Metal mold micron scale precision casting technology was developed successfully,and three-dimension complicated microgear castings in micron scale were produced.Evolvement regularity of microgear castings were observe...Metal mold micron scale precision casting technology was developed successfully,and three-dimension complicated microgear castings in micron scale were produced.Evolvement regularity of microgear castings were observed by optical microscope and scanning electron microscope.Compared with conventional casting,microcasting is characterized by typical nonequilibrium solidification,for example,its grain size can be refined significantly,eutectic structure is transformed from lamellar morphology to rod eutectic,and the ratio of primary phase is increased.This kind of microstructure can promote mechanical properties of microcasting.展开更多
Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most mold...Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most molds are made of silicon or silicon-based soft templates,and have poor wear resistant or vulnerability to high temperature,limiting their use in large-scale manufacturing.Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties.However,the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging.In this study,using electrodeposition techniques,the shape of the micropores is modified to obtain end-controlled pores.The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated.Furthermore,the mechanism of non-uniformity evolution of the microporous morphology is revealed.The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process.As a result,typical bionic adhesives with tip-expansion are obtained.Moreover,corresponding adhesion mechanics are analyzed.The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures,providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.展开更多
High-nitrogen nickel-free stainless steels were fabricated by the metal injection molding technique using high nitrogen alloying powders and a mixture of three polymers as binders.Mixtures of metal powders and binders...High-nitrogen nickel-free stainless steels were fabricated by the metal injection molding technique using high nitrogen alloying powders and a mixture of three polymers as binders.Mixtures of metal powders and binders with various proportions were also investigated, and an optimum powder loading capacity was determined as 64vol%.Intact injection molded compacts were successfully obtained by regulating the processing parameters.The debinding process for molded compacts was optimized with a combination of thermo-gravimetric analysis and differential scanning calorimetry analysis.An optimum relative density and nitrogen content of the specimens are obtained at 1360℃,which are 97.8%and 0.79wt%,respectively.展开更多
Sodium chloride(NaCl)was added as a space holder in synthesis of porous titanium by using metal injection molding(MIM)method.The microstructure and mechanical properties of porous titanium were analyzed by mercury por...Sodium chloride(NaCl)was added as a space holder in synthesis of porous titanium by using metal injection molding(MIM)method.The microstructure and mechanical properties of porous titanium were analyzed by mercury porosimeter, scanning electron microscope(SEM)and compression tester.The results show that the content of NaCl influences the porosity of porous titanium significantly.Porous titanium powders with porosity in the range of 42.4%-71.6%and pore size up to 300μm were fabricated.The mechanical test shows that with increasing NaCl content,the compressive strength decreases from 316.6 to 17.5 MPa and the elastic modulus decreases from 3.03 to 0.28 GPa.展开更多
Antioxidation effects on Sm （Co, Cu, Fe, Zr）z-sintered magnets treated by different methods were studied through TGA and DTA. Microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets was analyzed through SEM and EDS...Antioxidation effects on Sm （Co, Cu, Fe, Zr）z-sintered magnets treated by different methods were studied through TGA and DTA. Microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets was analyzed through SEM and EDS. The results indicate that the antioxidation effect of the alloy powder treated in silane solution is better than that of the other methods. The alloy powders treated in stearic acid （SA） solution and polymethyl methacrylate （PMMA） solution can prevent powders from oxidation for a short period of time. Silane solution is not suitable for metal injection molding （MIM） because it severely damages the magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets. SA solution can not only prevent powders from oxidizing in MIM, but also does not damage magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z magnets. The oxygen content of Sm（Co, Cu, Fe, Zr）z-sintered magnets by MIM is 3300μg·g^-1.展开更多
Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe ...Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.展开更多
Nanocrystalline nonferrous metals (Cu, Al, and Ag) were synthesized by flow-levitation-molding method. The microstructure of the as-prepared nanocrystalline metals was characterized by XRD and FESEM. The microhardness...Nanocrystalline nonferrous metals (Cu, Al, and Ag) were synthesized by flow-levitation-molding method. The microstructure of the as-prepared nanocrystalline metals was characterized by XRD and FESEM. The microhardness and electrical resistivity were tested by the HMV-2 type Microhardness Tester and 6157 type Electrometer, respectively. The synthesis process was also studied. The results show that the spheriform particles in nanocrystalline metals have average grain size of 20-30 nm. The relative density of nanocrystalline Cu, Al, and Ag are 95.1%, 98.1% and 98.3%, respectively. The microhardness of nanocrystalline Cu, Al and Ag are 2.01, 2.11 and 1.26 GPa respectively, which are larger than those of their coarse-grained counterparts by the factor of 4.5, 14, and 2.5, respectively. The electrical resistivity of nanocrystalline Cu at room temperature is 1.5×10-7 Ω·m, which is higher than coarse-grained Cu by a factor of 7.5. The pressure is the predominant factor influencing the density of the as-prepared nanocrystalline nonferrous metals.展开更多
Ti-6Al-4V compacts were fabricated by metal injection molding(MIM). Influence of vacuum sintering time on mechanical properties and microstructure of the sintered compacts at 1 260 ℃ were investigated. The experiment...Ti-6Al-4V compacts were fabricated by metal injection molding(MIM). Influence of vacuum sintering time on mechanical properties and microstructure of the sintered compacts at 1 260 ℃ were investigated. The experimental results show that the compacts sintered at 1 260 ℃ for 36 h, which was made from hydrogenation-dehydrogenation(HDH) powder(average particles size is 45 μm), have a relative density of 95.6% 96.7%, ultimate tensile strength of 648686MPa and 0.2% yield strength of 526615MPa; but a lower elongation(<4%) and that the compacts sintered at 1 260 ℃ for 26 h, which was made from 90% gas-atomized powder(average particles size is 32.5 μm) and 10% HDH powder, have higher relative density(>95%), ultimate tensile strength of 800848MPa, 0.2% yield strength of 712762MPa and high elongation (7.4%9.5%). When the sintering time is increased, porosity decreases and microstructure of sintered products changes from equiaxed to typical Widmanstatten, the average sizes of prior β grains, α colonies and α phase thickness in the β grains increase accordingly. After HIP treatment, pores obviously become less, microstructure of alloy is refined and mechanical properties are greatly improved.展开更多
The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）,...The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The results show that the compressive stress exists in the products and the bend strength reaches 300MPa. ZrO2 phase and stainless steel phase are uniform in samples. The toughness of ceramic increases with the increasing the content of stainless steel. Through TEM study of the interface, some crystalline orientation relationships are determined.展开更多
基金Project(50475028)supported by the National Natural Science Foundation of China
文摘Metal mold micron scale precision casting technology was developed successfully,and three-dimension complicated microgear castings in micron scale were produced.Evolvement regularity of microgear castings were observed by optical microscope and scanning electron microscope.Compared with conventional casting,microcasting is characterized by typical nonequilibrium solidification,for example,its grain size can be refined significantly,eutectic structure is transformed from lamellar morphology to rod eutectic,and the ratio of primary phase is increased.This kind of microstructure can promote mechanical properties of microcasting.
基金the Natural Science Foundation of Jiangsu Province of China(No.BK20170796)the foundation of‘‘Jiangsu Provincial Key Laboratory of Bionic Functional Materials”of China(No.NJ2020026)+1 种基金the foundation of National Defense Key Laboratory of China(No.6142004190204)the National Natural Science Foundation of China(No.52075249)。
文摘Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most molds are made of silicon or silicon-based soft templates,and have poor wear resistant or vulnerability to high temperature,limiting their use in large-scale manufacturing.Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties.However,the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging.In this study,using electrodeposition techniques,the shape of the micropores is modified to obtain end-controlled pores.The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated.Furthermore,the mechanism of non-uniformity evolution of the microporous morphology is revealed.The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process.As a result,typical bionic adhesives with tip-expansion are obtained.Moreover,corresponding adhesion mechanics are analyzed.The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures,providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.
基金supported by the National High-Tech Research and Development Program of China(No.2006AA03Z502)
文摘High-nitrogen nickel-free stainless steels were fabricated by the metal injection molding technique using high nitrogen alloying powders and a mixture of three polymers as binders.Mixtures of metal powders and binders with various proportions were also investigated, and an optimum powder loading capacity was determined as 64vol%.Intact injection molded compacts were successfully obtained by regulating the processing parameters.The debinding process for molded compacts was optimized with a combination of thermo-gravimetric analysis and differential scanning calorimetry analysis.An optimum relative density and nitrogen content of the specimens are obtained at 1360℃,which are 97.8%and 0.79wt%,respectively.
基金Project(30770576)supported by the National Natural Science Foundation of ChinaProject(2007AA03Z114)supported by Hi-tech Research and Development Program of China
文摘Sodium chloride(NaCl)was added as a space holder in synthesis of porous titanium by using metal injection molding(MIM)method.The microstructure and mechanical properties of porous titanium were analyzed by mercury porosimeter, scanning electron microscope(SEM)and compression tester.The results show that the content of NaCl influences the porosity of porous titanium significantly.Porous titanium powders with porosity in the range of 42.4%-71.6%and pore size up to 300μm were fabricated.The mechanical test shows that with increasing NaCl content,the compressive strength decreases from 316.6 to 17.5 MPa and the elastic modulus decreases from 3.03 to 0.28 GPa.
基金Project supported by Specialized Research Fundfor the Doctoral Programof Higher Education (20040008015)ProgramforNew Century Excellent Talents in University (NCET)
文摘Antioxidation effects on Sm （Co, Cu, Fe, Zr）z-sintered magnets treated by different methods were studied through TGA and DTA. Microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets was analyzed through SEM and EDS. The results indicate that the antioxidation effect of the alloy powder treated in silane solution is better than that of the other methods. The alloy powders treated in stearic acid （SA） solution and polymethyl methacrylate （PMMA） solution can prevent powders from oxidation for a short period of time. Silane solution is not suitable for metal injection molding （MIM） because it severely damages the magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z-sintered magnets. SA solution can not only prevent powders from oxidizing in MIM, but also does not damage magnetic properties and microstructure of Sm（Co, Cu, Fe, Zr）z magnets. The oxygen content of Sm（Co, Cu, Fe, Zr）z-sintered magnets by MIM is 3300μg·g^-1.
基金Specialized Research Fund for the Doc-toral Program of Higher Education (No.20020613005)
文摘Powder segregation induced by mold filling is an important phenomenon that affects the final quality of metal injection molding （MIM）. The prediction of segregation in MIM requires a bi-phase flow model to describe distinctly the flows of metallic powder and polymer binder. Viscous behaviors for the flows of each phase should hence be determined. The coefficient of interaction between the flows of two phases should also be evaluated. However, only viscosity of the mixed feedstock is measurable by capillary tests. Wall sticking is supposed in the traditional model for capillary tests, while the wall slip is important to be taken into account in MIM injection. Objective of the present paper is to introduce the slip effect in bi-phase simulation, and search the suitable way to determine the viscous behaviors for each phase with the consideration of wall slip in capillary tests. Analytical and numerical methods were proposed to realize such a specific purpose. The proposed method is based on the mass conservation between the capillary flows in mono-phase model for the mixed feedstock and in bi-phase model for the flows of two phases. Examples of the bi-phase simulation in MIM were realized with the software developed by research team. The results show evident segregation, which is valuable for improving the mould designs.
基金Project(10475069) supported by the National Natural Science Foundation of China
文摘Nanocrystalline nonferrous metals (Cu, Al, and Ag) were synthesized by flow-levitation-molding method. The microstructure of the as-prepared nanocrystalline metals was characterized by XRD and FESEM. The microhardness and electrical resistivity were tested by the HMV-2 type Microhardness Tester and 6157 type Electrometer, respectively. The synthesis process was also studied. The results show that the spheriform particles in nanocrystalline metals have average grain size of 20-30 nm. The relative density of nanocrystalline Cu, Al, and Ag are 95.1%, 98.1% and 98.3%, respectively. The microhardness of nanocrystalline Cu, Al and Ag are 2.01, 2.11 and 1.26 GPa respectively, which are larger than those of their coarse-grained counterparts by the factor of 4.5, 14, and 2.5, respectively. The electrical resistivity of nanocrystalline Cu at room temperature is 1.5×10-7 Ω·m, which is higher than coarse-grained Cu by a factor of 7.5. The pressure is the predominant factor influencing the density of the as-prepared nanocrystalline nonferrous metals.
文摘Ti-6Al-4V compacts were fabricated by metal injection molding(MIM). Influence of vacuum sintering time on mechanical properties and microstructure of the sintered compacts at 1 260 ℃ were investigated. The experimental results show that the compacts sintered at 1 260 ℃ for 36 h, which was made from hydrogenation-dehydrogenation(HDH) powder(average particles size is 45 μm), have a relative density of 95.6% 96.7%, ultimate tensile strength of 648686MPa and 0.2% yield strength of 526615MPa; but a lower elongation(<4%) and that the compacts sintered at 1 260 ℃ for 26 h, which was made from 90% gas-atomized powder(average particles size is 32.5 μm) and 10% HDH powder, have higher relative density(>95%), ultimate tensile strength of 800848MPa, 0.2% yield strength of 712762MPa and high elongation (7.4%9.5%). When the sintering time is increased, porosity decreases and microstructure of sintered products changes from equiaxed to typical Widmanstatten, the average sizes of prior β grains, α colonies and α phase thickness in the β grains increase accordingly. After HIP treatment, pores obviously become less, microstructure of alloy is refined and mechanical properties are greatly improved.
文摘The injection molding products with different volume ratios of ZrO2 ceramic powder to 316L stainless steel powder were prepared. Properties and structure of the products were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM） and transmission electron microscope （TEM）. The results show that the compressive stress exists in the products and the bend strength reaches 300MPa. ZrO2 phase and stainless steel phase are uniform in samples. The toughness of ceramic increases with the increasing the content of stainless steel. Through TEM study of the interface, some crystalline orientation relationships are determined.
