The microstructure of the laser melted 1.0%C tool steel have been investigated.The region affected by the laser can be subdivided into 3 zones,which consist of a melted region at the surface,a zone with solid state tr...The microstructure of the laser melted 1.0%C tool steel have been investigated.The region affected by the laser can be subdivided into 3 zones,which consist of a melted region at the surface,a zone with solid state transformation and the area adjacent to the unaffected substrate where cementite is slightly dissolved.The melted zone possessed a cellular growth morphology consisting of austenite and martensite.The carbon content of the austenite was measured to be over 1 wt-%.A great deal of retained austenite and twinned martensite were found in the first two zones(the melted and solid transformed).展开更多
The influence of heating cycles during plasma metal inert gas (MIG) welding on the microstructure and corrosion properties of the AA5754 automotive alloy has been investigated. The high heat input during plasma-MIG we...The influence of heating cycles during plasma metal inert gas (MIG) welding on the microstructure and corrosion properties of the AA5754 automotive alloy has been investigated. The high heat input during plasma-MIG welding results in a significant modification in the microstructure of the AA5754 alloy adjacent to the fusion boundaries. As a consequence of partial melting of the Al-Fe-Mn-(Si) intermetallics at the partially melted zone (PMZ) and segregation of the high melting point elements (particularly Fe and Mn) toward the fusion zone, severe galvanic corrosion attacks can be enhanced along the PMZ of the AA5754 weld during exposure to aqueous corrosion environments.展开更多
Nb-22Ti-14Si-2Hf-2Al-xCr （x=2, 6, 10, 14, 17 at%） alloys are prepared by arc-melting under argon atmosphere. Microstructural characteristics, mechanical properties and oxidation resistance of the arc-melted alloys a...Nb-22Ti-14Si-2Hf-2Al-xCr （x=2, 6, 10, 14, 17 at%） alloys are prepared by arc-melting under argon atmosphere. Microstructural characteristics, mechanical properties and oxidation resistance of the arc-melted alloys are investigated. At 2 at% Cr content, the microstructure is composed of Nbss, Nb3Si and a small quantity of Nb5Si3, when the Cr contents increase, Nb3Si disappears. For the high Cr content （x ≥ 10 at%） alloys, besides the Nbss and Nb5Si3, Cr2Nb is also detected. With the increase of Cr content, the volume fractions of Cr2Nb and Nb5Si3 increase, while that of Nbss increases firstly and then begins to degrade when the Cr content is higher than 6 at%. For the alloy with 2 at% Cr, the room temperature fracture toughness is about 14.5 MPa·m1/2, but badly decreases to about 8.5 MPa·m1/2, when the Cr contents increase. Vickers hardness of Nbss tends to increase linearly from about 400 to 500, while that of silicides is not sensitive to Cr contents, about 950. The appearance of Cr2Nb phase significantly improves the high temperature oxidation resistance of the alloys with high Cr contents. The isothermal oxidation tests show that the oxidation kinetics of the alloys with various Cr contents follows parabolic oxidation kinetics.展开更多
As a revolutionary industrial technology,additive manufacturing creates objects by adding materials layer by layer and hence can fabricate customized components with an unprecedented degree of freedom.For metallic mat...As a revolutionary industrial technology,additive manufacturing creates objects by adding materials layer by layer and hence can fabricate customized components with an unprecedented degree of freedom.For metallic materials,unique hierarchical microstructures are constructed during additive manufacturing,which endow them with numerous excellent properties.To take full advantage of additive manufacturing,an in-depth understanding of the microstructure evolution mechanism is required.To this end,this review explores the fundamental procedures of additive manufacturing,that is,the formation and binding of melt pools.A comprehensive processing map is proposed that integrates melt pool energy-and geometry-related process parameters together.Based on it,additively manufactured microstructures are developed during and after the solidification of constituent melt pool.The solidification structures are composed of primary columnar grains and fine secondary phases that form along the grain boundaries.The post-solidification structures include submicron scale dislocation cells stemming from internal residual stress and nanoscale precipitates induced by intrinsic heat treatment during cyclic heating of adjacent melt pool.Based on solidification and dislocation theories,the formation mechanisms of the multistage microstructures are thoroughly analyzed,and accordingly,multistage control methods are proposed.In addition,the underlying atomic scale structural features are briefly discussed.Furthermore,microstructure design for additive manufacturing through adjustment of process parameters and alloy composition is addressed to fulfill the great potential of the technique.This review not only builds a solid microstructural framework for metallic materials produced by additive manufacturing but also provides a promising guideline to adjust their mechanical properties.展开更多
文摘The microstructure of the laser melted 1.0%C tool steel have been investigated.The region affected by the laser can be subdivided into 3 zones,which consist of a melted region at the surface,a zone with solid state transformation and the area adjacent to the unaffected substrate where cementite is slightly dissolved.The melted zone possessed a cellular growth morphology consisting of austenite and martensite.The carbon content of the austenite was measured to be over 1 wt-%.A great deal of retained austenite and twinned martensite were found in the first two zones(the melted and solid transformed).
文摘The influence of heating cycles during plasma metal inert gas (MIG) welding on the microstructure and corrosion properties of the AA5754 automotive alloy has been investigated. The high heat input during plasma-MIG welding results in a significant modification in the microstructure of the AA5754 alloy adjacent to the fusion boundaries. As a consequence of partial melting of the Al-Fe-Mn-(Si) intermetallics at the partially melted zone (PMZ) and segregation of the high melting point elements (particularly Fe and Mn) toward the fusion zone, severe galvanic corrosion attacks can be enhanced along the PMZ of the AA5754 weld during exposure to aqueous corrosion environments.
基金National Natural Science Foundation of China (51101005)
文摘Nb-22Ti-14Si-2Hf-2Al-xCr （x=2, 6, 10, 14, 17 at%） alloys are prepared by arc-melting under argon atmosphere. Microstructural characteristics, mechanical properties and oxidation resistance of the arc-melted alloys are investigated. At 2 at% Cr content, the microstructure is composed of Nbss, Nb3Si and a small quantity of Nb5Si3, when the Cr contents increase, Nb3Si disappears. For the high Cr content （x ≥ 10 at%） alloys, besides the Nbss and Nb5Si3, Cr2Nb is also detected. With the increase of Cr content, the volume fractions of Cr2Nb and Nb5Si3 increase, while that of Nbss increases firstly and then begins to degrade when the Cr content is higher than 6 at%. For the alloy with 2 at% Cr, the room temperature fracture toughness is about 14.5 MPa·m1/2, but badly decreases to about 8.5 MPa·m1/2, when the Cr contents increase. Vickers hardness of Nbss tends to increase linearly from about 400 to 500, while that of silicides is not sensitive to Cr contents, about 950. The appearance of Cr2Nb phase significantly improves the high temperature oxidation resistance of the alloys with high Cr contents. The isothermal oxidation tests show that the oxidation kinetics of the alloys with various Cr contents follows parabolic oxidation kinetics.
基金financial support of National Natural Science Foundation of China(No.51971149)the funding from Science and Technology Innovation Commission of Shenzhen(Nos.KQJSCX20180328095612712,GJHZ20190822095418365)+1 种基金Guangdong Basic and Applied Basic Research Foundation(Nos.2020A1515110869 and 2019A1515110515)Shenzhen-Hong Kong Science and Technology Innovation Cooperation Zone Shenzhen Park Project(No.HZQB-KCZYB-2020030)。
文摘As a revolutionary industrial technology,additive manufacturing creates objects by adding materials layer by layer and hence can fabricate customized components with an unprecedented degree of freedom.For metallic materials,unique hierarchical microstructures are constructed during additive manufacturing,which endow them with numerous excellent properties.To take full advantage of additive manufacturing,an in-depth understanding of the microstructure evolution mechanism is required.To this end,this review explores the fundamental procedures of additive manufacturing,that is,the formation and binding of melt pools.A comprehensive processing map is proposed that integrates melt pool energy-and geometry-related process parameters together.Based on it,additively manufactured microstructures are developed during and after the solidification of constituent melt pool.The solidification structures are composed of primary columnar grains and fine secondary phases that form along the grain boundaries.The post-solidification structures include submicron scale dislocation cells stemming from internal residual stress and nanoscale precipitates induced by intrinsic heat treatment during cyclic heating of adjacent melt pool.Based on solidification and dislocation theories,the formation mechanisms of the multistage microstructures are thoroughly analyzed,and accordingly,multistage control methods are proposed.In addition,the underlying atomic scale structural features are briefly discussed.Furthermore,microstructure design for additive manufacturing through adjustment of process parameters and alloy composition is addressed to fulfill the great potential of the technique.This review not only builds a solid microstructural framework for metallic materials produced by additive manufacturing but also provides a promising guideline to adjust their mechanical properties.
