The MAX Phases are layered, hexagonal carbides and nitrides have the general formula: M_n+1AX_n, (MAX) where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA, or groups 13 and 14) element and X is either carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 and/or nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

.

A list of the MAX phases known to date, in both bulk and thin film form:

211 Phases	312 Phases	413 Phases
Ti2CdC, Sc2InC, Ti2AlC, Ti2GaC, Ti2InC, Ti2TlC, V2AlC, V2GaC, Cr2GaC, Ti2AlN, Ti2GaN, Ti2InN, V2GaN, Cr2GaN, Ti2GeC, Ti2SnC, Ti2PbC, V2GeC, Cr2AlC, Cr2GeC, V2PC, V2AsC, Ti2SC, Zr2InC, Zr2TlC, Nb2AlC, Nb2GaC, Nb2InC, Mo2GaC, Zr2InN, Zr2TlN, Zr2SnC, Zr2PbC, Nb2SnC, Nb2PC, Nb2AsC, Zr2SC, Nb2SC, Hf2InC, Hf2TlC, Ta2AlC, Ta2GaC, Hf2SnC, Hf2PbC, Hf2SnN, Hf2SC	Ti3AlC2, V3AlC2, Ti3SiC2, Ti3GeC2, Ti3SnC2, Ta3AlC2,	Ti4AlN3, V4AlC3, Ti4GaC3, Ti4SiC3, Ti4GeC3, Nb4AlC3, Ta4AlC3,

History

In the 1990s, the ternary compound, Ti₃SiC₂, was synthesized and fully characterized for the first time by a research group in the Materials Engineering department at Drexel University. A year later they showed that this compound was but one of over sixty phases, most discovered and produced in powder form in the sixties by H. Nowotny and coworkers. In 1999 they discovered Ti₄AlN₃ and realized that they were dealing with a much larger family of solids that all behaved similarly. Since 1996, when the first paper was published on the subject, tremendous progress has been made in understanding the properties of these phases and the 1996 article has been cited over 650 times.

Properties

These carbides and nitrides possess unusual and, sometimes, unique chemical, physical, electrical, and mechanical properties that combine the best attributes of metals and ceramics.

Electrical

The MAX phases are electrically

Electrical resistivity and conductivity

Electrical resistivity is a measure of how strongly a material opposes the flow of electric current. A low resistivity indicates a material that readily allows the movement of electric charge. The SI unit of electrical resistivity is the ohm metre...

 and thermally

Thermal conductivity

In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

 conductive due to their metallic-like nature of bonding

Metallic bond

Metallic bonding is the electrostatic attractive forces between the delocalized electrons, called conduction electrons, gathered in an "electron sea", and the positively charged metal ions...

. Most of the MAX phases are better electric and thermal conductors than Ti.

Physical

While MAX phases are stiff, they can be machined as easily as metals. They can all be machined using a manual hacksaw, despite the fact that some of them are three times as stiff as titanium metal, with the same density as titanium. They can also be polished to a metallic luster because of their excellent electrical conductivities. They are not susceptible to thermal shock and exceptionally damage tolerant. Some are oxidation and corrosion resistant.

Mechanical

The MAX phases as a class are generally stiff, lightweight, and plastic at high temperatures. Some, like Ti₃SiC₂ and Ti₂Al_C, are also creep

Creep (deformation)

In materials science, creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to high levels of stress that are below the yield strength of the material....

  and fatigue

Fatigue (material)

'In materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The nominal maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue occurs...

resistant, and maintain their strengths to high temperatures.
They exhibit unique deformation characterized by basal slip, a combination of kink and shear band deformation, and delaminations of individual grains. During mechanical testing, it has been found that polycrystalline Ti3SiC2 cylinders can be repeatedly compressed at room temperature, up to stresses of 1 GPa, and fully recover upon the removal of the load while dissipating 25% of the energy. It was by characterizing these unique mechanical properties of the MAX phases that kinking non-linear solids and incipient kink bands (the micromechanism that is responsible for them) were discovered.

Potential Applications

Elements in differents shapes
,High temperature stable refractory material
,Coatings for electrical contacts
,Corrosion resistance at high temperature
,Corrosion resistance in corrosive chemical environments

External links

• http://max.materials.drexel.edu
• http://www.Kanthal.Com
• http://www.3one2.com/