Surface effects in field-assisted sintering
- PDF / 433,215 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 50 Downloads / 186 Views
M. Garcia Lawrence Livermore National Laboratory, Livermore, California 94551-0808
J.A. Schneider Department of Mechanical Engineering, Mississippi State University, Mississippi State, Mississippi 39762 (Received 5 August 1999; accepted 23 October 2000)
The more-stringent requirements for densification of new out-of-equilibrium powders have created a growing demand for nonconventional rapid sintering processes. Among those, field-assisted sintering techniques (FASTs) have seen a recent renewed interest motivated by their ability to consolidate a large variety of powder materials into high densities in short times. Characterization of a range of FAST-consolidated materials displayed relevant associated surface effects, such as grain boundary cleaning with direct grain-to-grain contact and advanced densification without sintering aids. These effects may be attributed to phenomena ranging from dielectric breakdown to a possible nonconventional plasma generation. Such surface effects provided a better intergranular bonding of powder particles during subsequent sintering.
I. INTRODUCTION
The electric-field effects on physical and chemical phenomena have attracted both theoretical and practical interest. The interaction between an externally applied electric field and atomic mobility, dislocation motion, evaporation, solidification, and crystallite growth has been the focus of intense fundamental investigations.1–3 On the practical side, numerous processes have been developed that apply an external current to assist powder consolidation, bonding, or chemical synthesis of compounds.4–6 In powder consolidation, the imposition of an electric current is known to enhance sintering kinetics and therefore achieve desired properties in shorter time with related productivity and quality benefits. Particularly, a short consolidation time becomes important to numerous present and new materials for which the final properties critically depend on the retention of initial microstructural features, such as fine grain size and/or metastable microstructures. Rapid sintering techniques, which use an external electric field, have been applied to nanometer-size powders to minimize the undesirable grain growth that inherently occurs during sintering.7,8 The initial idea to use resistance sintering of metal powders started with Taylor in 1933 in hot pressing of cemented carbides.9 Furthermore, resistance sintering under pressure was applied to metal powders by Lenel using equipment similar to spot-welding machines in the late 1950s.10 More recently, the effects of an electrical discharge have been studied in various consolidation 286
http://journals.cambridge.org
J. Mater. Res., Vol. 16, No. 1, Jan 2001 Downloaded: 09 Oct 2014
techniques, including electrical discharge compaction (EDC) by Okazaki11 and numerous variants of fieldactivated sintering techniques (FAST) such as spark sintering, plasma-activated sintering, resistance/spark sintering under pressure, or instrumented pulse electrodischarge consolidation.12–15 For these techniqu
Data Loading...
