Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves ...Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 min.With the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain structure.Moreover,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain boundaries.It was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic flow.Hence,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 alloy.These results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.展开更多
The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Opti...The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Optical microscope and TEM were applied to analyze the microstructure after RPC （Relaxation-precipitation-controlling phase transformation technique） and the evolution of dislocation configuration. The particle tracking autoradiography （PTA） technique, revealing the distribution of boron, was employed to show the change of boron segregation after different relaxation times. The results indicate that during the relaxation stage the recovery occurs in the deformed austenite, the dislocations rearrange and subgrains form. During the subsequent cooling the boron will segregate at the boundaries of subgrains.展开更多
Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a...Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a new strategy based onβ-subgrains-mediated hierarchicalα-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe(wt.%)alloy through a unique combination of hot rolling,short-term solid solution,and aging treatment,i.e.,RSST+A.Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of∼1581 MPa and decent ductility of∼8.4%,surpassing∼1060 MPa and∼2.7%of the corresponding RSST counterparts without final aging treatment.This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting ofβ-subgrains-mediated hierarchicalαprecipitates as a result of our specific processing approach.The designed short-term solution introduces abundantβsubgrains that are transformed from the retained intensive dislocations during hot rolling.Theβsubgrain boundaries subsequently promote a dramatic precipitation ofαallotriomorphs(αGB)and Widmanstätten side-plates(αWGB),which effectively subdividesβgrains into numerous tiny independent deformation units.Consequently,plastic strain is uniformly partitioned into a large number of small agedβsubgrains during tension,which strongly impedes strain localization that would typically occur across multipleβsubgrains in the fashion of long straight slip bands in the case of the RSST samples.Furthermore,the hierarchicalαstructure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining.These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing highstrength titanium alloys in the precipitation-hardening state.展开更多
The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging...The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging stock, the shape of the ingot was designed as the near net shape and its casting process was studied by the numerical simulation and experimental investigation. The results show that the shrinkage of the ingot was highly correlated to its shape parameters and could be successfully forecast by the stimulation model. The casting parameters of the near net shape ingot were optimized and the near net shape 6xxx aluminum alloy ingots free of defects were cast in the laboratory. In order to obtain high performance forged suspension parts, the hot compression tests of the ingot were carried out. The results show that the subgrain fraction of the forged ingot was strongly affected by Zener-Hollomon parameters （Z parameters）. The intermediate Z parameters, 1.09×10^16 s^-1, will contribute to the larger number fraction of subgrains inside the forged ingot, which contributes to the high performance of the forged products.展开更多
基金National Natural Science Foundation of China (Grant No.51822404 and 51804218)the Science and Technology Program of Tianjin (Grant No.19YFZCGX00790 and 18YFZCGX00070)+1 种基金supported by the Natural Science Foundation of Tianjin (Grant No.18JCYBJC17900)the Seed Foundation of Tianjin University (2018XRX-0005)。
文摘Fine cellular subgrain structure was formed in the Selective Laser Melting(SLM) manu factured IN718 alloy via optimizing the processing parameters.During the subsequent homogenization heat treatment process,the Laves phase dispersed at the subgrain boundaries can be eliminated while the cellular subgrain structure is reserved in the printed samples after holding at 1080℃ for 50 min.With the prolongation of the holding time,the subgrain boundaries undergo low angle rotation via the motion ofdislocation,which leads to the annihilation of the cellular subgrain structure.Moreover,during the subsequent double aging heat treatment process,the reserved cellular subgrain structure in the homogenized samples promotes the precipitation of γ" second phase nanoparticles,and these precipitated γ" phase nanoparticles prefer to distribute at subgrain boundaries.It was found that these unique subgrain boundaries with γ" phase precipitates can hinder but not fully terminate the motion of dislocation during the plastic deformation process,which contributes to increasing the strength as well as holding the stable plastic flow.Hence,the strength and ductility of final prepared IN718 alloy with cellular subgrain microstructure were improved simultaneously compared to the prepared alloy without cellular subgrain structure,which even exceed the mechanical properties standards(AMS 5662) of wrought IN718 alloy.These results in our work suggest that controlling the subgrain structure is a promising effective strategy to improve the mechanical properties of SLM manu factured nickel-based superalloy.
基金This work is financially supported by the National Natural Science Foundation of China (No. 50471089)
文摘The structure variation of deformed austenite during the relaxation stage after deformation at various temperatures in an Nb-B ultra low carbon bainitic steel and Fe-Ni alloy was studied by the thermo-simulation. Optical microscope and TEM were applied to analyze the microstructure after RPC （Relaxation-precipitation-controlling phase transformation technique） and the evolution of dislocation configuration. The particle tracking autoradiography （PTA） technique, revealing the distribution of boron, was employed to show the change of boron segregation after different relaxation times. The results indicate that during the relaxation stage the recovery occurs in the deformed austenite, the dislocations rearrange and subgrains form. During the subsequent cooling the boron will segregate at the boundaries of subgrains.
基金financially supported by the National Natural Science Foundation of China(Nos.52271113 and 92163201)the Key programme of National Natural Science Foundation of China(Nos.52431001 and 52431006)+1 种基金Jinyu Zhang is grateful for the Shaanxi Province Youth Innovation Team(No.22JP042)the Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58).
文摘Titanium alloys can achieve ultrahigh strength through precipitation hardening of secondaryα-phase(αs)fromβ-matrix but often compromise ductility due to the conventional strength-ductility trade-off.In this study,a new strategy based onβ-subgrains-mediated hierarchicalα-precipitation is devised to balance the conflict in Ti-6Al-2Mo-4Cr-2Fe(wt.%)alloy through a unique combination of hot rolling,short-term solid solution,and aging treatment,i.e.,RSST+A.Tensile testing reveals that the RSST+A samples exhibit ultrahigh strength of∼1581 MPa and decent ductility of∼8.4%,surpassing∼1060 MPa and∼2.7%of the corresponding RSST counterparts without final aging treatment.This remarkable strengthening and counterintuitive ductilizing is attributed to the architecting ofβ-subgrains-mediated hierarchicalαprecipitates as a result of our specific processing approach.The designed short-term solution introduces abundantβsubgrains that are transformed from the retained intensive dislocations during hot rolling.Theβsubgrain boundaries subsequently promote a dramatic precipitation ofαallotriomorphs(αGB)and Widmanstätten side-plates(αWGB),which effectively subdividesβgrains into numerous tiny independent deformation units.Consequently,plastic strain is uniformly partitioned into a large number of small agedβsubgrains during tension,which strongly impedes strain localization that would typically occur across multipleβsubgrains in the fashion of long straight slip bands in the case of the RSST samples.Furthermore,the hierarchicalαstructure also postpones uncontrollable cracking even when structural damage occurs at the last stage of straining.These findings demonstrate that appropriately manipulating microstructure through elaborately designing processing routes enables unexpectedly ductilizing highstrength titanium alloys in the precipitation-hardening state.
文摘The automobile suspension parts of a high strength 6xxx aluminum alloy were produced using a novel technique known as near net shape casting for forging stock preparation. Based on the outline dimension of the forging stock, the shape of the ingot was designed as the near net shape and its casting process was studied by the numerical simulation and experimental investigation. The results show that the shrinkage of the ingot was highly correlated to its shape parameters and could be successfully forecast by the stimulation model. The casting parameters of the near net shape ingot were optimized and the near net shape 6xxx aluminum alloy ingots free of defects were cast in the laboratory. In order to obtain high performance forged suspension parts, the hot compression tests of the ingot were carried out. The results show that the subgrain fraction of the forged ingot was strongly affected by Zener-Hollomon parameters （Z parameters）. The intermediate Z parameters, 1.09×10^16 s^-1, will contribute to the larger number fraction of subgrains inside the forged ingot, which contributes to the high performance of the forged products.
