Designing, Processing and Properties of Advanced Engineering Materials

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Authors: Dong Nyung Lee
Abstract: Asymmetric rolling, in which the circumferential velocities of the upper and lower rolls are different, can give rise to intense plastic shear strains and in turn shear deformation textures through the sheet thickness. The ideal shear deformation texture of fcc metals can be approximated by the <111> // ND and {001}<110> orientations, among which the former improves the deep drawability. The ideal shear deformation texture for bcc metals can be approximated by the Goss {110}<001> and {112}<111> orientations, among which the former improves the magnetic permeability along the <100> directions and is the prime orientation in grain oriented silicon steels. The intense shear strains can result in the grain refinement and hence improve mechanical properties. Steel sheets, especially ferritic stainless steel sheets, and aluminum alloy sheets may exhibit an undesirable surface roughening known as ridging or roping, when elongated along RD and TD, respectively. The ridging or roping is caused by differently oriented colonies, which are resulted from the <100> oriented columnar structure in ingots or billets, especially for ferritic stainless steels, that is not easily destroyed by the conventional rolling. The breakdown of columnar structure and the grain refinement can be achieved by asymmetric rolling, resulting in a decrease in the ridging problem.
Authors: James C. Williams
Abstract: Product performance including the cost of ownership is becoming increasingly dependent on the availability of high quality, high performance, affordable materials of construction. Today, the requirements placed on a new material for a high performance structural application extend well beyond the improvement of one or more material properties. This makes the introduction of a new material a multi-faceted activity. Modern structural materials derive their performance from a combination of composition and processing, the results of which are inextricably intertwined. This statement pertains to both metallic alloys and to fiber reinforced composite materials. In addition, material cost and the reproducibility of material properties are becoming more central as acceptance criteria for incorporating new materials into new products. This paper will use examples of recent developments in materials for aircraft gas turbines to depict the materials introduction process. Some of these developments have been successful and others have not. These examples illustrate the changing picture that represents the successful introduction of a new structural material, even in a high performance, high value product such as a gas turbine. Specific examples will include metal matrix composites, Ni-base alloys and improved reliability Ti alloys. The basis for successful introduction, or lack thereof will be discussed. While the examples are specific to gas turbines, they are generally instructive and depict the growing complexity of the process of developing and introducing new materials into a high value product. An additional issue for all new materials introduction is the time required to achieve product readiness. As the time required for product design decreases, there has been little commensurate reduction in materials development cycle time. This matter also will be discussed and some possible reasons and potential solutions will be described.
Authors: Toshiro Kobayashi
Abstract: To determine the toughness of materials, Charpy V notch test has been widely utilized over the world. This method is easy to conduct, but obtained values are some what qualitative. Instrumented test has also a long history and gives us a loading history during impact. However this method is also still remaining in the range of a screening test. The author has successfully developed CAI (Computer Aided Instrumented Impact Testing) System for the evaluation of dynamic fracture toughness. In this CAI system, dynamic fracture toughness parameters such as Kd, Jd, Tmat and various absorbed energies can be obtained from the load-deflection curve of a single precracked specimen for both ductile and brittle materials
Authors: Veeramuthu Vaithianathan, C. Wolverton, Long Qing Chen
Abstract: This short article reports our recent effort to integrate the mesoscale phase-field method with first-principles total energy calculations, linear response theory, as well as mixedspace cluster expansion. A particular example of applying such a multiscale approach to the case of precipitation of semicoherent θ' particles in an Al-matrix is presented.
Authors: Xin Hua Wu, D. Hu, M.H. Loretto
Abstract: The IRC has carried out a major research programme over the last ten or so years aimed at developing the processing and optimisation of TiAl-based alloys. This work has covered melting, the production of shaped castings, powder processing and a range of thermomechanical processing routes in parallel with alloy development. In this paper the work aimed at understanding the factors that influence the properties of thermo-mechanically processed and cast samples of TiAl-based alloys will be reviewed. It is shown that the use of boron to control the grain size of castings leads to limited ductility in the stronger and more highly alloyed TiAl alloys because ribbon-like borides up to 200µm in length can be formed. It is also shown that although a fully lamellar microstructure offers a good balance of properties their plastic anisotropy leads to pre-yield fracture and to reduced fatigue life. It is clear that grain size control is essential if an acceptable balance of properties is to be obtained but that if casting is to be used grain refinement via boron addition is not totally satisfactory. A simple heat treatment can be used to refine the microstructure of cast boron-free alloys, which leads to ductility comparable with that in wrought samples and the associated convoluted microstructure should also eliminate pre-yield cracking.
Authors: Yasuhiro Miura, Kentaro Ihara
Abstract: An experimental study on the microstructure development and stress–strain behavior during high temperature deformation of aluminum (Al) single crystals was made by using X-ray Laue technique and the electron backscatter pattern (EBSP) technique. The main purpose was to clarify the process of dynamic recrystallization (DRX). The measured stress-strain curves with large stress peaks and the new Laue spots without streaks at around the stress peaks confirmed the occurrence of DRX in Al single crystals with initial compression axis <111>, <011> or <001>. Crystallographic analysis by the Laue technique and EBSP technique show that the DRX grain and the matrix have an <121> axis in common in the <111> crystal, an <101> axsis in the <011> and <001> crystals. For the <111> crystal, the unrecrystallized region near the DRX grain consists of subgrains adjoined each other with <112> tilt boundaries and the size of subgrains becomes smaller and the misfit at subgrain boundaries becomes larger as the DRX grain boundaries are approached. These results suggest that DRX grains are nucleated through the development of subgrains.
Authors: Masahiko Morinaga, Hiroshi Yukawa
Abstract: A molecular orbital approach to alloy design has recently made great progress. This approach is based on the electronic structure calculations by the DV-Xα molecular orbital method. New PHACOMP and the d-electrons concept have been constructed and applied to alloy design. Recently, nickel-based single crystal superalloys for power generation gas turbine blades and high Cr ferritic steels for turbine rotors have been developed successfully with this approach.
Authors: Jun Akedo
Abstract: Aerosol deposition method (ADM) for shock-consolidation of fine ceramics powder to form dense and hard layers is reported. Submicron ceramic particles were accelerated by gas flow in the nozzle up to velocity of several hundred m/s. During interaction with substrate, these particles formed thick (10 ~ 100 µm), dense, uniform and hard ceramics layers. Depositions were fulfilled at room temperature. Every layer has polycrystalline structure with nano-meter order scale.􀀂 The results of fabrications, microstructure, mechanical and electrical properties of oxides (α-Al2O3; Pb(Zr0.52,Ti0.48)O3 etc.) and non-oxides materials are presented.
Authors: Hun Chul Kang, Sang Hwan Lee, Dong Hyuk Shin, Kyung Jong Lee, Seon Jin Kim, Kyung Sub Lee
Abstract: The quantitative analysis of precipitates in ferrite was investigated using the fact that the formation of precipitates in Nb, V and Ti added steels accelerated austenite/ferrite transformation. The major factors on austenite/ferrite transformation were cooling rate, austenite grain size, and deformation. The slower cooling rate, the smaller austenite grain size and the higher deformation accelerated austenite/ferrite transformation. In 0.34wt%V micro-alloyed steel, the influence of cooling rate and austenite grain size on austenite/ferrite transformation was investigated without deformation. In addition, the experimental method was set up to measure the amount of precipitates in ferrite by the transformation dilatometer. The amount of precipitates was controlled by the holding temperature and time in ferrite. Then, the specimen was inversely transformed without the formation or dissolution of precipitates. Volume fractions transformed were measured by dilatometer during cooling. Iso-precipitation kinetics was determined by comparing the mean transformation temperatures at various conditions, respectively. The result was compared with the calculated.

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