PERGAMON Progress in Materials Science 47(2002)463-557 cience The martensitic transformation in ceramics its role in transformation toughening Patrick M. Kelly a, * L.R. Francis Rose Department of Mining, Minerals and Materials Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia b Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation Fisherman's Bend. victoria 3207. Australia Received I March 2000; accepted 3 July 2000 Abstract e This paper reviews the current knowledge and understanding of martensitic transforma- ons in ceramics-the tetragonal to monoclinic transformation in zirconia in particular. This martensitic transformation is the key to transformation toughening in zirconia ceramics. A ery considerable body of experimental data on the characteristics of this transformation is now available. In addition, theoretical predictions can be made using the phenomenological theory of martensitic transformations. As the paper will illustrate, the phenomenological theory is capable of explaining all the reported microstructural and crystallographic features f the transformation in zirconia and in some other ceramic systems. Hence the theory, sup ported by experiment, can be used with considerable confidence to provide the quantitative data that is essential for developing a credible, comprehensive understanding of the transfor- mation toughening process A critical feature in transformation toughening is the shape strain that accompanies the transformation. This shape strain, or nucleation strain, determines whether or not the stress- induced martensitic transformation can occur at the tip of a potentially dangerous crack. If transformation does take place, then it is the net transformation strain left behind in the transformed region that provides toughening by hindering crack growth. The fracture mechanics based models for transformation toughening, therefore, depend on having a full inderstanding of the characteristics of the martensitic transformation and, in particular, on being able to specify both these strains. A review of the development of the models for transfor mation toughening shows that their refinement and improvement over the last couple of decades has been largely a result of the inclusion of more of the characteristics of the stress-induced martensitic transformation. The paper advances an improved model for the stress-induced Corresponding author. Tel: +61-7-3365-3738: fax: +61-7-3365-3888. - mail address: p. kelly minmet uq. edu. au(P. M. Kelly) 0079-6425/02/S- see front matter C 2002 Elsevier Science Ltd. All rights reserved.
                               
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