Phase-specific elastic/plastic interface interactions in layered NiAl–Cr(Mo) structures R.I. Barabash a,⇑ , W. Liu b , J.Z. Tischler a , H. Bei a , J.D. Budai a a Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA b Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA Received 10 February 2012; received in revised form 23 February 2012; accepted 26 February 2012 Available online 6 April 2012 Abstract The depth-dependent, as-grown and deformation-induced strain and dislocations partitioned through the interfaces in a two-phase layered NiAl–Cr(Mo) structure are directly measured at the mesoscale using 3-D X-ray microdiffraction. It is demonstrated that in the as-grown, undeformed state, neighboring submicron Cr solid solution and NiAl eutectic lamellae (doped with 3% Mo) form a het- erointerface with 180° rotation around a h112i pole. It is shown that the mechanical response to the indentation of a layered composite with alternating Cr(Mo)–NiAl lamellae is distinct from the response of single-phase materials. In the center of the indent, after the load is released, the NiAl lamellae are under compressive forward stresses (with the same sign as the indentation-induced compression) while Cr solid solution lamellae are under tensile back stresses (with opposite sign from the indentation load). The depth-dependent alternation of compressive/tensile residual strains in the neighboring Cr solid solution and NiAl lamellae is understood in the framework of the Mugh- rabi’s composite model considering two types of structure elements: harder and softer regions. Under indentation, both kinds of lamellae are assumed to deform compatibly. After the load is released, residual forward stresses are formed in the harder lamellae, and back stres- ses are formed in the mechanically softer lamellae. Line-broadening analysis of the intensity distribution along the diffraction vector reveals a 15-times increase in dislocation density in the near-surface zone in the center of the indent. Such a large increase is typical for severe deformation. Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Micromechanics; Deformation; Composites; X-ray synchrotron radiation; Micro-/nanoindentation 1. Introduction Mesoscale science, encompassing the regime of hun- dreds of nanometers where classical, microscale and nano- scale science meet, is increasingly the focus of current research into the origins of the properties of materials. In particular, interfaces play a crucial role in such properties, in part because interfaces themselves possess unique phys- ical properties distinct from the bulk constituent phases [1–5]. In layered composites, the overall interfacial area is very large. Interfaces between the phases are key elements responsible for the unique micromechanisms of plasticity in composites [1]. Interfaces and boundaries can block dis- location slippage. The discontinuity in chemical composi- tion, elastic moduli, coefficients of thermal expansion, lattice parameters and chemical potential at the interfaces between the matrix and the second phase determine their mechanical performance. NiAl-based composites with chromium as the second phase represent promising alloys satisfying requirements for prospective energy-conversion technologies operating up to 1300 °C in corrosive environ- ments. Superelasticity was observed in a fine-grained NiAl– Cr alloy [6]. Thus, they have great potential for use as structural components under high thermal and mechanical loading in energy conversion facilities [7,8]. Huai et al. [9] emphasized that NiAl–Cr(Mo) is “the most logical choice of the multi-element system examined today because of 1359-6454/$36.00 Ó 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.actamat.2012.02.052 ⇑ Corresponding author. Tel.: +1 865 2417230; fax: +1 865 5747659. E-mail address: barabashr@ornl.gov (R.I. Barabash). www.elsevier.com/locate/actamat Available online at www.sciencedirect.com Acta Materialia 60 (2012) 3279–3286