Materials Science and Engineering A 463 (2007) 89–93 Spark plasma sintering: A high strain rate low temperature forming tool for ceramics Dongtao Jiang a,∗ , Dustin M. Hulbert a , Joshua D. Kuntz b , Umberto Anselmi-Tamburini a , Amiya K. Mukherjee a a Department of Chemical Engineering and Materials Science, University of California, One Shields Avenue, Davis, CA 95616, United States b Lawrence Livermore National Lab, Livermore, CA 94550, United States Received 10 March 2006; received in revised form 29 June 2006; accepted 9 July 2006 Abstract Spark plasma sintering (SPS) technique is being widely used to produce nanocrystalline materials by virtue of rapid sintering at relatively lower temperatures. In this investigation, fully dense Al 2 O 3 –ZrO 2 –MgAl 2 O 4 composite was superplastically formed into a complex shape using SPS equipment with a strain rate of approximately 10 -2 s -1 at temperatures as low as 1150 ◦ C which is impossible to obtain by using conventional forming methods. Furthermore, a powder compact can be directly shaped into a complex shape, combining sintering and forming into one step. The product is fully dense and free of surface cracks. These results indicate that SPS can be a very competitive forming tool for ceramics as well other hard materials. © 2006 Elsevier B.V. All rights reserved. Keywords: Spark plasma sintering; Forming; Ceramics; Superplasticity 1. Introduction A cost-effective shaping technology for achieving the com- plex shapes is very important for hard materials such as ceramics. Due to their brittleness and hardness, they are difficult to machine via mechanical processes. Conventional methods of producing shaped ceramic articles normally involve two steps: shaping and subsequent sintering. There exist varied shaping methods including dry pressing, isostatic compaction, cast- ing (slip casting, pressure casting, tape casting, gel casting), extrusion, injection molding. In all these shaping methods, elab- orately selected dispersants, binders, plasticizers or lubricants are needed for different ceramic compositions. The grain size of the sintered part is normally large due to slow heating rate, high temperature and long time sintering. For some advanced appli- cations, hot-isostatic-pressing is imperative in order to eliminate the pores and to ensure better mechanical properties. As one can see, the whole process of producing a shaped ceramic compo- nent along these routes is rather time-consuming and expensive. ∗ Corresponding author. Tel.: +1 530 752 6290; fax: +1 530 752 9554. E-mail address: dtjiang@ucdavis.edu (D. Jiang). Spark plasma sintering (SPS) technique has been extensively used to produce a wide range of materials including metals, ceramics, glass and biomaterials, etc. [1–16]. The fast heating rate makes it unique for investigating bulk nano materials since the nano-scale structure may be retained due to the rapid sinter- ing cycle. A fully dense part may be sintered in minutes using SPS instead of hours using conventional methods like hot press- ing. Using SPS as a forming tool is a relatively new idea. Shen et al. [15] first explored the superplasticity of silicon nitride using SPS and a complex shape was successfully obtained. Our group has performed intensive investigations on the forming capability by SPS using different methods. These near-net-shape forming methods mean that no machining or a very minor amount of machining or polishing is needed, depending upon varied sur- face finish requirements for different applications. Obviously, the overall cost for making a shaped part by using this method is drastically decreased. The fast heating and forming process also ensure minimized grain growth; therefore, the unique properties of nano-scale materials may be retained. Superplasticity is an important forming process. It is well known that strain rate is sensitive to grain size and superplastic- ity can easily be realized for nanostructured materials [17,18]. The constitutive relationship for superplastic deformation 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2006.07.163