Tribology of Ceramics

Modern ceramics are different from traditional ceramics (tiles, building materials, porcelain); they are distinguished by adjectives such as "technical", "industrial" or "thermomechanical".

Industrial ceramics are characterized by their marked refractory character and high hardness. Their mediocre toughness explains their sensitivity to the presence of defects, hence their reputation for low strength and brittleness.

Technical ceramics are used for :

• their electrical or dielectric properties;

• their magnetic properties and as superconductors;

• their optical properties ;

• their chemical properties ;

• their biological properties;

• their nuclear properties.

Ceramics fall into four groups: a. alumina (Al ₂ O ₃ ), b. zirconia (ZrO ₂ ), c. silicon nitride (Si ₃ N ₄ ) and d. silicon carbide (SiC). But there are also compounds, such as silicon-infiltrated silicon carbide (SiSiC), or alumina-reinforced zirconia (ATZ for Alumina Tonghened Zirconia) and zirconia-reinforced alumina (ZTA for Zirconia Tonghened Alumina). They are used for their mechanical, thermo-mechanical and tribological properties, as well as for their resistance to corrosion. We will be focusing on their tribological behavior, which represents the main application of ceramics, particularly for protection against wear and abrasion. Ceramic shaping differs from that of metal alloys. The transformation of a raw material in powder form into a coherent object takes place by sintering in a solid state (not fusion), which limits the size of ceramic parts. The various classes of ceramics have established themselves in a wide range of applications. Wear rates vary over 8-10 decades in different applications. This article presents the evolution of tribological properties of ceramics as a function of stress, enabling us to identify which grades will show favorable behavior for a given application.

Ceramics are also present in materials in the form of alloys, to which metals are added to form combinations known as metal matrix composites, cermets or hard metals. This type of material will not be discussed in detail in this document, which will focus mainly on pure ceramics. Nevertheless, the tribological properties of a few hard metals or cermets will be presented to give a better understanding of the tribological behavior of...