China Science

The article examines the position of the University of Cape Town (UCT) on academic freedom and institutional autonomy. It also provides information on the Mafeje Affair, in which its 40th anniversary was celebrated through a public symposium held at UCT in South Africa in August 2008. The concept of a social policy or racial segregation, as compared to liberal universities was also discussed, as well as their differences in policies and practices. The article also offers a narrative account of the UCT’s decision-making process on the appointment of Archie Mafeje as the senior lecturer in the Department of Social Anthropology.

Hendricks, Fred1
[1]Rhodes University, Grahamstown

The fatigue behavior of as-cast Mg–12%Zn–1.2%Y–0.4%Zr alloy has been investigated. The S–N curve showed that the fatigue strength at 107 cycles was 45 MPa. Scanning electron microscopy observations on the surfaces of the failed and unfailed specimens (after up to 1 × 107 cycles) suggested that the slip bands could act as preferential sites for non-propagating fatigue crack initiation, and the I-phase could effectively retard fatigue crack propagation (FCP). The macro fracture morphology clearly indicated that the overall fracture surface was composed of three regions, i.e. a fatigue crack initiation region (Region 1), a steady crack propagation region (Region 2) and a tearing region (Region 3). High-magnification fractographs showed that only porosities can act as the crack initiation sites for all specimens. Moreover, for specimens with fatigue lifetimes lower than 2 × 105 cycles, the cracks mostly initiated at the subsurface or surface of the specimen. However, when the fatigue lifetime was equal to or higher than 2 × 105 cycles, the fatigue crack initiation sites transferred to the interior of the specimen. The maximum stress intensity factors corresponding to the transition sites between Regions 1, 2 and 3 were 2 and 4.2 MPa m1/2, respectively. When the maximum stress intensity factor Kmax was lower than 4.2 MPa m1/2, in the steady crack propagation region, due to the retarding effect of I-phase/?-Mg matrix interfaces, the fatigue cracks tended to pass the I-phase/?-Mg matrix eutectic pockets directly and propagated through the grain cells, resulting in the formation of many flat facets on the fracture surface. However, when the maximum stress intensity factor was higher than 4.2 MPa m1/2, in the sudden failure region, the rigid bonding of I-phase/?-Mg matrix interfaces was destroyed and the cracks preferentially propagated along the interfaces, which resulted in the fracture surface being almost completely composed of cracked I-phase/?-Mg matrix eutectic pockets. Based on microstructural observation and the fracture characteristics of the two regions, it is suggested that with an increase in crack tip driving force, the FCP mode changes from transgranular propagation to intergranular propagation.

D.K. Xua?L. Liub?Y.B. Xub?E.H. HanaEmail:ehhan@imr.ac.cn
[a]Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China;[b]Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

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 transformation of the grain boundary fct ?-MnNi precipitates to thermodynamically stable austenite was investigated in an Fe–Mn–Ni alloy using transmission electron microscopy (TEM). During aging of Fe–Mn–Ni alloys, fine bands began to develop in the ?-MnNi intermetallic particles. The HAADF images revealed these thin bands to be stacking faults and twins that were formed by the glide of -type Shockley partial dislocations on {1 1 1} planes. The presence of iron in the twin bands was detected by electron energy-loss spectroscopy (EELS) analysis. These observations supported the conclusion that the crystal structure of the twin bands was transformed to that of face-centered cubic (fcc) austenite by iron diffusion into the twin bands. A further transformation of the ?-MnNi particle to austenite was proceeded by the development of new austenite bands rather than by the broadening of the existing bands. The mechanism of this transformation was discussed based on the crystal structure of both phases.

Yoon-Uk Heoa?Miyoung Kima?Hu-Chul LeeaEmail:huchul@snu.ac.kr
[a]School of Materials Science; Engineering, Seoul National University, Seoul 151-744, Republic of Korea

The Soret effect, as it occurs in the diffusion of solutes in crystals, is analyzed using the principle of microscopic reversibility whereby an approach is developed for interpreting and computing Q*, the heat of transport. To compute the transport of energy during the diffusion jump process, and then Q*, the processes of thermal activation to the transition state and the decay from the transition state are considered to be inverses; thus the net process is reduced to the analysis of the purely mechanical decay process. Molecular statics and dynamics are then suggested as the means to simulate the decay process and the case of carbon diffusion in body-centered cubic ?-iron is so analyzed as an example. Our results show that, for the case Q* ? ?Qm, where Qm is the activation energy for carbon diffusion, this is in agreement with experimental evidence reported in the literature. Thus both the sign and magnitude of Q* are correctly predicted. Various cases, such as the diffusion of substitutional solutes and vacancies, are also considered within our approach along with implications for future study.

Robert J. AsaroaEmail:rasaro@ucsd.edu?Diana Farkasb?Yashashree Kulkarnia
[a]Department of Structural Engineering, University of California, San Diego, La Jolla, CA 92093, USA;[b]Department of Materials Science; Engineering, Virginia Tech, Blacksburg, VA 24061, USA

The texture, microstructure and mechanical behavior of bulk ultrafine-grained (ufg) Zr fabricated by accumulative roll bonding (ARB) is investigated by electron backscatter diffraction, transmission electron microscopy and mechanical testing. A reasonably homogeneous and equiaxed ufg structure, with a large fraction of high angle boundaries (HABs, 70%), can be obtained in Zr after only two ARB cycles. The average grain size, counting only HABs (? > 15°), is 400 nm. (Sub)grain size is equal to 320 nm. The yield stress and UTS values are nearly double those from conventionally processed Zr with only a slight loss of ductility. Optimum processing conditions include large thickness reductions per pass (? 75%), which enhance grain refinement, and a rolling temperature (T 0.3Tm) at which a sufficient number of slip modes are activated, with an absence of significant grain growth. Grain refinement takes place by geometrical thinning and grain subdivision by the formation of geometrically necessary boundaries. The formation of equiaxed grains by geometric dynamic recrystallization is facilitated by enhanced diffusion due to adiabatic heating.

L. Jianga?M.T. Pérez-PradoaEmail:tpprado@cenim.csic.es?P.A. Gruberc?E. Arztc?O.A. Ruanoa?M.E. Kassnerb
[a]Department of Physical Metallurgy, National Center for Metals Research (CENIM), CSIC, Avda. de Gregorio del Amo, 8, 28040 Madrid, Spain;[b]Department of Aerospace; Mechanical Engineering, University of Southern California, 3650 McClintock Ave, Los Angeles, CA 90089-1453, USA;[c]Max Planck Institute for Metals Research, Heisenberg Strasse 3, 70569 Stuttgart, Germany;[d]Institute for Physical Metallurgy, Universitt Stuttgart, Heisenberg Strasse 3, 70569 Stuttgart, Germany ;[1] Current address: INM Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany.

Ga+ ions at a dose of 0.1 at.% (1.5 × 1014 ions cm?2) were irradiated by focused ion beam (FIB) onto L10 FePt films with a [0 0 1] crystalline texture normal to the film plane, and two-dimensional patterns composed of squares with high-coercivity (L10 structure, 300 × 300 nm2 and 100 × 100 nm2) separated by a soft magnetic region (A1 structure) 100 nm wide were fabricated. The magnetic domain structure of patterned film was observed by in-field magnetic force microscopy (MFM). In the remanent state, the domain with magnetization normal to the film surface was observed in the central part of the L10 square, while the narrow domain with reversed magnetization is at the circumference of the square. The magnetization process is discussed based on the MFM observations.

Takashi Hasegawaa Email:d9506009@wm.akita-u.ac.jp?W. Peib?T. Wangc?Y. Fuc?T. Washiyaa?H. Saitoa?S. Ishioa
[a]Department of Materials Science; Engineering, Akita University, 1-1 Gakuen-machi, Tegata, Akita 010-8502, Japan;[b]College of Materials; Metallurgy, Northeastern University, Shenyang 110004, China;[c]Venture Business Laboratory, Akita University, 1-1 Gakuen-machi, Tegata, Akita 010-8502, Japan

There is increasing demand for oxide-dispersion-strengthened ferritic alloys that possess both high-temperature strength and irradiation resistance. Improvement of the high-temperature properties requires an understanding of the operative deformation mechanisms. In this study, the microstructures and creep properties of the oxide-dispersion-strengthened alloy 14YWT have been evaluated as a function of annealing at 1000 °C for 1 hour up to 32 days. The ultra-fine initial grain size (approx. 100 nm) is stable after the shortest annealing time, and even after subsequent creep at 800 °C. Longer annealing periods lead to anomalous grain growth that is further enhanced following creep. Remarkably, the minimum creep rate is relatively insensitive to this dramatic grain-coarsening. The creep strength is attributed to highly stable, Ti-rich nanoclusters that appear to pin the initial primary grains, and present strong obstacles to dislocation motion in the large, anomalously grown grains.

T. Hayashia?P.M. Sarosia Email:sarosi.2@osu.edu?J.H. Schneibelb?M.J. Millsa
[a]Department of Materials Science; Engineering, The Ohio State University, Columbus, OH, USA;[b]Materials Science; Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA