MAX phases: development, properties and applications

Ceramics' lack of plasticity severely limits their field of application in structural materials. Several avenues are being explored to increase fracture toughness and resistance:

• particle dispersion ;

• design of ceramic matrix ceramics (CMC) ;

• to imitate natural materials such as mother-of-pearl.

All these solutions offer real performance gains, and are based on the possibility of making the material less susceptible to cracking.

Mechanical properties can also be improved by formulating new ceramics.

MAX phases are a unique family of technical ceramics. They combine the properties of ceramics with those of metals:

• refractoriness ;

• high Young's modulus ;

• moderate density ;

• resistance to oxidation ;

• machinability ;

• thermal and electrical conductivity ;

• resistance to thermal shock.

A major research effort began in the late 1990s to develop MAX phases in various forms:

• powders ;

• massive ;

• thin films.

Once these different shapes had been obtained, research efforts then focused on assessing their mechanical and functional properties, enabling them to be compared with other materials operating in harsh environments.

In parallel with the evaluation of their properties, production methods have been developed up to industrial scale. These include hot sintering to produce powders and solid parts, and sputtering to produce coatings.

MAX phases are therefore relatively young compared with technical ceramics. Despite this, they compare favourably with their predecessors, even surpassing them in certain structural properties, while combining them with typically metallic properties:

• thermal and electrical conductivity ;

• machinability ;

• resistance to thermal shock.

However, there are still many challenges to be met if MAX phases are to develop and establish themselves against high-temperature (T > 1,000°C) technical ceramics and metal alloys.

This article has been written to provide an overview of the various possible shaping techniques, from elaboration to assembly and machining....