The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experim...The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).展开更多
Zn-1.0Cu-0.5Ca(TA15)alloy has shown promising characteristics of enhanced mechanical properties and biodegradability for absorbable cardiovascular stents,endovascular devices,and wound closure devices applications.In ...Zn-1.0Cu-0.5Ca(TA15)alloy has shown promising characteristics of enhanced mechanical properties and biodegradability for absorbable cardiovascular stents,endovascular devices,and wound closure devices applications.In this study,the TA15 alloy for bioabsorbable biomedical applications is investigated.In the conventionally cast TA15(TA15-C)alloy,CaZn_(13) phase are present as a large dendritic network with an average size of 73.25±112.84μm,Hot rolling of the TA15-C alloy has broken the long and dendritic network of the CaZn_(13) phases,however,the refined phases are observed as segregations and the distribution is non-uniform.These segregated CaZn_(13) suffered heavy localised corrosion which lead to poor mechanical properties in the as-fabricated condition and after biodegradation.Ultrasonic treatment(UST)during casting is identified as an effective technique for the refinement and redistribution of CaZn_(13) particles in TA15 alloy,which successfully reduce the size of the CaZn_(13) phase to 10.91±4.65μm in the as-solidified condition.After hot rolling,the UST processed TA15(TA15-UST)shows improved mechanical properties due to grain refinement and the reduction in microstructural defects,i.e.the broken CaZn_(13) phase.Results of 8-week immersion corrosion tests showed that both alloys possess very similar corrosion rate.However,TA15-UST has markedly improved corrosion homogeneity compared to TA15-N which favours the retention of mechanical properties even after prolonged exposure to physiological fluids.展开更多
In this study,Cu nanoparticles-coated graphene nanoplatelets(Cu-NPs@GNPs)were synthesized by a simple in situ method with the assistance of Na Cl templates and used for reinforcing Al–10 Si composites through stir ca...In this study,Cu nanoparticles-coated graphene nanoplatelets(Cu-NPs@GNPs)were synthesized by a simple in situ method with the assistance of Na Cl templates and used for reinforcing Al–10 Si composites through stir casting process.The experimental results showed that the coating of Cu-NPs on the GNPs could compromise the density mismatch between GNPs and metal matrix and eff ectively hinder the float of GNPs during stirring.The reaction of Cu-NPs and Al matrix could protect the structural integrity of GNPs as well as improve the interfacial wettability between GNPs and the matrix,thus promoting the uniform dispersion of GNPs in the composites.As a result,the as-prepared 0.5 wt%Cu-NPs@GNPs/Al–10 Si composite exhibited a tensile strength of 251 MPa(45%higher than the Al–10 Si)with a total elongation of 15%.The strengthening eff ects were mainly attributed to the following three reasons:Firstly,the Cu-NPs coating improved the interfacial bonding between GNPs and Al matrix which promoted the load transfer from the matrix to the GNPs.Secondly,the nanoscale Al 2 Cu formed by the reaction of Cu-NPs and Al matrix played a role in precipitation strengthening.Thirdly,GNPs refined the silicon phases and improved the monolithic performances of the composites.展开更多
A common problem for Zn alloys is the trade-off between antibacterial ability and biocompatibility.This paper proposes a strategy to solve this problem by increasing release ratio of Ca^(2+)ions,which is realized by s...A common problem for Zn alloys is the trade-off between antibacterial ability and biocompatibility.This paper proposes a strategy to solve this problem by increasing release ratio of Ca^(2+)ions,which is realized by significant refinement of CaZn13 particles through bottom circulating water-cooled casting(BCWC)and rolling.Compared with conventionally fabricated Zn-0.3Ca alloy,the BCWC-rolled alloy shows higher antibacterial abilities against E.coli and S.aureus,meanwhile much less toxicity to MC3T3-E1 cells.Additionally,plasticity,degradation uniformity,and ability to induce osteogenic differentiation in vitro of the alloy are improved.The elongation up to 49%,which is the highest among Zn alloys with Ca,and is achieved since the sizes of CaZn_(13) particles and Zn grains are small and close.As a result,the long-standing problem of low formability of Zn alloys containing Ca has also been solved due to the elimination of large CaZn_(13) particles.The BCWC-rolled alloy is a promising candidate of making GBR membrane.展开更多
基金Project(E2016203256)supported by the Natural Science Foundation of Hebei Province,China
文摘The behaviors of the precipitation and decomposition of carbides in AISI M2 high-speed steel modified by nitrogen and mischmetal were investigated using DSC, XRD, SEM and TEM. The as-cast microstructure of the experimental steel consists of dendrites of iron matrix, networks of eutectic carbides and secondary carbides. The average distance between networks is about 34 μm. The carbides mainly include M_2C, M(C,N) and M_6C, and their relative contents are 58.5%, 30.3% and 11.2%, respectively. The average spacing between the M_2C fibers is 1.5 μm. The decomposition of M_2C occurs from 897.2 to 1221.5 ℃(heating rate of 200 ℃/h). Some precipitated carbide particles occur in the M_2C matrix after holding for 15 min at 1100 ℃. With increasing holding time, the carbide fibers neck down more and more obviously until they are broken down. The spectral peaks of M_2C almost disappear after holding for 60 min. The spectral peaks of M_6C gradually strengthen with the holding time, and the relative content of M_6C increases to 79.8% after holding for 60 min. After holding for 180 min, the carbide fibers disappear, and the decomposition products consist of fine carbide particles(about 300 nm) and short rod-like carbides(about 3.5 μm).
基金support of the Australian Research Council through the ARC Research Hub for Advanced Manufacturing of Medical Devices(IH150100024)。
文摘Zn-1.0Cu-0.5Ca(TA15)alloy has shown promising characteristics of enhanced mechanical properties and biodegradability for absorbable cardiovascular stents,endovascular devices,and wound closure devices applications.In this study,the TA15 alloy for bioabsorbable biomedical applications is investigated.In the conventionally cast TA15(TA15-C)alloy,CaZn_(13) phase are present as a large dendritic network with an average size of 73.25±112.84μm,Hot rolling of the TA15-C alloy has broken the long and dendritic network of the CaZn_(13) phases,however,the refined phases are observed as segregations and the distribution is non-uniform.These segregated CaZn_(13) suffered heavy localised corrosion which lead to poor mechanical properties in the as-fabricated condition and after biodegradation.Ultrasonic treatment(UST)during casting is identified as an effective technique for the refinement and redistribution of CaZn_(13) particles in TA15 alloy,which successfully reduce the size of the CaZn_(13) phase to 10.91±4.65μm in the as-solidified condition.After hot rolling,the UST processed TA15(TA15-UST)shows improved mechanical properties due to grain refinement and the reduction in microstructural defects,i.e.the broken CaZn_(13) phase.Results of 8-week immersion corrosion tests showed that both alloys possess very similar corrosion rate.However,TA15-UST has markedly improved corrosion homogeneity compared to TA15-N which favours the retention of mechanical properties even after prolonged exposure to physiological fluids.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51771130,51531004,and 51422104)the Tianjin youth talent support program+1 种基金the Tianjin Natural Science Funds for Distinguished Young Scholars(Grant No.17JCJQJC44300)the Tianjin Science and Technology Support Project(Grant No.17ZXCLGX00060)。
文摘In this study,Cu nanoparticles-coated graphene nanoplatelets(Cu-NPs@GNPs)were synthesized by a simple in situ method with the assistance of Na Cl templates and used for reinforcing Al–10 Si composites through stir casting process.The experimental results showed that the coating of Cu-NPs on the GNPs could compromise the density mismatch between GNPs and metal matrix and eff ectively hinder the float of GNPs during stirring.The reaction of Cu-NPs and Al matrix could protect the structural integrity of GNPs as well as improve the interfacial wettability between GNPs and the matrix,thus promoting the uniform dispersion of GNPs in the composites.As a result,the as-prepared 0.5 wt%Cu-NPs@GNPs/Al–10 Si composite exhibited a tensile strength of 251 MPa(45%higher than the Al–10 Si)with a total elongation of 15%.The strengthening eff ects were mainly attributed to the following three reasons:Firstly,the Cu-NPs coating improved the interfacial bonding between GNPs and Al matrix which promoted the load transfer from the matrix to the GNPs.Secondly,the nanoscale Al 2 Cu formed by the reaction of Cu-NPs and Al matrix played a role in precipitation strengthening.Thirdly,GNPs refined the silicon phases and improved the monolithic performances of the composites.
基金financially supported by Xiongan New Area Science and Technology Innovation Project(2022XACX0600)the National Natural Science Foundation of China(No.52231010 and No.52071028)Beijing Nova Program(2022 Beijing Nova Program Cross Cooperation Program No.20220484178).
文摘A common problem for Zn alloys is the trade-off between antibacterial ability and biocompatibility.This paper proposes a strategy to solve this problem by increasing release ratio of Ca^(2+)ions,which is realized by significant refinement of CaZn13 particles through bottom circulating water-cooled casting(BCWC)and rolling.Compared with conventionally fabricated Zn-0.3Ca alloy,the BCWC-rolled alloy shows higher antibacterial abilities against E.coli and S.aureus,meanwhile much less toxicity to MC3T3-E1 cells.Additionally,plasticity,degradation uniformity,and ability to induce osteogenic differentiation in vitro of the alloy are improved.The elongation up to 49%,which is the highest among Zn alloys with Ca,and is achieved since the sizes of CaZn_(13) particles and Zn grains are small and close.As a result,the long-standing problem of low formability of Zn alloys containing Ca has also been solved due to the elimination of large CaZn_(13) particles.The BCWC-rolled alloy is a promising candidate of making GBR membrane.
