Alumina-base plasma-sprayed materials part I: Phase stability of alumina and alumina-chromia


Aluminum oxide is a relatively cheap, abundant material that is widely used for plasma- spray applications. This material, however, exists in many crystallographic modifications with different properties. In addition, most of these modifications are metastable and cannot be used in applications employed at elevated temperatures. Usually γ, δ, or other phases form after spraying, while α phase (corundum) is often the most desirable phase due to high corrosion resistance and hardness. This paper first reviews the method of α stabilization in the as- sprayed materials offered in literature. Then, as an example, it summarizes the results of an extensive study of chromia additions to alumina. Chromia was chosen because of its complete solid solubility in alumina and its crystal lattice type, which is similar to that of alumina. It was demonstrated that the addition of approximately 20 wt% chromia results in the formation of one solid solution of (Al- Cr)2O3 in the α- modification.

Finally, this paper discusses the thermal stability of various alumina phases. Phase change routes of heating for different starting alumina modifications are discussed, and a case study of alumina- chromia is presented. Both types of as-sprayed structures, a mixture of α, δ, and γ phases, and 100% (Al- Cr)2O3 were annealed up to 1300 °C and the phase composition checked. At lower temperatures and shorter holding times, the amount of α phase decreases while another metastable θ phase appears, and the fraction of γ + δ, if present, increases. At temperature above 1100 °C, the amount of α phase increases again.

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  1. 1.

    R.C. Garvie, R.H. Hannink, and R.T. Pascoe, Ceramic Steel?, Nature, Vol 258,1975, p 703–704

    Article  CAS  Google Scholar 

  2. 2.

    J.R. Brandon and R. Taylor, Thermal Properties of Ceria and Yttria Partially Stabilized Zirconia Thermal Barrier Coatings, Surf. Coat. Technol., Vol 39,40,1989, p 143–151

    Article  Google Scholar 

  3. 3.

    Powder Diffraction File, Alphabetical index, JCPDS, International Centre for Diffraction Data, PA, USA, 1986

  4. 4.

    P. Chráska, J. Dubsky, B. Kolman, J. Ilavsky, and J. Forman, Study of Phase Changes in Plasma Sprayed Deposits, J. Therm. Spray Technol.,, Vol 1 (No. 4), 1992, p 301–306

    Google Scholar 

  5. 5.

    C.X. Ding, R.A. Zatorski, and H. Herman, Oxide Powders for Plasma Spraying—The Relationship between Powder Characteristic and Coating Properties, Thin Solid Films, Vol 118, 1984, p 467–475

    Article  CAS  Google Scholar 

  6. 6.

    N.N. Ault, Characteristics of Refractory Oxide Coatings Produced by Flame-Spraying, J. Am. Ceram. Soc, Vol 40 (No. 3), 1957, p 69–74

    Article  CAS  Google Scholar 

  7. 7.

    J. Dubsky, B. Kolman, and P. Chráska, The Influence of Cooling Rate on Phase Transformations in Al2O3, Proc. of 7th Metallographic Symposium, Part 1, J. Šujan, Ed., CSVTS Košice, Vysoké Tatry, Czechoslovakia, 1989, p 168–171

    Google Scholar 

  8. 8.

    M. Kumagai and G.L. Messing, Enhanced Densification of Boehmite Sol-Gels by α-Alumina Seeding, J. Am. Ceram. Soc, Vol 67, 1984, C230–231

    Article  CAS  Google Scholar 

  9. 9.

    Y. Suwa, R. Roy, and S. Komarneni, Lowering Crystallization Temperatures by Seeding in Structurally Diphasic Al2O3-MgO Xerogels, J. Am. Ceram. Soc, Vol 68,1985, C238

    Article  Google Scholar 

  10. 10.

    G.L. Messing, M. Kumagai, R.A. Shellman, and J.L. McArdle, Seeded Transformation for Microstructural Control in Ceramics, The Science of Ceramic Chemical Processing, L.L. Hench and D.R. Ulrich, Ed., Wiley, 1986, p 259–271

  11. 11.

    G.C. Bye and G.T. Sympkin, Influence of Cr and Fe on the Formation of α-Al2O3 from γ-A12O3, J. Am. Ceram. Soc, Vol 57,1974, p 367–371

    Article  CAS  Google Scholar 

  12. 12.

    T. Tushida, R. Furuichi, T. Ishii, and K. Itoh, The Effect of Cr3+ and Fe3+ Ion on the Transformation of Different Aluminum Hydroxides to α-Al2O3, Thermochim. acta, Vol 64,1983, p 337–353

    Article  Google Scholar 

  13. 13.

    I.A. Bonder, V.B Glushkova, and P.A. Ceitlin, Study of Phase Changes in Al2O3,Neorg. Mater., Vol7, 1971,p 1367–1371

    Google Scholar 

  14. 14.

    R. McPherson, On the Formation of Thermally Sprayed Alumina Coatings, J. Mater. Scl, Vol 15,1980, p 3141–3149

    Article  CAS  Google Scholar 

  15. 15.

    R. McPherson, The Structure of Al2O3-Cr2O3 Powders Condensed from a Plasma, J. Mater. Sci., Vol 8,1973, p 859–862

    Article  CAS  Google Scholar 

  16. 16.

    B.C. Lippens and J.H. DeBoer, Study of Phase Transformations During Calcination of Aluminum Hydroxides by Selected Area Electron Diffraction, Acta Crystallogr., Vol 17, 1964, p 1312

    Article  CAS  Google Scholar 

  17. 17.

    G. Ervin, Structural Interpretation of the Diaspore-Corundum and Boehmite-γ-Al2O3,4cto Crystallogr., Vol 5,1952, p 103–108

    Article  CAS  Google Scholar 

  18. 18.

    A.M. Lejus, Metastable Phases Formation in Aluminum Hydroxides, Rev. Int. Hautes. Temp. Refract., Vol 1,1964, p 53–59

    CAS  Google Scholar 

  19. 19.

    A. Nukui, H. Tagai, H. Morikawa, and S.I. Iwai, Structural Conformation and Solidification of Molten Alumina, J. Am. Ceram. Soc, Vol 59, 1976, p 534

    Article  CAS  Google Scholar 

  20. 20.

    R. McPherson, Formation of Metastable Phases in Flame- and Plasma- Prepared Alumina, J. Mater. Sci., Vol 8,1973, p 851 -858

    Article  CAS  Google Scholar 

  21. 21.

    F.B. Vurzel,V.A. Khmel’nik,V.F. Nazarov,and G.V. Kosoruchkin,Production of Thermally Deposited Aluminas, Phys. Chem. Mater. Treat., (Russia), Vol 3, 1988, p 86–91

    Google Scholar 

  22. 22.

    H. Meyer, On the Application of Chromium Oxide-Containing Alumina to Flame Spraying, Ber. Deutsche Keramik. Ges., Vol 40,1963, p385

    CAS  Google Scholar 

  23. 23.

    T.I. Barry, R.K. Bayliss, and L.A. Lay, Mixed Oxides Prepared with an Induction Plasma Torch, Part 1 Chromia/Alumina, J. Mater. Sci., Vol 3, 1968, p 229–238

    Article  CAS  Google Scholar 

  24. 24.

    T.J. Davies, H.G. Emblem, C.S. Nwobodo, A.A. Ogwn, and V. Tsatzalou, Preparation and Properties of Some Alumina-Chrome Refractories, J. Mater. Sci., Vol 26,1991, p 1061

    Article  CAS  Google Scholar 

  25. 25.

    S. Safai and H. Herman, Plasma-Sprayed Materials, Treat. Mater. Sci. Tech., Vol 20,1981, p 183–214

    CAS  Google Scholar 

  26. 26.

    A. Krauth and H. Meyer, Modifications Produced by Chilling and Their Crystal Growth in the System Containing Zirconium Dioxide, Ber. Deutsche Keramik. Ges., Vol 42, 1965, p 61–72

    CAS  Google Scholar 

  27. 27.

    J. Dubsky, V. Brozek, B. Kolman, and P. Chráska, Stabilization of α-AI2O3 by Chromia, Ceramics Adding the Value, Proc. of the Inter. Ceram. Conf. AUSTCERAM 92, Vol 2, M.J. Bannister, Ed., CSIRO, Australia, 1992, p 793–797

    Google Scholar 

  28. 28.

    J. Dubsky, B. Kolman, V. Brozek, and P. Chráska, The Chemical Inhomogeneity of Al2O3-Cr2O3 Powders for Plasma Spraying, Proc. of 16th Symposium on Plasma Physics and Technology, Czech Technical University, Prague, Czechoslovakia, 1993, p 267–273

    Google Scholar 

  29. 29.

    V. Costa, C. Pacheco de Silva, T. Puig, and A.M. Dias, Influence of H.I.P. and Laser Treatments on Ceramic Plasma Sprayed Coatings, Proc. 2nd Plasma-Technik-Symposium, Vol 1, Luzern, Switzerland, 1991, p 363–372

  30. 30.

    J. Dubsky, B. Kolman, and P. Chráska, Stability of Alpha Phase in Alumina-Chromia Plasma Sprayed Deposits After Annealing, 1994 Ther-mal Spray Industrial Applications, C.C. Berndt and S. Sampath, Ed., ASM International, 1994, p 779–782

  31. 31.

    R. McPherson, Formation of Metastable Monoclinic Rare Earth Sesquioxides from the Melt, J. Mater. Sci., Vol 18 (No. 5), 1983, p 1341- 1345

    Article  CAS  Google Scholar 

  32. 32.

    V. Gourlaouen, G. Schnedecker, A. Grimaud, P. Fauchais, A.M. Lejus, and R. Collengues, Metastable Phase in Yttrium Oxide Plasma Spray Deposits and Their Effect on Coating Properties, 1994 Thermal Spray Industrial Applications, C.C. Berndt and S. Sampath, Ed., ASM International, 1994, p 615–619

  33. 33.

    J. Ilavsky, K. Neufuss, and P. Chráska, Influence of Spraying Parameters on Properties of AI2O3 Deposits, Proc. of 5th Conference on Aluminum Oxide, Prague Institute of Chemical Technology, Prague, Czech Republic, 1990, p 65–70

    Google Scholar 

  34. 34.

    J. Dubsky, B. Kolman, and P. Chráska, Effect of Spraying Parameters on Phase Composition of Deposits Prepared by the WSP Process, 1995 Advances in Thermal Spray Science & Technology, C.C. Berndt and S. Sampath, Ed., ASM International, 1995, p 421–424

  35. 35.

    J. Dubsky, B. Kolman, and J. Forman, High-Temperature Stability of Plasma Sprayed AI2O3 Coatings, Proc. of 1st Czech National Thermal Conference, J. Musil, J. Kubícek, and S. Korcák, Ed., Technical University Brno, Czech Republic, 1994, p 150–153

    Google Scholar 

  36. 36.

    W.D. Kingery, Introduction to Ceramics, J. Wiley, 1960, p 566

  37. 37.

    S.J. Geller, Crystal Structure of β-Ga2O3, J. Chem. Phys., Vol 33, 1960, p 676–681

    Article  CAS  Google Scholar 

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Chráska, P., Dubsky, J., Neufuss, K. et al. Alumina-base plasma-sprayed materials part I: Phase stability of alumina and alumina-chromia. J Therm Spray Tech 6, 320–326 (1997).

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  • alumina
  • oxide ceramics
  • phase composition
  • temperature stability