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Advanced Materials

The development of new creep-resistant Mg-alloys1a) was guided by Computational Thermodynamics. The new quaternary Mg-alloys with a substantially reduced content of expensive Sc-alloying addition performed with about 100 times lower creep rate compared to commercial benchmark alloys [01Sch, 01Gro]. Applications to the processing of Sc-additons to Al- and Mg-alloys were also demonstrated [00Pis]. The generation and extension of a comprehensive thermodynamic Mg-alloy database is an ongoing long-term effort [05Sch, 03Gro, 02Gro, 01Kev2]. Recently the as-cast microstructure development in modified AZ and AM alloys is investigated in an integrated approach (thermodynamics, phase field simulation and casting experiments)1b). Another project concerns the application to thixoforming processes and development of customized Mg-alloys1c).

Multicomponent monotectic Al-alloys are investigated1d), which are of interest for self-lubricating bearings. A monotectic four-phase reaction was detected in Al-Bi-Zn alloys, opening the window to new microstructures that cannot be obtained in binary alloys [05Gro2].

The stability of nitride semiconductors, important for optoelectronic applications, was studied in thin films [98Pis] and in bulk crystals [03Unl, 02Ond]. It is demonstrated that fugacity plays a crucial role in crystal synthesis at high pressure.

Ti-Al based alloys, intermetallics and nitrides and their thermodynamic behavior during nitridation were studied1e). It is shown that both the Ti- and N2- partial pressures must be controlled in synthesis or processing of such materials [99Zen, 97Sch, 96Zen].

  • [05Sch] R. Schmid-Fetzer, A. Janz, J. Gröbner and M. Ohno: Aspects of quality assurance in a thermodynamic Mg alloy database. Advanced Engineering Materials (2005) accepted
  • [05Gro2] J. Gröbner, D. Mirkovic and R. Schmid-Fetzer: Monotectic four-phase reaction in Al-Bi-Zn alloys. Acta Materialia, 53, 3271-3280 (2005)
  • [03Unl] J. Unland, B. Onderka, A. Davydov, R. Schmid-Fetzer: Thermodynamics and Phase Stability in the Ga-N System. J. Cryst. Growth 256, 33-51 (2003)
  • [03Gro] J. Gröbner, D. Kevorkov, I. Chumak and R. Schmid-Fetzer: Experimental Investigation and Thermodynamic Calculation of Ternary Al-Ca-Mg Phase Equilibria. Z. Metallkde. 94, 976-982 (2003)
  • [02Ond] B. Onderka, J. Unland, R. Schmid-Fetzer: Thermodynamics and Phase Stability in the In-N System. J. Mater. Res. 17, 3065-3083 (2002)
  • [02Gro] J. Gröbner, D. Kevorkov, R. Schmid-Fetzer: Thermodynamic Modeling of Al-Ce-Mg Phase Equilibria Coupled with Key Experiments. Intermetallics 10, 415-422 (2002)
  • [01Sch] R. Schmid-Fetzer, J. Gröbner: Focused Development of Magnesium Alloys using the Calphad Approach. Adv. Eng. Mater. 3, 947-961 (2001)
  • [01Kev2] D. Kevorkov, R. Schmid-Fetzer: The Al-Ca system, Part 1: Experimental Investigation of Phase Equilibria and Crystal Structures. Z.Metallkde., 92, 946-952 (2001)
  • [01Gro] J. Gröbner and R. SchmidFetzer: Selection of Promising Quaternary Candidates from MgMn(Sc, Gd, Y, Zr) for Development of Creepresistant Magnesium Alloys. J. Alloys Comp., 320, 296-301 (2001)
  • [00Pis] A. Pisch, J. Gröbner, R. Schmid-Fetzer: Application of Computational Thermochemistry to Al- and Mg-alloy processing with Sc additions. Mater. Sci. Eng. A, A289, 123-129 (2000)
  • [99Zen] K. Zeng, R. Schmid-Fetzer, B. Huneau, P. Rogl, and J. Bauer: The Ternary System Al-Ni-Ti, Part II: Thermodynamic Assessment and Experimental Investigation of Polythermal Phase Equilibria. Intermetallics, 7, 1347-1359 (1999)
  • [98Pis] A. Pisch and R. Schmid-Fetzer: In-situ decomposition study of GaN thin films. J. Cryst. Growth, 187, 329-332 (1998)
  • [97Sch] R. Schmid-Fetzer and K. Zeng: Nitridation of Ti-Al Alloys: A Thermodynamic Approach. Metall. Mater. Trans. A, 28A, 1949-1951 (1997)
  • [96Zen] K. Zeng and R. Schmid-Fetzer: Critical Assessment and Thermodynamic Modeling of the Ti-N System. Z. Metallkde.,87, 540-554 (1996)

Cooperations

1a) DFG-SFB 390, especially IWW, TU Clausthal
1b) RWTH Aachen, Gießerei-Institut and ACESS e.V., joint project in DFG-SPP1168
1c) GKSS, Geesthacht and University Erlangen/ Neue Materialien Fürth GmbH; DFG-SPP1168
1d) DLR Köln, Institut für Raumsimulation; TU Chemnitz, Institut für Physik; DFG-SPP-1120
1e) University of Vienna, Institut für Physikalische Chemie; Universite de Rennes I, Laboratoire de Chimie du Solide et Inorganique Moleculaire, UMR CNRS; COST507
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