Hello everyone. In this lecture, I'd like to talk about the fast sintering technique which can be used for the publication of nanostructured material and defect engineered material. So you know that due to the thermodynamics of sintering, it's very difficult to control the size and defect structure during the sintering process. So we need faster sintering technique in order to maintain the characteristic size of starting materials. One important the fast sintering technique is microwave sintering. It enhances the suitability compared to conventional heating process due to the direct energy coupling with electric dipoles within the body. Small temperature gradient makes short sintering time, and this provides us the minimization of grain growth during the sintering process. Rapid heating rate of microwave sintering can bypass the low temperature region. So rate of grain growth is higher than the rate of densification. So this like a sintering technique can be used to for the publication of ceramic nanoparticles such as titanium dioxide, aluminum oxide, and lead zirconate titanate. Another type of fast sintering is shockwave consolidation, another name of this technique is dynamic consolidation. In this, the sintering technique, the large amplitude compressive stress generated by plate impact or explosion without any external heating. The peak pressure value may be on the order of tens of gigapascal. So this sintering technique can be used to further the densification of metals and ceramics. Localized heating during the shockwave consolidation sintering process due to the interparticle friction enables good inter-particle bonding of the bulk material. Another type of faster sintering is transformation assisted consolidation. In the presence of two degrees of freedom, it is their pressure, and temperature. The phase transformation assisted with the volume reduction is possible. High pressure reduces the nucleation activation energy and increase the nucleation rate of the phases that is being transformed. For example, aluminum and titanium retain nanostructures as a result of phase transformation. The titanium dioxide, the anatase phase can be transformed into rutile phase that between the 400 to 1200 degree C. The nucleation rate of rutile phase increases with increase in pressure, so the bulk part denser due to the ability of the material to fill in pores easily based on the the phase transformation. The hot isostatic pressing, HIP, another type of a fast sintering technique. The process of using high hydrostatic pressure and high temperature to compress fine particles into coherent part. The HIP enabled engineers to design component, so they could meet specifications for use in critical, highly stressed application. An HIP process also provides a method for producing components from diverse powdered materials, including metals and ceramics. The steps of HIP consist of the first, a powder mixture is placed in a container, typically steel can. The second, the container is subjected to elevate the temperature and are very high vacuum to remove air and moisture from the powder. The final step is container is then sealed and HIPed. The application of high inert gas pressures and elevated temperatures result in the removal of internal void, so can create a strong bond throughout the material. So we can obtain the homogeneous material with uniform fine grain and near 100 percent relative density. The advantages of HIP are reduce the porosity and clean grain structure and ability to create near-net shape that require better machining. Hot pressing, HP, is a process used to consolidate metal powder and ceramic compact to full density with controlled microstructure. Due to the high production processing cost of HIP, they're compared with the HIP, this like HP is widely used for the publication of metals and ceramic works. The HP is an alternative route to sintering to achieve high densification. So simultaneous application of pressure and the heat to a green body makes high density. The pressure is applied statically, while dynamically to the heated components in one or two opposing directions along a single axis. Heat can be applied directly by using induction or resistance heating system, or in directly by using convection or radiation heating. A vacuum or a controlled atmosphere is required to prevent oxidation in case of metals or other sensitive materials. The recently developed a new important faster sintering technique is spark plasma sintering, SPS. The growing need for processing and consolidating nanoparticles this like SPS. They can be developed, retaining the initial microstructure in the fabricated component. So when processing times at higher temperatures makes grain growth, so we should reduce the sintering time, and attractive properties of initial nanoparticles are well conserved by fabrication of bulk material through spark plasma sintering. The consolidation of metals, composite, ceramics, intermetallics, cermets, the nanocomposite and carbon nanotube reinforces ceramics has been accomplished by this processing technique. Another name of SPS are electric field assisted sintering, EFAS, the field assisted sintering technique, FAST, the plasma assisted sintering, PAS, and plasma pressure consolidation, PPC. This is the schematic diagram for the SPS. Due to the direct applying on of DC pulse current to the sample, we can generate the spark and plasma-state between the particles, and this activates the sintering during the SPS process. So this like SPS sintering technique provide us so many advantages including synergetic combination of electric energy and mechanical pressure drastically reduces the consolidation time. So initial internet structure of powder particles is preserved even in nanomaterials. Fast resistance heating makes localize the plasma between powder particles, so maintains integrity of starting microstructure without grain coarsening. Pulse discharges, the plasma generated between metal particles can aid in removing surface oxide layer and can increase in surface activity adjoining clean surfaces and can lead it to the enhanced particle sintering. So this like SPS process can be used for sintering. For example, lapidus sintering, grain boundary controlled sintering, the temperature gradient sintering, and magnetic field sintering. Also can be used to for sinter bonding surface treatment, and synthesis such as sinter bonding, gradient bonding, solid-state bonding, the modification of a plasma spray coated layer, and hardening of a thin surface layer, the porous layer surface treatment, the growth of a single crystal, and synthesis eutectic materials. This like faster sintering technique, such as spark plasma sintering can be used to make this like controlled boundary structure. As shown in the left side figure, we can maintain the characteristic size of nanoparticles even in compacted bulk material. Also as shown in the right side of the figure, the heterostructure of the BS and BT can be maintained even after sintering process. So in this lecture, we briefly leave you the several faster sintering technique, which can provide us for developing the nanostructure and sometimes defect engineered materials. Thank you.
