Am Cera Sn.86|121225-272003 journa Martensitic Relief Observation by Atomic Force microscopy in Yttria-Stabilized Zirconia Sylvain Deville and Jerome Chevalier National Institute of Applied Science, Materials Science Department(INSA-GEMPPM) Associate Research Unit CNRS 5510, 69621 Villeurbanne. france The tetragonal to monoclinic(I-m) phase transformation of I. Experimental Procedure zirconia has been the object of extensive investigations of the past 20 years and is now recognized as being of martensitic Samples were processed using yttria-stabilized zirconia powder nature. However, martensitic transformation has only been (3Y-TZP, Tosoh TZ-3YS. Tosoh Corp, Tokyo, Japan).Green observed by transmission electron microscopy or indirect bodies. after uniaxial cold pressing at 10 bar. were isostatically methods, Though the benefit on the fracture toughness and cold pressed at 1300 bar and finally sintered at 1773 K for 5 h in crack resistance was the main interest, the transformation is air. The obtained plates were machined to small bars. The side of now considered for its consequences on the degradation of the each bar on which analysis was to be performed was mimor material. The use of atomic force microscopy reported lier polished with diamond slurries and pastes, reaching surface allowed the observation of the first stages of martensite r roughness (Ra) values as low as 2 nm. Samples were thermally growth and of new martensitic features. etched for 18 min at 1673 K, i.e., 100 K below the sintering temperature to form slight thermal graves of grain boundaries without affecting the physical properties. The agi Ing treatments L. Introduction were conducted in an autoclave (Fisher Bioblocl France)at 383 K, ensuring a 100%o water vapor atmosphere. The tetragonal to monoclinic (I-m) phase transformation of surface was observed zirconia has been probably the most studied phase transfor- surface was observed using AFM(D3100, Digital Instruments)in contact mode with a scanning speed of 10 ums mation among ceramics, since the transformation toughening There is now regained interest from a biomedical point of view since degradation and rupture of hip joint prostheses related to the IlL. Results and Discussion transformation have been reported recently. Phase transformation A transformed zone is shown in Fig. 1. The aFm deflection occurring with time at the surface of zirconia implants is now referred to as aging. Zirconia is indeed retained in its tetragonal image provides a very clear image of the surface, showing typical metastable structure at ambient temperature after processing, and martensitic self-accommodating variants within almost each grair of the zone. after I h of aging treatment. Most of the theories phase transformation to its stable monoclinic phase might occur developed so far predict the apparition of a regular pattern of derlying chemical mechanism is still a point of debate, the orientation of the gran ma n, related to the crystallographic transformation is now commonly recognized as being of marten- sitic nature. i.e., diffusionless and athermal, involving shape change dominated by shear and occurring at high speed. Indirect methods such as X-ray diffraction(XRD) or differential thermal analysis(DTA) provide information on the global behavior of the material, Further progress into understanding the nucleation and growth(NG) mechanism was accomplished by using optical interferometry, and martensitic relief observations were also reported with use of interferometry and Nomarski interference One atomic force microscopy(AFM)observation, performed at high scanning speed and in tapping mode, has confirmed the NG nature of the transformation. Transmission electron microscopy (TEM) on thin foils has confirmed". 5.I6 the presence of mono- clinic laths within the grains. The next step in the mechanistic understanding is the observation of the transformation initiation Thus, AFM observations brought new features to light, associated with the relief, that were not accessible by other conventional D. Marshall contributing editor inscript No, 10219 Received May 16, 2003: approved July 17, 2003 devilleeins, Fig. I. AFM deflection image. The observed relief is undoubtedly characteristic of a martensitic transformation