This study is conducted to develop an innovative and attractive selective laser melting(SLM)method to produce 316 L stainless steel materials with excellent mechanical performance and complex part shape.In this work,t...This study is conducted to develop an innovative and attractive selective laser melting(SLM)method to produce 316 L stainless steel materials with excellent mechanical performance and complex part shape.In this work,the subregional manufacturing strategy,which separates the special parts from the components using an optimized process,was proposed.The results showed that produced 316 L materials exhibited superior strength of^755 MPa and good ductility.In the as-built parts,austenite with preferred orientation of the(220)plane,δ-ferrite,and a small amount of CrO phases were present.In addition,the crystal size was fine,which contributed to the enhancement of the parts’mechanical properties.The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions.This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears,demonstrating its strong potential for use in practical applications.展开更多
A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were ...A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were compared with those of the unreinforced samples,and their potentials were assessed by comparison with traditional cermet/hardmetal systems.The results showed that with the addi-tion of 20wt%Ti(C,N),the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals.The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment en-hanced the wear resistance.Although the presence of excessive in situ carbides improved the hardness,the low indentation fracture resistance(IFR)value resulted in brittle fracture,which in turn resulted in poor wear property.Moreover,the operative wear mechanisms were investig-ated.This study provides a practical and cost-effective approach to prepare steel-Ti(C,N)composites as potential wear-resistant materials.展开更多
Anisotropic magnets were obtained by hot deformation with the partial crystallized precursor prepared via spark-plasma sintering (SPS). Amorphous powders with the nominal composition of Nd_28.72Fe_balCo_5.66 Ga_0.59...Anisotropic magnets were obtained by hot deformation with the partial crystallized precursor prepared via spark-plasma sintering (SPS). Amorphous powders with the nominal composition of Nd_28.72Fe_balCo_5.66 Ga_0.59B_0.92 (wt%) were used as the starting material. The results show that the amorphous powders would suffer varying degrees of crystallization even below the crystal- lization point during the SPS process under high pressure. And the pre-crystallized grains in precursors have great impacts on the microstructure and magnetic properties of the hot-deformed magnets. The final obtained anisotropic magnets exhibit homogeneous microstructure consisting of well-aligned and platelet-shaped Nd_2Fe_14B grains without abnormal growth. It can be found that a reasonable pro- portion of pre-crystallized gains could promote the pref- erential orientation in the magnet, leading to the achievement of optimal magnetic properties among the magnets with identical composition and best magnetic performance is achieved in the magnet hot deformed from the 490 ℃ high-pressure hot-pressed precursor.展开更多
Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer...Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.展开更多
The disproportionated phases of Nd Hx, Fe2B,and a-Fe from Nd2Fe14B were applied to prepare Nd Fe B magnets by two different routes. The results show that the route of annealing in horizontal vacuum sintering furnace c...The disproportionated phases of Nd Hx, Fe2B,and a-Fe from Nd2Fe14B were applied to prepare Nd Fe B magnets by two different routes. The results show that the route of annealing in horizontal vacuum sintering furnace cannot reach the purpose of complete recombination after the hot pressing and hot deformation process due to the lack of dehydrogenation channel. The route of applying low pressure of 4–25 MPa on the as-disproportionated green compact during the desorption recombination process in situ hot deformation in a spark plasma sintering(SPS)system can obtain completely recombined Nd Fe B magnet with good anisotropy and magnetic properties. The maximum magnetic properties,(BH)max= 201 kJ m^-3,Br= 1.142 T and Hcj= 469 k A m^-1, are obtained after being treated for 15 min at 750 ℃ under low pressure.展开更多
The effects of initial density on the magnetic properties of NdFeB magnets prepared by single-stage hot deformation were investigated in this work. The results show that the values of maximum energy product (BH)m an...The effects of initial density on the magnetic properties of NdFeB magnets prepared by single-stage hot deformation were investigated in this work. The results show that the values of maximum energy product (BH)m and coercivity Hcj decrease with the increase of initial density. Under optimum condition, an anisotropic magnet with a maximum energy product of 264 kJ-m-3 was pro- duced using the initial density of 4.4 g-cm-3. The influence of initial density on the magnetic properties was discussed on the basis of microstructure and strain energy. It is concluded that the thicker platelet grains are obtained along the Nd2Fe14B base plane with the initial density increasing. It is mainly because that grain rotation is restricted by high strain energy, which results from high initial density.展开更多
基金supported by the Key R&D Programs of Sichuan Province of China (No. 2018GZ0145)the Science and Technology Planning Projects of Zigong of Sichuan Province (No. 2018CDZG-1)the Major Scientific and Technological Key Bidding Projects in Panzhihua Experimental Zone (No. 1640STC30166/01)
文摘This study is conducted to develop an innovative and attractive selective laser melting(SLM)method to produce 316 L stainless steel materials with excellent mechanical performance and complex part shape.In this work,the subregional manufacturing strategy,which separates the special parts from the components using an optimized process,was proposed.The results showed that produced 316 L materials exhibited superior strength of^755 MPa and good ductility.In the as-built parts,austenite with preferred orientation of the(220)plane,δ-ferrite,and a small amount of CrO phases were present.In addition,the crystal size was fine,which contributed to the enhancement of the parts’mechanical properties.The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions.This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears,demonstrating its strong potential for use in practical applications.
基金This work was financially supported by the National Key Research and Development Plan of China(No.2017YFB0305900).
文摘A series of novel steel-Ti(C,N)composites was fabricated by spark plasma sintering(SPS)and subsequent heat treatment.The hardness,indentation fracture resistance,and wear behaviour of the steel-Ti(C,N)composites were compared with those of the unreinforced samples,and their potentials were assessed by comparison with traditional cermet/hardmetal systems.The results showed that with the addi-tion of 20wt%Ti(C,N),the wear rates of the newly examined composites reduced by a factor of about 2 to 4 and were comparable to those of cermets and hardmetals.The martensitic transformation of the steel matrix and the formation of in situ carbides induced by heat treatment en-hanced the wear resistance.Although the presence of excessive in situ carbides improved the hardness,the low indentation fracture resistance(IFR)value resulted in brittle fracture,which in turn resulted in poor wear property.Moreover,the operative wear mechanisms were investig-ated.This study provides a practical and cost-effective approach to prepare steel-Ti(C,N)composites as potential wear-resistant materials.
基金supported by the National Natural Science Foundation of China (No. 51171122)the Sichuan Province Science and Technology Support Program (Nos. 2014GZ0090 and 2016GZ0262)
文摘Anisotropic magnets were obtained by hot deformation with the partial crystallized precursor prepared via spark-plasma sintering (SPS). Amorphous powders with the nominal composition of Nd_28.72Fe_balCo_5.66 Ga_0.59B_0.92 (wt%) were used as the starting material. The results show that the amorphous powders would suffer varying degrees of crystallization even below the crystal- lization point during the SPS process under high pressure. And the pre-crystallized grains in precursors have great impacts on the microstructure and magnetic properties of the hot-deformed magnets. The final obtained anisotropic magnets exhibit homogeneous microstructure consisting of well-aligned and platelet-shaped Nd_2Fe_14B grains without abnormal growth. It can be found that a reasonable pro- portion of pre-crystallized gains could promote the pref- erential orientation in the magnet, leading to the achievement of optimal magnetic properties among the magnets with identical composition and best magnetic performance is achieved in the magnet hot deformed from the 490 ℃ high-pressure hot-pressed precursor.
基金financially supported by the National High Technology Research and Development Program of China (No. 2011AA03A403)the National Natural Science Foundation of China (No. 51171122)the Sichuan Provence Science and Technology Support Program (Nos. 2011GZ0117 and 2013GZ0056)
文摘Radially oriented Nd-Fe-B ring magnets were prepared by backward extrusion of MQ-C powder. The punch chamfer radius has a great impact on the microstructure and magnetic properties of the ring magnet. With the chamfer radius changing from 2, 5 to 8 mm, the cracks in the inner wall decrease obviously while the crystallographic alignment drops. Furthermore, the mechanism of caxis growth was suggested to be a combination of shear deformation in the corner and solution-precipitation under the stress parallel to radial direction. The alignment drops on the top of ring because the grains grow freely and some textured grains grow through nucleation and recrystallization. In the present work, the optimal punch chamfer radius is found to be 2 mm, and in this case, the remanence,coercivity, and maximum energy product of the ring magnet achieve 1.4 T, 670 kJám, and 342 kJám,respectively.
基金financially supported by the National Natural Science Foundation of China (No. 51171122)
文摘The disproportionated phases of Nd Hx, Fe2B,and a-Fe from Nd2Fe14B were applied to prepare Nd Fe B magnets by two different routes. The results show that the route of annealing in horizontal vacuum sintering furnace cannot reach the purpose of complete recombination after the hot pressing and hot deformation process due to the lack of dehydrogenation channel. The route of applying low pressure of 4–25 MPa on the as-disproportionated green compact during the desorption recombination process in situ hot deformation in a spark plasma sintering(SPS)system can obtain completely recombined Nd Fe B magnet with good anisotropy and magnetic properties. The maximum magnetic properties,(BH)max= 201 kJ m^-3,Br= 1.142 T and Hcj= 469 k A m^-1, are obtained after being treated for 15 min at 750 ℃ under low pressure.
基金financially supported by the National High Technology Research and Development Program of China(No.2011AA03A403)the National Natural Science Foundation of China(No.51171122)the Sichuan Province Science and Technology Support Program(Nos.2011GZ0117 and 2013GZ0056)
文摘The effects of initial density on the magnetic properties of NdFeB magnets prepared by single-stage hot deformation were investigated in this work. The results show that the values of maximum energy product (BH)m and coercivity Hcj decrease with the increase of initial density. Under optimum condition, an anisotropic magnet with a maximum energy product of 264 kJ-m-3 was pro- duced using the initial density of 4.4 g-cm-3. The influence of initial density on the magnetic properties was discussed on the basis of microstructure and strain energy. It is concluded that the thicker platelet grains are obtained along the Nd2Fe14B base plane with the initial density increasing. It is mainly because that grain rotation is restricted by high strain energy, which results from high initial density.