This review article aims to provide an updated and comprehensive description of the development of the Electric Current Activated/assisted Sintering technique (ECAS) for the obtainment of dense materials including nanostructured ones. The use of ECAS for pure sintering purposes, when starting from already synthesized powders promoters, and to obtain the desired material by simultaneously performing synthesis and consolidation in one-step is reviewed. Specifically, more than a thousand papers published on this subject during the past decades are taken into account. The experimental procedures, formation mechanisms, characteristics, and functionality of a wide spectrum of dense materials fabricated by ECAS are presented. The influence of the most important operating parameters (i.e. current intensity, temperature, processing time, etc.) on product characteristics and process dynamics is reviewed for a large family of materials including ceramics, intermetallics, metal–ceramic and ceramic–ceramic composites. In this review, systems where synthesis and densification stages occur simultaneously, i.e. a fully dense product is formed immediately after reaction completion, as well as those ones for which a satisfactory densification degree is reached only by maintaining the application of the electric current once the full reaction conversion is obtained, are identified. In addition, emphasis is given to the obtainment of nanostructured dense materials due to their rapid progress and wide applications. Specifically, the effect of mechanical activation by ball milling of starting powders on ECAS process dynamics and product characteristics (i.e. density and microstructure) is analysed. The emerging theme from the large majority of the reviewed investigations is the comparison of ECAS over conventional methods including pressureless sintering, hot pressing, and others. Theoretical analysis pertaining to such technique is also proposed following the last results obtained on this topic.

Consolidation/synthesis of materials by electric current activated/assisted sintering

Nanocrystalline WC–Co materials have been the subject of interests and focus of research programs around the world for the past two decades owing to the expectations that the mechanical behavior of the material may improve significantly when grain sizes reduce to nanometer scale. However, although numerous technologies are available for making nanosized tungsten carbide powders, obtaining true nanocrystalline WC–Co (average WC grain size

Synthesis, sintering, and mechanical properties of nanocrystalline cemented tungsten carbide - A review

Of late, nanotechnology seems to be rapidly thrusting its applications in all aspects of life including engineering and medicine. Materials science and engineering has experienced a tremendous growth in the field of nanocomposite development with enhanced chemical, mechanical, and physical properties. A wide array of research has been conducted in the processing of nanocomposites. Consolidation of these systems from loose particles to bulk free form entities has always been a challenge. To name a few, traditional consolidation techniques such as cold pressing and sintering at high temperatures, hot pressing, and hot isostatic pressing have strong limitations of not being able to retain the nanoscale grain size due to the excessive grain growth during processing. This article reviews in detail the results from numerous studies on various methods for manufacturing nanocomposites with improved properties and retained nanostructures. Both challenges and recent advances are discussed in detail in this review.

Challenges and advances in nanocomposite processing techniques

Safe radioisotope thermoelectric generators and heat sources for space applications

Cemented carbide is an old and well-known WC-based hardmetal, which has been widely applied in geo-engineering as drill buttons and various wear-resistant parts. In order to extend the service life of cemented carbide components and enhance their efficiency for rock drilling under various conditions, the recent research efforts have focused on their failure mechanisms and developing nanostructured, functionally graded and Co-free cemented carbides. With the advance in synthesizing nanosized powders and advent of electric field assisted fast sintering techniques, the consolidation of nanostructured and Co-free cemented carbides and even pure WC materials has been possible; and because of their high hardness and wear resistance, they are much promising in geo-engineering drilling. Functionally graded cemented carbide provides a combination of high wear resistance and toughness in a single component, which is also much favorable for geo-engineering drillers. In addition, by replacing the binder phase Co with Ni or carbide binder, and even without binder phase, the corrosion and oxidation of the resultant materials can be significantly improved without considerable deterioration of fracture toughness.

A review of cemented carbides for rock drilling: An old but still tough challenge in geo-engineering

Spark plasma sintering on nanometer scale WC–Co powder

Nanometer WC–Co powder was hot pressed in order to develop new processes and improve the properties of WC–Co cemented carbides. Density and hardness were measured. The microstructures of sintered alloys were observed by SEM. And the grain size of WC in alloys was also measured. The results show that hot pressing can lower the sintering temperature by about 100 °C, increases the density (more than 99%) and circumscribes the growth of grain size (smaller than 1 μm) of alloys. Hardness can also be improved up to HRA 92 by this process. Hot pressing is an effective method to get WC–Co cemented carbides with fine grain size and good properties.

Hua Tang

Papers

Spark plasma sintering on nanometer scale WC–Co powder

Hot pressing of nanometer WC–Co powder