Technical Paper: PIM International, Vol.1 No. 2 June 2007, pages 57-62, 3699 words

Authors: J. L. Fan, Z. X. Li, B. Y. Huang, H. C. Cheng and T. Liu

The State Key Laboratory for Powder Metallurgy, Central South University, Hunan, Changsha, 410083, China

Abstract

By using a type of traditional paraffin wax based multicomponent binder and an improved oil+paraffin wax based binder, fully sintered hardmetal was manufactured by metal injection moulding process. The processes of thermal debinding in hydrogen atmosphere, solvent debinding in heptane and subsequent thermal debinding in hydrogen atmosphere were studied. Optimising the debinding process parameters controlled the carbon content. The results showed that the improved oil+paraffin wax based binder had better thermal and solvent debinding characteristics. Through the optimisation of debinding process and carbon content control during debinding, the fully sintered WC-8Co hardmetals with good bending strength was manufactured after the brown part was sintered at 1400oC for 80 minutes in vacuum atmosphere.

Introduction

Powder Injection moulding (PIM) is a relatively new technology for fabricating complicated parts, which combines the advantages of traditional PM with those of plastic injection moulding[1-2]. Freedom in shape-design and economic predominance in manufacturing of large series of small sintered cemented carbide parts with complex geometry are the most important advantages of PIM[3-5]. The studies of cemented carbides using PIM has become a key area of attention and many researchers have studied the PIM process of cemented carbides from common micron, superfine to nanosize particles [6-7]. However, due to the complex process and many controlling factors in PIM, there are still a lot of difficulties in improving and stabilising the properties of injected cemented carbides to match the requirement of cemented carbides for industries. Though the process of PIM is quite mature in iron-based products, it has not developed adequately in cemented carbides. In the process of PIM, binder chemistry and binder removal are the most important factors affecting PIM[8]. In PIM of cemented carbides, large volumes of high molecule organic polymer is added and must be removed completely before sintering without carburization and decarburisation, otherwise it would be harmful to the mechanical properties of sintered parts. Here, the authors alter the binder composition and have researched their thermal debinding and solvent debinding, then analyzed the carbon content under the conditions of different binder and debinding processes.

Further sections of this article include:

- Experimental
- Optimisation of thermal debinding process
- Solvent debinding
- Subsequent thermal debinding
- Sintering
- Conclusions
- References

Figures and Tables:

Fig. 1 The optimal thermal debinding processes of the injection parts

Fig. 2 The curves between binder loss and debinding time during solvent debinding

Fig. 3 SEM photograph of the mixed WC-8Co powder

Fig. 4 SEM photograph of 2# specimen before debinding

Fig. 5 SEM photographs of 2# specimen after solvent debinding for 6h

Fig. 6 The optimal thermal debinding process after solvent debinding

Fig. 7 SEM micrograph of the brown part after solvent and thermal debinding

Table 1 Chemical composition and particle size of the WC-8Co powder mixture

Table 2 Mixing and injection parameters of the two kinds of feedstock

Table 3 Carbon content of the brown parts in different debinding process

Table 4 Properties and grain size of YG8 cemented carbides sintered after solvent + thermal debinding