Preparation Of Nano-composite Ti(C,N)-based Cermets

The history of Ti(C,N) based cermets, properties and characters, and the main usages were presented; the progress of nano-technology; nano-modification on Ti(C,N) based cermets by nano-hard phase, and some ways to sinter the nano-composite Ti(C,N) based cermets were also presented. TG was used to analyze the different plasticizer; the relation between density and plasticizer was studied; metalloscope was used to analyze the porosity of sintering samples; the results indicated: PVA+ glycerin plasticizer has the best molding performance, and the sample made from PVA+ paraffin plasticizer has the lowest porosity. Different factors during the pressing process were studied, the results indicated: the relative density of micro-powder is higher than nano-powder's; and the relative density of nano-powder which has low content oxygen is higher than the high content oxygen's; pressing pressure just has little influence to the relative density when the pressing pressure is below 150MPa; the relative density of green compacts increased when the powder temperature grew; and the holding time of pressing pressure has little influence to he relative density. OM, SEM, EDX and other techniques were used to analyze the porosity, microstructure and of nano-composite Ti(C,N)-based cermets produced by Spark Plasma Sintering(SPS). The mechanical properties of Ti(C,N)-based cermets produced in different conditions were discussed. The results indicated: (1) At 1250℃for 8min by elevating directly it can obtain better mechanical performance; (2)Except the microstructure of black core/white rim, white core/black rim also was presented, which resulted from the existence of nano-powders which changed the evolution of microstructure; (3) The fracture mainly originated from cavity, and the intergranular fracture was the leading fracture mode, besides the cleavage fracture and transgranular fracture. Spark plasma sintering (SPS) and vacuum sintering (VS) were employed to fabricate nano-composite Ti(C,N)-based cermets. The shrinkage behavior, microstructure, porosity and mechanical properties of samples fabricated by SPS were compared with VS using optical microscopy, scanning electron microscopy, universal testing machine and rockwell tester. The results indicated:(1) The shrinkage process occurred mainly in the range of 1000℃to 1300℃during the VS process, and only 0.2% linear shrinkage ratio appeared below 800℃, yet ,during the SPS process,60% dimensional change occurred below 8000C as a result of pressure action; (2)It is difficult to obtain fully dense Ti(C,N)-based cermets by SPS due to the plenty of pores and uncombined carbon, and mechanical properties of sintered samples by SPS are inferior to VS; (3) Main microstructures of sintered samples by SPS are white core/grey shell, some even haven't typical core/shell microstructures, whereas by VS show typical black core/grey shell structure.