In the present manuscript numerical analysis on the ballistic performance of a tungsten particle/metallic glass matrix(WP/MG) composite rod is conducted by integrating with related experimental investigations. In the ...In the present manuscript numerical analysis on the ballistic performance of a tungsten particle/metallic glass matrix(WP/MG) composite rod is conducted by integrating with related experimental investigations. In the corresponding finite element method(FEM) simulations a modified coupled thermomechanical constitutive model is employed to describe the mechanical properties of metallic glass(MG)matrix, and geometrical models of the WP/MG composite rod are established based on its inner structure. The deformation and failure characteristics of the rod and target materials are analyzed in detail,and the influences of various factors on the ballistic performance of the WP/MG composite long rod are discussed. Related analysis demonstrates that the penetrating performance of the WP/MG rod is similar to that of the tungsten fiber/metallic glass matrix(WF/MG) composite long rod, i.e., a "self-sharpening" behavior also occurs during the penetration process, and correspondingly its penetrating capability is better than that of the tungsten heavy alloy(WHA) rod. However, the mass erosion manner of the WP/MG rod is different and the erosion is relatively severe, thus its penetrating capability is a little lower compared with that of the WF/MG one. Moreover, the impact velocity and the target strength have significant influences on the ballistic performance of the WP/MG composite rod, whereas the effect of initial nose shape is very little.展开更多
La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindenta...La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)22 BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.展开更多
In the current research, serrated flow is investigated under tensile and compressive loading in a ZrCubased bulk metallic glass composite (BMGC) that is well known for its plastic deformability, which is higher than t...In the current research, serrated flow is investigated under tensile and compressive loading in a ZrCubased bulk metallic glass composite (BMGC) that is well known for its plastic deformability, which is higher than that of metallic glasses. Statistical analysis on serrations shows a complex, scale free process, in which shear bands are highly correlated. The distribution of the elastic-energy density stored in each serration event follows a power-law relationship, showing a randomly generated serrated event under both tension and compression tests. The plastic deformation in the temporal space is explored by a timeseries analysis, which is consistent with the trajectory convergent evolution in critical dynamic behavior even in the low strain rate regime in both tests. The results demonstrate that the secondary phase in the BMGC can stabilize the shear band extension and facilitate the critical behavior in the low strain rate regime. This study provides a strong evidence of serrated flow phenomenon in BMGC under tension test, and offers a deep understanding of the correlation between serrations and shear banding in temporal space.展开更多
Pre-existing(multiple)shear bands were introduced into the ductile Zr56Co28Al16 and Zr65Ni10Cu15Al10bulk metallic glasses(BMGs)through the lateral-deformation,respectively.It was found that the pre-exiting shear b...Pre-existing(multiple)shear bands were introduced into the ductile Zr56Co28Al16 and Zr65Ni10Cu15Al10bulk metallic glasses(BMGs)through the lateral-deformation,respectively.It was found that the pre-exiting shear bands can further enhance the compressive plasticity of ductile BMGs.According to the serration analysis on the plastic deformation of the as-cast and the pre-deformed samples,the serration events in the stress-strain curves during deformation display a self-organized critical(SOC)behavior.Compared with the as-cast BMGs,a larger power-law scaling exponent calculated based on serrated flow behaviors becomes larger for the pre-deformed BMGs,implying that the shear banding stability of BMGs is effectively enhanced.This should be caused by the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs.However,by introducing a large amount of multiple shear bands into the glassy matrix,it also becomes easier for shear bands to propagate along the pre-existing shear bands,leading to a lower cut-off elastic energy density for the pre-deformed BMGs.More multiple shear bands with stronger interactions for the pre-deformed BMGs could provide a larger chance to activate the shear-band cracking but less local elastic energies are remained for the subsequent crack-linking.展开更多
A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treat...A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.展开更多
The advanced fabrication of in-situ dendrite/metallic glass matrix (MGM) composites is reviewed. Herein, the semi- solid processing and Bridgman solidification are two methods, which can make the dendrites homogeneo...The advanced fabrication of in-situ dendrite/metallic glass matrix (MGM) composites is reviewed. Herein, the semi- solid processing and Bridgman solidification are two methods, which can make the dendrites homogeneously dispersed within the metallic glass matrix. Upon quasi-static compressive loading at room temperature, almost all the in-situ composites exhibit improved plasticity, due to the effective block to the fast propagation of shear bands. Upon quasi-static tensile loading at room temperature, although the composites possess tensile ductility, the inhomogeneous deformation and associated softening dominates. High volume-fractioned dendrites and network structures make in-situ composites distinguishingly plastic upon dynamic compression. In-situ composite exhibits high tensile strength and softening (necking) in the supercooled liquid region, since the presence of high volume-fractioned dendrites lowers the rheology of the viscous glass matrix at high temperatures. At cryogenic temperatures, a distinguishingly-increased maximum strength is available; however, a ductile-to-brittle transition seems to be present by lowering the temperature. Besides, improved tension-tension fatigue limit of 473 MPa and four-point-bending fatigue limit of 567 MPa are gained for Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 MGM composites. High volume-fraction dendrites within the glass matrix induce increased effectiveness on the blunting and propagating resistance of the fatigue-crack tip. The fracture toughness of in-situ composites is comparable to those of the toughest steels and crystalline Ti alloys. During steady-state crack-growth, the confinement of damage by in-situ dendrites results in enhancement of the toughness.展开更多
A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix...A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.展开更多
Zr48.5Cu46.5Al5 bulk metallic glass (BMG) com- posites with diameters of 3 and 4 mm were prepared through suction casting in an arc melting furnace by modulating the alloy composition around the monothetic BMG composi...Zr48.5Cu46.5Al5 bulk metallic glass (BMG) com- posites with diameters of 3 and 4 mm were prepared through suction casting in an arc melting furnace by modulating the alloy composition around the monothetic BMG composition of the high glass forming ability. Microstructural charac- terization reveals that the composites contain micron-sized CuZr phase with martensite structure, as well as nano-sized Zr2Cu crystalline particles and Cu10Zr7 plate-like phase em- bedded in an amorphous matrix. Room temperature com- pression tests showed that the composites exhibited signifi- cant strain hardening and obvious plastic strain of 7.7% for 3 mm and 6.4% for 4 mm diameter samples, respectively.展开更多
Shear bands play a key role in the plastic deformation of metallic glasses(MGs).Even though there are extensive studies on the initiation and propagation of shear bands,the interactions among them have not been syst...Shear bands play a key role in the plastic deformation of metallic glasses(MGs).Even though there are extensive studies on the initiation and propagation of shear bands,the interactions among them have not been systematically studied yet.The interactions between the primary shear bands(PSBs)and secondary shear bands(SSBs)in a ductile Zr-based MG were studied.The residual stress near PSBs can deflect the propagation direction and reduce the propagation velocity of SSBs,which contributes to the plasticity and toughness of the MG.It was demonstrated that the probability and strength of the interactions between PSBs and SSBs would become stronger for MGs with larger Young′s modulus and smaller shear modulus,i.e.,larger Poisson′s ratio.These results are valuable in understanding the plastic deformation of MGs and may be helpful in designing new MGs with desirable mechanical properties.展开更多
By means of statistical analysis,the deformation mechanisms taking place in elastic loading and plastic shearing stages during serrated flows on the stress-strain curves for bulk metallic glasses were studied comprehe...By means of statistical analysis,the deformation mechanisms taking place in elastic loading and plastic shearing stages during serrated flows on the stress-strain curves for bulk metallic glasses were studied comprehensively.Normalized serration number presented a linear increasing tendency with the decrease of applied strain rates due to the reduction of free volumes.An excellent plastic deformation was illustrated from the influences of structure arrangement with activation energy.By using mean-field theory(MFT),maximum elastic-energy density at different strain rates could be predicted by MFT besides maximum stress drops during serrations.These results were helpful for understanding the serrated flow behavior or designing decent schemes to improve the plasticity of bulk metallic glasses at room temperature.展开更多
The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,t...The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.展开更多
The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Z...The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.展开更多
Fe-based bulk metallic glasses (BMGs) normally exhibit super high strength but significant brittleness at ambient temperature. Therefore,it is difficult to investigate the plastic deformation behavior and mechanism in...Fe-based bulk metallic glasses (BMGs) normally exhibit super high strength but significant brittleness at ambient temperature. Therefore,it is difficult to investigate the plastic deformation behavior and mechanism in these alloys through conven-tional tensile and compressive tests due to lack of distinct macroscopic plastic strain. In this work,the deformation behavior of Fe52Cr15Mo9Er3C15B6 BMG was in-vestigated through instrumented nanoindentation and uniaxial compressive tests. The results show that serrated flow,the typical plastic deformation feature of BMGs,could not be found in as-cast and partially crystallized samples during nanoinden-tation. In addition,the deformation behavior and mechanical properties of the alloy are insensitive to the applied loading rate. The mechanism for the appearance of the peculiar deformation behavior in the Fe-based BMG is discussed in terms of the temporal and spatial characteristics of shear banding during nanoindentation.展开更多
The metallic glass matrix composites(MGMCs)and bulk metallic glasses(BMGs)were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,resp...The metallic glass matrix composites(MGMCs)and bulk metallic glasses(BMGs)were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.展开更多
基金The authors acknowledge the financial support provided by the Knowledge Innovation Program of Chinese Academy of Sciences,No.KJCX2-SW-L05the National Natural Science Foundation of China,No.50101012.
基金supported by the Science and Technology Development Fund (2015B0201025)the key subject "Computational Solid Mechanics" of China Academy of Engineering Physics+1 种基金the National Outstanding Young Scientists Foundation of China (11225213)the National Natural Science Foundation of China (11521062,11602258)
文摘In the present manuscript numerical analysis on the ballistic performance of a tungsten particle/metallic glass matrix(WP/MG) composite rod is conducted by integrating with related experimental investigations. In the corresponding finite element method(FEM) simulations a modified coupled thermomechanical constitutive model is employed to describe the mechanical properties of metallic glass(MG)matrix, and geometrical models of the WP/MG composite rod are established based on its inner structure. The deformation and failure characteristics of the rod and target materials are analyzed in detail,and the influences of various factors on the ballistic performance of the WP/MG composite long rod are discussed. Related analysis demonstrates that the penetrating performance of the WP/MG rod is similar to that of the tungsten fiber/metallic glass matrix(WF/MG) composite long rod, i.e., a "self-sharpening" behavior also occurs during the penetration process, and correspondingly its penetrating capability is better than that of the tungsten heavy alloy(WHA) rod. However, the mass erosion manner of the WP/MG rod is different and the erosion is relatively severe, thus its penetrating capability is a little lower compared with that of the WF/MG one. Moreover, the impact velocity and the target strength have significant influences on the ballistic performance of the WP/MG composite rod, whereas the effect of initial nose shape is very little.
基金This work was financially supported by the National Natural Science Foundation of China (No.50571109, 10572142 and 10432050)the Knowledge Innovation Program of the Chinese Academy of Sciences.
文摘La57.6Al17.5(Cu,Ni)24.9 and La64Al14(Cu,Ni)22 bulk metallic glasses (BMGs) were prepared by copper-mould casting method. Plastic deformation behavior of the two BMGs at various loading rates was studied by nanoindentation. The results showed that the La57.6Al17.5(Cu,Ni)24.9 BMG with a glass transition temperature of 423 K exhibited prominent serrated flow at low loading rates, whereas less pronounced serrated flow at high rates during nanoindentation. In contrast, the La64Al14(Cu,Ni)22 BMG with a glass transition temperature of 401 K exhibited prominent serrated flow at high loading rates. The different rate dependency of serrated flow in the two La-based BMGs is related to the different glass transition temperature, and consequently the degree of viscous flow during indentation at room temperature. A smoother flow occurs in the alloy with relatively lower glass transition temperature, due to the relaxation of stress concentration.
基金financially supported by National Natural Science Foundation of China (Nos. 51671067, 51761135125 and 11771407)the Plan for Scientific Innovation Talent of Henan Province (No. 164200510011)the Innovative Research Team of Science and Technology in Henan Province (No. 17IRTSTHN007)
文摘In the current research, serrated flow is investigated under tensile and compressive loading in a ZrCubased bulk metallic glass composite (BMGC) that is well known for its plastic deformability, which is higher than that of metallic glasses. Statistical analysis on serrations shows a complex, scale free process, in which shear bands are highly correlated. The distribution of the elastic-energy density stored in each serration event follows a power-law relationship, showing a randomly generated serrated event under both tension and compression tests. The plastic deformation in the temporal space is explored by a timeseries analysis, which is consistent with the trajectory convergent evolution in critical dynamic behavior even in the low strain rate regime in both tests. The results demonstrate that the secondary phase in the BMGC can stabilize the shear band extension and facilitate the critical behavior in the low strain rate regime. This study provides a strong evidence of serrated flow phenomenon in BMGC under tension test, and offers a deep understanding of the correlation between serrations and shear banding in temporal space.
基金financially supported by the National Natural Science Foundation of China(51501104,51501103,and 51371108)the Young Scholars Program of Shandong University(Weihai)
文摘Pre-existing(multiple)shear bands were introduced into the ductile Zr56Co28Al16 and Zr65Ni10Cu15Al10bulk metallic glasses(BMGs)through the lateral-deformation,respectively.It was found that the pre-exiting shear bands can further enhance the compressive plasticity of ductile BMGs.According to the serration analysis on the plastic deformation of the as-cast and the pre-deformed samples,the serration events in the stress-strain curves during deformation display a self-organized critical(SOC)behavior.Compared with the as-cast BMGs,a larger power-law scaling exponent calculated based on serrated flow behaviors becomes larger for the pre-deformed BMGs,implying that the shear banding stability of BMGs is effectively enhanced.This should be caused by the pronounced interactions of shear bands during plastic deformation for the pre-deformed BMGs.However,by introducing a large amount of multiple shear bands into the glassy matrix,it also becomes easier for shear bands to propagate along the pre-existing shear bands,leading to a lower cut-off elastic energy density for the pre-deformed BMGs.More multiple shear bands with stronger interactions for the pre-deformed BMGs could provide a larger chance to activate the shear-band cracking but less local elastic energies are remained for the subsequent crack-linking.
基金supported through the Start-up research grant (No.SRG/2020/000095) of Science and Engineering Research Board,DST,Go INanyang Technological University was supported by the funding from A*STAR via the Structural Metals and Alloys Programme (No.A18B1b0061)+2 种基金Institute of Metal Research CAS was supported by the National Natural Science Foundation of China (Nos.52171164 and 51790484)the National Key Research and Development Program (No.2018YFB0703402)the Youth Innovation Promotion Association CAS (No.2021188)。
文摘A β-Ti dendrite reinforced Zr-based bulk metallic glass composite(BMGC) was found to be brittle when cast in a large size. The reasons for the embrittlement and the effectiveness of the cryothermal cycling(CTC) treatment in restoring the mode I fracture toughness are examined. Plasticity in all the CTC treated BMGC is estimated from the distribution and occurrence of pop-ins in nanoindentation tests and by measuring the magnitude of enthalpy of relaxation(△H_(rel)) via differential scanning calorimetry(DSC). This is further validated by examining the strain-to-failure(ε_(f)) in compression tests. Mode I fracture behaviour of the as-cast embrittled BMGC and the CTC treated BMGC, which exhibits maximum plasticity, is examined. Results show that both BMGCs are equally brittle and exhibit 5 times lower notch toughness(K_(QJ))than their tougher counterpart. Post-facto imaging of the side surfaces reveals the absence of notch-tip plasticity in both BMGCs. The lack of notch tip plasticity of CTC treated BMGC, despite exhibiting signatures of plasticity in nanoindentation and higher △Hrelis rationalized by reassessing the origin of pop-ins in nanoindentation tests and describing the variations in chemical and topological short range ordering during CTC, respectively. Implications of these results in terms of improving the fracture toughness of structurally relaxed BMGCs via CTC are discussed.
基金the financial support of the National Natural Science Foundation of China(No.51101110)the Youth Science Foundation of Shanxi Province.China(No. 2012021018-1)+2 种基金the Research Project Supported by Shanxi Scholarship Council of China(No.2012-032)Technology Foundation for Selected Overseas Chinese Scholar Ministry of Human Resources and Social Security of Chinathe Program for the Outstanding Innovative Teams of Higher Learning Institutions of Shanxi
文摘The advanced fabrication of in-situ dendrite/metallic glass matrix (MGM) composites is reviewed. Herein, the semi- solid processing and Bridgman solidification are two methods, which can make the dendrites homogeneously dispersed within the metallic glass matrix. Upon quasi-static compressive loading at room temperature, almost all the in-situ composites exhibit improved plasticity, due to the effective block to the fast propagation of shear bands. Upon quasi-static tensile loading at room temperature, although the composites possess tensile ductility, the inhomogeneous deformation and associated softening dominates. High volume-fractioned dendrites and network structures make in-situ composites distinguishingly plastic upon dynamic compression. In-situ composite exhibits high tensile strength and softening (necking) in the supercooled liquid region, since the presence of high volume-fractioned dendrites lowers the rheology of the viscous glass matrix at high temperatures. At cryogenic temperatures, a distinguishingly-increased maximum strength is available; however, a ductile-to-brittle transition seems to be present by lowering the temperature. Besides, improved tension-tension fatigue limit of 473 MPa and four-point-bending fatigue limit of 567 MPa are gained for Zr58.5Ti14.3Nb5.2Cu6.1Ni4.9Be11.0 MGM composites. High volume-fraction dendrites within the glass matrix induce increased effectiveness on the blunting and propagating resistance of the fatigue-crack tip. The fracture toughness of in-situ composites is comparable to those of the toughest steels and crystalline Ti alloys. During steady-state crack-growth, the confinement of damage by in-situ dendrites results in enhancement of the toughness.
基金This work was supported by the National Natural Science Foundation of China (51434008 (U1435204), 51531005), the China's Manned Space Station Project (Mission No: TGJZS00-2-RW024), Dongguan Innovative Research Team Program (2014607134), Shenyang Key R & D and Technology Transfer Pro-gram (Z17-7-001), Seed Fund Project of Shenyang National University Science and Technology Zone (20151019001) and Dou-ble-hundred Program of Shenyang Science and Technology Innova-tion Project (Y17-2-036).
文摘A Ta wire-reinforced Zr-based bulk metallic glass composite with a new type of structure was prepared successfully by the method of liquid metal infiltration. Ta wires distribute uniformly in the metallic glass matrix in the form of spirals. The composite exhibits two yield stages under compressive stress, and the samples are compressed into thin pancakes. The micro-cracks originate at the interface between the Ta wire and the metallic glass matrix and propagate perpendicularly to the interface, which then induce multiple shear bands in the metallic glass matrix due to the stress concentration. Shear cracks form in the metallic glass matrix during the continued loading process as a result of the interaction of shear bands. Deformation bands of Ta wires occur under the impact of shear bands. The local stress fields in the composite are changed obviously due to the introduction of the spiral-formed reinforcements. The investigation of the deformation behavior and mechanism suggests a new method for the application of bulk metallic glass composites as the structural materials.
基金supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(Project number:KJCX2-SW-L05)National Natural Science Foundation of China(Grant No.50101012).
文摘Zr48.5Cu46.5Al5 bulk metallic glass (BMG) com- posites with diameters of 3 and 4 mm were prepared through suction casting in an arc melting furnace by modulating the alloy composition around the monothetic BMG composition of the high glass forming ability. Microstructural charac- terization reveals that the composites contain micron-sized CuZr phase with martensite structure, as well as nano-sized Zr2Cu crystalline particles and Cu10Zr7 plate-like phase em- bedded in an amorphous matrix. Room temperature com- pression tests showed that the composites exhibited signifi- cant strain hardening and obvious plastic strain of 7.7% for 3 mm and 6.4% for 4 mm diameter samples, respectively.
基金Item Sponsored by China Postdoctoral Science Foundation(2014M551779)Ningbo Municipal Natural Science Foundation of China(2015A610005,2015A610064)One Hundred Talents Program of Chinese Academy of Sciences
文摘Shear bands play a key role in the plastic deformation of metallic glasses(MGs).Even though there are extensive studies on the initiation and propagation of shear bands,the interactions among them have not been systematically studied yet.The interactions between the primary shear bands(PSBs)and secondary shear bands(SSBs)in a ductile Zr-based MG were studied.The residual stress near PSBs can deflect the propagation direction and reduce the propagation velocity of SSBs,which contributes to the plasticity and toughness of the MG.It was demonstrated that the probability and strength of the interactions between PSBs and SSBs would become stronger for MGs with larger Young′s modulus and smaller shear modulus,i.e.,larger Poisson′s ratio.These results are valuable in understanding the plastic deformation of MGs and may be helpful in designing new MGs with desirable mechanical properties.
基金the financial support of National Natural Science Foundation of China(No.51371122)the Youth Natural Science Foundation of Shanxi Province,China(No.2015021005)
文摘By means of statistical analysis,the deformation mechanisms taking place in elastic loading and plastic shearing stages during serrated flows on the stress-strain curves for bulk metallic glasses were studied comprehensively.Normalized serration number presented a linear increasing tendency with the decrease of applied strain rates due to the reduction of free volumes.An excellent plastic deformation was illustrated from the influences of structure arrangement with activation energy.By using mean-field theory(MFT),maximum elastic-energy density at different strain rates could be predicted by MFT besides maximum stress drops during serrations.These results were helpful for understanding the serrated flow behavior or designing decent schemes to improve the plasticity of bulk metallic glasses at room temperature.
基金Item Sponsored by the Hong Kong Research Grant Council(RGC)of China(U102013,9042066,9054013)
文摘The rate dependence of serrated flow and its effects on the stability of shear banding were systematically investigated in a prototypic bulk metallic glass.It was found that with the increase of external strain rate,the serrated flow is gradually suppressed and could completely disappear at a critical strain rate.The serration size,characterized by the mean stress drop amplitude,decreases inversely with the strain rate,while the waiting time for serration decreases with the strain rate in a power-law manner.The rate dependence of the serrated flow has important effects on the dynamics and stability of shear banding process,and leads to an optimal plasticity achieved around the critical strain rate for the disappearance of serrated flow.These results are discussed and interpreted in terms of the microscopic deformation theory and the stick-slip dynamics of shear banding for bulk metallic glasses.
基金supported by the National Natural Science Foundation of China (Grant Nos. 50771006 and 50631010)the National Basic Research Program of China (Grant No. 2007CB613900)+1 种基金PCSIRT (Grant No. IRT0512)NCET (Grant No. NCET-07-0041)
文摘The present work found the plastic deformability of Zr65Cu17.5Ni10Al7.5 BMG dependent on the cooling rate during the formation from the molten state alloy. The deformation behavior in the compression test of φ 2 mm Zr65Cu17.5Ni10Al7.5 BMGs as-cast or lathed from different sizes as-cast samples was characterized, and they exhibited different plastic strains. The compressive plastic strain increases with the decreasing diameter of the as-cast specimens, i.e. with increasing the cooling rate. It is suggested that free volume content in the BMGs, which is related to the cooling rate during the rapid solidification, could play an important role in the deformation process of the BMGs.
基金the National Natural Science Foundation of China (Grant Nos. 50571109, 10572142 and 50771102) the National Basic Research Program of China (973 Program)(Grant No. 2007CB613900)
文摘Fe-based bulk metallic glasses (BMGs) normally exhibit super high strength but significant brittleness at ambient temperature. Therefore,it is difficult to investigate the plastic deformation behavior and mechanism in these alloys through conven-tional tensile and compressive tests due to lack of distinct macroscopic plastic strain. In this work,the deformation behavior of Fe52Cr15Mo9Er3C15B6 BMG was in-vestigated through instrumented nanoindentation and uniaxial compressive tests. The results show that serrated flow,the typical plastic deformation feature of BMGs,could not be found in as-cast and partially crystallized samples during nanoinden-tation. In addition,the deformation behavior and mechanical properties of the alloy are insensitive to the applied loading rate. The mechanism for the appearance of the peculiar deformation behavior in the Fe-based BMG is discussed in terms of the temporal and spatial characteristics of shear banding during nanoindentation.
基金Item Sponsored by National Natural Science Foundation of China(51371122,51471025,51210105006)Program for Innovative Talents of Higher Learning Institutions of Shanxi of China(2013)Youth Natural Science Foundation of Shanxi Province of China(2015021005)
文摘The metallic glass matrix composites(MGMCs)and bulk metallic glasses(BMGs)were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.