October 1996 ELSEVIER Materials Letters 28(1996)401-407 HREM study of the tetragonal/ monoclinic interfacial fine structure in Zro associated with the martensitic transformation Fangfang Xu Shulin Wen China Received 22 January 1996: 19 March 1996: accepted 25 March 1996 Abstract lycrystals (3Y-TZP)were chosen for the study of the interfacial fine structures resulting from ic transformation of Zro2. HREM observations revealed for the first time that there exists a transition area in-between the transformed martensitic phase(m-ZrO2 )and the parent tetragonal phase(t-zrO2).The dynamic process of this transformation induced by electron beams of variable intensity and its progression suggests that there may exist two different mechanisms with regard to nucleation and grain growth. The former is governed by the thermal stress produced by electron irradiation, whereas the latter is controlled by electron irradiation. Finally, a comparison of the nature of the twins formed during various transformation conditions was made Keywords: Tetragonal Zrc?: Monoclinic Zro,: Martensitic transformation: Interfacial fine structure; Electron irradiation; HREM: I wins 1. Introduction Using the metallurgical theory of martensitic transformations and applying it to the martensitic Apart from the stress generated during rapid transformation occurring in ceramic materials has quenching, extraneous stress generated during the given many important results. The phenomenological fracture of the material will induce the martensitic theory of martensitic transformation permits the de- transformation of t-Zr0,, and absorbing more fra termination of the habit plane of the transformed ture energy resulting in toughening the material. This region, its orientation relationship to the parent crys- is of great significance in enhancing the mechanical tal and the magnitude and direction of the shape properties through the martensitic transformation. strain. The only required input data are the lattice This consideration attracted our attention to reveal parameters of the two phases, the correspondence the details of the microstructural change and crystal- between them and the plane and direction of the lographic relationships accompanying the transfor- invariant lattice shear [1-5]. The theory also gives mation by use of high resolution electron microscopy three possible, simple correspondences depending on (hREM) which monoclinic axis is derived from the unique c axis of the tetragonal parent phase [6]. The tetragonal c axis can become the a, b or c axis of the mono- Corresponding author clinic phase. Hence the three correspondences-A 00167-577X/96/S12.00 Copyright o 1996 Elsevier Science B V. All rights reserved PHs0167577X(96)00093-6& *H __ __ !!!B ELSEVIER October 1996 Materials Letters 28 (1996) 401-407 HREM study of the tetragonal/monoclinic interfacial fine structure in ZrO, associated with the martensitic transformation Fangfang Xu * , Shulin Wen Shanghai Institute of Ceramics, Chinese Academy of Science, 200050 Shanghai, China Received 22 January 1996; revised 19 March 1996; accepted 25 March 1996 Abstract Y,O,, 3 vol%, stabilized tetragonal zirconia polycrystals (3Y-TZP) were chosen for the study of the interfacial fine structures resulting from the martensitic transformation of ZrO,. HREM observations revealed for the first time that there exists a transition area in-between the transformed martensitic phase (m-ZrO,) and the parent tetragonal phase (t-Z@). The dynamic process of this transformation induced by electron beams of variable intensity and its progression suggests that there may exist two different mechanisms with regard to nucleation and grain growth. The former is governed by the thermal stress produced by electron irradiation, whereas the latter is controlled by electron irradiation. Finally, a comparison of the nature of the twins formed during various transformation conditions was made. Keywords: Tetragonal ZrC,; Monoclinic ZrO,; Martensitic transformation; Interfacial fine structure; Electron irradiation; HREM; Twins 1. Introduction Apart from the stress generated during rapid quenching, extraneous stress generated during the fracture of the material will induce the martensitic transformation of t-ZrO,, and absorbing more frac￾ture energy resulting in toughening the material. This is of great significance in enhancing the mechanical properties through the martensitic transformation. This consideration attracted our attention to reveal the details of the microstructural change and crystal￾lographic relationships accompanying the transfor￾mation by use of high resolution electron microscopy (HREM). _ Corresponding author. Using the metallurgical theory of martensitic transformations and applying it to the martensitic transformation occurring in ceramic materials has given many important results. The phenomenological theory of martensitic transformation permits the de￾termination of the habit plane of the transformed region, its orientation relationship to the parent crys￾tal and the magnitude and direction of the shape strain. The only required input data are the lattice parameters of the two phases, the correspondence between them and the plane and direction of the invariant lattice shear [l-51. The theory also gives three possible, simple correspondences depending on which monoclinic axis is derived from the unique c axis of the tetragonal parent phase [6]. The tetragonal c axis can become the a, b or c axis of the mono￾clinic phase. Hence the three correspondences - A, 00167-577X/96/$12.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PII SOl67-577X(96)00093-6