In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed ener...In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.展开更多
Micro-forging(MF)is a novel surface modification technology which is capable of smoothening and strengthening the workpiece surface simultaneously.Based on analysis of the mechanism and energy conversion of micro-forg...Micro-forging(MF)is a novel surface modification technology which is capable of smoothening and strengthening the workpiece surface simultaneously.Based on analysis of the mechanism and energy conversion of micro-forging process,an electromagnetically driven microforging system is developed.To further grasp the kinetic characteristic of the equipment,a simulation model is established and its accuracy is verified.With the help of simulation and experimental results,we propose an input voltage optimization method,which drives the micro-forging head moving in a uniform and stable way.In this study,the influence of MF on surface integrity of Ti-6 Al-4 V(TC4)is firstly reported.Experimental results show that MF treatment reduces surface roughness(Ra)and increases micro-hardness by 48%and 11.8%at most,respectively.Besides,a compressive stress layer with an amplitude of-1000 MPa and a depth of 0.8 mm is observed.This study analyzes the performance and reveals the potential of micro-forging technology,which lays a solid foundation for expanding its application in TC4 surface modification.展开更多
基金supported by National Key Research and Development Program(No.2017YFB1103701)National Natural Science Foundation of China(No.51671101)+1 种基金Natural Science Foundation of Jiangxi Province(No.20171BCD40003)the Innovative Funding for Graduate Students in Nanchang University(No.CX2019068)。
文摘In this work,ultrasonic micro-forging treatment(UMFT)was introduced to achieve homogeneous microstructure,reduce defects and improve mechanical properties of GH3039 superalloy cladding layer processed by directed energy deposition(DED).The microstructure,defects and mechanical properties of the cladding layers treated by UMFT with different ultrasonic powers(UIPs)were investigated.Results revealed a gradient structure as equiaxed grains distributed at the top,a columnar-to-equiaxed transition(CET)region that mixed of columnar dendrites and equiaxed grains distributed at the middle and columnar dendrites at the bottom of the cladding layer was formed.After UMFT,the proportion of equiaxed grains was increased,the average size of equiaxed grains was refined to 10μm from 16μm,the orientation of grains was more uniform and the phases enriched of Al,Ti,C,Nb and Mo were precipitated.The grain refinement can be attributed to the fracture of columnar dendrites induced by the ultrasonic vibration during solidification.Besides,the porosity of the cladding layer was reduced after UMFT.The microhardness of the cladding layers exhibited a depth-dependent gradient at the top region.The microhardness of the top surface was the highest and showed an increasing trend with the increase of UIP.The microhardness of different grain morphologies exhibited no substantial difference.However,due to grain refinement and precipitation of strengthening phase induced by UMFT,the microhadness of some local locations were improved.These results indicated UMFT has a significant effect on improving the microstructure,defects and mechanical properties of the deposited cladding layer.
基金the National Major Science and Technology Projects of China(No.2018ZX04005001-002)State Administration for Science,Technology and Industry for National Defense of China(No.DE0904)Shanghai Academy of Spaceflight Technology of China(No.SAST2018-055)。
文摘Micro-forging(MF)is a novel surface modification technology which is capable of smoothening and strengthening the workpiece surface simultaneously.Based on analysis of the mechanism and energy conversion of micro-forging process,an electromagnetically driven microforging system is developed.To further grasp the kinetic characteristic of the equipment,a simulation model is established and its accuracy is verified.With the help of simulation and experimental results,we propose an input voltage optimization method,which drives the micro-forging head moving in a uniform and stable way.In this study,the influence of MF on surface integrity of Ti-6 Al-4 V(TC4)is firstly reported.Experimental results show that MF treatment reduces surface roughness(Ra)and increases micro-hardness by 48%and 11.8%at most,respectively.Besides,a compressive stress layer with an amplitude of-1000 MPa and a depth of 0.8 mm is observed.This study analyzes the performance and reveals the potential of micro-forging technology,which lays a solid foundation for expanding its application in TC4 surface modification.
