Effect Of Powder Sizes On Microstructure And Mechanical Properties Of Ti(C, N)-based Cermets

This thesis is composed of five chapters. In the first chapter, the microstructure and properties of Ti(C, N)-based cermets as well as its development history were introduced. Meanwhile, the development trend of nano-composite ceramics was also briefed.In chapter two, experimental raw materials and preparation techniques of Ti (C, N)-based cermets were introduced briefly. In chapter three, we focused on the testing method of mechanical properties and token method of microstructure of Ti (C, N)-based cermets.In chapter four, the role of TiC and TiN particle sizes on the microstructure and mechanical properties of Ti(C, N)-based cermets has been evaluated. Ti(C, N)-WC-Co cermets made from four groups of mixed raw powders of different sizes were manufactured by vacuum sintering. The microstructure and composition were studied using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectrum (EDX).The result shows that as size of TiC powder decreases and solid dissolution of elements Ti, W and N in TiC increases, diffraction peaks of hard phases show a little excursion correspondingly. The different distribution and cooling rates of Co, according to different TiC and TiN particle sizes, give rise to different crystal structures of Co correspondingly among the four samples; the changes of particle sizes of hard phases in Co-WC-Ti(C, N) cermets bring up different phase structures; The existence of TiCsub results in finer grains, and thinner areas of binder phase. The introduction of TiNnm brings on crystal lattice homogeneity of element Co, microstructure homogeneity, similar dimensions, and symmetrical distribution of grains, smooth boundaries of grains and refinement of grains. Moreover, when together with TiCμm as original powders, reduction of size of TiN powder takes a little effect on mechanical properties; when together with TiCsub, refinement of TiN particles takes much greater effect on properties, and promotion of TiNnm powder on bending strength and fracture toughness is quite visible. The general mechanical properties of the specimen manufactured with TiCsub and TiNnm was the best among the four samples.Chapter five summarized the whole thesis and gave some advices on future works.