Advanced Structural and Functional Materials Design

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Authors: M. Meshii
Abstract: The discipline of Materials Science is, we believe, in the midst of the second transformation. The research and education of most of the Materials Science and Engineering departments in the United States have traditionally emphasized hard materials. The recent surge in research of soft materials and our perceptions that the Materials Science Methodology (both experimental and numerical) holds the advantage in the research of the soft materials prompt us to expand the area of soft materials at the expense of hard materials. Clearly the struggle between the two types of materials will continue for some time to come. The current struggle in weighting will be described in an historical fashion comparing it to the struggle in the first transformation that took place in the 1950's and 1960's.
Authors: Václav Paidar
Abstract: Internal interfaces are decisive for many properties of materials. Both functional and structural properties of interfaces are briefly reviewed on selected examples. Approaches to the grain boundary classification are discussed in the context of the complex relationship between microstructure and material properties. Implications for grain boundary engineering are mentioned.
Authors: Yukichi Umakoshi, Hiroyuki Y. Yasuda
Abstract: A magnetic technique was applied to examine cyclic deformation behavior and deformation damage in ordered FeAl and Ni3(Al,Ti) single crystals. The fatigue lifetime of FeAl was evaluated by an abrupt increase in spontaneous magnetization. The morphology of γ precipitates in Ni3(Al,Ti) during annealing and deformation was examined by changes in spontaneous magnetization and coercive force.
Authors: Masao Toyoda, Masahito Mochizuki, Yoshiki Mikami
Abstract: Joint performances such as tensile strength and hardness in multi-pass welds are induced from both metallurgical and mechanical heterogeneity due to the difference of welding conditions. Hardness distribution in multi-pass weld metal is evaluated with a numerical simulation considering multiple heat cycles and phase transformation. Hardness of multipass weld metal is calculated with the rule of mixture by using fraction and hardness of each microstructure. In order to calculate fraction of each microstructure, CCT diagram was used. Conventional CCT diagrams of weld metal is not available even for single pass weld metal, thus new diagrams for multi-pass weld metals are created in this study. Modified diagrams for multi-pass weld metals with reheating effect were more dependent on the maximum temperature in reheating than the welding conditions. Hardness distribution is precisely predicted when the created CCT diagram for the multipass weld metal was used and the detailed calculation of weld thermal cycle is done.
Authors: Hiroyuki Y. Yasuda, Keisuke Yamaoka, Yukichi Umakoshi
Abstract: D03-ordered Fe3Al single crystals containing 23, 25 and 28at.%Al were cyclically deformed at [ 49 1 ] loading axis in tension-compression mode. Giant pseudoelasticity took place in Fe-23 and 25at.%Al single crystals at an early stage of cyclic deformation, while a slight strain recovery was observed in Fe-28at.%Al. In Fe-23 and 25at.%Al single crystals, superpartial dislocations with Burgers vector of 1/4[111] moved individually dragging the nearest neighbour anti-phase boundary (NNAPB). The NNAPB pulled back the superpartials during unloading, resulting in giant pseudoelasticity and low residual dislocation density. In contrast, a couplet of the superpartials was observed to bow out leaving two superpartials in Fe-28at.%Al. This means that the dislocation couplet dragged the next-nearest neighbour anti-phase boundary (NNNAPB). The surface tension of NNNAPB is lower than that of NNAPB resulting in a slight strain recovery in Fe-28at%Al. As cyclic deformation proceeded, residual dislocation density increased with an increase in the number of cycles even in Fe-23 and 25at.%Al. In particular, persistent slip bands (PSB) were formed in Fe-23at.%Al single crystals, though PSB is seldom observed in fatigued intermetallic compounds. To-and-fro motion of superpartials during loading and unloading was suppressed by dislocation bundles, resulting in a reduced shape recovery. However, large strain recovery occurred in Fe-25at.%Al single crystals at a strain amplitude of 1.0% even at 20cycles. It was also noted that Fe-23 and 25at.%Al demonstrated tension-compression asymmetry even at [ 49 1 ] orientation; the yield stress in compression was higher than that in tension. This implies that the core structure of <111> screw dislocation played an important role in the deformation behaviour of Fe3Al single crystals.
Authors: Takeshi Nagase, Mitsuo Nakamura, Yukichi Umakoshi
Abstract: Superplastic viscous deformation and thermal crystallization behavior of supercooled liquid in Zr60.0Al15.0Ni25.0 metallic glass were investigated. The temperature interval of the supercooled liquid region (∆Tx) was 83 K. The supercooled liquid showed significant viscous plasticity, resulting in large elongation and high strain rate deformation. The stress-strain behavior can be classified into three types: stress overshoot, stable viscous flow with constant flow stress and strain hardening. The strain hardening is due to the precipitation of Zr6Al2Ni crystalline phase with ellipsoidal morphology. Superplastic viscous deformation behavior is very sensitive to thermal crystallization as well as to deformation temperature and strain rate.
Authors: Ping Guang Xu, Fu Xing Yin, Kotobu Nagai
Abstract: We investigated the dendrite structures and the as-cast textures of low-carbon steel strips cast at different cooling rates in order to relate the δ-ferrite dendrite structure with the ferrite phase texture. Observations revealed that the orientation intensity of the texture component {111} was stronger than the texture component {001} in the as-cast steel strips obtained at different solidification cooling rates. These two texture components show a roof-shaped variation with the gradual decrease of the solidification cooling rate, reaching a maximum intensity at a cooling rate of about 2.0 K/s. This suggests that the solidification rate strongly influences the as-cast texture of low-carbon steel strips through changing the δ-ferrite dendrite structure.
Authors: S.V.S. Narayana Murty, Shiro Torizuka, Kotobu Nagai
Abstract: We examined the microstructure development in low carbon steel (0.15% C) during heavy warm deformation (HWD) using field emission scanning electron microscopy (FESEM) and electron back-scattering diffraction (EBSD). Plane strain compression tests have been conducted in the temperature range of 773-923 K at strain rates of 0.01 s-1 and 1 s-1 with the specimens deformed to 25% of their original thickness. We summarize the strain rate and temperature into the Zener-Hollomon parameter and investigate its variation with plastic strain on the basis of the evolved microstructures and grain boundary character with a view to understanding the critical conditions for forming ultrafine grains and classifying them. Once established, these compressive strain-Z parameter plots simplify the selection of processing parameters (such as strain, strain rate, and temperature), towards achieving tailor-made microstructures in industrial components.
Authors: Mao Qiu Wang, Eiji Akiyama, Kaneaki Tsuzaki
Abstract: We examine the hydrogen embrittlement susceptibility of a high-strength AISI 4135 steel by means of a slow strain-rate test (SSRT) using notched round bar specimens. Hydrogen was introduced into the specimens by electrochemical charging and its content was measured by thermal desorption spectrometry (TDS). It was found that the maximum tensile stress decreased in a power law manner with increasing diffusible hydrogen content. Finite element method (FEM) calculations demonstrated that the peak value of the maximum principal stress and the peak value of the locally accumulated hydrogen concentration at the maximum tensile stress were in good agreement with one power law relationship for the specimens with different stress concentration factors.

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