Laser powder bed fusion(L-PBF)was utilized to produce specimens in Ti-6Al-4V,which were subjected to a bi-lamellar heat treatment,which produces microstructures consisting of primary α-lamellae and a fine secondary ...Laser powder bed fusion(L-PBF)was utilized to produce specimens in Ti-6Al-4V,which were subjected to a bi-lamellar heat treatment,which produces microstructures consisting of primary α-lamellae and a fine secondary α-phase inside the inter-lamellar β-regions.The bi-lamellar microstructure was obtained as(i)a direct bi-lamellar heat treatment from the asbuilt condition or(ii)a bi-lamellar heat treatment preceded by a β-homogenization.For the bi-lamellar treatment with β-homogenization,cooling rates in the range 1-500 K/min were applied after homogenization in β-region followed by inter-critical annealing in the α+β region at various temperatures in the range 850-950℃.The microstructures were characterized using various microscopical techniques.Mechanical testing with Vickers hardness indentation and tensile testing was performed.The bi-lamellar microstructure was harder when compared to a soft fully lamellar microstructure,because of the presence of fine α-platelets inside the β-lamellae.Final low temperature ageing provided an additional hardness increase by precipitation hardening of the primary α-regions.The age hardened bi-lamellar microstructure shows a similar hardness as the very fine,as-built martensitic microstructure.The bi-lamellar microstructure has more favorable mechanical properties than the as-built condition,which has high strength,but poor ductility.After the bi-lamellar heat treatment,the elongation was improved by more than 250%.Due to the very high strength of the as-built condition,loss of tensile strength is unavoidable,resulting in a reduction of tensile strength of~18%.展开更多
Singular perturbation theory is applied for analytically estimating the effects of small acceleration terms on spacecraft orbital dynamics,which are representative of the action of a drag force or of an electric low-t...Singular perturbation theory is applied for analytically estimating the effects of small acceleration terms on spacecraft orbital dynamics,which are representative of the action of a drag force or of an electric low-thrust propulsion system.The effects of density variation with altitude and thrust magnitude as a function of distance from the primary body are included in the analysis.Comparisons with results obtained from numerical integration and other analytical and semianalytical methods demonstrate the validity of the approach in predicting the secular variation of orbit parameters in planar motion,with advantages in terms of accuracy and/or computational cost with respect to other approximations.展开更多
基金This research was conducted in connection with the AM-LINE4.0 project(No.7076-00074B)funded by the Danish Innovation Fund。
文摘Laser powder bed fusion(L-PBF)was utilized to produce specimens in Ti-6Al-4V,which were subjected to a bi-lamellar heat treatment,which produces microstructures consisting of primary α-lamellae and a fine secondary α-phase inside the inter-lamellar β-regions.The bi-lamellar microstructure was obtained as(i)a direct bi-lamellar heat treatment from the asbuilt condition or(ii)a bi-lamellar heat treatment preceded by a β-homogenization.For the bi-lamellar treatment with β-homogenization,cooling rates in the range 1-500 K/min were applied after homogenization in β-region followed by inter-critical annealing in the α+β region at various temperatures in the range 850-950℃.The microstructures were characterized using various microscopical techniques.Mechanical testing with Vickers hardness indentation and tensile testing was performed.The bi-lamellar microstructure was harder when compared to a soft fully lamellar microstructure,because of the presence of fine α-platelets inside the β-lamellae.Final low temperature ageing provided an additional hardness increase by precipitation hardening of the primary α-regions.The age hardened bi-lamellar microstructure shows a similar hardness as the very fine,as-built martensitic microstructure.The bi-lamellar microstructure has more favorable mechanical properties than the as-built condition,which has high strength,but poor ductility.After the bi-lamellar heat treatment,the elongation was improved by more than 250%.Due to the very high strength of the as-built condition,loss of tensile strength is unavoidable,resulting in a reduction of tensile strength of~18%.
文摘Singular perturbation theory is applied for analytically estimating the effects of small acceleration terms on spacecraft orbital dynamics,which are representative of the action of a drag force or of an electric low-thrust propulsion system.The effects of density variation with altitude and thrust magnitude as a function of distance from the primary body are included in the analysis.Comparisons with results obtained from numerical integration and other analytical and semianalytical methods demonstrate the validity of the approach in predicting the secular variation of orbit parameters in planar motion,with advantages in terms of accuracy and/or computational cost with respect to other approximations.
