Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites with nitrogen atmosphere protection. Microstructures and mechanical properties o...Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites with nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It is indicates that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550℃ and 28 MPa for 30 min are improved evidently. Based on mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistant, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All the above are beneficial to the improvement of mechanical properties of alumina matrix ceramic composites.展开更多
The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (...The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (inner layer near diamond, external layer near graphite and middle layer). The graphite cannot be directly transformed into diamond in the film at HTHP: there exists a parallelrelationship between (111) of γ-(Fe,Ni) and (110) of Fe3C in the inner layer; the sawtooth-like step morphology found by AFM on the film is similar to that of corresponding diamond surface. A new model for diamond growth at HPHT is proposed from the parallel relationship and sawtooth-like step morphology. It is believed that Fe3C may be a transitional phase in the course of diamond growth, γ-(Fe,Ni) in the inner layer can absorb carbon atom groups with lamella structure from Fe3C, and then the carbon groups stack on growing diamond.展开更多
文摘Mixed rare earth elements were incorporated into alumina ceramic materials. Hot-pressing was used to fabricate alumina matrix composites with nitrogen atmosphere protection. Microstructures and mechanical properties of the composites were tested. It is indicates that the bending strength and fracture toughness of alumina matrix ceramic composites sintered at 1550℃ and 28 MPa for 30 min are improved evidently. Based on mixed rare earth elements acting as a toughening phase, AlTiC master alloys were also added in as sintering assistant, which could prompt the formation of transient liquid phase, and thus nitrides of rare earth elements were produced. All the above are beneficial to the improvement of mechanical properties of alumina matrix ceramic composites.
基金This work was supported by the National Natural Science Foundation of China (Grant No. 59971027).
文摘The microstructures of metallic film surrounding diamond have been systemically studied using the transmission electron microscopy (TEM) and the atom force microscopy (AFM). The film can be divided into three layers (inner layer near diamond, external layer near graphite and middle layer). The graphite cannot be directly transformed into diamond in the film at HTHP: there exists a parallelrelationship between (111) of γ-(Fe,Ni) and (110) of Fe3C in the inner layer; the sawtooth-like step morphology found by AFM on the film is similar to that of corresponding diamond surface. A new model for diamond growth at HPHT is proposed from the parallel relationship and sawtooth-like step morphology. It is believed that Fe3C may be a transitional phase in the course of diamond growth, γ-(Fe,Ni) in the inner layer can absorb carbon atom groups with lamella structure from Fe3C, and then the carbon groups stack on growing diamond.
