Tape-cast alumina-zirconia laminates processing and mechanical properties FIRST SERIES PRESSED LAMINATED (21 LAY Load roller A210 A/A AZ5/AZ5 AZ10/AZ10AZ10/A25 Support rolle A25 +10 vol Zr02 SECOND SERIES 3A/A210A Fig. 2. Chevron-notched(CN)specimens used for the fracture 5A10 10A210 toughness and fracture energy determination 2A10 3AAz1o】A 3n5/3 2/2/2n02/2/2 span length and a cross-head speed of 0.1 mm Fig. I. Schematics of the two series of laminar composites min-l. The toughness was measured by four-point bending of4×3×50mm( height x width length)chevron-notched(CN) specimens( with a 60 V-notch angle, and a 0.15 mm samples, the pyrolysis was carried out with heat- width, inner and outer span of 20 and ing at rate of 1C min up to 120C, then with respectively, and cross-head speeds between 0-001 heating at rate of 0.lC min up to 550C with and 0.I mm min. The V-notch is cut perpendicu dwell time of 4 h. The samples were sintered in an lar to the laminae. However, two different orienta electric furnace with MoSi, heating elements, with tions of the V, relative to the orientation of the heating at rate of 5C min up to 1600C with laminae, were investigated to make the crack dwell time of 3 h propagate normal to the layers(N specimens)or transverse to them (T specimens). The mode I 2.6 Characterization fracture toughness Kic is then calculated from the Rheological measurements were performed using maximum load measured on the experimental a rotating cylinder viscometer(Rotovisco RV12, curves, using the polynomial equation of munz Haake)at a shear rate of 28s". The shear rate et al. 2 Chevron-notched specimens were used as evaluated according to the gap between because of their suitability for fracture toughnes he casting support and the moving blade, and to determination in brittle materials. Sharpness of the casting speed. the notch is not critical and in the absence of the The apparent densities of green samples, exclud- R-curve effect, Kc values are relatively indepen ing organic phases, were determined by measuring dent of the initial crack length and agree with the ht (mcal ) of samples values obtained from straight-through crack speci before and after calcination, respectively. The mens with notch thickness as low as 66 um(single apparent density is expressed by the Mcal/V ratio. edge notched beam specimens ). The elastic mod- Evaporation of solvent can causc visible crack- uli were measured by means of an ultrasonic tech ing of tapes. The tape shrinkage, and then the nique, using 10 MHz piezo-electric transducers in shrinkage rate, during drying were measured by a contact with specimens. Youngs modulus(E)and laboratory-made detector using a laser system.20 the shear modulus (G)are calculated from the ers in the green composite was detected using an shear(V) wave velocities according to 2O)and The presence of any delaminations between lay- measured values for the compressional (V)and ultrasonic method. 2 (3v2-4V3) The mechanical testing was conducted in bend E P and G=pV (1) ing on an INSTRon 8562 testing machine equipped with a differential measurement device, oy means of a Linear Variable Displacement where p is the specific mass, as measured by Transducer(LvdT)and mechanical contact with Archimedes mcthod using distilled watcr Poissons he specimen, to accurately measure the specimen ratio (v)is then given by deflection. Fracture tests were performed in three- point bending,on3×4×25mm( height width x length) rectangular bars with a 20 mmTape-cast alumina-zirconia laminates: processing und mechanical properties 301 FIRST SERIES PRESSED LAMINATED (21 LAYERS) A AZ10 AIA AiWAZ5 A21 OlAzlO AZ1 OIAZS A= Al203 A25= Al203+ 5VOl% 2fO2 AZ1 0 = A1203 + 10 VOl% LfD2 SECOND SERIES 3lAIAZl OIIA 2A 3(A/AZlOl/A 2A 7/5/7 3n 513 2/2/211012/212 Fig. 1. Schematics of the two series of laminar composites tested. samples, the pyrolysis was carried out with heat￾ing at rate of 1°C min’ up to 120°C then with heating at rate of O.l”C min’ up to 550°C with a dwell time of 4 h. The samples were sintered in an electric furnace with MoSi, heating elements, with heating at rate of 5°C min’ up to 1600°C with a dwell time of 3 h. 2.6 Characterization Rheological measurements were performed using a rotating cylinder viscometer (Rotovisco RV12, Haake) at a shear rate of 28 s&. The shear rate was evaluated according to the gap between the casting support and the moving blade, and to the casting speed. The apparent densities of green samples, exclud￾ing organic phases, were determined by measuring the volume (V) and weight (Mea,,) of samples before and after calcination, respectively. The apparent density is expressed by the M,,,,/V ratio. Evaporation of solvent can cause visible crack￾ing of tapes. The tape shrinkage, and then the shrinkage rate, during drying were measured by a laboratory-made detector using a laser system.20 The presence of any delaminations between lay￾ers in the green composite was detected using an ultrasonic method.2 The mechanical testing was conducted in bend￾ing on an INSTRON 8562 testing machine equipped with a differential measurement device, by means of a Linear Variable Displacement Transducer (LVDT) and mechanical contact with the specimen, to accurately measure the specimen deflection. Fracture tests were performed in three￾point bending, on 3 X 4 X 25 mm (height X width X length) rectangular bars with a 20 mm / Load roller Fig. 2. Chevron-notched (CN) specimens used for the fracture toughness and fracture energy determinations. span length and a cross-head speed of 0.1 mm min-‘. The toughness was measured by four-point bending of 4 X 3 X 50 mm (height X width X length) chevron-notched (CN) specimens (Fig. 2), with a 60” V-notch angle, and a 0.15 mm notch width, inner and outer span of 20 and 40 mm respectively, and cross-head speeds between 0.00 1 and 0.1 mm min’. The V-notch is cut perpendicu￾lar to the laminae. However, two different orienta￾tions of the V, relative to the orientation of the laminae, were investigated to make the crack propagate normal to the layers (N specimens) or transverse to them (T specimens). The mode I fracture toughness K,, is then calculated from the maximum load measured on the experimental curves, using the polynomial equation of Munz et ~1.~’ Chevron-notched specimens were used because of their suitability for fracture toughness determination in brittle materials. Sharpness of the notch is not critical and in the absence of the R-curve effect, K,, values are relatively indepen￾dent of the initial crack length and agree with the values obtained from straight-through crack speci￾mens with notch thickness as low as 66 pm (single edge notched beam specimens).2’ The elastic mod￾uli were measured by means of an ultrasonic tech￾nique, using 10 MHz piezo-electric transducers in contact with specimens. Young’s modulus (E) and the shear modulus (G) are calculated from the measured values for the compressional (V,) and shear (V,) wave velocities according to:22 and G = pV,’ (1) where p is the specific mass, as measured by Archimedes method using distilled water. Poisson’s ratio (v) is then given by:23 E v=__l 2G