28selfreinforced Ceramic Composites

A composite is a mixture of materials engineered with the intention of obtaining the best characteristic of each material. In the case of ceramics, composite microstructures can result in an increase in fracture toughness that can enhance durability and reliability. Several general approaches have been developed in recent years: self-reinforcement, addition of a ductile metal phase, addition of a dispersion of particles or whiskers, and addition of a network of continuous fibers [18, 19]. WC-Co cermets are examples of addition of a ductile metal but will not be discussed. Continuous fiber reinforcement is discussed in the

Ceramics

Tooling for making aluminum cans Wire-drawing capstans, pulleys, rolls, guides, and

Knife and scissor blades Cutting tool inserts Hip replacements Buttons some dies Dies for hot extrusion of metals next chapter. The following sections discuss self-reinforcement and addition of particles and whiskers.

The simplest and generally most cost-effective method of forming a ceramic composite microstructure is self-reinforcement. It is also often referred to as in situ reinforcement or toughening. That is because the composite microstructure is achieved in place during the sintering (densification) of the material by control of chemistry and temperature, rather than by mixing in a second phase prior to sintering. Self-reinforcement has been obtained in several ways: (1) forming a multiphase microstructure where one phase acts as the matrix and another acts as a reinforcement, (2) heat-treating to cause a phase to precipitate or crystallize into the matrix phase, and (3) growth of elongated intertwined grains.

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