Element W can effectively improve the density of energetic structural materials. However, W is an inert element and does not combust in air. To change the reaction characteristics of W, 60 at.% Al was introduced into ...Element W can effectively improve the density of energetic structural materials. However, W is an inert element and does not combust in air. To change the reaction characteristics of W, 60 at.% Al was introduced into W through mechanical alloying. XRD analysis shows that after 50 h of ball milling, the diffraction peak of Al completely disappears and W(Al60) super-saturated solid solution powder is obtained. Further observation by HAADF and HRTEM reveals that the W(Al60) super-saturated solid solution powder is a mixture of solid solution and amorphous phase. Based on the good thermal stability of W(Al60) alloy powder below 1000℃, W(Al60)-Al composite was synthesized by hot pressing process.Impact initiation experiments suggest that the W(Al60)-Al composite has excellent reaction characteristics, and multiple types of tungsten oxides are detected in the reaction products, showing that the modified W is combustible in air. Due to the combustion of tungsten, the energy release rate of the W(Al60)-Al composite at speed of 1362 m/s reaches 2.71 kJ/g.展开更多
The purity,preferred orientation,microstructure,microhardness,bonding strength,thickness uniformity and thermal stability of rhenium(Re)coatings prepared on graphite wafers by chemical vapor deposition(CVD)and electro...The purity,preferred orientation,microstructure,microhardness,bonding strength,thickness uniformity and thermal stability of rhenium(Re)coatings prepared on graphite wafers by chemical vapor deposition(CVD)and electrodeposition(ED)in molten salts were comparatively studied in this paper.It was found that carbon(0.0140 wt%)and oxygen(0.0067 wt%)were the primary impurities for CVD and ED Re coatings,respectively.The diffusion of carbon into CVD Re coating caused higher microhardness near the substrate and helped to improve the bonding strength at the same time.The preferred orientation,microstructure and microhardness of ED Re coating were all susceptible to oxygen.The coating deposition uniformity of ED Re is obviously better than that of CVD Re coating,due to its intrinsic characteristics.The(002)-oriented,coarse columnar CVD Re coating exhibited better thermal stability compared with that of the<110>-oriented,fiber-like columnar ED Re coating,while the ED Re grains grew remarkably and the microstructure evolved toward the similar structure of CVD Re after annealing treatment.The diversity of Re coatings in microstructure could be attributed to the mobility of grain boundaries(affected by temperature and impurity)during deposition processes.展开更多
An iridium/rhenium(Ir/Re)double-layer coating was prepared on carbon/carbon(C/C)composites by chemical vapor deposition(CVD)and electrodeposition.The morphologies and bond strengths of the coatings on the C/C substrat...An iridium/rhenium(Ir/Re)double-layer coating was prepared on carbon/carbon(C/C)composites by chemical vapor deposition(CVD)and electrodeposition.The morphologies and bond strengths of the coatings on the C/C substrate were examined.The ablation resistance of the Ir/Re coating was studied at 1800℃in an oxyacetylene torch flame for 300 s.The results show that Re interlayer increases the bond strength between Ir coating and C/C substrate by over 100%.During entire hightemperature ablation process,Ir/Re coating keeps intact without any signs of ablation damage.Ir coating gets smoother and the grain size becomes larger after ablation,with the preferred orientation changing from h311i to h220i:Although some voids are observed along the grain boundaries of the as-ablated Ir coating,Ir/Re coating keeps intact on C/C composites.The study indicates that Ir/Re coating can provide good ablation resistance up to 1800℃for C/C composites,especially for the continuous ablation applications.展开更多
基金supported by the National Natural Science Foundation of China, [Award number: 11972372] and [Award number: U20A20231]。
文摘Element W can effectively improve the density of energetic structural materials. However, W is an inert element and does not combust in air. To change the reaction characteristics of W, 60 at.% Al was introduced into W through mechanical alloying. XRD analysis shows that after 50 h of ball milling, the diffraction peak of Al completely disappears and W(Al60) super-saturated solid solution powder is obtained. Further observation by HAADF and HRTEM reveals that the W(Al60) super-saturated solid solution powder is a mixture of solid solution and amorphous phase. Based on the good thermal stability of W(Al60) alloy powder below 1000℃, W(Al60)-Al composite was synthesized by hot pressing process.Impact initiation experiments suggest that the W(Al60)-Al composite has excellent reaction characteristics, and multiple types of tungsten oxides are detected in the reaction products, showing that the modified W is combustible in air. Due to the combustion of tungsten, the energy release rate of the W(Al60)-Al composite at speed of 1362 m/s reaches 2.71 kJ/g.
基金financially supported by the National Natural Science Foundation of China(No.51501224)。
文摘The purity,preferred orientation,microstructure,microhardness,bonding strength,thickness uniformity and thermal stability of rhenium(Re)coatings prepared on graphite wafers by chemical vapor deposition(CVD)and electrodeposition(ED)in molten salts were comparatively studied in this paper.It was found that carbon(0.0140 wt%)and oxygen(0.0067 wt%)were the primary impurities for CVD and ED Re coatings,respectively.The diffusion of carbon into CVD Re coating caused higher microhardness near the substrate and helped to improve the bonding strength at the same time.The preferred orientation,microstructure and microhardness of ED Re coating were all susceptible to oxygen.The coating deposition uniformity of ED Re is obviously better than that of CVD Re coating,due to its intrinsic characteristics.The(002)-oriented,coarse columnar CVD Re coating exhibited better thermal stability compared with that of the<110>-oriented,fiber-like columnar ED Re coating,while the ED Re grains grew remarkably and the microstructure evolved toward the similar structure of CVD Re after annealing treatment.The diversity of Re coatings in microstructure could be attributed to the mobility of grain boundaries(affected by temperature and impurity)during deposition processes.
基金This study was financially supported by the National Natural Science Foundation of China(No.51371196)the Aid Program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province.
文摘An iridium/rhenium(Ir/Re)double-layer coating was prepared on carbon/carbon(C/C)composites by chemical vapor deposition(CVD)and electrodeposition.The morphologies and bond strengths of the coatings on the C/C substrate were examined.The ablation resistance of the Ir/Re coating was studied at 1800℃in an oxyacetylene torch flame for 300 s.The results show that Re interlayer increases the bond strength between Ir coating and C/C substrate by over 100%.During entire hightemperature ablation process,Ir/Re coating keeps intact without any signs of ablation damage.Ir coating gets smoother and the grain size becomes larger after ablation,with the preferred orientation changing from h311i to h220i:Although some voids are observed along the grain boundaries of the as-ablated Ir coating,Ir/Re coating keeps intact on C/C composites.The study indicates that Ir/Re coating can provide good ablation resistance up to 1800℃for C/C composites,especially for the continuous ablation applications.
