Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance.In this work,the heat treatment strat-egy for Inconel 7...Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance.In this work,the heat treatment strat-egy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition(L-DED)has been designed and systematically investigated for the first time.The results show that the designed ho-mogenization heat treatment at 1080℃ for 10 min can effectively dissolve most of the detrimental Lave phases existing in the rolling-assisted L-DED samples.Meanwhile,it results in a homogenous grain struc-ture through static recrystallization,while maintaining a similar prior-refined grain size of∼8μm.On this basis,a high number density ofγ″andγ′precipitates appear in the microstructure after applying a subsequent double-aging heat treatment.The optimized microstructure through such effective post-heat treatment designed in this work has led to a significant increase in material strength at both the room and elevated temperatures while maintaining good ductility.展开更多
The nanowire and whisker heterostructures of tin dioxide were fabricated by the chemical vapor deposition technique.It was demonstrated that various structures of tin oxide can be obtained by controlling the thickness...The nanowire and whisker heterostructures of tin dioxide were fabricated by the chemical vapor deposition technique.It was demonstrated that various structures of tin oxide can be obtained by controlling the thickness of gold layer and the partial pressure of source vapor at growing sites.12.5 and 25 nm thicknesses are preferable for the epitaxial growth of nanowires and heterostructure through vapor–liquid–solid mechanism,respectively.The tin dioxide whiskers with core-shell structure were fabricated by vapor–solid mechanism.Meanwhile,the influences of various factors on the tin dioxide growth are also discussed.展开更多
The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P...The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.展开更多
The nano-bainitic microstructures were compared in a 0.79C-1.5Si-1.98Mn-0.24Mo-1.06Al (wt%) steel after isothermal heat-treatment and a Fe-0.2C-1.5Mn-1.2Si-0.3Mo-0.6Al-0.02Nb (wt%) steel after controlled thermomechani...The nano-bainitic microstructures were compared in a 0.79C-1.5Si-1.98Mn-0.24Mo-1.06Al (wt%) steel after isothermal heat-treatment and a Fe-0.2C-1.5Mn-1.2Si-0.3Mo-0.6Al-0.02Nb (wt%) steel after controlled thermomechanical processing.The microstructure for both steels consisted of bainite.The microstructural characteristics of bainite,such as the morphology of the nano-bainite and thicknesses of bainitic ferrite and retained austenite layers,as a function of steel composition and processing was studied using transmission electron microscopy (TEM).It was found that the nano-bainitic structure can be formed in the low alloy steel through thermomechanical processing.Atom probe tomography (APT) was employed as a powerful technique to determine local composition distributions in three dimensions with atomic resolution.The important conclusions from the APT research were that the carbon content of bainitic ferrite is higher than expected from paraequilibrium level of carbon in ferrite for both steels and that Fe-C clusters and fine particles are formed in the bainitic ferrite in both steels despite the high level of Si.展开更多
文摘Post-heat treatment is a necessary and important step for additive-manufactured products to relieve residual stress and to further improve mechanical performance.In this work,the heat treatment strat-egy for Inconel 718 superalloy fabricated by rolling-assisted laser-directed energy deposition(L-DED)has been designed and systematically investigated for the first time.The results show that the designed ho-mogenization heat treatment at 1080℃ for 10 min can effectively dissolve most of the detrimental Lave phases existing in the rolling-assisted L-DED samples.Meanwhile,it results in a homogenous grain struc-ture through static recrystallization,while maintaining a similar prior-refined grain size of∼8μm.On this basis,a high number density ofγ″andγ′precipitates appear in the microstructure after applying a subsequent double-aging heat treatment.The optimized microstructure through such effective post-heat treatment designed in this work has led to a significant increase in material strength at both the room and elevated temperatures while maintaining good ductility.
基金supported by Deakin University under a postgraduate research scholarship,the Fundamental Scientific Research Funds for Chinese Academy of Tropical Agricultural Sciences (Nos.1630022011033 and 1630062013011)the Natural Science Foundation of Hainan Province,China (No.20155197)
文摘The nanowire and whisker heterostructures of tin dioxide were fabricated by the chemical vapor deposition technique.It was demonstrated that various structures of tin oxide can be obtained by controlling the thickness of gold layer and the partial pressure of source vapor at growing sites.12.5 and 25 nm thicknesses are preferable for the epitaxial growth of nanowires and heterostructure through vapor–liquid–solid mechanism,respectively.The tin dioxide whiskers with core-shell structure were fabricated by vapor–solid mechanism.Meanwhile,the influences of various factors on the tin dioxide growth are also discussed.
基金financially supported by the National Natural Science Foundation of China(No.51401050)the Fundamental Research Funding for the Central Universities(No.N160204001)supported by the Australian Research Council(ARC)Laureate Fellowship(Prof.Hodgson)
文摘The transformation behavior, microstructural evolution and mechanical properties were compared in a coldrolled Nb–Mo microalloyed 6.5Mn alloy after intercritical annealing（IA） and quenching and partitioning（Q ＆ P）,respectively. The thermodynamic calculation and theoretical analysis were used to determine the optimal heat treatment parameters. The Q ＆ P samples exhibited relatively higher strength with relatively low ductility, mainly due to the hard martensite matrix, which resulted in continuous yielding behavior upon loading, whereas the IA samples showed the significantly improved ductility, which benefited from the more sufficient transformation-induced plasticity（TRIP） effects and the softer ultrafine ferrite matrix. The dependence of yield point elongation（YPE） of IA samples on grain size demonstrated that the YPE value was in the reverse proportional relationship to the average grain size, which agreed well with theoretical analysis.
文摘The nano-bainitic microstructures were compared in a 0.79C-1.5Si-1.98Mn-0.24Mo-1.06Al (wt%) steel after isothermal heat-treatment and a Fe-0.2C-1.5Mn-1.2Si-0.3Mo-0.6Al-0.02Nb (wt%) steel after controlled thermomechanical processing.The microstructure for both steels consisted of bainite.The microstructural characteristics of bainite,such as the morphology of the nano-bainite and thicknesses of bainitic ferrite and retained austenite layers,as a function of steel composition and processing was studied using transmission electron microscopy (TEM).It was found that the nano-bainitic structure can be formed in the low alloy steel through thermomechanical processing.Atom probe tomography (APT) was employed as a powerful technique to determine local composition distributions in three dimensions with atomic resolution.The important conclusions from the APT research were that the carbon content of bainitic ferrite is higher than expected from paraequilibrium level of carbon in ferrite for both steels and that Fe-C clusters and fine particles are formed in the bainitic ferrite in both steels despite the high level of Si.
