D-K. Kim, W.M. Kriven/Materials Science and Engineering 4 380 (2004)237-244 Table I Mixing formulations for the oxide powders Binder(Elvax) Plasticizer(P) Lubricant(SA) 21 10 220 50 vol% Al203 2.4 40.8 50 voL% YAG In situ composite AlPO 40 9.6 4.4 AlO3 platelets 9.6 4.4 Note: All ingredients are in vol%, elvax: ethylene vinylacetate copolymer(Dupont, 210, 220, and 250 are products names, indicating a molecular weight crease from 210, 220 to 250), DP: dibutyl phthalate(99%, Aldrich), SA: stearic acid (95%, Aldrich). three-dimensional orientations, and induced constrained sin- 210, 220 to 250. The reason for using the mixture was to tering of ceramic powders, finally functioning as a debond- facilitate the binder removal process over a broad temper- ing interphase in the composite structures [3 ature range. Dibutyl phthalate(Aldrich, 99%)and stearic In this research, the processing of an oxide matrix-oxide acid(Aldrich, 95%)were used as a plasticizer and lubricant, nterphase, 2-layer, fibrous monolithic composite was respectively studied. Mullite and a 50 vol. alumina: 50 vol. YAG Ceramic powder, binder, plasticizer, and lubricant were in situ composite were used as possible high tempera- mixed in a computer controlled, high shear mixer(Model ture, structural, matrix materials. Aluminum phosphate 2100, C. W. Brabender, N). The mixing formulation is (AlPO4) and alumina platelets were investigated as inter- shown in Table 1. To make the fibrous monolithic texture phase materials. A two-layer, mullite-AlPO4 and a 50 vol. without intermixing between inner mullite matrix and AlPO4 alumina: 50 vol. YAG in situ composite matrix-alumina platelet, fibrous monolithic material were fabricated by co-extrusion using ethylene vinylacetate(EVA) copolymer as a binder. The powders used for making composites were characterized. The microstructure and room temperature mechanical behavior of the two composites were investi- 2. Experimental procedure platelet powders of 5-10 um diameter by I um thick(Elf Atochem, France) were used. AlPO4 and 50 vol % alu mina: 50 vol. YAG in situ composite powders were syn hesized by the organic, steric entrapment method [32-371 (a) The particle size of the powder was measured in a centrifu- gal, automated, particle size distribution analyzer (Model CAPA-700, Horiba, Kyoto, Japan). The specific surface area of samples was measured from seven-point BET analyses using nitrogen gas adsorption(Model ASAP2400, Micro- metrics,Norcross, GA). The bulk density of sintered alu mina platelet pellets was measured by Archimedes method (ASTM C373). The morphology of powders and the mi- crostructure of composites were investigated by scanning electron microscopy (SEM, Model S-4700, Hitachi, Osaka, Japan). The composite pellets for SEM were polished down to a 1 um using diamond paste finish, and then thermally etched at 1550C for 30 min A mixture of Elvax 210, 220, and 250 ethylene vinyl ac etate copolymers(Dupont, Wilmington, DEL) was used as binder phases. The molecular weight increased from Elvax Fig. 1. The stainless steel mouldings(a)and extrusion(b)dies.238 D.-K. Kim, W.M. Kriven / Materials Science and Engineering A 380 (2004) 237–244 Table 1 Mixing formulations for the oxide powders Powder Binder (Elvax) Plasticizer (DP) Lubricant (SA) 210 220 250 Mullite 50 vol.% Al2O3 52 2.4 4.8 40.8 – – 50 vol.% YAG 52 2.4 4.8 40.8 – – In situ composite AlPO4 40 9.6 24 14.4 9 3 Al2O3 platelets 40 9.6 24 14.4 9 3 Note: All ingredients are in vol%, elvax: ethylene vinylacetate copolymer (Dupont, 210, 220, and 250 are products names, indicating a molecular weight increase from 210, 220 to 250); DP: dibutyl phthalate (99%, Aldrich), SA: stearic acid (95%, Aldrich). three-dimensional orientations, and induced constrained sin￾tering of ceramic powders, finally functioning as a debond￾ing interphase in the composite structures [31]. In this research, the processing of an oxide matrix–oxide interphase, 2-layer, fibrous monolithic composite was studied. Mullite and a 50 vol.% alumina:50 vol.% YAG in situ composite were used as possible high tempera￾ture, structural, matrix materials. Aluminum phosphate (AlPO4) and alumina platelets were investigated as inter￾phase materials. A two-layer, mullite-AlPO4 and a 50 vol.% alumina:50 vol.% YAG in situ composite matrix–alumina platelet, fibrous monolithic material were fabricated by co-extrusion using ethylene vinylacetate (EVA) copolymer as a binder. The powders used for making composites were characterized. The microstructure and room temperature mechanical behavior of the two composites were investi￾gated. 2. Experimental procedure Commercial mullite (Kyoritsu, KM 101) and alumina platelet powders of 5–10
m diameter by 1
m thick (Elf Atochem, France) were used. AlPO4 and 50 vol.% alu￾mina:50 vol.% YAG in situ composite powders were syn￾thesized by the organic, steric entrapment method [32–37]. The particle size of the powder was measured in a centrifu￾gal, automated, particle size distribution analyzer (Model CAPA-700, Horiba, Kyoto, Japan). The specific surface area of samples was measured from seven-point BET analyses using nitrogen gas adsorption (Model ASAP2400, Micro￾metrics, Norcross, GA). The bulk density of sintered alu￾mina platelet pellets was measured by Archimedes’ method (ASTM C373). The morphology of powders and the mi￾crostructure of composites were investigated by scanning electron microscopy (SEM, Model S-4700, Hitachi, Osaka, Japan). The composite pellets for SEM were polished down to a 1
m using diamond paste finish, and then thermally etched at 1550 ◦C for 30 min. A mixture of Elvax 210, 220, and 250 ethylene vinyl ac￾etate copolymers (Dupont, Wilmington, DEL) was used as binder phases. The molecular weight increased from Elvax 210, 220 to 250. The reason for using the mixture was to facilitate the binder removal process over a broad temper￾ature range. Dibutyl phthalate (Aldrich, 99%) and stearic acid (Aldrich, 95%) were used as a plasticizer and lubricant, respectively. Ceramic powder, binder, plasticizer, and lubricant were mixed in a computer controlled, high shear mixer (Model 2100, C. W. Brabender, NJ). The mixing formulation is shown in Table 1. To make the fibrous monolithic texture, without intermixing between inner mullite matrix and AlPO4 Fig. 1. The stainless steel mouldings (a) and extrusion (b) dies