502 A.J. Sanchez Herencia et aL. / Composites: Part B 37(2006)499-508 Two compositions were formulated containing 95 vol% of Table 3 -Al2 O3 and 5 vol% of Y-TZP (named A-5YTZP) and Starting solid loading of the slurries and green density of the tapes used to 60 vol% of a-Al2O3 and 40 vol% of Y-TZP(named bricate the final compacts A-40YTZP) For each composition, two slurries with different Sample Starting solid loading Green density (th. %) solid content loading(solid content of 47 and 50 vol%)were (vol%) A-5YTZP(1) As tape casting additive a water-based polymeric emulsion A-5YTZP(2) 6.2±0.1 (Mowilith DM 765 E Celanese, Spain ) with a T of-6C and A-40YTZP(I) 55.1±0.1 solid content 50 vol%, particle size 0.05-0.15 um was added in A-4OYTZP(2) 53.5±0.1 a concentration of 5 wt% referred to solids. Tapes were cast using a moving carrier with a blades gap of 500 um. Full details of slurry preparation and tape casting procedure ar and minimum values. For lower pressures(up to 20 MPa) given elsewhere [53, 56] five samples were analyzed, in this cases error bars After casting the green ceramic tapes were dried in air for corresponded to the standard deviations. Green densities of 4 h, to further drying at 60C for 48 h. The final thickness of obtained specimens were determined by the Archimedes the green tapes obtained varied between 480 and 520 um. method in mercury, using five dry pieces fabricated under to those of 2. 2. Lamination of tapes dry green tapes. Reported values are the average of the five values and errors are the standard deviations Relative green Round shaped tapes(diameters 0 26 mm and 0 60 mm) densities were calculated as percent of the calculated were used to avoid heterogeneous stress distribution within the theoretical density for each composition, using 3.99 g/cm ecimens during pressing [56]. Green densities of the single for a-Al2O3(ASTM 42-1468)and 6.10 g/em' for Y-TZP tapes were determined using the geometrical method Reported (ASTM 83-113) values are the average of those obtained for four discs of 26 mm diameter processed under nominally identical Laminated and monolithic compacts with seven layers were a)100 obtained by piling up tapes with a gluing agent between them and further pressing. Before lamination some of the tapes were subjected tower pretreatment that consists of dipping the ceramic tape in distilled water during 1 min. The gluing agent consisted in a 5 wt%o dilution of the binder used in the formulation of the starting slurries(Mowilith DM 765 E). Full details of the gluing agent selection can be found elsewhere 王王王 [56 Symmetrical laminated samples were stacked in a way to keep the A-5YTZP composition tapes as outer layers. Obtained green laminates were co unlax 00.050.100.150.200250.300 a universal testing machine(Microtest SA, Spain) with steel compression plates. In order to avoid friction with the plates, the stacked pieces were placed between two sheets (b)300 of polypropylene film. The pressure was applied using a load frame displacement rate of 0.05 mm/min. The load and the displacement of the load frame were recorded during the essing process and engineering stress-apparent strain curves were calculated assuming uniaxial compression sing the dimensions of the pieces. The safe pressure interval was determined by analyzing the curves correspond ing to nominally identical samples, adjusted to third degree represent the behavior of the samples under the pressure 50 samples a Corresponding to two individual(@ 26 mm) The curves 00.020.040060080.100.12 each composition and pre-treatment recorded for samples pressed up to the maximum stress Fig. 1. Characteristic behavior of dry and wet samples made of stacked A values(=90 MPa). The corresponding stress-strain behavior 5YTZP(1)tapes during pressing. (a) Average polynomial curves for each was represented by the average of the corresponding treatment(error bars represent the upper and lower curves).(b) Derivative of polynomial fits and error bars indicated the maximum the average polynomial curves at low pressures.Two compositions were formulated containing 95 vol% of a-Al2O3 and 5 vol% of Y-TZP (named A-5YTZP) and 60 vol% of a-Al2O3 and 40 vol% of Y-TZP (named A-40YTZP). For each composition, two slurries with different solid content loading (solid content of 47 and 50 vol%) were prepared. As tape casting additive a water-based polymeric emulsion (Mowilith DM 765 E Celanese, Spain), with a Tg of K6 8C and solid content 50 vol%, particle size 0.05–0.15 mm was added in a concentration of 5 wt% referred to solids. Tapes were cast using a moving carrier with a blades gap of 500 mm. Full details of slurry preparation and tape casting procedure are given elsewhere [53,56]. After casting the green ceramic tapes were dried in air for 24 h, to further drying at 60 8C for 48 h. The final thickness of the green tapes obtained varied between 480 and 520 mm. 2.2. Lamination of tapes Round shaped tapes (diameters : 26 mm and : 60 mm) were used to avoid heterogeneous stress distribution within the specimens during pressing [56]. Green densities of the single tapes were determined using the geometrical method. Reported values are the average of those obtained for four discs of 26 mm diameter processed under nominally identical conditions. Laminated and monolithic compacts with seven layers were obtained by piling up tapes with a gluing agent between them and further pressing. Before lamination some of the tapes were subjected to ‘wet’ pretreatment that consists of dipping the ceramic tape in distilled water during 1 min. The gluing agent consisted in a 5 wt% dilution of the binder used in the formulation of the starting slurries (Mowilith DM 765 E). Full details of the gluing agent selection can be found elsewhere [56]. Symmetrical laminated samples were stacked in a way to keep the A-5YTZP composition tapes as outer layers. Obtained green laminates were cold uniaxially pressed using a universal testing machine (Microtest SA, Spain) with steel compression plates. In order to avoid friction with the plates, the stacked pieces were placed between two sheets of polypropylene film. The pressure was applied using a load frame displacement rate of 0.05 mm/min. The load and the displacement of the load frame were recorded during the pressing process and engineering stress–apparent strain curves were calculated assuming uniaxial compression using the dimensions of the pieces. The safe pressure interval was determined by analyzing the curves correspond￾ing to nominally identical samples, adjusted to third degree polynomials, and the average of the curves was used to represent the behavior of the samples under the pressure. The curves corresponding to two individual (: 26 mm) samples of each composition and pre-treatment were recorded for samples pressed up to the maximum stress values (z90 MPa). The corresponding stress–strain behavior was represented by the average of the corresponding polynomial fits and error bars indicated the maximum and minimum values. For lower pressures (up to 20 MPa) five samples were analyzed, in this cases error bars corresponded to the standard deviations. Green densities of obtained specimens were determined by the Archimedes method in mercury, using five dry pieces fabricated under nominally identical conditions, and compared to those of the dry green tapes. Reported values are the average of the five values and errors are the standard deviations. Relative green densities were calculated as percent of the calculated theoretical density for each composition, using 3.99 g/cm3 for a-Al2O3 (ASTM 42-1468) and 6.10 g/cm3 for Y-TZP (ASTM 83-113). Table 3 Starting solid loading of the slurries and green density of the tapes used to fabricate the final compacts Sample Starting solid loading (vol%) Green density (th.%) A-5YTZP(1) 50 59.1G0.1 A-5YTZP(2) 47 56.2G0.1 A-40YTZP(1) 50 55.1G0.1 A-40YTZP(2) 47 53.5G0.1 Fig. 1. Characteristic behavior of dry and wet samples made of stacked A- 5YTZP(1) tapes during pressing. (a) Average polynomial curves for each treatment (error bars represent the upper and lower curves). (b) Derivative of the average polynomial curves at low pressures. 502 A.J. Sa´nchez-Herencia et al. / Composites: Part B 37 (2006) 499–508