İbrahim İLGÜZ 030040113 (8th week)

Slip Casting (12:33 5.4.2011)
The slip casting method is commonly used in designs calling for bodies of intricate shape. In slip casting the material is placed into suspension to form a slurry or slip which is introduced into a mold of a liquid absorbing material. Common liquid and mold materials are water and plaster of paris. The slurry is allowed to remain in the mold until removal of liquid through the walls causes the desired amount of solids to be deposited on the mold form. The time of deposition is controlled so as to permit formation of either a thin wall or a solid piece remains in the mold will vary with its size and the absorbtion rate of the mold. This may vary from several minutes to days. When the piece becomes free of the mold it is removed for further drying prior to sintering.
(Vivian A. Johnson,Solid State Physics,pg:138)

Filament winding:(12:44 5.4.2011)
Filament winding is a relatively simple process in which a band of continuous reinforcements (fibres) or mono-filaments is wrapped around a rotating mandrel and cured to produce closed-form hollow parts. The winding operation is achieved by the use of specially designed machines. These machines, which can have up to 6 - axes (even 7-axes with robotic enhancements), allow the operator to control various parameters, includig the winding speed, winding angles, fibre placement, resin temperature and fibre tension. THe filaments (or reinforcement bands) are wrapped around the mandrel as adjacent bands of repeating patterns. These cover the mandrel surface to produce one complete layer. The winding is continued with successive layers, which can be in different winding angles until the number of layers required by the designer is reached. The winding angle may vary with respect to mandrel axis. Winding angles are very close to 90 degree are termed hoop winding, whereas winding using other angles is termed helical winding.
(Guneri Akovali, Handbook of Composite Fabrication, pg:103)

Slurry infiltration: (12:55 5.4.2011)
Continous-fiber composites are made b allowing fibers from a spool to pass through a glass powder slurry(containing water and a water-soluble acrylic binder), winding the slurry-impregnated fibers onto the sides of a hexagonal prism(mandrel or take-up drum), cutting up the flat unidirectional tapes from the mandrel, stacking up the pieces (plies) in the correct orientation, burning out the stack to remove the binder and hot pressing the stack at a temperature above the working temperature of the glass. This process is known as slurry infiltration.
(Deborah D. L. Chung, Compostie MAterails: Functional Materials for Modern Technologies, pg:47)

Melt Infiltration:(13:07 5.4.2011)
The melt infiltration method involves holding a porous body of the reinforcing phase in a mold and infiltrating it with the molten metallic material, which flows through the interstices to fill the pores, thus producing a composite material. This method can be divided into two categories:

-pressure-assisted infiltration
-pressure-less infiltrration

For pressure-assisted infiltration, either an inert gas or a mechanical device is used as the pressurizing medium. The composite produced using this method generally features a near pore-free matrix. There are also some drawbacks associated with this method:

-Reinforcement preform damage or breakage during infiltration
-Microstructural heterogenecity

In view of these disadvantages, other types of forces such as ultrasonic vibration, electromagnetic force and centrifugal force are used to more effectively force the molen metal into nonwetting reinforcement preforms.

In pressure-less infiltration, the liquid metal infiltrates a porous reinforcement preform without an external pressure or vacuum. This process is also known as spontaneous infiltration. In comparison with the pressure-assisted infiltration method, the composites formed exhibit a higher level of porosity.
(Manoj Gupta, Nai Mui Ling Sharon, Magnesium, Magnesium Alloys and Magnesium Composites, pg:20-21 )