5720 S. Deville et al. Acta Materialia 52(2004)5709-5721 size should be expected indeed, as it is not possible man- the first stage of the transformation. The transformed Ifacturing components with a grain size of a few relief allows interpreting the grain boundary path nanometers. However, it must be kept in mind this straightforwardly. The formation of microcracks, approach is reliable only if the shear and dilatational leading to grain pop-out, has been observed at the components are accommodated from the very beginning grain boundary, and is occurring more rapidly of the transformation. Hypotheses were proposed for between grains having a strong crystallographic the formation of the variants, although no direct obser disorientation vations were possible. If the variants are indeed nucleat-. The present experimental observations allow con ing within the volume at first, only the formation of the cluding to the absence of the existence of a critical four variants all at once, all of them reaching the sur- grain size for the transformation, as opposed to the face, would allow this very small critical size. This anal- spontaneous transformation during cooling, for ysis should however be fairly reliable for variants which the existence of a critical grain size below nucleating at the surface (external growth). For the case which the transformation is not occurring has been of low temperature aging, the transformation is there- previously demonstrated. Moreover, the aging behav fore very different of that occurring during the cooling or is essentially similar to that of Y-TZP, which was stage after sintering, where the tetragonal phase can not clearly established before transform spontaneously to its monoclinic structure and for which the existence of a critical size of grains for transformation have been predicted [7] and demon- strated [29] Acknowledgements The authors thank the clams fo 5. Conclusions e. financial ial support of the European Union under the GrOWTH2000 program, project BIOKER, refer anisms of tetragonal phase re opy, the growth mech- ence GRD2-2000-25039. Authors are grateful to H.El lting from the marten Attaoui for providing the samples of the study. sitic transformation of ceria stabilized zirconia (10 mol% CeO2) are investigated for the first time with a great precision and in a quantitative manner, transfor- References mation occurring during low temperature aging treat ments in water vapor. The observations are Wolten GM. J Am Ceram Soc 1963: 46: 418 rationalized by the recent analysis proposed for the crys- 2 Kelly PM, Rose LR. Prog Mater Sci 2002: 47: 463 tallographic ABCI correspondence choice 3 Kobayashi K, Kuwajima H, Masaki T Solid State Ionics 1981 The nucleation is controlled by the crystallographic [5] Winnubst AJA, Burggraaf AJ. Adv orientation of the grains. Grains having their cr axis Yamamoto N. Yanagida h. editors. ology of close the free surface normal are the first ones to irconia. vol. Ill. Columbus OH: The transform. Transformation is then propagating by nc.1988.p.39 activating different correspondences, less favorable [6 Watanabe M, lio S, Fukuura I. Adv Ceram. In: Cla Rahle aH. Heuer, editors. Science and technology of zirconia Il. in terms of transformation strains accommodation vol. 12. Columbus, OH: The American Ceramic Society Inc. Three different growth modes have been identified for 1984.D.415 the ABCI correspondence: the so-called isolated nee- [7 Lange FF. J Mater Sci 1982: 17: 225 dle growth and external growth, modes where the [8 Garvie RC, Swain MV. J Mater Sci 1985: 20: 1 19 transformation starts at surface. and the interna [9 Wechsler MS, Lieberman DS, Read TA. Trans AIME 1953:197:1503 growth, where the transformation is most probably [10 Bowles JS, MacKenzie JK. Acta Metall 1954: 2:129 nucleated in the volume and not at the surface. In [ll] Kajiwara S Trans Jpn Inst 1976; 17(7): 43 that case, an incubation period corresponding to the diffusion time of (OH) along the grain boundaries USA: Monterey Institute of Advanced Studies: 993.p. 66sA 12 Hugo GR, Muddle BC. ICOMAT 92 Monterey, should be expected. Three stages were identified 3] Wang YU, Jin YM, Khachaturyan AG. Acta Mater 2004:52:1039 for the variants growth kinetics, all of them being (14) Tsubakino H, Kuroda Y, Nibe M. Com Am Ceram Soc related to the degree of transformation strains 1999:82(10):2921 accommodation [15 Chen xY, Zheng XH, Fang HS, Shi Hz, Wang XF, Chen HM.J Grain boundaries presence and location have a great Mater Sci Lett 2002. 21- 41 influence on the transformation induced relief. The Deville S, Chevalier J. J Am Ceram Soc 2003: 86(12): 2225 penetration depth of the transformation is directly [17 Deville s, Guenin G, Chevalier J. Martensitic transformation in art I. Acta Mater [ related to the location of grain boundaries during [18 Lange FF, Dunlop GL, Davis BI. J Am Ceram Soc 1986: 69: 237size should be expected indeed, as it is not possible man￾ufacturing components with a grain size of a few nanometers. However, it must be kept in mind this approach is reliable only if the shear and dilatational components are accommodated from the very beginning of the transformation. Hypotheses were proposed for the formation of the variants, although no direct obser￾vations were possible. If the variants are indeed nucleat￾ing within the volume at first, only the formation of the four variants all at once, all of them reaching the sur￾face, would allow this very small critical size. This anal￾ysis should however be fairly reliable for variants nucleating at the surface (external growth). For the case of low temperature aging, the transformation is there￾fore very different of that occurring during the cooling stage after sintering, where the tetragonal phase can transform spontaneously to its monoclinic structure, and for which the existence of a critical size of grains for transformation have been predicted [7] and demon￾strated [29]. 5. Conclusions By using atomic force microscopy, the growth mech￾anisms of tetragonal phase resulting from the marten￾sitic transformation of ceria stabilized zirconia (10 mol% CeO2) are investigated for the first time with a great precision and in a quantitative manner, transfor￾mation occurring during low temperature aging treat￾ments in water vapor. The observations are rationalized by the recent analysis proposed for the crys￾tallographic ABC1 correspondence choice. The nucleation is controlled by the crystallographic orientation of the grains. Grains having their ct axis close the free surface normal are the first ones to transform. Transformation is then propagating by activating different correspondences, less favorable in terms of transformation strains accommodation. Three different growth modes have been identified for the ABC1 correspondence: the so-called isolated nee￾dle growth and external growth, modes where the transformation starts at surface, and the internal growth, where the transformation is most probably nucleated in the volume and not at the surface. In that case, an incubation period corresponding to the diffusion time of (OH)
along the grain boundaries should be expected. Three stages were identified for the variants growth kinetics, all of them being related to the degree of transformation strains accommodation. Grain boundaries presence and location have a great influence on the transformation induced relief. The penetration depth of the transformation is directly related to the location of grain boundaries during the first stage of the transformation. The transformed relief allows interpreting the grain boundary path straightforwardly. The formation of microcracks, leading to grain pop-out, has been observed at the grain boundary, and is occurring more rapidly between grains having a strong crystallographic disorientation. The present experimental observations allow con￾cluding to the absence of the existence of a critical grain size for the transformation, as opposed to the spontaneous transformation during cooling, for which the existence of a critical grain size below which the transformation is not occurring has been previously demonstrated. Moreover, the aging behav￾ior is essentially similar to that of Y–TZP, which was not clearly established before. Acknowledgements The authors thank the CLAMS for using the nano￾scope. Financial support of the European Union under the GROWTH2000 program, project BIOKER, refer￾ence GRD2-2000-25039. Authors are grateful to H. El Attaoui for providing the samples of the study. References [1] Wolten GM. J Am Ceram Soc 1963;46:418. [2] Kelly PM, Rose LR. Prog Mater Sci 2002;47:463. [3] Kobayashi K, Kuwajima H, Masaki T. Solid State Ionics 1981;3– 4:489. [4] Lawson S. J Eur Ceram Soc 1995;15:485. [5] Winnubst AJA, Burggraaf AJ. Adv Ceram 24. In: Somiya S, Yamamoto N, Yanagida H, editors. Science and technology of zirconia, vol. III. Columbus, OH: The American Ceramic Society, Inc.; 1988. p. 39. [6] Watanabe M, Iio S, Fukuura I. Adv Ceram. In: Claussen N, Ru¨hle AH, Heuer, editors. Science and technology of zirconia II, vol. 12. Columbus, OH: The American Ceramic Society Inc.; 1984. p. 415. [7] Lange FF. J Mater Sci 1982;17:225. [8] Garvie RC, Swain MV. J Mater Sci 1985;20:1193. [9] Wechsler MS, Lieberman DS, Read TA. Trans AIME 1953;197:1503. [10] Bowles JS, MacKenzie JK. Acta Metall 1954;2:129. [11] Kajiwara S. Trans Jpn Inst 1976;17(7):435. [12] Hugo GR, Muddle BC. ICOMAT 92. Monterey, CA, USA: Monterey Institute of Advanced Studies; 1993. p. 665. [13] Wang YU, Jin YM, Khachaturyan AG. Acta Mater 2004;52:1039. [14] Tsubakino H, Kuroda Y, Niibe M. Com Am Ceram Soc 1999;82(10):2921. [15] Chen XY, Zheng XH, Fang HS, Shi HZ, Wang XF, Chen HM. J Mater Sci Lett 2002;21:415. [16] Deville S, Chevalier J. J Am Ceram Soc 2003;86(12):2225. [17] Deville S, Gue´nin G, Chevalier J. Martensitic transformation in zirconia, part I. Acta Mater [submitted]. [18] Lange FF, Dunlop GL, Davis BI. J Am Ceram Soc 1986;69:237. 5720 S. Deville et al. / Acta Materialia 52 (2004) 5709–5721