F. Xu, S. Wen/ Materials Letters 28(1996)401-407 B or C. Theoretically, correspondence A is the least specimen was perforated. Then the ultra-thin plate likely, as the match between the lattice parameters is was sputtered with amorphous carbon to the thick the worst and the sum of the transformation strains is ness of about several decades of nanometers the highest. Experimental observations support the The XRD analysis was performed on a D/max-ra existence of correspondences B and C. They are with a copper target and an operating voltage of 40 The HREM examination was performed on a [010lao01l o10la101 JEM-200CX with an operating voltage of 200 kV 0019°to[100]1 0019to[0011 using a top entry double-tilt specimen holder ie.(001)K100) ie.(001)元nK001) An MS (microscanning spectrophotometer, Carl Zeiss K-100)was employed so as to precisely mea [O]n9°to[ool [0Ol9°to[001 sure the interplanar distances on the lattice micro (100)K(10 e.(100)mK100 [01O]—o011 010] 0011-|100 o0l|01 3. Results and discussion Since the phenomenological theory can only de- The addition of 3 vol%Y,0, can make the scribe the correspondence in position between atoms t-ZrO2 stable at room temperature when cooled from in the two structures, it tells nothing about the actual the hot-pressed environment. On the other hand paths chosen by the atoms during the transformation. preparation of the ultra-thin discs for the TEM obser- In our study, HREM was applied to determine such vations, including cutting, polishing and ion-thin paths. We followed the dynamics of the transforma- ning, may have induced the partial martensitic trans tion, obtained micrographs of the interfaces of the formation in the sample. XRD indicated that about transforming bands and revealed the fine structure on 20% of the tetragonal phase had transformed the atomic level of the interphases Fig. la shows the typical morphology of the These d there were hardly any glassy phases in the grain boundaries. During long time(about 45 min)irradia 2. Experimental tion with high intensity electron beams, thermal stress was produced and induced the transformation of the The materials used in this study were 3Y-TZP partially stabilized t-ZrO2. Fig. Ia-lc give the se- ceramics prepared by a wet chemical method. The quence of the dynamic process of transformation, raw materials were chemically pure YCl, and and these pictures were taken under weak electron ZrOCl,. The resulting powder material was hot beams. Though the grains and interfaces were homo- pressed at a pressure of 25 MPa and temperature of geneously irradiated by the electron beams, nucle 1650°C ation of the monoclinic phase took place exclusively The sintered material was then cut into bars with at the grain interfaces(indicated by an arrow in Fig dimensions of 5. x 2.5 X 35 mm. and then me- la) indicating that the thermal stress produced chanically polished. These bars were then examined through irradiation of electron beams was the main y XRD impetus for the nucleation of the transformation as Specimens for HREM studies were prepared by the interfaces were the sites of the stress concentra cutting thin disc sections from the hot-pressed bars. tion. As ZrO, is electrically insulating, we suggest The thin sections were mechanically polished to a that there are two interaction mechanisms with re thickness of less than 30 um. The diameter of the gard to the impact of the electrons on the sample discs was 2.3 mm. Finally, the discs were ion milled First, as the electrons impact the sample, they cannot using a Gatan-600 ion beam thinner at a voltage of 4 diffuse out of the material, their kinetic energy is kv and an incidence beam angle of 15 until the transferred to the sample and a thermal effect was402 F. Xu, S. Wen /Materials Letters 28 (19961401-407 B or C. Theoretically, correspondence A is the least likely, as the match between the lattice parameters is the worst and the sum of the transformation strains is the highest. Experimental observations support the existence of correspondences B and C. They are B-l C-l ~1001,1l[0101, ~0101,11[0011, [001],9” to [loo], i.e. (001),11(100), B-2 [ 100],9” to [OlO], i.e. (100),11(010), ~0101,11DN, [0011,11mN, ml,ll[1ool, bm,ll[w, [001],9” to [OOl], i.e. (001),11(001), c-2 [100],9” to [loo], i.e. (lOO),II(lOO), D101,11[0101, Kw,11m1, Since the phenomenological theory can only de￾scribe the correspondence in position between atoms in the two structures, it tells nothing about the actual paths chosen by the atoms during the transformation. In our study, HREM was applied to determine such paths. We followed the dynamics of the transforma￾tion, obtained micrographs of the interfaces of the transforming bands and revealed the fine structure on the atomic level of the interphases. 2. Experimental The materials used in this study were 3Y-TZP ceramics prepared by a wet chemical method. The raw materials were chemically pure YCl, and ZrOCl 2. The resulting powder material was hot pressed at a pressure of 25 MPa and temperature of 1650°C. The sintered material was then cut into bars with dimensions of 5.0 X 2.5 X 35 mm3, and then me￾chanically polished. These bars were then examined by XRD. Specimens for HREM studies were prepared by cutting thin disc sections from the hot-pressed bars. The thin sections were mechanically polished to a thickness of less than 30 pm. The diameter of the discs was 2.3 mm. Finally, the discs were ion milled using a Gatan-600 ion beam thinner at a voltage of 4 kV and an incidence beam angle of 15” until the specimen was perforated. Then the ultra-thin plate was sputtered with amorphous carbon to the thick￾ness of about several decades of nanometers. The XRD analysis was performed on a D/max-ra with a copper target and an operating voltage of 40 kV. The HREM examination was performed on a JEM-200CX with an operating voltage of 200 kV using a top entry double-tilt specimen holder. An MS (microscanning spectrophotometer, Carl Zeiss K-100) was employed so as to precisely mea￾sure the interplanar distances on the lattice micro￾graphs. 3. Results and discussion The addition of 3 ~01% Y203 can make the t-ZrO, stable at room temperature when cooled from the hot-pressed environment. On the other hand, preparation of the ultra-thin discs for the TEM obser￾vations, including cutting, polishing and ion-thin￾ning, may have induced the partial martensitic trans￾formation in the sample. XRD indicated that about 20% of the tetragonal phase had transformed. Fig. la shows the typical morphology of the sample. These tetragonal grains are linked closely and there were hardly any glassy phases in the grain boundaries. During long time (about 45 min) irradia￾tion with high intensity electron beams, thermal stress was produced and induced the transformation of the partially stabilized t-ZrO,. Fig. la- lc give the se￾quence of the dynamic process of transformation, and these pictures were taken under weak electron beams. Though the grains and interfaces were homo￾geneously irradiated by the electron beams, nucle￾ation of the monoclinic phase took place exclusively at the grain interfaces (indicated by an arrow in Fig. la) indicating that the thermal stress produced through irradiation of electron beams was the main impetus for the nucleation of the transformation as the interfaces were the sites of the stress concentra￾tion. As ZrO, is electrically insulating, we suggest that there are two interaction mechanisms with re￾gard to the impact of the electrons on the sample. First, as the electrons impact the sample, they cannot diffuse out of the material, their kinetic energy is transferred to the sample and a thermal effect was