MATERIALS 兴 HIENGE& ENGIEERING ELSEVIER Materials Science and Engineering A 438-440(2006)343-345 www.elsevier.com/locate/msea An alternative approach to the crystallography of martensitic transformation in Zro2 J F Nie. B C. Muddle Department of Materials Engineering, Monash University, Victoria 3800, Australia Received 20 June 2005; received in revised form 17 October 2005: accepted 20 December 2005 The crystallographic features of the tetragonal to monoclinic martensitic transformation in Zro2 have been analysed using the moire plane approach. It is found that the predicted orientation relationships and interface orientations of the transformations are in excellent agreement with those observed experimentally. The successful application of the approach indicates that such martensite interfaces are defined by edge-to-edge matching of lattice planes o 2006 Elsevier B v. All rights reserved Keywords: Crystallography: Lattice matching: Interface: Moire plane 1. Introduction of coupling crystallography and migration mechanisms more Zirconia(ZrO2) has a face-centred cubic structure(Fin3m) directly. It is the purpose of this paper to demonstrate appli- (P42/nmc)between 1200 and 2370.C and a primitive mono- [1,5 itic transformation in a Ceoz-stabilised ZrO2 at temperatures above 2370C, a primitive tetragonal structure martens clinic structure(P2,c)below 950C[1]. It is widely accepted that the structural change from tetragonal [2-7] to monoclinic in zirconia is displacive in nature, and under proper microstruc 2. Experimental observations tural design and control this transformation can be utilised to enhance the fracture toughness of zirconia and its alloys. In Fig. 1 shows a transmission electron microscopy image of the past 30 years, the crystallographic features of the tetrago- edge-on plates of the monoclinic phase and the corresponding nal => monoclinic transformation have been well documented selected area electron diffraction(SAED) pattern recorded from and it has been demonstrated [1-7)that such features can be these plates and the surrounding matrix of the tetragonal phase fully predicted by the phenomenological theory of martensitic [5. The image was obtained with the electron beam direction parallel to [00 1]. The orientation relationship implied by the A Moire plane approach, based on consideration of matching SAED pattern is such that(200)m//(200),[010Jm//[00 1] and of edges of lattice planes, has recently been developed [8, 9]to [00 1]m//[O 1 OJ. There are two variants in the image. For the account for the crystallography and migration mechanisms of plate labelled I in Fig. 1(a), the two broad surfaces of this plate planar interphase boundaries in phase transformations. with are parallel to each other and the angle between the broad surface input of lattice parameters and lattice plane correspondence, this and (200) is w16. While the orientation of the broad surface approach is capable of predicting the orientation relationship, does not appear to be parallel to any low-index planes of either and the orientation, structure and migration mechanisms of tragonal or monoclinic lattice, careful inspection of the image interphase boundaries. Compared to PTMC, this alternative and the corresponding SAED pattern suggests that the normal of approach is less complex mathematically and has the advantag the broad surface(habit plane)is parallel to the vector connectin (002)m and(020) reflections. If this observation is accepte as accurate and representative, then the habit plane of the plate Corresponding author. Tel: +61 399059605: fax: +6139905 4940 is parallel to the moire plane resulting from the intersection of E-mail address: nie@ spme. monash. edu. au (J.F. Nie) 002)m and(02 0) planes.Materials Science and Engineering A 438–440 (2006) 343–345 An alternative approach to the crystallography of martensitic transformation in ZrO2 J.F. Nie ∗, B.C. Muddle Department of Materials Engineering, Monash University, Victoria 3800, Australia Received 20 June 2005; received in revised form 17 October 2005; accepted 20 December 2005 Abstract The crystallographic features of the tetragonal to monoclinic martensitic transformation in ZrO2 have been analysed using the Moire plane ´ approach. It is found that the predicted orientation relationships and interface orientations of the transformations are in excellent agreement with those observed experimentally. The successful application of the approach indicates that such martensite interfaces are defined by edge-to-edge matching of lattice planes. © 2006 Elsevier B.V. All rights reserved. Keywords: Crystallography; Lattice matching; Interface; Moire plane ´ 1. Introduction Zirconia (ZrO2) has a face-centred cubic structure (Fm3¯m) at temperatures above 2370 ◦C, a primitive tetragonal structure (P42/nmc) between 1200 and 2370 ◦C and a primitive mono￾clinic structure (P21/c) below 950 ◦C [1]. It is widely accepted that the structural change from tetragonal [2–7] to monoclinic in zirconia is displacive in nature, and under proper microstruc￾tural design and control this transformation can be utilised to enhance the fracture toughness of zirconia and its alloys. In the past 30 years, the crystallographic features of the tetrago￾nal⇒monoclinic transformation have been well documented and it has been demonstrated [1–7] that such features can be fully predicted by the phenomenological theory of martensitic crystallography (PTMC). A Moire plane approach, based on consideration of matching ´ of edges of lattice planes, has recently been developed [8,9] to account for the crystallography and migration mechanisms of planar interphase boundaries in phase transformations. With an input of lattice parameters and lattice plane correspondence, this approach is capable of predicting the orientation relationship, and the orientation, structure and migration mechanisms of interphase boundaries. Compared to PTMC, this alternative approach is less complex mathematically and has the advantage ∗ Corresponding author. Tel.: +61 3 9905 9605; fax: +61 3 9905 4940. E-mail address: nie@spme.monash.edu.au (J.F. Nie). of coupling crystallography and migration mechanisms more directly. It is the purpose of this paper to demonstrate appli￾cation of this approach to the tetragonal⇒monoclinic martensitic transformation in a CeO2-stabilised ZrO2 [1,5,6]. 2. Experimental observations Fig. 1 shows a transmission electron microscopy image of edge-on plates of the monoclinic phase and the corresponding selected area electron diffraction (SAED) pattern recorded from these plates and the surrounding matrix of the tetragonal phase [5]. The image was obtained with the electron beam direction parallel to [0 0 1]t. The orientation relationship implied by the SAED pattern is such that (2 0 0)m//(2 0 0)t, [0 1 0] ¯ m//[0 0 1]t and [0 0 1]¯ m//[0 1 0] ¯ t. There are two variants in the image. For the plate labelled 1 in Fig. 1(a), the two broad surfaces of this plate are parallel to each other and the angle between the broad surface and (2 0 0)t is ∼16◦. While the orientation of the broad surface does not appear to be parallel to any low-index planes of either tetragonal or monoclinic lattice, careful inspection of the image and the corresponding SAED pattern suggests that the normal of the broad surface (habit plane) is parallel to the vector connecting (0 0 2)m and (0 2 0)t reflections. If this observation is accepted as accurate and representative, then the habit plane of the plate is parallel to the Moire plane resulting from the intersection of ´ (0 0 2)m and (0 2 0)t planes. 0921-5093/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2005.12.064