Technical Paper: PIM International, Vol.2 No. 1 March 2008, pages 55-58, 1596 words

Authors: A. Baumann, M. Brieseck, S. Höhn, T. Moritz & R. Lenk

Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Winterbergstr. 28, D-01277 Dresden, Germany

Abstract

Multi-component powder injection moulding is a new field of advanced research in structural and functional ceramic engineering since it offers the possibility to combine at least two different powder materials, e.g. ceramic and steel, in one component by having just one co-shaping step [1,2,3]. The near net shape characteristics, the possibility of large scale production and the high level of automation make this technology so attractive.

In conventional multi-component injection moulding two feedstock materials are injected into one mould. In order to simplify this process and tool technology the inmould labelling technology known from plastic shaping can be used: Green tapes made of ceramics (yttria stabilised ZrO2) and/or metal (17-4PH) powders are put into the mould as semi-manufactured products and injected with a ceramic or metal feedstock material.

Considering the limits for the co-sintering process as well as the chemical compatibility of the used binder systems it was shown that the geometrical modification of the green tapes especially in the third dimension can be seen as a value adding process step that can significantly simplify the manufacturing process for multi-component shaping.

Experimental Work: preparation of green tapes and feedstocks

For tape casting a slurry was prepared by mixing ZrO2 or 17-4PH powder, water (75%), PVA (15%), glycerine (6%), additives (defoamer, pH-agent, dispersant) (4%), and by homogenising the slurry in a roll mill for 12 h. For feedstock preparation ZrO2 or 17-4PH powder were mixed with abietin acid (55%), polyamid PA6/12 (40%) and stearin acid (5%) in a torque kneader (110°C, 50rpm) W50EHT from Brabender GmbH.

The linear sintering shrinkage in the ZrO2 and 17-4PH tapes as well as the feedstocks was adjusted to 16% at 1350°C (under H2 atmosphere). Both, the slurry and the feedstock had a powder packing density of 60 vol%. The processed ZrO2 powder contained 60 % Y5-5 powder (d80= 1.91 µm) from Unitec Ceramics Ltd. and 40 % TZ-3Y-E powder (d50= 0.57 µm) from Tosoh Corp. The 17-4PH powder from Sandvik Osprey had a particle size of less than 22 µm (d80 = 22 µm). Tape casting was carried out on a laboratory tape casting machine from Netzsch GmbH. For tape casting a siliconized polyester tape was used as career tape. The prepared green tapes had a thickness of 600 µm.

Further sections of this article include:

- Inmould labelling
- Binder removal and sintering
- Characterisation
- Dilatometric investigation
- Process capability
- Dishing of green tapes
- Co-sintering
- Conclusion
- Acknowledgement
- References

Figures and Tables:

Fig. 1 Inmould labelling of green tapes

Fig. 2 Test geometry and dished green tape

Fig. 3 Dilatometric data of different ZrO2 and 17-4PH powders under H2 atmosphere

Fig. 4 Sintered interface of ZrO2-tape (above) and ZrO2 feedstock (below)

Fig. 5 Sintered interface of 17-4PH-tape (above) and 17-4PH feedstock (below)

Fig. 6 Ion beam preparation of a dished 17-4PH/ZrO2 green tape

Fig. 7 Sintered interface between 17-4PH tape and ZrO2 feedstock (debinded under air (400°C))

Fig. 8 Sintered interface between Ti-doted 17-4PH/ZrO2 tape (debinded under varigon (600°C))

Table 1 Material properties of stainless steel (* Tm - melting point)