March 2004 Tetragonal-to-Monoclinic Transformation in Mg-PSZ Studied by in Situ Neutron Diffraction shear transformation is strongly dependent on the degree of coherence References between the transforming region and its surrounding In Mg-PSZ, it has been postulated that a very strong coherent Advances in Ceramics, Vol. 3. Science and Technology of Zirconia boundary between the transforming t crystals and the surrounding nces in Ceramics, Vol. 12, Science and Techmology of Zirconia II c and 8 phases, and considerable dilatational thermal mismatch Claussen, M. Ruhle, and A. H. Heuer. American Ceramie Society, Columbus. stresses, are responsible for the I-o transformation replacing the Advances in Ceramics, Vol 24A and B, Science and Technology of r-m transformation at low temperature. 4>However, external Edited by S. Somiya, N, Yamamoto, and H. Yanagida, American Ce loads generate shear stresses that are able to overcome the Westerville. OH. 1988 coherence and initiate the I- m transformation, The transforma- 4A. G. Evans and A: H. Heuer, "Transformation Toughening in Ceramics Martensitic Transformations in Cracks Tip Stress Fields. "J. Am. Ceram. Soe, ion is restricted in extent by the microstructural complexity in 15-61 241-48(1981) Mg-PSZ. The t phase is present as extremely small crystallites and R. M. MeMccking and A G. Evans."Mechanics of Transformation-Toughening the transformation is necessarily impeded or arrested at the in Brittle Materials. "J, Am. Ceram Soc. 65 151 242(1982 interphase boundary. This is not the case in Ce-TZP, where large R. H J. Hannink, and R. C, Garvie. ""Sub- Eutectoid Aged Mg-PSZ Alloy with Enhanced Thermal Up-Shock Resistance. "J, Mater. Sci. 17, 2637-43(1982) crystals of the t phase form the entire microstructure. It is well Microstructure Evolution and Ordering in documented that the t- m transformation in that material occurs Commercial Mg-PSZ.J. Mater. Sel, 19. 2934-42(1984 in large bursts that are auto-catalytic Unlike Mg-PSZ, there is little crystallographically oriented 290AMuM数14 ment of Sub- Eutectoid Aged Mgo. R. H. J. Hannink. C. J. Howard, E. H. Kisi, and M. V. Swain, "Relationship residual stress in the microstructure of Ce-TZP, as it is comprised ween Fracture Toughness and Phase Assemblage in Mg-PSZ" J, Am. Ceram Soc. from a single phase and therefore the t-o transformation is not seen on cooling or under load. Some ferroelasticity was ob- R. Stevens, Zirconia and Zirconia Ceranics. Magnesium Elektron Ltd, Twick served; however, this was strongly associated with the 1-m enham U. K D J. Green, R. H J. Hannink, and M. V, Swain, Transformation Toughening e transformation (i.e. the same critical stress and reversion under the Ceramics, CRC Press, Boca Raton, Florida, 1989 same conditions ). The microstructure of Ce-TZP does not rou R. H. J. Hannink and M. V. Swain, "Progress in Transformation Toughening of tinely contain many twin domains and so ferroelasticity is not ct,24.359-408(1994 accessible as a major deformation mechanism 3Y-TZP has the R. H J. Hannink, P. M. Kelly, and B C. Muddle, "Transformation Toughening in Zirconia-Containing Ceramics. "J. Am. Cera, Soc, 83 [31 461-87(2000 highest critical stress and does not transform on cooling. It must IR. C. Garvie. R. H. J Hannink, and R. T. Pascoe, " Ceramic Steel?"Natur therefore be concluded that the t phase that makes up 80-95 wt% London.258.703-704(1975 of the microstructure is highly stabilized. The presence of 5-20 M. Ruhle and A H. Heuer, "Phase Transformation in ZrO, Containing Cera wt% of c phase" reinforces this notion. However, the micro- Science and Technology of Zirconia /I, Edited by N. Claussen, M. Ruhle, and A. H structure does routinely contain a high density of twin do- Heuer, Amencan Ceramic Society, Columbus, OH, 1985 mans6、474t and ferroelastic reorientation can occur at lower D. Michel, L. Mazerolles, and M. Perez Qqy Jorba, "Polydomain stresses than the t-m transformation under uniaxial compressio It must be remembered that the in situ neutron diffraction lL. Edited by N. Claussen. M. R(hle, and A H. Heuer. American Ceran xperiments were conducted under compressive loads. The critical Columbi resses observed for Mg-PSZ are much higher than previously M. V Swain and R H J. Hannink."R-Curve Behaviour in Zirconia Ceramics" observed in tensile room temperature creep samples, presumabl 224-239 in Advances in Ceramics, Vol 12. Science and Technology of irconia because of interaction of the volume expansion associated with the Edited by N. Claussen, M. Ruhle, and A H. Heuer. American Ceramic Society Columbus, OH, 198 I- m transformation and the constraint exercised on the sample P E Reyes-Morel and 1-w. Chen, "Transformation Plasticity of CeO, Stabilized by the compression platens. Although it is felt that the general Tetragonal Zirconia Polycrystals, 1: Stress Assistance and Autocatalysis, "/.Am. differences between the ceramics would also be present under tensile loading, the details may differ. P. E. Reyes. Morel. J-S. Cherng, and 1-w. Chen, "Transformation Plasticity of cOr Stabilized Tetragonal Zirconia Polycrystals, Il: Pseudoelaticity and Sha Memory Effect, "J. Am. Ceram. Soc. 71 18] 648-57(1988) T.R. Finlayson, K. A Gross, J. R, Griffiths, and E. H, Kisi. "Creep of Mg-PSZ C.J. Howard and R J Hill. "The Polymorphs of Zirconia: Phase Abundance and rom the experimental results and the analysis, the following / Mater. Sci. 26, 127-34(1991) (1) Stress-induced tetragonal-to-monoclinic transformation is "C, J. Howard, R, J, Hill, and B. E Reichert. "Structures of the Zro Polymorphs at Room Temperature by High-Resolution Neutron Powder Diffraction. "Acta Cryst the toughening mechanism in 9.4Mg-PSZ, even when the defor- B44.116-20(1988 mation is conducted in uniaxial compression. This behavior is C.J. Howard and E H. Kisi. "POlymorph Method: Determination of Monoclinic similar to that for Ce-TZP but unlike that for Y-TZP where no Zirconia in Partially Stabilized Zirconia Ceramics. "J, Am. Ceram. Soc., 73 [101 transformation was observed 3096-99(1990 E H Kisi and C. Howard. "Neutron Diffraction Studies of Zirconia- (2) Most of the stress-induced monoclinic phase in 9. 4M Toughened Eng PSZ was produced during creep at constant stress and not during E. H. Kisi. C. J. Howard, and R. J. Hill. Crystal Structure of Orthorhombic the initial stress change, as was the case in 12Ce-TZP. Thi difference is considered to be from the microstructure of Mg-PSZ rhombic Zirconias. "J. An. Ceram. Soc. 74 [91 2321-23(1991) separated from each other and can communicate only via trans. Din D. N Argyriou. C: J. Howard, and R, I. Smith,"Al-Temperature Neutron where small precipitates of the tetragonal phase are physically formation stress fields transmitted by the c +8 matrix Zirconia. J. A, Ceram. Soc. 77 [121 3073-76(1994) (3) The stress-induced monoclinic phase exhibited strong E H. Kisi, T.R. Finlayson and J. R, Griffiths, "Phase Determination in Partially Stabilised Zirconia Creep Specimens, "Muter. Set Foram, 56-58. 351-56(1990 transformation-induced texture during loading and appeared to T. R. Finlayson, J. R. Griffiths, A. K. Gross, and E. Tsesmelis reorient partially during the initial unloading steps Partially- Stabilized Zirconia", Pp. 99-104 in The Material Wealth of the Nation Proceedings of the Bicentennial Conference of the Institute of Metals and Materials 山 ing the transformation. This provides the driving force for tl The reversion is considerably slower than that in Ce-TZP, presum of Ferroelastic Domain Switching and Tetragonal-to-Monoclinie Transformation in ably for the reasons outlined in No. 2 above Ce-TZP.J Am, Ceram. So, 80 31 621-28(1997). JE H. Kisi. Y. Ma, and S. J. Kennedy. "In-situ Neutron Diffraction Study of Ceramics under Load": pp. 693-9% in Materials gs, Proceedings of the Biennial Materials Conference of The Institute of Materials Engineering, Australia(Wollen nt gong, July 1998). Edited by Michael Ferry, University of Wollongong, Wollongong. Australia, 1998 The authors wish to thank Professor P. M. Kelly for helpful discussion during th Y Ma, E H Kisi, and S, J. Kennedy, "Neutron Diffraction Study of Ferroelas. ticity in a 3 mol% Y,OrZO."JAm. Cera. Soe. 84[ 399-405(2001)