Ti(C, N)-TiB2 composite coatings were deposited by means of reactive low pressure plasma spraying (LPPS) based on the technology of self-propagating high-temperature synthesis (SHS). The original powders were mixtures...Ti(C, N)-TiB2 composite coatings were deposited by means of reactive low pressure plasma spraying (LPPS) based on the technology of self-propagating high-temperature synthesis (SHS). The original powders were mixtures of Ti and B4C powders. The powders were mixed by ball mill and then spray-dried and at last sintered to be suitable for spraying. Two spraying distances were selected for LPPS. Scanning electron microscopy (SEM) was used to investigate the morphologies of powders for spraying and the microstructures of the coatings. The phase compositions of coatings were measured by X-ray diffraction (XRD). Spray-dried and sintered powders are denser and better bond than only spray-dried powders. The composite coating is composed of TiB2, TiC0.3N0.7, TiN0.3, Ti4N3-x and impurity phase of Ti5Si3 with 300 mm spraying distance. Partly unreacted B4C powders remained in the coating for 240 mm spraying distance, which may be inadequate reaction. No titanium oxide was detected in the composite coating for the relative high vacuum degree of LPPS. The anti-corrosion property of LPPS sprayed Ti(C, N)-TiB2 composite coating with 300 mm spraying distance in electrolytic solution is superior to that of 240 mm spraying distance. Microhardness of Ti(C, N)-TiB2 composite coating is relatively low due to the unconsolidated structure of the coating. The solving methods to improve property of composite coating are finally put forward in the paper.展开更多
The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The resu...The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The results showed that the addition of needle cork could significally increase the permeability of the molds by a factor of about 4 because the burning of needle cokes increased the porosities of the molds.Meanwhile,the needle coke modified molds exhibited higher green strength and greater thickness both on flat section and at sharp edges compared with the full fused silica mold.Taking account of the mold thickness,the needle coke modified molds had increased adjusted fracture load(AFL)by a factor of about 2 at the test temperature of 25—1200℃.The addition of needle coke significally improved the permeability of the molds during both autoclaving and casting,and optimized the correlation between the permeability and green strength of the molds.展开更多
Magnesium alloys are well applied in aerospace and aviation because of their mass saving potential,good electromagnetic shielding performance,and high damping capacity. To further promote the applications,in this pape...Magnesium alloys are well applied in aerospace and aviation because of their mass saving potential,good electromagnetic shielding performance,and high damping capacity. To further promote the applications,in this paper,the applications of magnesium alloys are reviewed,which could provide insights for researchers and application designers. Firstly,the applications in aerospace are reviewed,including missile,satellite,rocket,and spacecraft.Secondly,the applications and commercial magnesium alloys in aviation are summarized. Thirdly,the bottleneck and existing problems for such magnesium alloys applied in aerospace and aviation are discussed. The requirements for the magnesium alloy performance in aerospace and aviation are evaluated and elaborated.展开更多
The morphology and structure of melt spinning Ni-33.6at% Al doped with B and RE were investigated.The results show that the alloy consists of L10 martensitic grains and L12 Ni3Al at the grain boundaries when it contai...The morphology and structure of melt spinning Ni-33.6at% Al doped with B and RE were investigated.The results show that the alloy consists of L10 martensitic grains and L12 Ni3Al at the grain boundaries when it contains no B and RE.The addition of 0.11-0.31wt% B can suppress the martensitic transformation and Ni3Al separation at the boundaries,and a supersaturated B2 single phase NiAl is obtained.The addition of 0.05wt% RE can eliminate Ni3Al precipitated at the boundaries and get complete martensite,but 0.2-0.8wt% RE addition can suppress the martensitic transformation, and supersaturated B2 single phase NiAl is obtained.The formation mechanism of supersaturated B2 single phase NiAl has been analyzed.展开更多
The paper investigated the effects of RE on the microstructure and ductility of melt-spun Al-63.3at.%Ni and Al-66.4at%Ni.For Al-63.3at.%Ni without RE the microstructure is a mixture of equiaxed martensitic grains and ...The paper investigated the effects of RE on the microstructure and ductility of melt-spun Al-63.3at.%Ni and Al-66.4at%Ni.For Al-63.3at.%Ni without RE the microstructure is a mixture of equiaxed martensitic grains and B2 NiAl grains,but after addition of 0.2wt% RE a complete supersaturated B2 NiAl results,and its elongation is enhanced from 0.9%(without RE) to 1.4%(with 0.2wt%RE).For Al-66.4at.%Ni without RE the microstructure is coarse equiaxed martensitic grains with Ni3Al precipitated at the GBs.But complete martensitic grains and supersaturated single phase,B2 NiAl,would result with addition of 0.05wt%RE and 0.2-0.8wt%RE respectively.The elongation of Al-66.4at.%Ni without RE is only 0.8%.With the addition of 0.05, 0.2 and 0.8wt%RE.the elongation can reach 2.6,3.0 and 3.2% respectively.The addition of RE can change the fracture mode from intergranular fracture(without RE) to a mixture of intergranular and transgranular fracture or entirely transgranular fracture.The mechanisms of microstructure formation and ductility enhancement are analyzed.展开更多
The Fe-Ti-N mater alloy was prepared through the in-situ reaction of nitrogen gas with the Fe-Ti melt.Scanning electron microscope results show that the particles uniformly distributed in the iron matrix were TiN.The ...The Fe-Ti-N mater alloy was prepared through the in-situ reaction of nitrogen gas with the Fe-Ti melt.Scanning electron microscope results show that the particles uniformly distributed in the iron matrix were TiN.The deliberately prepared Fe-Ti-N master alloy was employed for the 409L ferritic stainless steel in an attempt to refine the as-cast solidification structure.It was found that the effectiveness of Fe-Ti-N master alloy on refining of the as-cast 409L ferritic stainless steel was affected by addition level,holding time and melts temperature.It was found that the average equiaxed grain size decreased from 1503μm to 303μm,the proportion of equiaxed grain zone increased from 14%to 100%with increasing the Fe-Ti-N master alloy addition level to 2.5%.The proportion of equiaxed grain decreased from 85%to 4%as the solidification temperature increased from 1803 K to 1883 K.When the holding time reached to 8min,the solidification structures of 409L ferritic stainless steel show extreme points in the proportion of equiaxed grain.It is clear that the grain refining efficiency gradually fade away with the increasing of the holding time at the very beginning.However,when the holding time continues to increase and exceeds the extreme point,the grain refining efficiency of the Fe-Ti-N master alloy recovered to a certain degree.The experimental results mentioned above have been analyzed in terms of thermodynamics.Under appropriate conditions,the Fe-Ti-N master alloy used for grain refinement of the solidification structure of 409L ferritic stainless steel may have good prospects for industrial applications.展开更多
The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investiga...The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investigate dynamic recrystallization behavior,as cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure.Tensile test was used and the deformation temperature is in the range of 900℃to 1100℃and strain rates are 0.01 s^(-1),0.1 s^(-1),1 s^(-1).The activation energy and stress exponent were determined as 306kJ/mol and 4.69 respectively.The ratio of critical strain to the peak strain is 0.65,and that of critical stress to the peak stress is 0.92.The dependence of the peak strain on the initial grain size and Zener-Hollomon parameters Z isε_p=9.1×10^(-4)×D_0^(0.48)Z^(0.13).The kinetics of the dynamic recrystallization and recrystallized grain size was predicted using models published.The as cast coarse austenite were dramatically refined after complete dynamic recrystallization.For static recrystallization,the tensile test was carried out on Gleeble-3500 thermo-mechanical simulator.The deformation temperature is in the range of 800℃to 1200℃with strain rate 0.01 s^(-1)to 1s^(-1).The pre strain is fixed at 0.04 to 0.12 and the inter-hit delay time varies from 1 s to 3000 s.The activation energy and Avrami exponent of static recrystallization were determined as 241 kJ/mol and 0.54 respectively.A kinetics model was proposed to describe the static recrystallization kinetics.The predicted results were in good agreement with the experimental results.展开更多
文摘Ti(C, N)-TiB2 composite coatings were deposited by means of reactive low pressure plasma spraying (LPPS) based on the technology of self-propagating high-temperature synthesis (SHS). The original powders were mixtures of Ti and B4C powders. The powders were mixed by ball mill and then spray-dried and at last sintered to be suitable for spraying. Two spraying distances were selected for LPPS. Scanning electron microscopy (SEM) was used to investigate the morphologies of powders for spraying and the microstructures of the coatings. The phase compositions of coatings were measured by X-ray diffraction (XRD). Spray-dried and sintered powders are denser and better bond than only spray-dried powders. The composite coating is composed of TiB2, TiC0.3N0.7, TiN0.3, Ti4N3-x and impurity phase of Ti5Si3 with 300 mm spraying distance. Partly unreacted B4C powders remained in the coating for 240 mm spraying distance, which may be inadequate reaction. No titanium oxide was detected in the composite coating for the relative high vacuum degree of LPPS. The anti-corrosion property of LPPS sprayed Ti(C, N)-TiB2 composite coating with 300 mm spraying distance in electrolytic solution is superior to that of 240 mm spraying distance. Microhardness of Ti(C, N)-TiB2 composite coating is relatively low due to the unconsolidated structure of the coating. The solving methods to improve property of composite coating are finally put forward in the paper.
基金the 13th Five-Year Common Technology Equipment Development Project(No.41423040206)the Industry-University-Research Cooperation Annual Plan of Shanghai(No.CXY2016004)
文摘The permeability of a new investment casting mold system prepared by adding needle cokes has been investigated in this work.The permeability tests of the molds were carried out at the temperature of 25—1200℃The results showed that the addition of needle cork could significally increase the permeability of the molds by a factor of about 4 because the burning of needle cokes increased the porosities of the molds.Meanwhile,the needle coke modified molds exhibited higher green strength and greater thickness both on flat section and at sharp edges compared with the full fused silica mold.Taking account of the mold thickness,the needle coke modified molds had increased adjusted fracture load(AFL)by a factor of about 2 at the test temperature of 25—1200℃.The addition of needle coke significally improved the permeability of the molds during both autoclaving and casting,and optimized the correlation between the permeability and green strength of the molds.
基金the National Natural Science Foundation of China(No. U2037601 and No. 52074183)the Opening Foundation of the National Key Laboratory of Rare Metal Specialty Materials(No. SKL2018K001)the China Scholarship Council(No. 201906230111)。
文摘Magnesium alloys are well applied in aerospace and aviation because of their mass saving potential,good electromagnetic shielding performance,and high damping capacity. To further promote the applications,in this paper,the applications of magnesium alloys are reviewed,which could provide insights for researchers and application designers. Firstly,the applications in aerospace are reviewed,including missile,satellite,rocket,and spacecraft.Secondly,the applications and commercial magnesium alloys in aviation are summarized. Thirdly,the bottleneck and existing problems for such magnesium alloys applied in aerospace and aviation are discussed. The requirements for the magnesium alloy performance in aerospace and aviation are evaluated and elaborated.
文摘The morphology and structure of melt spinning Ni-33.6at% Al doped with B and RE were investigated.The results show that the alloy consists of L10 martensitic grains and L12 Ni3Al at the grain boundaries when it contains no B and RE.The addition of 0.11-0.31wt% B can suppress the martensitic transformation and Ni3Al separation at the boundaries,and a supersaturated B2 single phase NiAl is obtained.The addition of 0.05wt% RE can eliminate Ni3Al precipitated at the boundaries and get complete martensite,but 0.2-0.8wt% RE addition can suppress the martensitic transformation, and supersaturated B2 single phase NiAl is obtained.The formation mechanism of supersaturated B2 single phase NiAl has been analyzed.
文摘The paper investigated the effects of RE on the microstructure and ductility of melt-spun Al-63.3at.%Ni and Al-66.4at%Ni.For Al-63.3at.%Ni without RE the microstructure is a mixture of equiaxed martensitic grains and B2 NiAl grains,but after addition of 0.2wt% RE a complete supersaturated B2 NiAl results,and its elongation is enhanced from 0.9%(without RE) to 1.4%(with 0.2wt%RE).For Al-66.4at.%Ni without RE the microstructure is coarse equiaxed martensitic grains with Ni3Al precipitated at the GBs.But complete martensitic grains and supersaturated single phase,B2 NiAl,would result with addition of 0.05wt%RE and 0.2-0.8wt%RE respectively.The elongation of Al-66.4at.%Ni without RE is only 0.8%.With the addition of 0.05, 0.2 and 0.8wt%RE.the elongation can reach 2.6,3.0 and 3.2% respectively.The addition of RE can change the fracture mode from intergranular fracture(without RE) to a mixture of intergranular and transgranular fracture or entirely transgranular fracture.The mechanisms of microstructure formation and ductility enhancement are analyzed.
文摘The Fe-Ti-N mater alloy was prepared through the in-situ reaction of nitrogen gas with the Fe-Ti melt.Scanning electron microscope results show that the particles uniformly distributed in the iron matrix were TiN.The deliberately prepared Fe-Ti-N master alloy was employed for the 409L ferritic stainless steel in an attempt to refine the as-cast solidification structure.It was found that the effectiveness of Fe-Ti-N master alloy on refining of the as-cast 409L ferritic stainless steel was affected by addition level,holding time and melts temperature.It was found that the average equiaxed grain size decreased from 1503μm to 303μm,the proportion of equiaxed grain zone increased from 14%to 100%with increasing the Fe-Ti-N master alloy addition level to 2.5%.The proportion of equiaxed grain decreased from 85%to 4%as the solidification temperature increased from 1803 K to 1883 K.When the holding time reached to 8min,the solidification structures of 409L ferritic stainless steel show extreme points in the proportion of equiaxed grain.It is clear that the grain refining efficiency gradually fade away with the increasing of the holding time at the very beginning.However,when the holding time continues to increase and exceeds the extreme point,the grain refining efficiency of the Fe-Ti-N master alloy recovered to a certain degree.The experimental results mentioned above have been analyzed in terms of thermodynamics.Under appropriate conditions,the Fe-Ti-N master alloy used for grain refinement of the solidification structure of 409L ferritic stainless steel may have good prospects for industrial applications.
文摘The dynamic and static recrystallization behaviors of twin roll cast low carbon steel strip were investigated with an attempt to provide guiding deformation parameters for the on line hot rolling.In order to investigate dynamic recrystallization behavior,as cast strip was reheated and soaked with austenite grain size similar to the width level of the as cast columnar structure.Tensile test was used and the deformation temperature is in the range of 900℃to 1100℃and strain rates are 0.01 s^(-1),0.1 s^(-1),1 s^(-1).The activation energy and stress exponent were determined as 306kJ/mol and 4.69 respectively.The ratio of critical strain to the peak strain is 0.65,and that of critical stress to the peak stress is 0.92.The dependence of the peak strain on the initial grain size and Zener-Hollomon parameters Z isε_p=9.1×10^(-4)×D_0^(0.48)Z^(0.13).The kinetics of the dynamic recrystallization and recrystallized grain size was predicted using models published.The as cast coarse austenite were dramatically refined after complete dynamic recrystallization.For static recrystallization,the tensile test was carried out on Gleeble-3500 thermo-mechanical simulator.The deformation temperature is in the range of 800℃to 1200℃with strain rate 0.01 s^(-1)to 1s^(-1).The pre strain is fixed at 0.04 to 0.12 and the inter-hit delay time varies from 1 s to 3000 s.The activation energy and Avrami exponent of static recrystallization were determined as 241 kJ/mol and 0.54 respectively.A kinetics model was proposed to describe the static recrystallization kinetics.The predicted results were in good agreement with the experimental results.
