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
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
Ti-Mo getters have been fabricated via metal injection molding (MIM) using three kinds of Ti powders with different mean particle sizes of 46 μm,35 μm and 26 μm,respectively. The surface morphology,porosity,and hyd...Ti-Mo getters have been fabricated via metal injection molding (MIM) using three kinds of Ti powders with different mean particle sizes of 46 μm,35 μm and 26 μm,respectively. The surface morphology,porosity,and hydrogen sorption properties of Ti-Mo getters formed by MIM using paraffin wax as a principal binder constituent were examined. It has been proven that the powder injection molding is a viable forming technique for porous Ti-Mo getters. The particle size of Ti powders and the powder loading influence...展开更多
17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, sc...17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.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
In this study, the influence of hot isostatic pressing(HIP) process on the 418 alloy produced by metal injection molding(MIM) technique(named as MIM 418)was investigated based on the characteristic analysis of 4...In this study, the influence of hot isostatic pressing(HIP) process on the 418 alloy produced by metal injection molding(MIM) technique(named as MIM 418)was investigated based on the characteristic analysis of 418 alloy powder. And comparison analysis of the microstructure and mechanical property between the MIM 418 and as-cast 418 alloys was performed by scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS),and X-ray diffraction(XRD). The results show that MIM418 alloy exhibits fine grain(~30 μm) and uniform microstructure. The defects existing in MIM 418 alloy formed during sintering process can be eliminated through HIP treatment, and the relative density increases from97.0 % to 99.5 %. The mechanical property can be improved significantly because of the elimination of defects, and the tensile strength and elongation are1,271 MPa and 16.8 %, respectively, which are increased by 34.5 % and 180 % compared with K418 alloy after solution heat treatment.展开更多
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 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.
文摘Ti-Mo getters have been fabricated via metal injection molding (MIM) using three kinds of Ti powders with different mean particle sizes of 46 μm,35 μm and 26 μm,respectively. The surface morphology,porosity,and hydrogen sorption properties of Ti-Mo getters formed by MIM using paraffin wax as a principal binder constituent were examined. It has been proven that the powder injection molding is a viable forming technique for porous Ti-Mo getters. The particle size of Ti powders and the powder loading influence...
基金financially supported by the National High-Tech Research and Development Program of China (No. 2009AA033901)the National Natural Science Foundation of China (No. 51004019)
文摘17-4PH stainless steel powders were prepared using a supersonic nozzle in a close-coupled gas atomization system. The characteristics of powder particles were carried out by means of a laser particle size analyzer, scanning electron microscopy (SEM), and the X-ray diffraction (XRD) technique. The results show that the mass median particle diameter is about 19.15 prn. Three main types of surface microstructures are observed in the powders: well-developed dendrite, cellular, and cellular dendrite structure. The XRD measurements show that, as the particle size decreases, the amount of fcc phase gradually decreases and that of bcc phase increases. The cooling rate is inversely related to the particle size, i.e., it decreases with an increase in particle size.
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financially supported by the National High Technology Research and Development Program of China (No. 2012AA03AA514)
文摘In this study, the influence of hot isostatic pressing(HIP) process on the 418 alloy produced by metal injection molding(MIM) technique(named as MIM 418)was investigated based on the characteristic analysis of 418 alloy powder. And comparison analysis of the microstructure and mechanical property between the MIM 418 and as-cast 418 alloys was performed by scanning electron microscopy(SEM), energy-dispersive spectroscopy(EDS),and X-ray diffraction(XRD). The results show that MIM418 alloy exhibits fine grain(~30 μm) and uniform microstructure. The defects existing in MIM 418 alloy formed during sintering process can be eliminated through HIP treatment, and the relative density increases from97.0 % to 99.5 %. The mechanical property can be improved significantly because of the elimination of defects, and the tensile strength and elongation are1,271 MPa and 16.8 %, respectively, which are increased by 34.5 % and 180 % compared with K418 alloy after solution heat treatment.