to dynamic recrystallization(DRX).PWHT at 900℃for 1 h led to grain coarsening(12.91μm the bottom SZ)but enhanced CSL boundaries from 24.6%to 30.2%,improving grain boundary stability.PWHT reduced the kernel average misorientation(KAM)by 14.9%in the SZ-top layer and 20.4%in the SZ-bottom layer,accompanied by a 25%decrease in hardness in the SZ-top layer and 26.7%in the SZ-bottom layer,indicating strain recovery and reduced dislocation density.Potentiodynamic polarization tests(PDP)showed a 18%increase in pitting potential and a 76%reduction in corrosion rate after PWHT.The improvement in corrosion resistance is attributed to the increase inΣ3 twin boundaries,which enhance grain boundary stability and reduce susceptibility to localized corrosion.These findings highlight the role of PWHT in refining the microstructure and strengthening corrosion resistance,making HNASS a promising material for demanding applications.
基金supported by the Natural Science Foundation of Nanjing Institute of Technology (CKJA201603)the Natural Science Foundation of Jiangsu Province(BK20170761,BK20160774)+3 种基金the Jiangsu Key Laboratory Opening Project of Advanced Structural Materials and Application Technology (ASMA201707)Science Innovation Project for Undergraduates of Jiangsu Province (201811276023Z)Outstanding Scientific and Technological Innovation Team in Colleges and Universities of Jiangsu ProvinceJiangsu Overseas Visiting Scholar Program for University Prominent Young & Middle-aged Teachers and Presidents
文摘In this study,based on two attractive energetic compounds pentazole(PZ) and tetraazacubane(TAC),a new family of high energy and high nitrogen compounds pentazolyltetraazacubanes were designed.Then,a different number of NH2 or NO2 groups were introduced into the system to further adjust the property.The structures,properties,and the structure-property relationship of designed molecules were investigated theoretically.The results showed that all nine designed compounds have extremely high heat of formation(HOF,1226-2734 kJ/mol),good density(1,73-1.88 g/cm3),high detonation velocity(8.30-9.35 km/s),high detonation pressure(29.8-39.7 GPa) and acceptable sensitivity(△V:41-87 A3).These properties could be effectively positive adjusted by replacing one or two PZ rings by NH2 or/and NO2 groups,especially for the energy and sensitivity performance,which were increased and decreased obviously,respectively.As a result,two designed pentazolyltetraazacubanes were predicted to have higher energy and lower sensitivity than the famous high energy compound in use 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane,while two others have better co mbination property than 1,3,5-Trinitro-1,3,5-triazacyclohexane.In all,four new pentazolyltetraazacubanes with good combination performance were successfully designed by combining PZ with TAC,and the further property adjustment strategy of introducing a suitable amount of NH2/NO2 groups into the system.This work may help develop new cage energetic compounds.
