| Hardmetal extrusion molding is a novel near-net-shape technology which has been widely applied to preparing hardmetal rods.Binder system improvement and debinding technology development are two most important research subjects because of binders playing a fundamental role in increasing fluidities of feedstocks and keeping shapes of extruded parts in the process.On the basis of predecessors' studies, binders designing and debinding and some other technologies which are helpful to research and pilot production,are investigated in this thesis.The main research topics of this thesis are as follows:(1) 6 binders are designed based on the hardmetal powder characteristics and the binder design requirements,and high-density paraffin wax(HDPW),carnauba wax (CW) and liquid paraffin wax(LPW) are chosen as plastifying ingredients; high-density polyethylene(HDPE),polypropylene(PP) and ethylene-vinyl acetate (EVA) are chosen as polymer ingredients;stearic acid(SA) is chosen as surfactant ingredient.The differences of 6 binders are their relative contents of polymer ingredients HDPE,PP and EVA.The results indicate that these binder ingredients are compatible.The basic characteristics of 6 binders have been investigated preliminarily. The results show that each thermogravimetry curve of 6 binders' is divided into 3 steps,it not only means that these 6 binders are propitious to thermal debinding step by step but simultaneously provides the foundation of parameters setting for thermal debinding.(2) The mixing process and extrusion process of feedstocks are studied,both the relationship between mixing time and uniformity of feedstocks and the influence of extrusion temperature/pressure to the quality of extruded parts are investigated.The results show that the uniformity of feedstocks will exceed 98%after 5 hours' mixing with conditions of a powder loading of 48%and a mixing temperature of 80℃. Feedstocks should be slowly performed in vacuum and a sifting process before it is necessary.The extrusion temperatures of 6 feedstocks are determined and eligible extruded parts are finally obtained.(3) Based on the analysis of solvent debinding mechanism,the factors causing cracking in solvent debinding are investigated.The results show that different shape retention of solvent-debound specimens is due to different binder designing.When the binder is propitious to solvent debinding,residual stress is the fatal reason that results in cracking.An annealing process of the extruded parts should be performed to avoid the cracking.The binder design,the shape of solvent-debound specimens,the solvent debinding temperature and time determine the solvent debinding behaviors together.(4) Based on the analyses of thermal debinding mechanism and the thermal characteristics of feedstocks,R2# solvent-debound specimens are thermal debound and sintered.The results indicate that the thermal debinding atmosphere should not contain any water and oxygen.There are numerous small holes distributed homogeneously in sintered parts because of lots of binder used in hardmetal powder extrusion molding.An extra hot isotactic pressing process can eliminate the holes but cobalt lakes are generated.In this study,the metallographic examination shows that neither type A,type B porosity nor free carbon phase,ηphase are found in the sintered parts of R2# of which processed with solvent debinding,one step thermal debinding and sintering,hot isotactic pressing.The performance of obtained YG10 hardmetal rods is improved,with the desity of 14.33g/cm~3～14.37g/cm~3,the average transverse rupture strength of 3550MPa,the highest transverse rupture strength of 4000MPa,the Rockwell hardness of 92.0HRA～92.5HRA,the coercive force of 18.5kA/m～20.0kA/m,the cobalt magnetism of 9.09%～9.35%.
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