R.F. Cabral

Development and Characterization of the Al2O3-YAG Ceramic Composites

YAG (Y3Al5O12) and Al2O3 ceramics have high resistance to oxidation and corrosion in harsh environments and high temperatures, which turns into a quite attractive material as compared to other ceramics. Thus, lately oxide ceramic YAG has been extensively used as reinforcement phase to Al2O3 in order to obtain a composite with improved mechanical properties. This research focused on the development of sintered Al2O3-Y2O3 powder mixtures for the production of Al2O3-YAG composite. Powder mixtures composed of 63.65:36.35wt.% and 80.00:20.00wt.% of Al2O3 and Y2O3, respectively, were milled by planetary milling for 2h. The compositions were compacted by cold uniaxial pressing, at 70 MPa, for 30s. The two mixtures were sintered at 1500 and 1600°C for 3h. The samples were evaluated for relative density, shrinkage, weight loss, and X-Ray Diffraction (XRD). Scanning Electron Microscopy (SEM) was used for microstructural characterization. The X-Ray Diffraction showed the presence of Al2O3 and Y3Al5O12 as crystalline phases in both compositions. Samples composed by 80:20wt.% of Al2O3/Y2O3 powder sintered at 16000C-3h presented the higher relative density ranging around 86% of theoretical density.

Síntese e caracterização do compósito Al2O3 -YAG e do Al2O3-YAG e Al2O3 aditivados com Nb2O5

The Al2O3-YAG composite exhibits high corrosion and creep resistance in aggressive environments, which provides quite glimpse attractive applications such as jet engine vanes and as gas turbines. This composite also shows high hardness and wear resistance allowing its use in ballistic armor. In this study, precursor powders of Al2O3, Y2O3 and Nb2O5 were homogeneously mixed in a planetary ball mill for 4 h, dried in an oven at 120 oC for 48 h, sieved and deagglomerated. The Al2O3-YAG composite was produced from mixtures of Al2O3-Y2O3 at 1300 oC for 2 h. Samples of Al2O3-YAG, Al2O3-YAG with Nb2O5 and Al2O3 with Nb2O5 were produced. Each powder composition was uniaxially pressed at 70 MPa. Sintering was performed at 1400 and 1450 oC. The powders as received and as processed were characterized for specific surface area and particle size. The sintered materials were characterized by apparent density and porosity by the Archimedes method and evaluated for shrinkage and loss of mass. The obtained results showed that further adjustments are needed in the sintering conditions of Al2O3-YAG composition with Nb2O5 in order to improve the densification and shrinkage, which were low, 60% and 3%, respectively. The Al2O3 with Nb2O5 addition, on the other hand, presented a satisfactory densification of 96% and shrinkage around 15%.

Processamento e caracterização morfológica do compósito Al2O3-YAG aditivado com nióbia

The Al2O3-YAG composite has high mechanical strength at high temperatures which allows its use in air craft applications, since it increases the thermal efficiency of jet engines and helps the development of high performance gas turbines. This composite also exhibits some favorable properties toward military applications such as armor, due to its high hardness. In this study, Al2O3-YAG and Al2O3-YAG with 4wt.% Nb2O5 (niobia) samples were produced. The precursors powders were ground in a planetary ball mill for 4 h, dried in an oven at 120 oC during 48 h, deagglomerated and sieved. The powder mixtures were then uniaxially pressed at 70 MPa. Sintering was carried out at 1450 oC for 2, 3, and 4 h, with heating and cooling rates of 10 oC/min. The materials were characterized by scanning electron microscopy (SEM) in order to characterize the microstructure. X-ray diffraction with Rietveld refinement was performed to determine and quantify the structural phases, whereas density was measured by the Archimede´s method. The samples with niobia addition revealed approximately 5wt.% of yttrium niobate (YNbO4) phase. It is worth pointing out that there is no citation in the literature involving niobia addition to the Al2O3-YAG composite. On the other hand, the obtained results indicated that additional experiments regarding the sintering conditions are necessary to optimize density.

Evaluation of Hardness and the Fracture Toughness of Composite Biphasic Alumina-YAG

Currently the composite two-phase Al2O3-YAG laser has been widely exploited by having good properties such as high abrasion resistance and deformation in harsh environments. Thus, one can predict that this material has very attractive applications such as fins of jet engines and gas turbines. In this study, five mixtures were processed Y2O3-Al2O3-Nb2O5, in proportions of 0, 1, 5, 15 and 35 wt% Y2O3 and 4% by weight of Nb2O5. These samples were sintered at 1550 to 1650 °C in air where it was detected by X-Ray Diffraction (XRD) with Rietveld refinement training YAG and also two intermediate stages, and AlNbO4 YNbO4. Finally they were characterized by hardness by Vickers microindentation and fracture toughness. The highest hardness and fracture toughness were 15 GPa and 5.5 MPa.m1/2, respectively.

Al2O3-YAG Biphasic Composite Phase Determination Using Rietveld Method Measurements

TheAl2O3-YAG biphasic composite has been extensively studied since this system has important properties such as high resistance to corrosion and creep in harsh environments. This material system is potentially very attractive for high temperatures applications. In this work, the precursor powders of Al2O3 and Y2O3, were homogenized in planetary ball mill for 2h, dried in oven at 120oC for 48h, sieved and deagglomerated. It was performed a series of heat treatments over the powder for verification of the YAG phase formation, using1100, 1200, 1300°C and 1400 °C for 3.0 h time. The powders of the starting mixture after grinding and calcinations were characterized for phase quantification using the Rietveld method. The complete formation of the YAG phase in the composite was determined at1300°C after 3h.

Niobophosphate Glass as Sintering Additive for Al2O3-YAG

In this study, the following compositions were produced: Al2O3-YAG laser with 2, 4, 6 and 15% by weight of niobophosphate glass (30mol%P2O5-30mol%Nb2O5-20mol%CaO-20mol%CaF2). Sintered discs were characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD) with the refinement by the Rietveld method and density. The YAG-Al2O3 composite sintered at 1450 °C showed densification of 90%, which indicates the effectiveness of the sintering additive.

Mechanical Properties Evaluation of Al2O3-YAG Ceramic Composites

Y3Al5O12 (YAG - Yttrium Aluminum Garnet) ceramic oxides has been widely used as a reinforcing phase to Al2O3 in order to achieve a composite with good mechanical properties. These factors are possible because the Al2O3 and YAG oxides possess thermal compatibility and high resistance to oxidation and corrosion, which makes your job quite attractive relative to other ceramics. This research was performed in two compositions, one in the eutectic composition with 63.65% Al2O3 and Y2O3 36.35wt.% and one with 80.00% of Al2O3 and 20.00wt.% of Y2O3. After milling for 2h, the powder mixtures were dried for 48h at 120°C. Mixtures were then comminuted by mortar and pestle and sieved using a 100 mesh sieve. The compositions were compacted uniaxially at 70MPa for 30s. The two mixtures were sintered at 1500°C or 1600°C for 3h. The samples were evaluated for hardness by Vickers indentation, fracture toughness by the indentation method (KIC) and Scanning Electron Microscopy (SEM). It was verified that the eutectic composition sintered at 1600°C-3h showed the highest hardness among the others, 10GPa, and a fracture toughness of 3.8MPa.m1/2, both consistent with the literature results. The SEM images showed a reduction in porosity with increasing of sintering temperature.

Study of the Sintering of Mixtures Al2O3-Nb2O5 and Y2O3-Nb2O5

Al2O3-Nb2O5 has been widely explored as one of the most used material for sintering mixing in the literature, due to its excellent hardness properties, used in armor. In this study, Al2O3-Nb2O5 and Y2O3-Nb2O5 powders were prepared, with 50% in mole fraction of each oxide. The mixtures were subjected to high energy milling in an eccentric ball mill for 3 h, dried and sieved in a sieve vibrator. The green bodies were compacted at 70 MPa and sintered from 1250 to 1650 °C for 3 h, at 100 °C steps. The materials were characterized by quantitative X-Ray diffraction (XRD) using Rietveld method and by mass loss. The Al2O3-Nb2O5 mixtures experienced a weight loss of 84% at sintering temperatures of 1550 and 1650 °C.