Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloy...Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.展开更多
Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the au...Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.展开更多
Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for ...Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for high-performance materials.To reveal the deformation and strengthening mechanisms,the molecular dynamics(MD)simulations and experimental analysis were carried out upon Ti-Ti_(2)Cu lamellae.In this work,we focused on revealing the interface dislocations(IDs)pattern and its effects on the dynamic evolution of the lattice dislocations(LDs)at the Ti/Ti_(2)Cu interface with(0001)α//(013)Ti_(2)Cu orientation relationship.Atomistic simulations depicted that the equilibrium Ti/Ti_(2)Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy.Each ID consists of several segments,connected by atomic steps with identical direction.The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step,which is related to the local high atom strain.Under compression deformation,the100{011}and331{103}slip systems in Ti_(2)Cu,and the112¯3{101¯1}slip system inα-Ti are activated,achieving a co-deformation mechanism in the Ti-Ti_(2)Cu multilayers.The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening.During nanoindentation tests,larger hardness(∼6.2 GPa)and smaller activation volume(∼12b3)were found in the Ti-Ti_(2)Cu lamellae,which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip,resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening.The MD simulations,nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions.展开更多
Al-Ti diffusion couples were made by embedded technology and treated at the temperature between the melting points of Al and Ti. The microstructure evolution and growth mechanism of the Al-Ti DRZ were investigated. Th...Al-Ti diffusion couples were made by embedded technology and treated at the temperature between the melting points of Al and Ti. The microstructure evolution and growth mechanism of the Al-Ti DRZ were investigated. The result shows that the DRZ, the mixture of TiAl3 and Al, grows layer by layer along their chemical equilibrium zone. In the course, the growth interface moves toward the aluminum side. TiAl3 is the only new phase which forms earliest in the course of heat-treatment. The growth mechanism of the DRZ changes after the phase transition of titanium. Before the phase transition of titanium, the growth of the DRZ is controlled by the dissolution speed of the titanium to the molten aluminum, while after the phase transition of titanium, the growth is controlled by the chemical reaction speed of Al and Ti atoms, and consequently, its growth rate is greatly increased.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52425401 and 52374384)the Foundation of National Key Laboratory for Precision Hot Processing of Metals(No.JCKYS2021603C001)the Fundamental Research Funds for the Central Universities(No.2023FRFK06014).
文摘Nb-Si-based in situ composites are receiving attention as a substitute for Ni-based alloys in aerospace,while poor toughness limits its application.In this work,the toughness of Nb_(4)FeSi-containing Nb-Si-based alloys was improved by hot deformation.The different deformation behaviors of reinforcements from traditional alloys,including the eutectoid decomposition ofβ-Nb_(5)Si_(3),and the stacking faults(SFs)and reorientation-induced plasticity(RIP)effect of Nb_(4)FeSi,are revealed.During hot deformation,theβ-Nb_(5)Si_(3)phase undergoes the eutectoid decomposition to obtain theα-Nb_(5)Si_(3)and niobium-based solid solutions(Nbss)phases,whichα-Nb_(5)Si_(3)and Nbss satisfy the relationship{110}_(α)//{110}_(Nbss).The[110]SFs and lath-like reoriented variants are formed in the Nb_(4)FeSi phase,where the matrix and variants follow[001]_(m)//[111]v,(110)_(m)//(110)v.Furthermore,the interface between matrix and variant isΣ33c symmetrical tilt boundaries,manifested as(110)/60°.The fracture toughness of the deformed alloy reaches 18.31 MPa·m1/2 at 1300℃/0.005 s^(-1)/0.7,which is 49%higher than the initial alloy.
基金financially supported by the National Natural Science Foundation of China(Nos.52293395 and 52293393)the Xiongan Science and Technology Innovation Talent Project of MOST,China(No.2022XACX0500)。
文摘Understandings of the effect of hot deformation parameters close to the practical production line on grain refinement are crucial for enhancing both the strength and toughness of future rail steels.In this work,the austenite dynamic recrystallization(DRX)behaviors of a eutectoid pearlite rail steel were studied using a thermo-mechanical simulator with hot deformation parameters frequently employed in rail production lines.The single-pass hot deformation results reveal that the prior austenite grain sizes(PAGSs)for samples with different deformation reductions decrease initially with an increase in deformation temperature.However,once the deformation temperature is beyond a certain threshold,the PAGSs start to increase.It can be attributed to the rise in DRX volume fraction and the increase of DRX grain with deformation temperature,respectively.Three-pass hot deformation results show that the accumulated strain generated in the first and second deformation passes can increase the extent of DRX.In the case of complete DRX,PAGS is predominantly determined by the deformation temperature of the final pass.It suggests a strategic approach during industrial production where part of the deformation reduction in low temperature range can be shifted to the medium temperature range to release rolling mill loads.
基金supports by the National Nature Science Foundation of China(No.52275354)the Na-tional Key R&D Program of China(No.2018YFA0702900).
文摘Ti-Cu eutectoid or near-eutectoid alloys were found to possess exceptional high strength owning to the nano-scale lamellar structure of Ti_(2)Cu andα-Ti after additive manufacturing,they are potential candidates for high-performance materials.To reveal the deformation and strengthening mechanisms,the molecular dynamics(MD)simulations and experimental analysis were carried out upon Ti-Ti_(2)Cu lamellae.In this work,we focused on revealing the interface dislocations(IDs)pattern and its effects on the dynamic evolution of the lattice dislocations(LDs)at the Ti/Ti_(2)Cu interface with(0001)α//(013)Ti_(2)Cu orientation relationship.Atomistic simulations depicted that the equilibrium Ti/Ti_(2)Cu interface contains three groups of partial dislocations which dictate two interfacial coherent structures with low stacking fault energy.Each ID consists of several segments,connected by atomic steps with identical direction.The nucleation sites of LDs under external loading locate at the intersection between the dislocation segment and the atomic step,which is related to the local high atom strain.Under compression deformation,the100{011}and331{103}slip systems in Ti_(2)Cu,and the112¯3{101¯1}slip system inα-Ti are activated,achieving a co-deformation mechanism in the Ti-Ti_(2)Cu multilayers.The dislocation-interface interactions are responsible for the deformation plasticity and in turn governs the mechanical strengthening.During nanoindentation tests,larger hardness(∼6.2 GPa)and smaller activation volume(∼12b3)were found in the Ti-Ti_(2)Cu lamellae,which is mainly ascribed to the presence of high-density lamellae interface and confined layer slip,resulting in interface-mediated dislocation annihilation/deposition and consequent high strain hardening.The MD simulations,nanoindentation tests and TEM investigations of interlayer dislocation activity support the strengthening mechanism of dislocation-interface interactions.
基金Project (ZR2011EL023) supported by the Natural Science Foundation of Shandong Province,ChinaProject (12CX04057A) supported by the Fundamental Research Funds for the Central Universities,China
文摘Al-Ti diffusion couples were made by embedded technology and treated at the temperature between the melting points of Al and Ti. The microstructure evolution and growth mechanism of the Al-Ti DRZ were investigated. The result shows that the DRZ, the mixture of TiAl3 and Al, grows layer by layer along their chemical equilibrium zone. In the course, the growth interface moves toward the aluminum side. TiAl3 is the only new phase which forms earliest in the course of heat-treatment. The growth mechanism of the DRZ changes after the phase transition of titanium. Before the phase transition of titanium, the growth of the DRZ is controlled by the dissolution speed of the titanium to the molten aluminum, while after the phase transition of titanium, the growth is controlled by the chemical reaction speed of Al and Ti atoms, and consequently, its growth rate is greatly increased.
