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.

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[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.
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[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