China Science

This work characterizes the feathery-like structures produced in a Ti–46.8Al–1.7Cr–1.8Nb (at.%) alloy during rapid continuous cooling from the domain. Their morphology and crystallography are described using different microscopy and orientation mapping techniques. These feathery-like structures are divided into many small domains, characterized by low-angle misorientations (rotated less than 15°) between the domains. The domains comprise multiple parallel ? lamellae and rare traces of 2. These lamellae follow the Blackburn orientation relationship and have a {1 1 1}? habit plane. Two types of ?-feathery structures were identified according to their location and crystallography. The grain-boundary ?-feathery structures originate from lamellar structures that grow into a neighboring grain. Alternatively, the internal ?-feathery structures are located in the interior of prior grains and show an average misorientation of 36° around one axis of the lamellar structure in which it is embedded. This paper describes these two ?-feathery structures in detail and discusses their development in light of the mechanisms available in the literature, particularly sympathetic nucleation.

S.R. Dey1?E. Bouzya?A. Hazotte aEmail:alain.hazotte@univ-metz.fr
[a]Laboratoire d’Etude des Textures et Application aux Matériaux, UMR CNRS/UPVM 7078, Ile du Saulcy, 57045 Metz Cedex 1, France

In this study, the bainitic microstructure of a furnace-cooled electro-slag-refined 5% Cr steel was studied by the electron backscattered diffraction (EBSD) technique. The pole figures suggest a strong orientation relationship close to the Nishiyama–Wassermann type, i.e. there are 12 variants of the bainite sheaf that emerge from the three Bain correspondences. The microstructure consists of the bainite variants arranged in four sheaf colonies or morphological groups. Each sheaf colony, in turn, is made of one crystallographic group composed of 3 variants of bainite – one from each of the three Bain correspondences. Computations based on the phenomenological theory of martensitic crystallography (PTMC) show that the observed morphology is a product of stress-coupled autocatalytic nucleation. The 1 1 1Austenite 3-variant tension-coupled sheaf group predicted by the computations is the one that is experimentally observed.

V. Pancholia?Madangopal Krishnanb Email:madangk@barc.gov.in?I.S. Samajdarc?V. Yadavc?N.B. Ballalc
[a]Department of Metallurgical; Materials Engineering, IIT-Roorkee, Roorkee-247667, Uttarakhand, India;[b]Materials Science Division, Bhabha Atomic Research Centre, Mumbai-400085, India;[c]Department of Metallurgical Engineering; Materials Science, IIT-Bombay, Powai, Mumbai-400076, India

We have used thermodynamically calculated phase diagrams of Cu–Zr–Ti to identify two low-melting Cu-rich alloys denoted by A and B as bulk amorphous alloys where none were thought to exist. These alloys show greater stability of the glassy phase than previously discovered alloys in the same system, as evidenced by the critical casting diameter of 5 mm. We also calculated a temperature-composition diagram for alloy A as a function of Y using an approximate thermodynamic description of Cu–Zr–Ti–Y. This diagram shows that the liquidus temperature of alloy A decreases with the addition of Y, reaches a minimum, and increases again. Our experiments indeed showed the glass-forming ability of A reaches a maximum diameter of 10 mm when 2 at.% Y was added and then decreases again. We thus propose that the thermodynamically calculated liquidus temperature is an excellent guide to synthesize bulkier glasses, which can be readily obtained from calculated phase diagrams.

Hongbo Caoa?Ye Panb?Ling Dinga?Chuan Zhanga?Jun Zhua?Ker-Chang Hsiehc?Y. Austin Changa Email:chang@engr.wisc.edu
[a]Department of Materials Science; Engineering, University of Wisconsin-Madison, 1509 University Avenue, Madison, WI 53706, USA;[b]School of Materials Science; Engineering, Southeast University, Nanjing 210096, China;[c]Institute of Materials Science; Engineering, Sun Yat Sen University, Kaohsiung 80424, Taiwan

Transmission electron microscopy characterizations and elastic properties of two quaternary carbides, i.e. Zr2(Al(Si))4C5 and Zr3(Al(Si))4C6 are reported. The space group and atomic-scale microstructures of both compounds were determined using a combination of selected area electron diffraction, convergent beam electron diffraction, high-resolution transmission electron microscopy and Z-contrast scanning transmission electron microscopy. In addition, the combined experimental and theoretical studies on elastic properties for Zr2(Al(Si))4C5 are presented. A full set of second-order elastic constants, bulk modulus, shear modulus, and Young’s modulus were calculated using first-principles calculations. Both experimental and theoretical works demonstrated that quaternary Zr–Al–Si–C ceramics possess close elastic properties to ZrC. Furthermore, Zr2(Al(Si))4C5 retained a high Young’s modulus up to about 1580 °C, which can be attributed to its comparable activation energy of lattice drag process to that of ZrC.

Z.J. Lina?L.F. Hea?J.Y. Wanga?M.S. Lia?Y.W. Baoa?Y.C. Zhoua Email:yczhou@imr.ac.cn
[a]Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;[b]Graduate School of Chinese Academy of Sciences, Beijing 100049, China

The faceted morphology and dislocation structures in all the facets of austenite precipitates in a duplex stainless steel were investigated with an extended near-coincidence-sites (NCS) method based on the orientation relationship (OR) generated by the O-line model. The prominent facets of the precipitates are parallel to three sets of principal Moiré planes containing high areal density of NCS, respectively. The Burgers vector and the spacing of the misfit dislocations were determined by a Moiré plane trace analysis and a displacement decomposition method. The observed misfit dislocations were consistently explained by the current approach, but the calculated fine dislocations were not observed experimentally. The terrace-ledge-kink structures in terms of both ferrite and austenite lattices were also graphically illustrated. The present geometric approach can also be applied to other systems containing lath- or rod-shaped precipitates, especially when the interfacial structures cannot be described by periodic O-lattice elements.

D. Qiu aEmail:d.qiu@minmet.uq.edu.au?W.-Z. Zhanga
[a]Laboratory of Advanced Materials, Department of Materials Science; Engineering, Tsinghua University, Beijing 100084, China

Three-dimensional (3D) quantitative analysis is indispensable for the unambiguous characterization and objective classification of complex microstructures. Focused ion beam (FIB) nanotomography provides complete information of the spatial arrangement, chemistry and orientation of different phases of real microstructures on scales especially important in materials science (10 nm–100 ?m). Complex graphite particles were analyzed in three-dimensions. Whereas nodular, vermicular and temper graphite particles can be characterized individually, the whole network of flake graphite has to be considered due to the high spatial interconnection of particles. The characterization method was verified in comparison to established two-dimensional stereological methods. The influence of anisotropy and image resolution was discussed. Basic stereological characteristics (volume, surface area, integrals of mean and total curvature) as well as 3D connectivity (Euler number) and shape parameters objectively differentiate these graphite morphologies and contribute to the understanding of their growth mechanisms and the properties of the cast iron.

A. Velichkoa Email:a.velitchko@matsci.uni-sb.de?C. Holzapfela?A. Siefersa?K. Schladitzb?F. Mücklicha
[a]Materials Science Department, Chair of Functional Materials, Saarland University, P.O. Box 151150, D-66041 Saarbrücken, Germany;[b]Fraunhofer-Institut für Techno- und Wirtschaftsmathematik [ITWM], Fraunhofer-Platz 1, 67663 Kaiserslautern, Germany

Finite-element modeling (FEM) was used to predict the contact stress at which the transition from elastic to plastic deformation occurs in a metallic substrate underneath a hard tribological coating. Using model systems of diamond-like nanocomposite (DLN) coatings on electroformed Ni, NiMn alloy and Inconel 718, friction measurements were made at contact stresses ranging from 540 to 1720 MPa. Cross-sections of wear scars suitable for visualization of friction-induced plastic deformation in the substrate were prepared by focused ion beam microscopy and analyzed by electron backscatter diffraction. At contact stresses below the FEM-predicted elastic–plastic limit, the coefficient of friction decreased linearly with increase in contact stress, suggesting that interfacial shear is the major mechanism of friction in DLN. Contact stresses above the FEM-predicted elastic–plastic limit resulted in plastic deformation of the metallic substrate, and in extreme cases fracture and removal of the coating resulting in a sudden increase in friction.

J.M. Jungka?J.R. Michaela?S.V. Prasad aEmail:svprasa@sandia.gov
[a]Sandia National Laboratories, Albuquerque, NM 87185-0889, USA

Discrete dislocation dynamics simulations in three dimensions are performed on micro-sized bending beams and the results are compared with experiments. A strong size dependence of the flow stress ?f (or bending moment) is found. The flow stress scales approximately inversely with the beam thickness t. The simulations show that the dislocation structure exhibits pronounced pile-ups around the neutral plane of the beam. The back stress from these pile-ups on the dislocation sources is analyzed by means of an analytical pile-up model. It is shown that the scaling behavior ?f?t-1 can be explained by a combination of pile-up and source size limitation. Subsequently, the applicability of strain gradient plasticity models on micro-bending is discussed.

C. MotzaEmail:motz@unileoben.ac.at?D. Weyganda?J. Sengera?P. Gumbscha
[a]IZBS, University of Karlsruhe [TH], Kaiserstrasse 12, 76131 Karlsruhe, Germany;[b]Erich Schmid Institute, Austrian Academy of Sciences, Jahnstrasse 12, 8700 Leoben, Austria