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On the relevance of kinking to reversible hysteresis in MAX phases

DOI: 10.1016/j.actamat.2014.01.045 DOI Help

Authors: N. G. Jones (University of Cambridge) , C. Humphrey (University of Cambridge) , L. D. Connor (Diamond Light Source) , O. Wilhelmsson (Sandvik Heating Technology AB, SE-734 27 Hallstahammar, Sweden) , L. Hultman (Thin Film Physics Division, Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden) , F. Giuliani (Imperial College London) , W. J. Clegg (University of Cambridge) , H. J. Stone (University of Cambridge)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Acta Materialia , VOL 69 , PAGES 149 - 161

State: Published (Approved)
Published: May 2014
Diamond Proposal Number(s): 4791

Open Access Open Access

Abstract: This paper examines the idea that reversible hysteresis in MAX phases is caused by the formation, growth and collapse of unstable, or incipient, kink bands. In situ X-ray diffraction of polycrystalline Ti3SiC2 in compression showed that residual elastic lattice strains developed during the first loading cycle and remained approximately constant afterwards. These residual strains were compressive in grains with a low Schmid factor and tensile in grains with a high Schmid factor, consistent with previous observations of plastically deformed hexagonal metals. In contrast, incipient kink bands would be expected to collapse completely, without any residual strain. Elastoplastic self-consistent simulations showed that reversible hysteresis is predicted if some grains yield by slip on the basal plane, while others remain predominantly elastic, giving both the experimentally observed magnitude of the work dissipated and its dependence on the maximum applied stress. The reversible hysteresis in single crystals was studied by cyclically indenting thin films of Ti3SiC2 and Ti3SiC2/TiC multilayers on Al2O3 substrates. The work dissipated in the multilayer films was greater than in Ti3SiC2 alone, despite the reduction in volume fraction of Ti3SiC2. Reversible hysteresis was also observed during indentation of single-crystal cubic MgO, demonstrating that this behaviour can occur if there are insufficient slip systems to accommodate the strain around the indentation. These results show that reversible hysteresis is associated with conventional dislocation flow, without the need for unstable kinking.

Journal Keywords: Mechanical properties; X-ray synchrotron radiation; Lattice strains; Polycrystal; MAX phases

Subject Areas: Materials


Instruments: I12-JEEP: Joint Engineering, Environmental and Processing

Added On: 27/05/2014 12:31

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