China Science

Two-point statistics describe the first-order spatial correlations between the constituent distinct local states in the internal structure of the material. These are usually recovered by randomly throwing vectors of all sizes and orientations into the material microstructure. Building on very recent advances in this emerging field, it is demonstrated in this paper that the complete set of 2-point correlations carry all of the information needed to uniquely reconstruct an eigen microstructure to within an translation and/or an inversion. For this purpose, novel algorithms based on phase-recovery methods used in signal processing have been developed and successfully implemented. The computational speed and the versatility of these new mathematical procedures are demonstrated through reconstruction of several two- and three-dimensional microstructures from their 2-point statistics.

David T. Fullwooda?Stephen R. Niezgodab?Surya R. KalidindibEmail:skalidin@coe.drexel.edu
[a]Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602, USA;[b]Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA

The influence of the addition of mischmetal (MM) and tin (Sn) (total content of mischmetal and tin = 4 wt.%) on the microstructure, aging behavior and mechanical properties of Mg–6Zn–5Al-based alloys has been investigated. The microstructure of the as-cast alloys consists of ?-Mg, Mg32(Al, Zn)49, Al2Mg5Zn2, Mg2Sn and Al2MMZn2 phases, and the morphology of these intermetallic phases varies with different MM and Sn additions. The hardness vs. aging time curves of all the alloys exhibit two peaks, and nanocrystalline Mg32(Al, Zn)49 and Mg2Sn precipitates are formed in the matrix. The alloys exhibit high tensile properties at 200 °C, which indicates that the high thermal stability of the Mg32(Al, Zn)49, Mg2Sn and Al2MMZn2 phases can hinder dislocation and grain-boundary sliding at elevated temperatures.

Wenlong Xiaoa?Shusheng Jiab?Jianli Wanga?Jie Yanga?Limin WangaEmail:lmwang@ciac.jl.cn
[a]State Key Laboratory of Application of Rare Earth Resources, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China;[b]Key Laboratory of Automobile Materials, Ministry of Education, Jilin University, Changchun 130025, China

The wetting phase transition of grain boundaries (GBs) and grain-boundary triple junctions (GB TJs) by the melt has been studied in the Al–30 wt.%Zn and Al–10 wt.%Zn–4 wt.%Mg polycrystals. The condition of complete wetting is weaker for TJs (?GB > ?SL) than that for GBs (?GB > 2?SL), ?GB being the GB energy and 2?SL being the energy of the solid/liquid interphase boundary. As a result the temperature of TJ wetting transition should be lower than that of GB wetting transition TwGB. It has been experimentally observed for the first time that TJs become completely wetted at TwTJ, which is about 10–15 °C below TwGB.

B.B. StraumalaEmail:straumal@issp.ac.ru?O. Kogtenkovab?P. Zibac
[a]Max-Planck-Institut für Metallforschung, Heisenbergstrasse 3, 70569 Stuttgart, Germany;[b]Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow District 142432, Russia;[c]Institute of Metallurgy and Materials Science, Polish Academy of Sciences, Reymonta Street 25, 30-059 Cracow, Poland

Finite element simulations of indentations on elastic and elastic–plastic materials have been performed to systematically study the effects of indenter geometry and mechanical properties, namely Poisson’s ratio and the E/?y ratio, on the correction factor for Sneddon’s equation used for analysis of nanoindentation data. Two indenter geometries, namely conical and Berkovich indenters, have been considered. It has been shown that the first-order correction for conical indentation on elastic materials previously developed by Hay et al. [Hay JC, Bolshakov A, Pharr GM. J Mater Res 1999;14:2296–305] can be applied only to conical indentation of elastic deformation-dominated materials but not to Berkovich indentation. A new general relationship for the estimation of the correction factor for Berkovich indentation is proposed based on the finite element simulation results. This relationship gives a better estimation of correction factor for Berkovich indentations on both elastic and elastic–plastic materials.

Zhi-Hui Xua?Xiaodong LiaEmail:lixiao@engr.sc.edu
[a]Department of Mechanical Engineering, University of South Carolina, 300 Main Street, Columbia, SC 29208, USA

The composition, structure and electrical properties of alumina barrier layers grown by anodic oxidation in F?-containing (FC) and F?-free (FF) oxalic acid solutions were studied using the re-anodizing/dissolution technique, Fourier-transformed infrared and X-ray photoelectron spectroscopy. These results confirmed formation in FC anodizing solutions of films structurally different from ones grown in FF oxalic acid baths. It was found that the barrier layer of FC alumina films is composed of two layers differing in the dissolution rate. These differences are related to the formation in the FC electrolyte of a barrier layer composed of a more microporous outer part and a thin, non-porous and non-scalloped inner part consisting of aluminum oxide and aluminum fluoride.

A. JagminasaEmail:jagmin@ktl.mii.lt?I. Vrublevskyb?J. Kuzmarskyta?V. Jasulaitiena
[a]Institute of Chemistry, A. Gotauto 9, LT-01108 Vilnius, Lithuania;[b]Department of Microelectricals, Belarusian State University of Informatics; Radioelectricals, 6 Brovka Street, Minsk 220013, Belarus

Bulk ceramic materials based on TiC–TiB2–MexOy systems have been produced by means of pressure-assisted self-propagating high-temperature synthesis (SHS). The selection of the SHS systems was based on thermodynamic analyses in order to obtain regimes of synthesis with formation of liquid phase allowing a proper densification. The liquid phase formed in the products consisted of either melted oxides or TiC–TiB2 eutectic depending on the combustion temperature. The mechanisms of structure formation and the effect of grain growth inhibition due to the metal oxide particles have been evaluated. The microstructural investigations have confirmed the role of the metal oxides as promoter of the final products densification and of the grain refinement in the SHS ceramic materials. A core–shell model is proposed to explain the structure formation of the SHS composites through a chemical interaction involving two stages. The good agreement between calculated and experimental results confirmed the validity of the core–shell mechanism.

D. VallauriaEmail:dario.vallauri@polito.it?V.A. Shcherbakovb?A.V. Khitevb?F.A. Deorsolaa
[a]Department of Material Science; Chemical Engineering, Politecnico di Torino, Torino, Italy;[b]Institute of Structural Macrokinetics; Materials Science, Russian Academy of Science, Chernogolovka, Russia

Nano and microcrystalline, Mn/CeO2 solid solutions (5 mol.% Mn) have been prepared by solution combustion synthesis using urea, glycine or polyethylene glycol (PEG) as fuel. The nature of the fuel and its concentration (fuel to metal mole ratio, F/M) have a strong influence on the physical and chemical characteristics of the resulting Mn/CeO2 solid solutions. The variations in the physicochemical properties are attributed to differences in (i) the adiabatic/real flame temperature realized with these fuels at different F/M ratios; (ii) the sustenance of the temperature or the quenching effect of the fuel at higher F/M ratios; (iii) combustion or decomposition of the precursors as the main course of the reaction; and (iv) the generation of gaseous products during combustion. Since the addition of the fuel to the initial precursor solution does not change the pH of the medium, the differences in the type of Mn species formed are mainly attributed to the combustion process.

B. Murugana?A.V. Ramaswamya Email:avram@iitm.ac.in?D. Srinivasb?C.S. Gopinathb?Veda Ramaswamyb
[a]Department of Chemistry, University of Pune, Pune 411 007, India;[b]Catalysis Division, National Chemical Laboratory, Pune 411 008, India

The cyclic plastic response of a single crystalline thin beam subject to combined cyclic tension and bending is analyzed using two-dimensional discrete dislocation plasticity. In this contribution, special attention is paid to the difference in the inherent mechanism of the size effect for different cyclic loads. Results show that the cyclic plastic response has a strong size effect for both cyclic pure tension–compression and pure bending. However, the inherent mechanisms are different. The dislocation starvation mechanism dominates the cyclic tension–compression while the geometrically necessary dislocation dominates the cyclic pure bending. When the combined cyclic tension and bending are applied to the thin beam, the cyclic moment–rotation response shows strong size effect while the stress–strain response shows weak or even no size effect. In addition, it is also found that the cyclic loading paths have considerable influences on the shape of the cyclic stress–strain loops

Chuantao Houa?Zhenhuan Li aEmail:zhli68@263.net?Minsheng Huanga?Chaojun Ouyanga
[a]Department of Mechanics, Huazhong University of Science; Technology, 1037 Luoyu Road, Wuhan 430074, China