Consolidation methods powder pressing

The particle size of powder most often used for consolidation is —200 mesh (74 /xm sieve aperture), and the most widely practised method of consolidation is hot pressing in vacuo. 

Common consolidation methods include variations on pressing powders, plastic forming, slip casting and tape casting. The choice of which method to use for a given application is very dependent upon the shape, size and required dimensional tolerances of the final product, available capital outlay and desired productivity. Each of these methods is examined in turn below, followed by sintering, which turns the consolidated powders into a monolithic body with mechanical integrity. 

When the die is suitably charged with powder the preferential method of applying the pressure is by a technique known as double ending pressing. This process involves keeping the die in a fixed position while the top and bottom punches move to consolidate the powder. This produces a more evenly compacted body when compared to bodies made by single ended pressing in which... 

The die-and-punch method of compact imparts an anisotropic pressure to the compact. It is possible to apply pressure equally in all directions using a process called isostatic pressing, in which the powder is compacted with a fluid, such as hydraulic fluid, water, or an inert gas. Isostatic pressing is carried out using formed, flexible molds, called cans, that contain the powder and allow the pressure from the fluid to be transferred to the powder. The flexible molds are then stripped off the compact after densification. Isostatic pressing eliminates the die-wall friction inherent in die compaction and allows for consolidation of large components. However, isostatic pressing... 

Plasma spraying is a consolidation process for powders with the additional capability of a composition control of the spray formed structures. The paper reports on the first steps to adapt this method to the production of functionally graded thermoelectric materials with a locally maximized figure of merit. Iron disilicide (FeSi2) was used to test the performance of the technique on thermoelectric material. It was found that plasma spray forming is applicable to produce dense materials with thermoelectric properties comparable to hot pressed ones. Problems were however found with the thermal stability of the microstructure. 

A two-step pressing method was reported to be able to significantiy improve the optical properties of alumina ceramics with SPS at high heating rates [69]. In this case, commercial alumina powder could be consolidated at 1150 °C at a heating... 

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