Effect Of Carbon Nano-Tubes On The Microstructure And Mechanical Properties Of Ti(C,N)-Based Cermets

The study progress and developmental trend of Ti(C,N)-based cermets and nano- ceramics have been overviewed, and the influences of carbon nano-tubes(CNTs) on the microstructure and mechanical properties of metal and ceramics materials also have been summarized . Based on above work, the purpose and significance of the dissertation have been pointed out, that is to say by adding CNTs to the Ti(C,N)-based cermets, the transverse strength and Rockwell hardness of the material can be improved and the Ti(C,N)-based cermets with high strength and toughness can be development, at the same time the effect of CNTs on the microstructure and mechanical properties of Ti(C,N)-based cermets will be studied.In the study, the fracture morphologies and microstructure have been observed by field emission scanning electron microscope and transmission electron microscope. And composition profiles have been analysed by energy dispersive spectroscopy. Transverse strength test was conducted by three-point transverse method (span 14.5 mm) and Rockwell hardness (HRA) has been tested. And relationship among composition, microstructure and mechanical properties has been systematically investigated.The discussion and test on the surface modification and cladding Ni to CNTs with electroless plating has enabled the researcher to obtain a continuous and uninformative cladding material. The test also reveals that the cladding is more continuous and uninformative when pH value is in 4.5 than in 9, and the successive analysis shows the main composition of the cladding material is Ni.The effects of Mo contents and sintering temperatures on the microstructure and mechanical properties of Ti(C,N)-based cermets with low Ni contention has studied systematically. After being sintered, the carbide phase of the cermets exhibits classical core-rim morphology under microscope, but with the growth of the molybdenum contention, the grain size reduces and the rim phase increases. With the same Mo contention, the mechanical properties of the cermets are the best at 1450°C when the cermets is sintered at the temperature of 1430°C, 1440°C, 1450°C, and 1460°C individually. At the same sintering temperature, the grain size is uniformity, the thickness of the rim phase is moderated and the transverse strength is the best when the Mo contention is 8 wt.%. The hardness variation is not apparent while Mo contents vary from 4 to 12wt.% at the same sintering temperature. Comprehensively, the dissertation indicates that the mechanical properties of the transverse strength and the hardness are the best when the Mo contention is 8 wt.% and sintering temperature is 1450℃.Observations of the fracture morphology of the cermets with different Mo contents sintered at different temperature reveal the fracture is a mixed one. Both trans-granular and inter-granular fractures are in existence, the inter-granular fracture takes the main part, and cleavage fracture is obvious.Research on the microstructure of Ti(C,N) based cermets with low Ni and high Ni content after adding carbon nano-tubes (CNTs) exhibits the classical core-rim morphology. The microstructure is black core with obvious rim phase, and white core with unapparent rim phase and binder phase.The influence of CNTs on the properties of Ti(C, N) based cermets with low Ni content has been carefully studied: the transverse strength of the cermets with same composition is the best at 1450°C when sintered individually at the temperature of 1440, 1450, and 1460°C, but it reduces with the increase of CNTs content from 0 to 1wt.% even at the same sintering temperature.The effects of CNTs by surface modification and Ni cladding as well as CNTs by the unmodified on the mechanical properties of Ti(C, N) based cermets with low Ni contention have been discussed. The findings indicate that the properties of the cermets with addition CNTs by surface modification and Ni cladding are better than that with addition CNTs unmodified.The influence of adding CNTs with Ni cladding to the cermets with high Ni contention has been studied. The mechanical properties of the cermets is the best at 1420°C when the variation of CNTs contention is from 0 to 0.5wt%, and the sintered temperature is at 1400, 1410, 1420, and 1430°C individually. Meanwhile, the transverse strength grows with the increase of CNTs contention from 0 to 0.5wt% at the same sintering temperature. At the same sintering temperature, the microstructure of the cermets with high Ni contention and addition CNTs contention has been under close observation and analysis under TEM. Some nano grains precipitate inside the grains, and inlay into the rim phase of the big grains, these nano grains improve the durability of the material. Simultaneously, on the symmetry {111} of the crystal face and benefits the properties of the cermets.The microstructure of the cermet with high Ni content and with addition CNTs has been observed and analysed by TEM. Some nano grains precipitate inside the grains, and some nano grains inlay into the rim phase of the big grains, this can improve the strength and toughness. Simultaneously, the twin crystal has been formed and that is benefit for the properties. And the zone axis of the matrix is [011] and the zone axis of the twin crystal is [011] by measuring the diffraction pattern of Ti(C,N).The effect of 0.8wt%Y and different CNTs content on the microstructure and mechanical properties of the cermets with high Ni contents has been discussed. The core-rim structure is evidence when CNTs content is less; The black carbide phase is reduced remarkably and the global aggregation phenomena is observed when CNTs content is increased. The transverse strength is the best when the content is 0.5wt.%. But when the Y content is 0.8wt.% and CNTs content is 1wt.%, the distribution of Y is not uniformity and composition aliquation occurs on the interface between rim and binder phase, which brings the reduction to the mechanical properties.