Hall-Petch relation was widely applied to evaluate the grain size effect on mechanical properties of metallic material. However, the sample size effect on the Hall-Petch relation was always ignored. In the present stu...Hall-Petch relation was widely applied to evaluate the grain size effect on mechanical properties of metallic material. However, the sample size effect on the Hall-Petch relation was always ignored. In the present study, the mechanical test and microstructure observation were performed to investigate the combined effects of grain and sample sizes on the deformation behaviors of gold microwires. The polycrystalline gold microwires with diameter of 16 ?m were annealed at temperatures from 100°C to 600°C, leading to different ratios(t/d) of wire diameter(t) to grain size(d) from 0.9 to 16.7. When the t/d was lower than 10, the yield stress dropped fast and deviated from the Hall-Petch relation. The free-surface grains played key role in the yield stress softening, and the volume fraction of free-surface grains increased with the t/d decreasing. Furthermore, the effects of t/d on work-hardening behaviors and fracture modes were also studied. With t/d value decreasing from 17 to 3.4, the samples exhibited necking fracture and the dislocation pile-ups induced work-hardening stage was gradually activated.With the t/d value further decreasing(t/d < 3.4), the fracture mode turned into shear failure, and the work-hardening capability lost. As the gold microwire for wire bonding is commonly applied in the packaging of integrated circuit chips, and the fabrication of microwire suffers multi-pass cold-drawing and annealing treatments to control the grain size. The present study could provide instructive suggestion for gold microwire fabrication and bonding processes.展开更多
The strength-ductility trade-offhas been a longstanding dilemma in metallic materials.Here we report an innovative approach to achieve a high strength-ductility synergy via dual precipitation of sheared and bypassed p...The strength-ductility trade-offhas been a longstanding dilemma in metallic materials.Here we report an innovative approach to achieve a high strength-ductility synergy via dual precipitation of sheared and bypassed precipitates.(Ni_(2) Co_(2) FeCr)_(96-x) Al_(4) Nb_(x)(at.%)alloys strengthened by nanoscale L12 particles and Laves precipitates were selected as a model for this study,and their precipitate microstructures and mechanical properties were thoroughly investigated.The dual-precipitation-strengthened alloys exhibit a yield strength of more than 1400 MPa,an ultimate tensile strength of over 1800 MPa,and a uniform elon-gation of 18%,thus achieving a high strength-ductility synergy.Our analysis reveals that the nanoscale L1_(2) precipitates contribute to the strength via the particle shearing mechanism,whereas the Laves phase provides the strengthening through the Orowan bypass mechanism.The study of deformation microstruc-tures shows that the L1_(2) precipitates are sheared by stacking faults,which facilitates long-range disloca-tion gliding through the matrix.As a result,deformation induces the formation of hierarchical stacking fault networks and immobile Lomer-Cottrell locks,which effectively enhance the work hardening ca-pability and plastic stability,thereby resulting in a high ductility at high strength levels.Dislocations are piled-up against the interface between the Laves precipitates and matrix,which increases the work hardening capability at the early stages of plastic deformation but causes stress concentrations.The dual precipitation strategy may be useful for many other alloys for achieving superior mechanical properties for technological applications.展开更多
基金financially supported by the National Key R&D Program of China(Project No.2017YFA0204403)the Shenzhen Virtual University Park(R-IND1710)+5 种基金the Innovation and Technology Commission via the Hong Kong Branch of National Precious Metals Material Engineering Research Centersupported by the Research Grants Council of the Hong Kong Special Administrative Region,China(No.CityU 11209914)General Research Fund of Hong Kong(No.CityU 11247516)the National Natural Science Foundation of China(No.51301147)supported by Province-Institute/Province-College Cooperation Project underGrant No.2017IB016The financial support from SZSTI(Ref:JSGG20141020103826038)
文摘Hall-Petch relation was widely applied to evaluate the grain size effect on mechanical properties of metallic material. However, the sample size effect on the Hall-Petch relation was always ignored. In the present study, the mechanical test and microstructure observation were performed to investigate the combined effects of grain and sample sizes on the deformation behaviors of gold microwires. The polycrystalline gold microwires with diameter of 16 ?m were annealed at temperatures from 100°C to 600°C, leading to different ratios(t/d) of wire diameter(t) to grain size(d) from 0.9 to 16.7. When the t/d was lower than 10, the yield stress dropped fast and deviated from the Hall-Petch relation. The free-surface grains played key role in the yield stress softening, and the volume fraction of free-surface grains increased with the t/d decreasing. Furthermore, the effects of t/d on work-hardening behaviors and fracture modes were also studied. With t/d value decreasing from 17 to 3.4, the samples exhibited necking fracture and the dislocation pile-ups induced work-hardening stage was gradually activated.With the t/d value further decreasing(t/d < 3.4), the fracture mode turned into shear failure, and the work-hardening capability lost. As the gold microwire for wire bonding is commonly applied in the packaging of integrated circuit chips, and the fabrication of microwire suffers multi-pass cold-drawing and annealing treatments to control the grain size. The present study could provide instructive suggestion for gold microwire fabrication and bonding processes.
基金This research was supported by the National Natural Science Foundation of China(Grant Nos.52171162 and 51801169)Research Grants Council of Hong Kong(Nos.ECS 25202719,GRF 15227121,C1017-21GF,and C1020-21GF)+3 种基金State Key Laboratory for Advanced Metals and Materials Open Fund(2021-ZD04)Shenzhen Science and Technology Program(Grant No.JCYJ20210324142203009)Re-search Institute for Advanced Manufacturing Fund(No.P0041364 and P0046108)PolyU Fund(Nos.P0038814,P0039624,P0042933,and P0043467).
文摘The strength-ductility trade-offhas been a longstanding dilemma in metallic materials.Here we report an innovative approach to achieve a high strength-ductility synergy via dual precipitation of sheared and bypassed precipitates.(Ni_(2) Co_(2) FeCr)_(96-x) Al_(4) Nb_(x)(at.%)alloys strengthened by nanoscale L12 particles and Laves precipitates were selected as a model for this study,and their precipitate microstructures and mechanical properties were thoroughly investigated.The dual-precipitation-strengthened alloys exhibit a yield strength of more than 1400 MPa,an ultimate tensile strength of over 1800 MPa,and a uniform elon-gation of 18%,thus achieving a high strength-ductility synergy.Our analysis reveals that the nanoscale L1_(2) precipitates contribute to the strength via the particle shearing mechanism,whereas the Laves phase provides the strengthening through the Orowan bypass mechanism.The study of deformation microstruc-tures shows that the L1_(2) precipitates are sheared by stacking faults,which facilitates long-range disloca-tion gliding through the matrix.As a result,deformation induces the formation of hierarchical stacking fault networks and immobile Lomer-Cottrell locks,which effectively enhance the work hardening ca-pability and plastic stability,thereby resulting in a high ductility at high strength levels.Dislocations are piled-up against the interface between the Laves precipitates and matrix,which increases the work hardening capability at the early stages of plastic deformation but causes stress concentrations.The dual precipitation strategy may be useful for many other alloys for achieving superior mechanical properties for technological applications.