Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(X...Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that at a temperature of 700℃,the peak yield stress(YS)and ultimate tensile stress(UTS)of alloy are 534 and 575 MPa,respectively,and the alloy shows satisfactory comprehensive mechanical properties at 850℃.The alloy exhibits superplastic characteristics at 1000℃with an initial strain rate of 5×10^−5 s^−1.When the tensile temperature is below 750℃,the deformation mechanisms are dislocation movements and mechanical twinning.Increasing the tensile temperature above 800℃,grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.展开更多
Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefi...Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefits （i.e. reduce the unit cost of goods and fabrication process etc.） to fabrication of metallic foams. In this article, the fabrication characteristic of near net-shape metallic foams by direct foaming method was evaluated. Al and Plaster was used for base material and mould material respectively. Ca and TiH2 were added to molten Al as thickening and blowing agent for stable condition of bubbles. Thickening time was about 10 min with a stirring speed of 600 r/min. Foaming time was 30-120 s for evaluation of the optimum foaming condition. Amount of agent was selected by pre-experimental data. Porosity of near net-shape goods was measured by Archimedes method. On the other hand, it seems that increasing poring time and thickening agent make the poor porosity展开更多
Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die c...Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting （Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy）, die casting （A356, A1-7Si-0.3Mg）, and semi-solid casting （A356, A1-TSi-0.3Mg）, respectively. Unlike die casting （second part）, low-pressure die casting （first part） sig- nificantly reduced the formation of casting defects （i.e., porosity） due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi- solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.展开更多
In order to overcome the shortcomings of conventional hot pressing, a novel near net-shape technique, called radial hot pressing, for P/M parts with large height-to-diameter (H/D) ratio was introduced. Effects of proc...In order to overcome the shortcomings of conventional hot pressing, a novel near net-shape technique, called radial hot pressing, for P/M parts with large height-to-diameter (H/D) ratio was introduced. Effects of processing parameters on the microstructures and density of P/M TiAl base alloy valves were studied. Results show that the radial hot pressing is an effective technique for manufacturing valves with a H/D ratio of about 10:1, and the perfect joint interface between the Mo sheet and the parts is helpful for subsequent HIPing.展开更多
The effects of the direction of current on the drag on fish cages are studied in the present paper. The drags on cages of different shapes, including cylindrical, tnmcated conical, cuboidal and hexagonal, are compared...The effects of the direction of current on the drag on fish cages are studied in the present paper. The drags on cages of different shapes, including cylindrical, tnmcated conical, cuboidal and hexagonal, are compared. The drag on the tnmcated conical net is smaller than that on other shapes of the same area. This net shape with a small apex angle is suggested for the design of fish cages.展开更多
Bézier surfaces play an important role in Computer-aided Geometric Design(CAGD),and coordinate curve nets are widely discussed in differential geometry. In this paper, we study the Bézier surfaces with speci...Bézier surfaces play an important role in Computer-aided Geometric Design(CAGD),and coordinate curve nets are widely discussed in differential geometry. In this paper, we study the Bézier surfaces with special coordinate curve nets, such as orthogonal coordinate net, curvature coordinate net and asymptotic coordinate net. In addition, we develop the Bézier surfaces which satisfy some shape constraints with the help of energy terms. Moreover, some applicable sufficient conditions based on geometrical structure of control nets are deduced and several representative examples are given.展开更多
Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer depos...Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.展开更多
The present paper finds out that the geometric entity which characterizes the best Lipschitz constants for the Bezier nets and Bernstein polynomials over a simplex sigma is an angle Phi determined by sigma, and proves...The present paper finds out that the geometric entity which characterizes the best Lipschitz constants for the Bezier nets and Bernstein polynomials over a simplex sigma is an angle Phi determined by sigma, and proves that (1) if f(x) is Lipschitz continuous over sigma, i.e., f(x) is an element of Lip(A)(alpha,sigma), then both the n-th Bezier net <(f)over cap (n)> and the n-th Bernstein polynomial B-n(f;x) corresponding to f(x) belong to Lip(B)(alpha,sigma) , where B = Asec(alpha)Phi; and (2) if n-th Bezier net <(f)over cap (n)> is an element of Lip(A)(alpha,sigma), then the elevation Bezier net <E(f)over cap (n)> and the corresponding Bernstein polynomial. B-n(f,;x) also belong to Lip(A)(alpha,sigma). Furthermore, the constant B = Asec(alpha)Phi, in case (1) is best in some sense.展开更多
基金Project(51774335)supported by the National Natural Science Foundation of ChinaProject(2019JJ40374)supported by the Natural Science Foundation of Hunan Province,ChinaProject(CSUZC202004)supported by the Open Sharing Fund for the Large-scale Instruments and Equipments of Central South University,China。
文摘Near net shaped Ti−45Al−7Nb−0.3W alloy(at.%)parts were manufactured by hot isostatic pressing(HIP).The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that at a temperature of 700℃,the peak yield stress(YS)and ultimate tensile stress(UTS)of alloy are 534 and 575 MPa,respectively,and the alloy shows satisfactory comprehensive mechanical properties at 850℃.The alloy exhibits superplastic characteristics at 1000℃with an initial strain rate of 5×10^−5 s^−1.When the tensile temperature is below 750℃,the deformation mechanisms are dislocation movements and mechanical twinning.Increasing the tensile temperature above 800℃,grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.
文摘Fabrication characteristics are unstable in direct foaming method. Therefore, most of near net-shape metallic foams are produced, and investigated by powder metallurgy. Direct foaming method, however, has many benefits （i.e. reduce the unit cost of goods and fabrication process etc.） to fabrication of metallic foams. In this article, the fabrication characteristic of near net-shape metallic foams by direct foaming method was evaluated. Al and Plaster was used for base material and mould material respectively. Ca and TiH2 were added to molten Al as thickening and blowing agent for stable condition of bubbles. Thickening time was about 10 min with a stirring speed of 600 r/min. Foaming time was 30-120 s for evaluation of the optimum foaming condition. Amount of agent was selected by pre-experimental data. Porosity of near net-shape goods was measured by Archimedes method. On the other hand, it seems that increasing poring time and thickening agent make the poor porosity
文摘Three types of near-net shape casting alumi- num parts were investigated by computed tomography to determine casting defects and evaluate quality. The first, second, and third parts were produced by low-pressure die casting （Al-12Si-0.8Cu-0.5Fe-0.9Mg-0.7Ni-0.2Zn alloy）, die casting （A356, A1-7Si-0.3Mg）, and semi-solid casting （A356, A1-TSi-0.3Mg）, respectively. Unlike die casting （second part）, low-pressure die casting （first part） sig- nificantly reduced the formation of casting defects （i.e., porosity） due to its smooth filling and solidification under pressure. No significant casting defect was observed in the third part, and this absence of defects indicates that semi- solid casting could produce high-quality near-net shape casting aluminum parts. Moreover, casting defects were mostly distributed along the eutectic grain boundaries. This finding reveals that refinement of eutectic grains is necessary to optimize the distribution of casting defects and reduce their size. This investigation demonstrated that computed tomography is an efficient method to determine casting defects in near-net shape casting aluminum parts.
文摘In order to overcome the shortcomings of conventional hot pressing, a novel near net-shape technique, called radial hot pressing, for P/M parts with large height-to-diameter (H/D) ratio was introduced. Effects of processing parameters on the microstructures and density of P/M TiAl base alloy valves were studied. Results show that the radial hot pressing is an effective technique for manufacturing valves with a H/D ratio of about 10:1, and the perfect joint interface between the Mo sheet and the parts is helpful for subsequent HIPing.
基金This workis financially supported by the National Natural Science Foundation of China (No.10272118) ,the Key Scientific and Technological Program of China (No.2004BA526B03) and the Research Fund for the Doctoral Program of the Ministry of Education of China (No.20020558013)
文摘The effects of the direction of current on the drag on fish cages are studied in the present paper. The drags on cages of different shapes, including cylindrical, tnmcated conical, cuboidal and hexagonal, are compared. The drag on the tnmcated conical net is smaller than that on other shapes of the same area. This net shape with a small apex angle is suggested for the design of fish cages.
基金Supported by the National Natural Science Foundation of China(Grant Nos.11801490 11671068 11501488)
文摘Bézier surfaces play an important role in Computer-aided Geometric Design(CAGD),and coordinate curve nets are widely discussed in differential geometry. In this paper, we study the Bézier surfaces with special coordinate curve nets, such as orthogonal coordinate net, curvature coordinate net and asymptotic coordinate net. In addition, we develop the Bézier surfaces which satisfy some shape constraints with the help of energy terms. Moreover, some applicable sufficient conditions based on geometrical structure of control nets are deduced and several representative examples are given.
基金Project(51461010101JB3501) supported by National Key Laboratory for High Energy Density Beam Processing Technology Foundation of China
文摘Laser engineered net shaping(LENS) process was investigated using Co-based superalloy powder with a high power continuous wave CO2 laser. Thin wall part with smooth surface was obtained by LENS of layer-by-layer deposition of the powder materials. This thin wall sample was tested for metallographic examinations, micro-hardness, X-ray diffraction and mechanical property test. Microstructural results show that the layers possess rapid solidification microstructural feature, fine dendritic crystal and M7C3-type carbides (essentially chromium-rich carbide) dispersed in theγ(Co,Cr) phase matrix. Dendrite spacing as well as the solidification mode can be controlled through control process parameters. In addition, this microstructural feature of the as-formed Co-base sample leads to an evident hardening and a superior tensile strength and toughness.
文摘The present paper finds out that the geometric entity which characterizes the best Lipschitz constants for the Bezier nets and Bernstein polynomials over a simplex sigma is an angle Phi determined by sigma, and proves that (1) if f(x) is Lipschitz continuous over sigma, i.e., f(x) is an element of Lip(A)(alpha,sigma), then both the n-th Bezier net <(f)over cap (n)> and the n-th Bernstein polynomial B-n(f;x) corresponding to f(x) belong to Lip(B)(alpha,sigma) , where B = Asec(alpha)Phi; and (2) if n-th Bezier net <(f)over cap (n)> is an element of Lip(A)(alpha,sigma), then the elevation Bezier net <E(f)over cap (n)> and the corresponding Bernstein polynomial. B-n(f,;x) also belong to Lip(A)(alpha,sigma). Furthermore, the constant B = Asec(alpha)Phi, in case (1) is best in some sense.
