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The Max phases and kinking nonlinear elastic solids A newly identified class of solids

Michel W. Barsoum 

Drexel University, 3141 Chestnut St, Philadelphia 19104, United States

Abstract

The layered, hexagonal carbides and nitrides with the general formula: Mn+1AXn, (MAX) where n = 1 to 3, M is an early transition metal, A is an A-group (mostly IIIA and IVA) element and X is either C and/or N combine some of the best attributes of metals and ceramics. Like metals, they are electrically and thermally conductive, most readily machinable (manual hack saw will suffice) not susceptible to thermal shock, plastic at high temperatures, and exceptionally damage tolerant. Like ceramics, they are elastically rigid, lightweight, and maintain their strengths to high temperatures. The ternaries Ti3SiC2 and Ti2AlC are creep, fatigue and oxidation resistant. More recently we have also shown that the MAX phases are but a subset of solids that we termed kinking nonlinear elastic, KNE, because one of their important – and in many cases only - deformation mode is the formation of fully reversible, dislocation-based incipient kink bands, IKBs. The ramifications of these results are far-reaching. First, they identify the hysteretic mesoscopic units invoked to explain the behavior of nonlinear mesoscopic elastic solids in geology – that to date had remained a mystery – as incipient KBs. Second, they elucidate, for the first time, why graphite responds to stress the way it does; a 50 + year old problem. We further claim, and present compelling evidence, that most if not all solids with c/a ratios > 1.5 - which per force are plastically anisotropic – will deform by kinking. KNE solids include most layered solids, such as mica, LiNbO3, Mg, Ti, Zn, Co, and other hexagonal metals, h-BN, GaN, MoS2, as well as sapphire, among many others. Given the diversity and ubiquity of KNE solids it is clear that incipient IKBs play a much more important role in our daily life than has hitherto been appreciated.

 

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Related papers

Presentation: Oral at E-MRS Fall Meeting 2008, Symposium I, by Michel W. Barsoum
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 17:23
Revised:   2009-06-07 00:48