Technique Research On Powder Injection Molding Of Ti(C,N)-Based Cermets

Ti(C,N)-based cermets is a high hardness and wearable structural materials, which is used widely as cutting tools and wear resistance materials for its excellent properties. Conventionally, Ti(C,N)-based cermets is made by compression moulding which can not produce complex product. At the same time, the products are difficult to further machining, so the field of application is restricted. Powder injection molding (PIM) is an advanced near-net-shape technique. It will be a new method to produce Ti(C,N)-based cermets parts with complex shape, which will widen the application range of the materials. Thus, the research fruit is summarized about powder injection molding lately decade. It is analyzed briefly that the difficulty of processing Ti(C,N)-based cermets using PIM. The technique and some basal aspect relating on powder injection molding of Ti(C,N)-based cermets are also investigated in this paper. Key work is as following. The assistant component of the binder such as stearic acid (SA), oleic acid(OA), titanium ester coupling agent (TC) are evaluated concerning the effect of modifying on Ti(C,N)-based cermets powders surface. It is analyzed that commixing high density polyethylene (HDPE) and ethylene vinyl acetate (EVA) using kinetics, thermodynamics, rheology. The commixing crystal distributing in Paraffin Wax is analyzed by polar polarizer. The microstructure of the cross-section is observed using SEM. A wax-based binder of PIM on Ti(C,N)-based cermets is developed. Its composition is as follows: 68PW-20EVA -10HDPE-2TC (wt.%), which has good dissolve between polymers and un-polymer. The crystal polymer is homogeneously dispersed in the PW. The wetting angle of the powder and binder is reduced to compare no-modifying agent with modifying one. The gas PW diffuse in the binder liquid is the control step of kinetics at the initial and middle stage of the pyrogenation of heat debinding with researching kinetics. It is necessary that the controlling pressure of heat debinding in N₂ for high steam pressure result in many wastes during pulling out of PW at 170℃～300℃. But there is few wastes between 0.11 MPa～0.12MPa for pyrolysis gas and diffuse of gas in the liquid binder are equal approximately in the rate of speed. The collapse and craze are taken place during debinding due to the high saturated vapour pressure of PW and fast diffuse of gas PW in the liquid binder at the low pressure in debinding furnace and the fast heating-up. But the air chamber is easily created for the gas PW diffuse is slowly in the liquid binder and the gas PW cannot be removedin time above 0.12MPa at the pressure in debinding furnace. The decomposition of polymer (HDPE, EVA) is primary stage after debinding PW above 300℃. The low vacuum or vacuum may be used to heat debinding for there are a lot of the holes in samples after debinding PW. As a result, the debinding rate is enhanced and the debinding time is reduced. The effect of solvent ingredient, debinding temperature, debinding time on solvent debinding is investigated by kinetics. It shows that PW diffuse in the solvent is the control step of kinetics at the initial stage of the solvent debinding. The debinding processing is controlled together by the binder solvent and binder diffuse during the middle step. The carbon content in Ti(C,N)-based cermets can be easily controlled with heat debinding and solvent one. However, there are some disadvantages, such as: technique complexity, strict condition, pollution of environment. The influence of the rate of heating-up, the top sintering temperature and holding time, cooling rate on the microstructure and mechanical properties of Ti(C,N)-based cermets have been researched. It is compared the conventional sintering technique with two-step sintering one. The result shows the waste rate of the samples is reduced with two-step sintering technique because holding time at the top sintering temperature is shortened, sintering time at the second stage is prolonged (≥5h). The microstructure of the samples is homogeneous, mechanical properties are enhanced with two-step sintering technique. The mixing process of binder and powders was investigated with the method of mathematical statistics. The uniformity parameters (Hs) and mixed times (n) are established. Hs = 90 +exp(0.04n+1.88) Key influence of injection molding process parameters on the quality of PIM samples is studied using orthogonal arrays experimental design and statistical analysis method. The result shows that the great influence on the quality of the green parts is not only the levels of parameters but also some interaction between parameters. The optimized injection parameters are as following: injection pressure 8 MPa, injection temperature 135℃, injection speed 40 mm/s and holding pressure 8 MPa. It is compared the compression moulding with PIM. It shows that the Processing of Ti(C,N)-based Cermets by PIM must be improved and the mechanical properties of PIM want to be enhanced.