Research On The Fabrication Of Graded Structure Ti(C,N) Based Cermets By Carburication

Ti(C,N) based cermets with suitable mechanical properties were prepared by vacuum sintering. The as-sintered materials were heat treated by double-glow plasma carburication and solid carburication, The relationship among manufacturing process, microstructures and properties of the as-sintered materials and the graded structure materials were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDS) and transmission electron microscope (TEM).In the first part of the thesis, the development and present research situation of Ti(C, N) based cermets were critically overviewed, which included the influence of composition and sintering process on the microstructures and properties, and then the present research situation of graded structure hardmetals and cermets was also summarized. Based on above, the purpose and significance of the thesis were pointed out.The influence of cooling mode, the content of carbon addtion and the content of the binder on the microstructures and properties of Ti(C, N)-based cermets was studied. It was found that the mechanical performance of the cermets under furnace cooling after liquid phase sintering was better than others. The appropriate carbon additon of Ti(C, N)-based cermets would not only improve the wetting of the ceramic grains by liquid metal during sintering, but also decreased the content of Ti, W and Mo dissolved in the binders. The good mechanical properties were found in the cermets with 1.0 wt.% carbon addtion. With the increase of Ni content, the uniformity of the microstructure of cermets increased while the hardness decreased and the transverse rupture strength increased.The influence of main parameters of double glow plasma carburization and the carbon additon of the as-sintered materials on the microstructure and mechnics performance of Ti(C, N)-based cermets was studied. Some conclusions were drawn as follows: there was the binder-deficient layer of the cermets in the surface zone after carburization. Surface hardness of the cermets was increased by carburization, while transverse rapture strength(TRS) was hardly changed. At the same carburizing temperature the thickness of the binder-deficient layer became thicker with increasing carburizing time. At the same carburizing time, the higher the carburizing temperature was, the thicker the binder-deficient layer was formed. The development of the binder-deficient layer was controlled by the diffusion of the metallic elements and the growth rate did not follow the parabolic law. Heated at at 1200℃for 180min, the binder-deficient layer of the cermets with 1.0wt.% carbon addtion was thicker than that of the cermets with 0 wt.% carbon addtion.The influence of solid carburication on the microstructures and properties of Ti(C, N)-based cermets was studied. The result showed that a binder-deficient layer with a thickness of about 20μm was formed at 1350℃after 240min by solid carburication. Surface hardness of the cermets enhanced remarkably, but the transverse rapture strength apparently decreased.