Papers by Author: Tao Jiang

Abstract: The Fe₃Al/Al₂O₃ composites were fabricated by hot-pressing process at 1300°C for 2h under the pressure of 35MPa, by using the Fe₃Al intermetallics compounds powders fabricated by mechanical alloying and heat treatment. The phase composition and microstructure of the Fe₃Al intermetallics compounds powders and Fe₃Al/Al₂O₃ composites were investigated. The XRD patterns results showed that the Fe-Al intermetallics compounds powders were prepared by mechanical alloying for 60h and heat treatment process at 800°C and 1000°C. The XRD patterns results showed that there existed Fe₃Al phase and Al₂O₃ phase in sintered composites. The Fe₃Al/Al₂O₃ composites exhibited homogenous and compact microstructure, the Fe₃Al particles were homogenously distributed in Al₂O₃ matrix. The mean particles size of Fe₃Al was about 3-4μm and the mean particles size of Al₂O₃ matrix was about 4-5μm.

Abstract: The Fe-Al intermetallic compound powders were fabricated by mechanical alloying and heat treatment process. In this research, the phase composition and microstructure of the Fe-Al intermetallic compound powders produced by different milling time and heat treatment at 800oC and 1000oC were investigated. The XRD patterns results showed that the Fe-Al intermetallic compound powders were fabricated by mechanical alloying for 60h. After heat treatment at 800oC and 1000oC, the Fe-Al intermetallic compound powders transformed into the Fe3Al powders. With the increase of milling time, the mechanical alloying extent of Fe-Al intermetallic compound powders would be increased remarkably, and the particles sizes decreased remarkably. The microstructure showed that the mean particles size of the Fe-Al intermetallic compound powders after milling for 60h was rather fine and about 4-5μm. The microstructures showed that mean particles size of the Fe3Al intermetallic compound powders produced by heat treatment at 800oC and 1000oC was also about 4-5μm.

Abstract: The B4C/BN composites were fabricated by hot-pressing process. The microstructure, mechanical properties and oxidation resistances of the B4C/BN composites were investigated. It was shown that the h-BN particles were distributed in the B4C ceramics matrix. The mechanical properties of the B4C/BN microcomposites and the B4C/BN nanocomposites decreased gradually with the increasing content of h-BN. The mechanical properties of the B4C/BN nanocomposites were significantly improved in comparison with the B4C/BN microcomposites. The oxidation processes were performed at 1000oC, 1100oC, 1200oC, 1300oC for 20h. The oxidation curves of the B4C monolith, the B4C/BN microcomposites and the B4C/BN nanocomposites decreased gradually with the increase of oxidation temperature and oxidation time. The specimen’s weight and the oxidation resistance decreased gradually with the increase of oxidation temperature and oxidation time. The specimens remained good oxidation resistance at 1000oC; the oxidation resistance decreased remarkably at 1300oC. The decreasing specimen’s weight was attributed to the evaporation of B2O3 which produced by oxidation process of B4C and h-BN. The phase composition and microstructure of specimen’s surface after oxidation process were investigated by XRD and SEM.

Abstract: In this article, the microstructure, mechanical properties and machinability of the B4C/BN microcomposites and the B4C/BN nanocomposites were investigated. Homogenous distribution of the h-BN particles in the B4C ceramics appeared. The mechanical properties decreased gradually with the increasing content of h-BN for the both composites, while the nanocomposites demonstrated high performance. Machinability increased gradually with the increasing content of h-BN, and excellent machinability exhibited for both composites with more than 20wt% h-BN. The weak interface between the B4C matrix grains and the h-BN particles as well as the cleavage behavior of the laminate structured h-BN particles significantly attributed to the machinability of the B4C/BN composites.

Abstract: The B4C/BN nanocomposites were fabricated by hot-pressing sintering of the B4C/BN nanocomposite powders at 1850oC for 1h under the pressure of 30MPa. The composite powders with the microstructure of B4C particles coated with nano-sized BN particles were prepared by the chemical reaction of H3BO3 and CO(NH2)2 on the surface of B4C particles at high temperature. The microstructure investigation of the nanocomposites sintered samples showed that the nano-sized h-BN particles were homogenously distributed in the B4C matrix. With the increasing content of h-BN, the density of the B4C/BN nanocomposites decreased gradually; the fracture strength and fracture toughness of the B4C/BN nanocomposites decreased gradually, the strength and toughness of the B4C/BN nanocomposites with the h-BN content of 10wt% and 20wt% achieved high values. The Vickers hardness of the B4C/BN nanocomposites decreased remarkably with the increasing content of h-BN, while the machinability of the B4C/BN nanocomposites was significantly improved. The B4C/BN nanocomposites with the h-BN content more than 20wt% exhibited excellent machinability.

Abstract: The machinable B4C/BN ceramics composites were fabricated by hot-pressing sintering process at 1850oC for 1h under the pressure of 30MPa. The mechanical property, thermal shock behavior and machinability of the B4C/BN ceramics composites were investigated in this article. The experimental results showed that the fracture strength and fracture toughness of the B4C/BN nanocomposites were significantly improved in comparison with the B4C/BN microcomposites. The Vickers hardness of the B4C/BN nanocomposites and B4C/BN microcomposites decreased gradually with the increasing content of h-BN, while the machinability of the B4C/BN nanocomposites and B4C/BN microcomposites were significantly improved. The B4C/BN ceramics composites with the h-BN content more than 20wt% exhibited excellent machinability. The thermal shock resistances of the B4C/BN ceramics composites were better than that of the B4C monolith, and the thermal shock resistance of the B4C/BN nanocomposites was much better than that of the B4C/BN microcomposites. The thermal shock temperature difference (-Tc) of B4C monolith was about 300oC, while the -Tc of the B4C/BN microcomposites was about 500oC, the -Tc of the B4C/BN nanocomposites was about 600oC.