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Ceramic Tool Types

Ceramic grade tools are typically classified into three general categories: oxide, nitride, and matrix ceramics. 

Oxide ceramics are alumina-based and are generally used in roughing and finishing applications of the cast and gray irons. Increasingly, oxide ceramics are being used in dry machining applications at high speeds. This is due to the advancements within materials science, including the incorporation of whisker-based materials. 

Nitride ceramics exhibit extremely high fracture toughness and are used for roughing and semi-roughing of cast irons under harsh conditions, such as when there is considerable starting and stopping that would typically increase fracturing.

CMCs contain ceramics mixed with other hard materials like cemented and titanium carbides. They can also contain reinforcing whiskers and other materials to increase wear resistance and toughness under hot machining conditions. These are commonly referred to as SiC-whisker reinforced. Alumina reinforced with SiC whiskers is the toughest and most resistant to thermal shock of the oxide-based ceramics due to the extremely high tensile strength of the SiC whiskers. It offers the additional benefit of being able to be run without coolant, thus making dry machining a common application while also being able to offer an increase in machining rates up to 800%.

All ceramic cutting tools have excellent wear resistance at high cutting speeds.

There is a range of ceramic grades available for a variety of applications.

Oxide ceramics are aluminum oxide-based (Al2O3), with added zirconia (ZrO2) for crack inhibition. This generates a material that is chemically very stable but lacks thermal shock resistance.

(1) Mixed ceramics are particles reinforced through the addition of cubic carbides or carbonitrides (TiC, Ti(C, N)). This improves toughness and thermal conductivity.

(2) Whisker-reinforced ceramics use silicon carbide whiskers (Siew) to dramatically increase the toughness and enable the use of coolant. Whisker-reinforced ceramics are ideal for machining Ni-based alloys.

(3) Silicon nitride ceramics (Si3N4) represent another group of ceramic materials. Their elongated crystals form a self-reinforced material with high toughness. Silicon nitride grades are successful in gray cast iron, but a lack of chemical stability limits their use in other workpiece materials.

These benefits lead to increases in efficiency. For example, many machinists would slow cutting speed if temperatures were to approach maximum carbide limits. It is the opposite for ceramic tools, which excel in higher temperature conditions.

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