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Motivation of this Work

The micromechanical behavior of grain boundaries is one of the key components in the understanding of heterogeneous deformation of metals [1]. To investigate the nature of the strengthening effect of grain boundaries, slip transmission across interfaces has been investigated through bicrystal deformation experiments during the sixty past decades [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14] and [15]. Originally, interactions between dislocations and grain boundaries have been observed in the transmission electron microscope (TEM) after strain test or in situ [4], [5] and [15]. Some authors observed as well slip transmission during indentation tests performed close to grain boundaries [16], [17], [18], [19] and [20].

To better understand the role played by the grain boundaries, we developed a |matlab| toolbox with Graphical User Interfaces (GUI), to analyze and to quantify the micromechanics of grain boundaries. This toolbox aims to link experimental results to crystal plasticity finite element (CPFE) simulations [23].

Strategy

Comparison of topographies of indentations at grain boundaries to simulated indentations as predicted by 3D CPFE modelling.

The goals of this research are:

1 - Carry out indentation within the interiors of large grains of alpha-titanium to effectively collect single crystal data coupled with extensive (three-dimensional) characterization of the resulting plastic defect fields surrounding the indents [21]. By correlating with models of the indentation, a precise constitutive description of the anisotropic plasticity of single-crystalline titanium shall be developed [22] and [23].

2 - Extension of this methodology to indentations close to grain boundaries, i.e. quasi bi-crystal deformation.

3 - Comparison of the measured characteristics of indentations at grain boundaries to simulated indentations as predicted by a constitutive model calibrated using the single crystal indentations.

4 - Based on this qualitative understanding, a grain boundary transmissivity description will be developed validated against the collected indent characteristics.

[1]T.R. Bieler et al., "Grain boundaries and interfaces in slip transfer.", Current Opinion in Solid State and Materials Science (2014), 18(4), pp. 212-226.
[2]K.T. Aust et al., "Solute induced hardening near grain boundaries in zone refined metals.", Acta Metallurgica (1968), 16(3), pp. 291-302.
[3]J.D. Livingston and B. Chalmers, "Multiple slip in bicrystal deformation.", Acta Metallurgica (1957), 5(6), pp. 322-327.
[4](1, 2) Z. Shen et al., "Dislocation pile-up and grain boundary interactions in 304 stainless steel.", Scripta Metallurgica (1986), 20(6), pp. 921–926.
[5](1, 2) Z. Shen et al., "Dislocation and grain boundary interactions in metals.", Acta Metallurgica (1988), 36(12), pp. 3231–3242.
[6]J. Luster and M.A. Morris, "Compatibility of deformation in two-phase Ti-Al alloys: Dependence on microstructure and orientation relationships.", Metal. and Mat. Trans. A (1995), 26(7), pp. 1745-1756.
[7]M.J. Marcinkowski and W.F. Tseng, "Dislocation behavior at tilt boundaries of infinite extent.", Metal. Trans. (1970), 1(12), pp. 3397-3401.
[8]W. Bollmann, "Crystal Defects and Crystalline Interfaces", Springer-Verlag (1970)
[9]L.C. Lim and R. Raj, "Continuity of slip screw and mixed crystal dislocations across bicrystals of nickel at 573K.", Acta Metallurgica (1985), 33, pp. 1577.
[10]T.C. Lee et al., "Prediction of slip transfer mechanisms across grain boundaries.", Scripta Metallurgica, (1989), 23(5), pp. 799–803.
[11]T.C. Lee et al., "An In Situ transmission electron microscope deformation study of the slip transfer mechanisms in metals", Metallurgical Transactions A (1990), 21(9), pp. 2437-2447.
[12]W.A.T. Clark et al., "On the criteria for slip transmission across interfaces in polycrystals.", Scripta Metallurgica et Materialia (1992), 26(2), pp. 203–206.
[13]W.Z. Abuzaid et al., "Slip transfer and plastic strain accumulation across grain boundaries in Hastelloy X.", J. of the Mech. and Phys. of Sol. (2012), 60(6) ,pp. 1201–1220.
[14]J.R. Seal et al., "Analysis of slip transfer and deformation behavior across the α/β interface in Ti–5Al–2.5Sn (wt.%) with an equiaxed microstructure.", Mater. Sc. and Eng.: A (2012), 552, pp. 61-68.
[15](1, 2) J. Kacher et al., "Dislocation interactions with grain boundaries.", Current Opinion in Solid State and Materials Science (2014), in press.
[16]P.C. Wo and A.H.W. Ngan, "Investigation of slip transmission behavior across grain boundaries in polycrystalline Ni3Al using nanoindentation.", J. Mater. Res. (2004), 19(1), pp. 189-201.
[17]W.A. Soer et al. ,"Incipient plasticity during nanoindentation at grain boundaries in body-centered cubic metals.", Acta Materialia (2005), 53, pp. 4665–4676.
[18]T.B. Britton et al., "Nanoindentation study of slip transfer phenomenon at grain boundaries.", J. Mater. Res., 2009, 24(3), pp. 607-615.
[19]S. Patthak et al., "Studying grain boundary regions in polycrystalline materials using spherical nano-indentation and orientation imaging microscopy.", J. Mater. Sci. (2012), 47, pp. 815–823.
[20]S.K. Lawrence et al., "Grain Boundary Contributions to Hydrogen-Affected Plasticity in Ni-201.", The Journal of The Minerals, Metals & Materials Society (2014), 66(8), pp. 1383-1389.
[21]C. Zambaldi et al., "Orientation informed nanoindentation of α-titanium: Indentation pileup in hexagonal metals deforming by prismatic slip", J. Mater. Res. (2012), 27(01), pp. 356-367.
[22]F. Roters et al., "Overview of constitutive laws, kinematics, homogenization and multiscale methods in crystal plasticity finite-element modeling: Theory, experiments, applications.", Acta Materialia (2010), 58(4), pp. 1152-1211.
[23](1, 2) DAMASK — the Düsseldorf Advanced Material Simulation Kit
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