Advanced Engineering Materials

Cover image for Advanced Engineering Materials

August, 2004

Volume 6, Issue 8

Pages 609–693

    1. Contents: Adv. Eng. Mater. 8/2004 (pages 609–612)

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200490006

    2. Tailored Microstructures: Can a Dream come True? (pages 617–625)

      G. Gottstein

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400049

      The mechanical properties of crystalline solid are determined by the spatial distribution of chemical elements and crystal defects, which is referred to as microstructure. Microstructure changes during processing and its evolution can be influenced by processing conditions and external fields. Advanced microstructure codes can cover the through-process microstructural evolution and allow first predictions of terminal materials properties.

    3. Continuum Models for the Thermomechanical Behavior of Discontinuously Reinforced Materials (pages 626–633)

      H.J. Böhm

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400026

      Continuum micromechanical models have become important tools for understanding the thermomechanical behavior of composite materials. This work presents the most important continuum-level approaches for modeling the thermomechanical behavior of discontinuously reinforced composites. Analytical and numerical models are covered, special emphasis being put on multi-inclusion unit cell methods. The fields of application of the different models are discussed and selected applications are demonstrated.

    4. Superalloy IN625 with Cellular Microstructure – Fabrication Route and Mechanical Properties (pages 635–639)

      P. Quadbeck, J. Kaschta and R.F. Singer

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400054

      Cellular microstructures are of special interest for applications in filtering, heat transfer or acoustic absorption. In the present paper a new route for the preparation of such structures from superalloys will be presented. Polyoxymethylene (POM) is used as space holder which can be injection molded into any desired shape. Densification of the cell walls and struts is achieved by supersolidus liquid phase sintering (SLPS).

    5. Evolution of the Mechanical Properties of Aluminum Containing Al8Fe2Si Precipitates During Equal Channel Angular Pressing (pages 639–643)

      A. Korchef, N. Njah, J. Masmoudi, A. Kolsi, Y. Champion, S. Guérin and C. Leroux

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400081

      Mechanical behaviour of submicrometer grain sized aluminium (99.1%), containing a low volume fraction of Al8Fe2Si precipitates, processed by Equal Channel Angular (ECA) pressing was investigated using Vickers microhardness, compression and tensile tests. In compression, samples machined along three orthogonal directions exhibited different yield strengths and cylindrical samples became elliptic after pressing. Tensile results showed an increase of the yield strength without loss of ductility. After ECA pressing for one pass, annealing at 200°C leads to a significant strengthening. A dependence of the ductility with strain rate was also observed.

    6. Electroforming of Metallic Microparts on Sacrificial Molds made by Two-component Injection Molding (pages 643–653)

      N. Holstein, V. Piotter, J. Lorenz, E. Oskotski, R. Ruprecht, G. Schanz and J. Hausselt

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400028

      One of the process developments required in Micro System Technology (MST) is oriented to the mass production of metallic microsystem components with high aspect ratios and high surface qualities by galvanic replication. The limiting factor is the generation of suitable templates for electroforming. A production of metallic microsystems or components in large numbers requires on one side the transcription of the special technique of the electroforming step in the LIGA process and on the other side replication and fast multiplication into a mass production process. The envisaged possibility will be given by thermoplastic injection molding of sacrificial molds and the following electroforming on these polymer molds.

    7. Comparison of Single Crystal Simple Shear Deformation Experiments with Crystal Plasticity Finite Element Simulations (pages 653–656)

      F. Roters, Y. Wang, J.-C. Kuo and D. Raabe

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400079

      The crystal plasticity finite element method is an ideal approach to simulate the mechanics, texture, and elastic-plastic anisotropy of materials. Experimental validation of such simulations requires to measure these quantities without the disturbing influence of friction known for instance from channel-die experiments. This work presents results obtained form simple shear deformation experiments of aluminium single crystals together with corresponding crystal plasticity finite element simulations.

    8. Technical Cost Modeling for the Mechanical Milling at Cryogenic Temperature (Cryomilling) (pages 656–664)

      J. Ye and J.M. Schoenung

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400074

      Cryomilling is one of the few technologies available to fabricate a large quantity of nanostructured materials. No matter how exciting and promising a technology is, its ultimate realization is invariably dependent on economic success. Technical cost modeling was employed in this paper to analyze the processing cost of cryomilling. The results demonstrated that cryomilling has the potential to be commercially economical to fabricate nanostructured materials.

    9. Deformation and Failure Modeling of Fiber Reinforced Ceramics with Porous Matrix (pages 664–669)

      K. Tushtev, J. Horvath, D. Koch and G. Grathwohl

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400094

      A 2D reinforced carbon/carbon-composite was investigated in tensile tests with variable fiber orientation relative to the loading direction. The experimental results from two different orientations (0° and 45°) are used to derive material parameters which are implemented into a macroscopic model. The model describes the materials response, i.e. the stress-strain behavior and the ultimate failure of the composite, under any angle between fiber orientation and loading direction. The predicted data are confirmed by experimental results.

    10. Microwave Detection of Defects and Inhomogeneities in Low Pressure Injection Moulded β-TCP Ceramic (pages 669–672)

      S.T. Martins, H. Dannheim, H. Hädrich, J. Weinzierl, F.A. Müller and P. Greil

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400038

      The feasibility of a nondestructive microwave inspection to detect internal processing defects in low pressure injection moulded ceramic parts was investigated. A β-TCP (β-tricalcium phosphate, Ca3(PO4)2) slurry with paraffin, ethylene vinyl acetate copolymer and stearic acid as binder system was injection moulded with a pressure of 0.2 MPa and subsequently inspected in a 94.1 GHz microwave testing device. The transmitting amplitude and phase displacement images were compared with visual inspection of the samples. The novel method was able to detect, localize and geometrically characterize inhomogeneities and non-visible defects present in green ceramic compacts.

    11. Improved Green Strength of Ceramics Through Aqueous Gelcasting (pages 672–676)

      I. Santacruz, C. Baudín, R. Moreno and M.I. Nieto

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400053

      Aqueous gelcasting of alumina is optimised by preparing concentrated agarose solutions under overpressure conditions. The better dissolution reduces the viscosity and improves the microstructural control leading to green densities higher than 60 % of TD. The enhancement of the green strength is not accompanied by a significant increase of the plastic behaviour during fracture for agarose contents < 1 wt.%. Sintered densities > 99 % of theoretical are obtained.

    12. Cross Linking Behavior of Preceramic Polymers Effected by UV- and Synchrotron Radiation (pages 676–680)

      M. Schulz, M. Börner, J. Göttert, T. Hanemann, J. Haußelt and G. Motz

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400082

      Ceramic properties are important for applications in micro system technologies. Various lithographic methods are being widely used for the direct fabrication of very precise plastic or metal micro structured surfaces. High temperature stable ceramics can be achieved from preceramic polymers using relatively low pyrolysis temperatures. A direct lithographic process to produce ceramic microstructures has been developed.

    13. In Situ Nondestructive Evaluation of the Accumulative Damage in Continuous Ceramic Fiber-Ceramic Matrix Composites (CFCCs) using Submillimeter Range Electromagnetic Wave (pages 681–683)

      S. Guo, T. Mamiya and Y. Kagawa

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400033

      Monolithic ceramic materials usually show catastrophic failure behavior and this property limits application as structural components because the failure occurs easily from a small flaw that usually exists in the materials. To overcome this, incorporation of a fine ceramic fiber into a brittle ceramic has been examined and the obtained material is named as continuous fiber-ceramic matrix composites (CFCCs).

    14. Cutting Temperatures and Their Effects on the Machining Behaviour in Drilling Reinforced Plastic Composites (pages 684–689)

      K. Weinert and C. Kempmann

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200400025

      Construction parts consisting of modern composite materials made of fiber reinforced polymers still need to be machined, whereby special attention has to be paid to the machining quality. The machining quality implies dimensional accuracy as well as a defect-free peripheral zone. Machining defects often occur as a consequence of excessive mechanical loads, which are often caused by wrong process conditions. Besides mechanical loads, the thermal influence on the composite material, which is induced by the cutting process itself, has to be considered as crucial. According to the thermo physical material properties of fiber reinforced polymers the boundary conditions differ from the machining of metals. Especially in drilling operations the heat removal is difficult, when dry machining is employed. Here, temperature measurements in drilling polymer composites are introduced and moreover the machining defects, which occurs according to the process temperatures, are presented.

    15. Effect of Injection Parameters on Velocity and Temperature Distributions of Alumina-Titania In-Flight Particles in Atmospheric Plasma Spraying (pages 689–693)

      S. Guessasma, G. Montavon and C. Coddet

      Article first published online: 30 AUG 2004 | DOI: 10.1002/adem.200300584

      Three injection parameters (carrier gas flow rate, injector diameter and injection distance) were correlated to the characteristic distributions in the case of alumina titania in-flight particles. A high speed two color pyrometer was implemented to measure, at the centre of the particle flow, individual in-flight particle characteristics, which were used to build velocity and temperature distributions. Results showed that mean characteristic variations were explained by distribution width flattening and centre shift. These were not significant compared to energetic parameter effects.