Work-hardening mechanisms of the Ti 60 Cu 14 Ni 12 Sn 4 Nb 10 nanocomposite alloy
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Jordi Sort Institucio´ Catalana de Recerca i Estudis Avanc¸ats and Departament de Fı´sica, Facultat de Cie`ncies, Edifici Cc, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain
Jordina Fornell Departament de Fı´sica, Facultat de Cie`ncies, Edifici Cc, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain
Emma Rossinyol Servei de Microscopia, Facultat de Cie`ncies, Edifici Cs, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain
Santiago Surin˜ach Departament de Fı´sica, Facultat de Cie`ncies, Edifici Cc, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain
Annett Gebert IFW Dresden, Institute for Metallic Materials, D-01171 Dresden, Germany
Jurgen Eckertb) IFW Dresden, Institute for Complex Materials, D-01171 Dresden, Germany; and TU Dresden, Institute of Materials Science, D-01062 Dresden, Germany
M. Dolors Baro´ Departament de Fı´sica, Facultat de Cie`ncies, Edifici Cc, Universitat Auto`noma de Barcelona, 08193 Bellaterra, Barcelona, Spain (Received 14 November 2008; accepted 27 April 2009)
The work-hardening mechanisms of the Ti60Cu14Ni12Sn4Nb10 nanocomposite alloy were studied. This material is composed of micrometer-sized dendrites embedded in a nanostructured eutectic matrix and a CuTi2 intermetallic phase. Our study shows that, in the as-quenched state, the nanostructured eutectic matrix behaves softer than the dendrites. During mechanical deformation, both the dendrites and the eutectic matrix harden, whereas the hardness of the CuTi2 intermetallic phase remains unaltered. The high strength of the dendrites is caused by the interplay between solid solution hardening and dislocation networks during plastic flow. Interestingly, the mechanical hardening of the nanoeutectic matrix is also assisted by a martensitic transformation of the NiTi phase. Transmission electron microscopy studies clearly show that the martensitic transformation of this phase is accompanied with grain size refinement, which also plays a role in the deformation-induced mechanical hardening.
I. INTRODUCTION
Composite materials consisting of micrometer-sized grains surrounded by a glassy or nanostructured matrix have attracted much attention because of their appealing a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr_policy DOI: 10.1557/JMR.2009.0369 3146
J. Mater. Res., Vol. 24, No. 10, Oct 2009
combination of mechanical properties, i.e., high strength, typical of glassy and nanostructured materials, together with enhanced plasticity.1–5 A recent example of glassmatrix composites studied by Hofmann et al.5 exhibited tensile ductility exceeding 10%, yield strengths of 1.2– 1.5 GPa, and toughness and fracture energy surpassing those achievable in the toughest titanium or steel alloys. Moreover, the effects of a ductile toughening phase on f
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