3D reconstruction and 2D observation were conducted to characterize the microstructure of the castings produced through high pressure die casting with different parameters.Our results indicate that shrinkage pores gen...3D reconstruction and 2D observation were conducted to characterize the microstructure of the castings produced through high pressure die casting with different parameters.Our results indicate that shrinkage pores generally co-existed with externally solidified crystals(ESCs).In specimen produced without fast slow shot speed,big net-shrinkage pores accompanied with ESCs were found in the center of the specimen.When the casting pressurization was introduced,the shrinkage pores gathered to the specimen center and became much less due to the optimization of melt feeding.Much more porosity was found near the gate rather than in the middle of the rod bar,especially gas pores.Thefilling process simulation reveals that the middle position of the bars wasfirstlyfilled and followed by the near gate position accompanied with one intense turbulentflow.展开更多
In order to enhance the ablation-resistant performance of stainless-steel conductive rails,Mo coating,410 stainless steel coating and 15 wt%Cr_(2)AlIC particles reinforced 410 stainless steel composite coating were pr...In order to enhance the ablation-resistant performance of stainless-steel conductive rails,Mo coating,410 stainless steel coating and 15 wt%Cr_(2)AlIC particles reinforced 410 stainless steel composite coating were prepared and evaluated.Different from the weak interfacial strength caused by the dissimilar metals between Mo and steel rails,410 stainless steel coating has better interfacial contact with steel rails.The introduction of Cr_(2)AlC into 410 stainless steels further strengthened the mechanical properties of coating by alloy strengthening effect and particle strengthening effect,as the decomposition of Cr_(2)AlC into nano CrC particles is accompanied with the diffusion of Al atoms into 410 stainless steels.It was found that the composite coating can still resist arc erosion at 150 A current,as a dense oxide film formed during the ablation process and the decomposition of Cr_(2)AlC contributed to the heat absorption.展开更多
To investigate the effect of AlsMn4Gd phase on microstructural and mechanical properties of Mg-Al-Ca magnesium alloy,two Mg-2.5AbCa and Mg-2.5Al2Ca-0.1 Al8Mn4Gd alloys were designed and compared in this work.The resul...To investigate the effect of AlsMn4Gd phase on microstructural and mechanical properties of Mg-Al-Ca magnesium alloy,two Mg-2.5AbCa and Mg-2.5Al2Ca-0.1 Al8Mn4Gd alloys were designed and compared in this work.The results show that a small amount of Gd can significantly refine a-Mg grains and change the morphology of AUCa particles.Indeed,the formed Al8Mn4Gd phase could serve as a heterogeneous nucleation site for the a-Mg grains and AbCa particles.Furthermore,the introduction of Gd not only optimized the mechanical properties of Mg-Al-Ca alloy,but also facilitated the thermal deformation(such as hot rolling).展开更多
In recent decades, the demand for lightweight and high specific strength materials brings about the development of magnesium matrix composites. Different from some traditional binary ceramic particles, such as SiC, Al...In recent decades, the demand for lightweight and high specific strength materials brings about the development of magnesium matrix composites. Different from some traditional binary ceramic particles, such as SiC, Al_(2)O_(3), the novel ternary nano-layered M_(n+1)AX_(n)(MAX)phase carbide or nitride ceramics exhibit metal-like properties and self-lubricate capacity(where “M” is an early transition metal, “A” belongs to the group A element, “X” is C or/and N, and n = 1–3). Ti_(2)AlC, as the representative of the MAX phase, was interestingly introduced into the magnesium matrix. Layered Ti_(2)AlC MAX phased reinforced AZ91D magnesium composites manufactured through the stir casting exhibit sufficient deformation capacity due to unique deformation behaviors of MAX, namely delamination and the formation of kinking band. Further,the Ti_(2)AlC-AZ91D composites exhibit a distinctive characteristic in strengthening mechanism, damping mechanism and tribological capacity due to the other special properties of MAX phase, such as self-lubricated property. Accordingly, to give a comprehensive understanding, we overviewed the fabrication process, microstructural characterization, mechanical properties, damping property and tribological capacity on these composites. In order to understand the A-site effect in MAX phase on the microstructure, we introduced another representative Ti_(3)SiC_(2)MAX phase to explain the interfacial evolution. In addition, due to the high aspect ratio of MAX, MAX particles could be orientationally regulated in Mg matrix by plastic deformation such as hot extrusion. Herein, we discussed the anisotropic mechanical and physical properties of the textured composites produced by hot extrusion. Moreover, the potential applications and future development trends of MAX phases reinforced magnesium matrix composites were also given and prospected.展开更多
To clarify the relationship between externally solidified crystals(ESCs)and other defects,e.g.,defect bands and pores,two dimensional(2D)and three dimensional(3D)characterization methods were adopted to analyze castin...To clarify the relationship between externally solidified crystals(ESCs)and other defects,e.g.,defect bands and pores,two dimensional(2D)and three dimensional(3D)characterization methods were adopted to analyze castings produced using a modified ingate system equipped with and without an ESC collector.The reduction of ESCs strongly reduced defect band width and shrinkage pore quantity.By reducing the quantity and size of ESCs,net-shrinkage pores were transformed into isolated island-shrinkage pores.We determined via statistical analysis that the mechanical properties of high pressure die castings were strongly related to the size and fraction of the ESCs rather than porosity volume.The reduction of ESCs also caused tensile transgranular fracture modes to transform into intergranular fracture modes.Additionally,casting pressurization strongly reduced pore morphology,volume,and size.展开更多
Magnesium composites reinforced by N-deficient Ti_(2)AlN MAX phase were first fabricated by non-pressure infiltration of Mg into three-dimensional(3D)co-continuous porous Ti_(2)AlN_(x)(x=0.9,1.0)preforms.The relations...Magnesium composites reinforced by N-deficient Ti_(2)AlN MAX phase were first fabricated by non-pressure infiltration of Mg into three-dimensional(3D)co-continuous porous Ti_(2)AlN_(x)(x=0.9,1.0)preforms.The relationship between their mechanical properties and micro-structure is discussed with the assessment of 2D and 3D characterization.X-ray diffraction(XRD)and scanning electron microscopy detected no impurities.The 3D reconstruction shows that the uniformly distributed pores in Ti_(2)AlN_(x) preforms are interconnected,which act as infiltra-tion tunnels for the melt Mg.The compressive yield strength and microhardness of Ti_(2)AlN_(0.9)/Mg are 353 MPa and 1.12 GPa,respectively,which are 8.55%and 6.67%lower than those of Ti_(2)AlN/Mg,respectively.The typical delamination and kink band occurred in Ti_(2)AlN_(x) under compressive and Vickers hardness(V_(H))tests.Owing to the continuous skeleton structure and strong interfacial bonding strength,the crack ini-tiated in Ti_(2)AlN_(x) was blocked by the plastic Mg matrix.This suggests the possibility of regulating the mechanical performance of Ti_(2)AlN/Mg composites by controlling the N vacancy and the hierarchical structure of Ti_(2)AlN skeleton.展开更多
It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable M...It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.展开更多
The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting (HPDC) process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the sho...The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting (HPDC) process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the shot sleeve, inverse method has been developed to determine the interfacial heat transfer coefficient in the shot sleeve. Under static condition, Interracial heat transfer coefficient (IHTC) peak values are 11.9, 7,3, 8.33kWm-2K-1 at pouring zone (S2), middle zone (S5), and end zone (510), respectively. During the casting process, the IHTC curve displays a second peak of 6.1 kWm-2 K-1 at middle zone during the casting process at a slow speed of 0.3 ms 1 Subsequently, when the high speed started, the IHTC curve reached a second peal〈 of 12.9 kW m-2K-1 at end zone. Furthermore, under different slow casting speeds, both the calculated initial temperature (TIDs) and the maximum temperature (Tsimax) of shot sleeve surface first decrease from 0.1 ms-1 to 0.3 ms-1, but increase again from 0.3 ms-1 to 0.6 ms-1. This result agrees with the experimental results obtained in a series of "plate-shape" casting experiments under different slow speeds, which reveals that the amount of ESCs decreases to the minimum values at 0.3 m s-1 and increase again with the increasing casting slow speed.展开更多
The dry sliding wear behavior of Ti_2AlC reinforced AZ91 magnesium composites was investigated at sliding velocity of 0.5 m/s under loads of 10, 20, 40 and 80 N using pin-on-disk configuration against a Cr15 steel dis...The dry sliding wear behavior of Ti_2AlC reinforced AZ91 magnesium composites was investigated at sliding velocity of 0.5 m/s under loads of 10, 20, 40 and 80 N using pin-on-disk configuration against a Cr15 steel disc. Wear rates and friction coefficients were registered during wear tests. Worn tracks and wear debris were examined by scanning electron microscopy, energy dispersive X-ray spectrometry and transmission electron microscopy in order to obtain the wear mechanisms of the studied materials. The main mechanisms were characterized as the magnesium matrix oxidation and self-lubrication of Ti_2AlC MAX phase. In all conditions, the composites exhibit superior wear resistance and self-lubricated ability than the AZ91 Mg alloy. In addition, the anisotropic mechanisms in tribological properties of textured Ti_2AlC-Mg composites were confirmed and discussed.展开更多
Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So f...Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.展开更多
Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).How...Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).However,such healing ability to repair damages in vacuum or low oxygen partial pressure conditions remains unknown.Here,we report on the self-healing behavior of Ti_(2)AlC at a low oxygen partial pressure of about 1 Pa.The experimental results showed that the strength recovery depends on both healing temperature and time.After healing at 1400℃for 1–4 h,the healed samples exhibited the recovered strengths even exceeding the original strength of 375 MPa.The maximum recovered strength of~422 MPa was achieved in the healed Ti_(2)AlC sample after healing at 1400 for 4 h,about 13%higher than the original strength.Damages were healed by the formed℃TiCx from the decomposition of Ti_(2)AlC.The decomposition-induced crack healing as a new mechanism in the low oxygen partial pressure condition was disclosed for the MAX ceramics.The present study illustrates that key components made of Ti_(2)AlC can prolong their service life and keep their reliability during use at high temperatures in low oxygen partial pressures.展开更多
Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vo...Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.展开更多
A seed blend refuge has been implemented in the U.S.Corn Belt for Bt maize resistance management.The fall armyworm,Spodoptera frugiperda(J.E.Smith),is a target pest of Bt maize in the Americas.The larvae of this pest ...A seed blend refuge has been implemented in the U.S.Corn Belt for Bt maize resistance management.The fall armyworm,Spodoptera frugiperda(J.E.Smith),is a target pest of Bt maize in the Americas.The larvae of this pest are mobile,which may affect the efficacy of seed blend refuges.In this study,field and greenhouse trials were conducted to determine the performance of Bt-susceptible(aabb)and-heterozygous dual-gene-resistant(AaBb)genotypes of S.frugiperda in seed blends of non-Bt and pyramided Bt maize.Three field trials evaluated larval survival,larval growth,and plant injury with aabb in seed blends of Bt maize expressing Cry1A.105/Cry2Ab2/Vip3A with 0–30%non-Bt seeds.Greenhouse tests investigated the performance of aabb and AaBb in seed blends of Cry1A.105/Cry2Ab2 with 0–30% non-Bt seeds.In pure non-Bt maize plots,after 9–13 d of neonates being released on the plants,0.39 and 0.65 larvae/plant survived with leaf injury ratings of 4.7 and 5.9(Davis's 1–9 scale)in the field and greenhouse,respectively.In contrast,live larvae and plant injury were virtually not observed on Bt plants across all planting patterns.Larval occurrence and plant injury by aabb on non-Bt plants were similar between seed blends and pure non-Bt plantings,suggesting that the blended refuges could provide an equivalent susceptible population as structured refuge under the test conditions.In the greenhouse,the two insect genotypes in seed blends performed similarly,indicating that the seed blends did not provide more favorable conditions for AaBb over aabb.The information generated from this study should be useful in managing S.frugiperda and evaluating if send blends could be suitable refuge options for Bt resistance management in the regions where the insect is a primary target pest.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 52175284)the State Key Lab of Advanced Metals and Materials (2021-ZD08)technical support of BL13W1 Beamline in Shanghai Synchrotron Radiation Facility (SSRF) and Gaomi Xiangyu company
文摘3D reconstruction and 2D observation were conducted to characterize the microstructure of the castings produced through high pressure die casting with different parameters.Our results indicate that shrinkage pores generally co-existed with externally solidified crystals(ESCs).In specimen produced without fast slow shot speed,big net-shrinkage pores accompanied with ESCs were found in the center of the specimen.When the casting pressurization was introduced,the shrinkage pores gathered to the specimen center and became much less due to the optimization of melt feeding.Much more porosity was found near the gate rather than in the middle of the rod bar,especially gas pores.Thefilling process simulation reveals that the middle position of the bars wasfirstlyfilled and followed by the near gate position accompanied with one intense turbulentflow.
基金supported by Beijing Natural Science Foundation(3232011)the Pre-Research Program in National 14th Five-Year Plan(80923010304)the National Natural Science Foundation of China(52130509).
文摘In order to enhance the ablation-resistant performance of stainless-steel conductive rails,Mo coating,410 stainless steel coating and 15 wt%Cr_(2)AlIC particles reinforced 410 stainless steel composite coating were prepared and evaluated.Different from the weak interfacial strength caused by the dissimilar metals between Mo and steel rails,410 stainless steel coating has better interfacial contact with steel rails.The introduction of Cr_(2)AlC into 410 stainless steels further strengthened the mechanical properties of coating by alloy strengthening effect and particle strengthening effect,as the decomposition of Cr_(2)AlC into nano CrC particles is accompanied with the diffusion of Al atoms into 410 stainless steels.It was found that the composite coating can still resist arc erosion at 150 A current,as a dense oxide film formed during the ablation process and the decomposition of Cr_(2)AlC contributed to the heat absorption.
基金the National Science Foundation of China(No.51701010)Beijing Government Funds for the Constructive Project of Central Universities(No.353139535)Thanks to Gaomi Xiangyu Company(Shandong province,China)for the gravity casting.
文摘To investigate the effect of AlsMn4Gd phase on microstructural and mechanical properties of Mg-Al-Ca magnesium alloy,two Mg-2.5AbCa and Mg-2.5Al2Ca-0.1 Al8Mn4Gd alloys were designed and compared in this work.The results show that a small amount of Gd can significantly refine a-Mg grains and change the morphology of AUCa particles.Indeed,the formed Al8Mn4Gd phase could serve as a heterogeneous nucleation site for the a-Mg grains and AbCa particles.Furthermore,the introduction of Gd not only optimized the mechanical properties of Mg-Al-Ca alloy,but also facilitated the thermal deformation(such as hot rolling).
基金supported by the National Natural Science Foundation of China (No. 52175284, 52130509 and 52075543)the State Key Lab of Advanced Metmals and Materials (2021-ZD08)。
文摘In recent decades, the demand for lightweight and high specific strength materials brings about the development of magnesium matrix composites. Different from some traditional binary ceramic particles, such as SiC, Al_(2)O_(3), the novel ternary nano-layered M_(n+1)AX_(n)(MAX)phase carbide or nitride ceramics exhibit metal-like properties and self-lubricate capacity(where “M” is an early transition metal, “A” belongs to the group A element, “X” is C or/and N, and n = 1–3). Ti_(2)AlC, as the representative of the MAX phase, was interestingly introduced into the magnesium matrix. Layered Ti_(2)AlC MAX phased reinforced AZ91D magnesium composites manufactured through the stir casting exhibit sufficient deformation capacity due to unique deformation behaviors of MAX, namely delamination and the formation of kinking band. Further,the Ti_(2)AlC-AZ91D composites exhibit a distinctive characteristic in strengthening mechanism, damping mechanism and tribological capacity due to the other special properties of MAX phase, such as self-lubricated property. Accordingly, to give a comprehensive understanding, we overviewed the fabrication process, microstructural characterization, mechanical properties, damping property and tribological capacity on these composites. In order to understand the A-site effect in MAX phase on the microstructure, we introduced another representative Ti_(3)SiC_(2)MAX phase to explain the interfacial evolution. In addition, due to the high aspect ratio of MAX, MAX particles could be orientationally regulated in Mg matrix by plastic deformation such as hot extrusion. Herein, we discussed the anisotropic mechanical and physical properties of the textured composites produced by hot extrusion. Moreover, the potential applications and future development trends of MAX phases reinforced magnesium matrix composites were also given and prospected.
基金financially supported by the National Natural Science Foundation of China(No.52175284)the State Key Lab of Advanced Metals and Materials in University of Science and Technology Beijing(No.2021-ZD08)。
文摘To clarify the relationship between externally solidified crystals(ESCs)and other defects,e.g.,defect bands and pores,two dimensional(2D)and three dimensional(3D)characterization methods were adopted to analyze castings produced using a modified ingate system equipped with and without an ESC collector.The reduction of ESCs strongly reduced defect band width and shrinkage pore quantity.By reducing the quantity and size of ESCs,net-shrinkage pores were transformed into isolated island-shrinkage pores.We determined via statistical analysis that the mechanical properties of high pressure die castings were strongly related to the size and fraction of the ESCs rather than porosity volume.The reduction of ESCs also caused tensile transgranular fracture modes to transform into intergranular fracture modes.Additionally,casting pressurization strongly reduced pore morphology,volume,and size.
基金financially supported by the National Natural Science Foundation of China(No.52175284)the State Key Lab of Advanced Metals and Materials(No.2021-ZD08)the Beijing Government Funds for the Cons tructive Project of Central Universities(No.353139535)。
文摘Magnesium composites reinforced by N-deficient Ti_(2)AlN MAX phase were first fabricated by non-pressure infiltration of Mg into three-dimensional(3D)co-continuous porous Ti_(2)AlN_(x)(x=0.9,1.0)preforms.The relationship between their mechanical properties and micro-structure is discussed with the assessment of 2D and 3D characterization.X-ray diffraction(XRD)and scanning electron microscopy detected no impurities.The 3D reconstruction shows that the uniformly distributed pores in Ti_(2)AlN_(x) preforms are interconnected,which act as infiltra-tion tunnels for the melt Mg.The compressive yield strength and microhardness of Ti_(2)AlN_(0.9)/Mg are 353 MPa and 1.12 GPa,respectively,which are 8.55%and 6.67%lower than those of Ti_(2)AlN/Mg,respectively.The typical delamination and kink band occurred in Ti_(2)AlN_(x) under compressive and Vickers hardness(V_(H))tests.Owing to the continuous skeleton structure and strong interfacial bonding strength,the crack ini-tiated in Ti_(2)AlN_(x) was blocked by the plastic Mg matrix.This suggests the possibility of regulating the mechanical performance of Ti_(2)AlN/Mg composites by controlling the N vacancy and the hierarchical structure of Ti_(2)AlN skeleton.
基金supported by the Hubei Provincial Natural Science Foundation of China(Nos.2021CF349 and 2020CFA042).
文摘It has been demonstrated that microplastics (MPs) can accumulate heavy metals from the environment and transfer them into organisms via the food chain. However, adsorption and desorption capacities for biodegradable MPs relative to those for conventional MPs remain poorly understood. In this study, cadmium (Cd(II)) adsorption and desorption characteristics of polylactic acid (PLA), a typical biodegradable MP, were investigated. Two conventional MPs, i.e., polypropylene (PP) and polyamide (PA) were used for comparison. The maximum Cd(II) adsorption capacities of the MPs studied in the adsorption experiments decreased in the order PA (0.96 ± 0.07 mg/g) > PLA (0.64 ± 0.04 mg/g) > PP (0.22 ± 0.03 mg/g). The Pseudo-second-order kinetic model and Freundlich isothermal model described the Cd(II) adsorption behaviors of PLA MPs well. X-ray photoelectron spectroscopy and two-dimensional Fourier transform infrared correlation spectroscopy analysis indicated that oxygen functional groups were the major and preferential binding sites of PLA MPs, which contributed to their high Cd(II) adsorption capacities. Simulated gastric and intestinal fluids both significantly enhanced the desorption capacities of the examined MPs. Notably, degradation of the PLA MPs during in vitro human digestion made the Cd(II) on the PLA MPs more bioaccessible (19% in the gastric phase and 62% in the intestinal phase) than Cd(II) on the PP and PA MPs. These results indicate the remarkable capacities of biodegradable MPs to accumulate Cd(II) and transfer it to the digestive system and show that biodegradable MPs might pose more severe threats to human health than conventional nonbiodegradable MPs.
基金financially supported by the National Major Science and Technology Program of China(No.2012ZX04012011)the National Natural Science Foundation of China(No.51275269)
文摘The interfacial heat transfer behavior at the metalJshot sleeve interface in the high pressure die casting (HPDC) process of AZ91D alloy is carefully investigated. Based on the temperature measurements along the shot sleeve, inverse method has been developed to determine the interfacial heat transfer coefficient in the shot sleeve. Under static condition, Interracial heat transfer coefficient (IHTC) peak values are 11.9, 7,3, 8.33kWm-2K-1 at pouring zone (S2), middle zone (S5), and end zone (510), respectively. During the casting process, the IHTC curve displays a second peak of 6.1 kWm-2 K-1 at middle zone during the casting process at a slow speed of 0.3 ms 1 Subsequently, when the high speed started, the IHTC curve reached a second peal〈 of 12.9 kW m-2K-1 at end zone. Furthermore, under different slow casting speeds, both the calculated initial temperature (TIDs) and the maximum temperature (Tsimax) of shot sleeve surface first decrease from 0.1 ms-1 to 0.3 ms-1, but increase again from 0.3 ms-1 to 0.6 ms-1. This result agrees with the experimental results obtained in a series of "plate-shape" casting experiments under different slow speeds, which reveals that the amount of ESCs decreases to the minimum values at 0.3 m s-1 and increase again with the increasing casting slow speed.
基金supported by the National Natural Science Foundation of China (No. 51701010)the Beijing Jiaotong University Foundation for youth scientists (No. No.2017RC013)+1 种基金the Project National United Engineering Laboratory for Advanced Bearing Tribology-Henan University of Science and Technology (No. 201805)the Beijing Government Funds for the Constructive Project of Central Universities (No. 353139535)
文摘The dry sliding wear behavior of Ti_2AlC reinforced AZ91 magnesium composites was investigated at sliding velocity of 0.5 m/s under loads of 10, 20, 40 and 80 N using pin-on-disk configuration against a Cr15 steel disc. Wear rates and friction coefficients were registered during wear tests. Worn tracks and wear debris were examined by scanning electron microscopy, energy dispersive X-ray spectrometry and transmission electron microscopy in order to obtain the wear mechanisms of the studied materials. The main mechanisms were characterized as the magnesium matrix oxidation and self-lubrication of Ti_2AlC MAX phase. In all conditions, the composites exhibit superior wear resistance and self-lubricated ability than the AZ91 Mg alloy. In addition, the anisotropic mechanisms in tribological properties of textured Ti_2AlC-Mg composites were confirmed and discussed.
基金supported by the National Natural Science Foundation of China(No.51772020)Beijing Natural Science Foundation(No.2182058)+1 种基金Beijing Government Funds for the Constructive Project of Central UniversitiesEquipment Development Department of the National Military Commission Foundation of China(No.JZX7Y20190262063601)。
文摘Two-dimensional(2D)Ti3C2Tx MXene is an attractive additive not only used in base oil due to its low friction coefficient,but also used in composites due to its high aspect ratio and rich surface functional groups.So far there has been intense research into polymer matrix composites reinforced with Ti3C2Tx,Here we report on the use of 2D Ti3C2Tx to enhance the mechanical and frictional properties of Al matrix composites.Ti3C2Tx/Al composites were designed and prepared by pre s sureless sintering followed by hot extrusion technique.The prepared composites exhibit a homogeneous distribution of Ti3C2Tx.The Vickers hardness and the tensile strength continuously increase with increasing Ti3C2Tx content.A hardness of 0.52 GPa and a tensile strength of 148 MPa were achieved in the 3 wt%Ti3C2Tx/Al composite.The frictional properties of pure Al and the Ti3C2Tx/Al composite were comparably studied under dry sliding.A low friction coefficient of 0.2,twice lower than that of pure Al,was achieved in the 3 wt%Ti3C2Tx/Al composite.Ti3C2Tx acting as a solid lubricant reduces the abrasive wear in the composite,improving the frictional properties of Al matrix composites.
基金supported by the National Natural Science Foundation of China(No.52275171)the PreResearch Program in National 14th Five-Year Plan(No.80923010304).
文摘Ti_(2)AlC,a MAX phase ceramic,has an attractive self-healing ability to restore performance via the oxidation-induced crack healing mechanism upon healing at high temperatures in air(high oxygen partial pressures).However,such healing ability to repair damages in vacuum or low oxygen partial pressure conditions remains unknown.Here,we report on the self-healing behavior of Ti_(2)AlC at a low oxygen partial pressure of about 1 Pa.The experimental results showed that the strength recovery depends on both healing temperature and time.After healing at 1400℃for 1–4 h,the healed samples exhibited the recovered strengths even exceeding the original strength of 375 MPa.The maximum recovered strength of~422 MPa was achieved in the healed Ti_(2)AlC sample after healing at 1400 for 4 h,about 13%higher than the original strength.Damages were healed by the formed℃TiCx from the decomposition of Ti_(2)AlC.The decomposition-induced crack healing as a new mechanism in the low oxygen partial pressure condition was disclosed for the MAX ceramics.The present study illustrates that key components made of Ti_(2)AlC can prolong their service life and keep their reliability during use at high temperatures in low oxygen partial pressures.
基金This work was supported by the National Natural Science Foundation of China(No.51772020)Beijing Government Funds for the Constructive Project of Central Universities.
文摘Novel MoAlB composites reinforced with 5–15 vol% SiC have been firstly prepared and characterized in the present study. The SiC reinforcement is stable with MoAlB at a sintering temperature of 1200 ℃ in Ar. The 5 vol% SiC/MoAlB composite exhibited improved mechanical properties and enhanced oxidation resistance. A flexural strength of 380 MPa and a Vickers hardness of 12.7 GPa were achieved and increased by 24% and 51%, respectively, as compared with those for MoAlB, indicating the enhanced strengthening effect of SiC. Cyclic oxidation tests at 1200 and 1300 ℃ for 10 h in air showed that the 5 vol% SiC/MoAlB composite has better oxidation resistance than MoAlB due to the formation of a dense and continuous scale composed of Al_(2)O_(3) and SiO_(2), which prevents the oxygen inward diffusion and the evaporation of oxides. We expect that the general strategy of second phase reinforcing for materials will help to widen the applications of MoAlB composites.
基金This article is published with the approval of the Director of the Louisiana Agri-cultural Experiment Station as manuscript No.2020-234-34595This project represents work supported by Bayer Crop Science(St.Louis,MO,USA),USDA Regional Research Project NC-246Hatch funds from the USDA National Institute of Food and Agriculture.
文摘A seed blend refuge has been implemented in the U.S.Corn Belt for Bt maize resistance management.The fall armyworm,Spodoptera frugiperda(J.E.Smith),is a target pest of Bt maize in the Americas.The larvae of this pest are mobile,which may affect the efficacy of seed blend refuges.In this study,field and greenhouse trials were conducted to determine the performance of Bt-susceptible(aabb)and-heterozygous dual-gene-resistant(AaBb)genotypes of S.frugiperda in seed blends of non-Bt and pyramided Bt maize.Three field trials evaluated larval survival,larval growth,and plant injury with aabb in seed blends of Bt maize expressing Cry1A.105/Cry2Ab2/Vip3A with 0–30%non-Bt seeds.Greenhouse tests investigated the performance of aabb and AaBb in seed blends of Cry1A.105/Cry2Ab2 with 0–30% non-Bt seeds.In pure non-Bt maize plots,after 9–13 d of neonates being released on the plants,0.39 and 0.65 larvae/plant survived with leaf injury ratings of 4.7 and 5.9(Davis's 1–9 scale)in the field and greenhouse,respectively.In contrast,live larvae and plant injury were virtually not observed on Bt plants across all planting patterns.Larval occurrence and plant injury by aabb on non-Bt plants were similar between seed blends and pure non-Bt plantings,suggesting that the blended refuges could provide an equivalent susceptible population as structured refuge under the test conditions.In the greenhouse,the two insect genotypes in seed blends performed similarly,indicating that the seed blends did not provide more favorable conditions for AaBb over aabb.The information generated from this study should be useful in managing S.frugiperda and evaluating if send blends could be suitable refuge options for Bt resistance management in the regions where the insect is a primary target pest.