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Shear melting and high temperature embrittlement: theory and application to machining titanium

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http://arxiv.org/abs/1503.08662
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.165501
Original languageEnglish
Article number165501
Number of pages5
JournalPhysical Review Letters
Volume114
Issue number16
DOIs
Publication statusPublished - 30 Mar 2015

Abstract

We describe a dynamical phase transition occurring within a shear band at high temperature and under extremely high shear rates. With increasing temperature, dislocation deformation and grain boundary sliding is supplanted by amorphization in a highly localized nanoscale band, which allows massive strain and fracture. The mechanism is similar to shear melting and leads to liquid metal embrittlement at high temperature. From simulation, we find that the necessary conditions are, lack of dislocation slip systems, low thermal conduction and temperature near the melting point. The first two are exhibited by bcc titanium alloys, and we show that the final one can be achieved experimentally by adding low-melting point elements: specifically we use insoluble rare earth metals (REMs). Under high shear, the REM becomes mixed with the titanium, lowering the melting point within the shear band and triggering the shear-melting transition. This in turn generates heat which remains localized in the shear band due to poor heat conduction. The material fractures along the shear band. We show how to utilize this transition in the creation of new titanium-based alloys with improved machinability.

    Research areas

  • MOLECULAR-DYNAMICS, POTENTIALS, TRANSITION, CRYSTAL, COPPER

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