Net shape technology

Kubel, E.J., Jr. Titanium Near-Net-Shape Technology Shaping Up, Advanced Materials Processes, 46 (February 1987). 

Figure 3-2. Schematic diagram of film preparation by net shape technology...

Another important feature of the net shape technology is that it does not follow percolation theory. This gives an opportunity to design materials with unique properties. As an example Ni-ceria cermet with low Ni content was prepared and investigated [16]. The net shape processed Ni-ceria cermet, which was prepared according to procedure presented in Figure 3-13, features ... 

The preceding discussion has shown examples which used the net shape technology for the preparation of dense electrolyte films, nanocrystalline bulk electrolyte, and electrode support. However, the net shape technology can also be successfully used for electrode film preparation. In this case this technology allows the tailoring of the ionic and electronic conductivity of the electrodes and their porosity. Below the examples of processing and properties of anode and cathode films will be presented. 

Fuel cell performance of the composite LSM-YSZ/YSZ/Ni-YSZ cell was investigated using forming gas (10 vol% H2 in N2) as the fuel (Figure 3-25). The results showed that a maximum power density of about 0.26 W cm2 as obtained at a temperature of 850°C. The temperature dependence of the area specific resistances of the asymmetrical cell is shown in Figure 3-26. The electrode overpotential was estimated to 0.3 Q cm2 at 800°C, which is the total of anode and cathode overpotential. It appeared that about half of the overpotential originated from the anode, because the cathode overpotential determined from the symmetrical cell test was found to be about 0.14 Q cm2 at 800°C. The performance of the cell was mainly limited by the electrolyte resistance. The decrease in the electrolyte thickness would decrease electrolyte resistance. It can be concluded that the net shape technology can be successfully applied for the fabrication of cathode and anode electrodes. 

A selection of essential bulk metal forming techniques to be used for realizing near-net-shape technologies in part manufacturing is given in Table 3. 

The thixoprocesses are regarded as an interesting option for both the forging industries and foundries. With them near-net-shape technology is added to conventional procedures. 

The shaping of these fine, submicrometer powders into complex components and their subsequent consoHdation into dense ceramic parts of ideally zero porosity is a major technological challenge. The parts formed need to be consoHdated to near-net shape because Si N machining requires expensive diamond grinding. Additionally, Si N dissociates at or near the typical densiftcation temperatures used in the fabrication of stmctural ceramics and, therefore, special measures have to be taken to preserve the compositional integrity of the material. 

SOL-GEL TECHNOLOGY. The goal of sol-gel technology is lo use low temperature chemical processes to produce net-shape, net-surfacc objects, films, fibers, particulates, or composites that can be used commercially after a minimum of additional processing steps. See also Thin Films. Sol-gel processing can provide control of microstructures in the nanometer size range, i.e 1-100 nm (0.001-0.1 pm), which approaches the molecular level These materials often have unique physical and chemical characteristics. See also Nanotechnology (Molecular). 

Figure 3. Residual stresses in automotive steel crown gears (a) net-shaped and submitted to nitrocarburation surface treatment machined by standard technology and submitted to (b) multi-frequency induction tempering, (c) quenching and nitriding, (d) case-hardening.

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