Investigations on the Applicability of Pressure Slip Casting and 3D Printing for Alumina (Al2O3) and Aluminum Titanate (Al2TiO5) Systems

Abstract

Since the previous few decades, researchers have tried to increase fracture toughness and microstructure modification in an effort to address the issue of ceramics intrinsic brittleness, which has limited its use in structural applications. Researchers have looked into how ceramic materials can be altered so that one or more mechanisms can be activated to improve the desired properties. Every facet of a ceramic component’s material performance is governed by the processing history, the inherent material qualities, and other variables. Colloidal forming is a common technique for shaping ceramics because it has the advantages of increased uniformity, densification at lower temperatures, and flexibility in complex design. The goal of the current study was to create oxide-based ceramic products using various ceramic processing techniques in order to achieve the necessary complicated shapes and densification levels for best mechanical properties. Pressure slip casting is a technique known in table ware industry for producing near net-shaped green bodies with shorter processing cycles and very good consistency. Of-late, the possibility of utilizing the pressure slip casting technique for making advanced ceramic components started being looked at to exploit the advantages associated with it such as the higher green densities, near net shaping, consistency and the productivity. The preparation and control of stable, well-dispersed ceramic slip is considered as key parameter to achieve the desired properties in the green bodies. An emerging preparation method for pressure-assisted casting of advanced ceramics allows for the use of colloidal slips during pressure-based shaping. In addition to good homogeneity, outstanding green density, strength, and high productivity, the application of pressure allows for flexibility in the formation of complex structures. The current study contrasts the methods used to prepare alumina green bodies, including conventional slip casting (CSC), pressure slip casting (PSC), and cold isostatic pressing (CIP). Additionally, the ceramic products were created using ceramic 3D printing and contrasted with colloidal techniques such as CSC, PSC, and CIP. Corresponding mechanical properties of the dense ceramics were also characterised, along with their microstructural characteristics. For this purpose, both the polymer based and Plaster of Paris moulds were fabricated by designing to cast objects in the standard shapes of a cylindrical disc ϕ 80 mm, square of 60 mm, and a spherical ball of ϕ 60 mm. Present work has been undertaken with a focus on studying the shaping of Al2O3 and its combinations by pressure slip casting process and understanding the results in comparison xi with that of the conventional slip casting method. Aluminum Titanate (Al2TiO5) and Alumina (Al2O3) products are prepared from powder state in a variety of proportions and to optimise slip preparation for appropriate rheological behaviour and colloidal ceramic processing processes (CSC, PSC). The same initial alumina powder produced by mixing powders with two different average particle sizes (7 µm and 1.43 µm) in the ratio of 65:35 was utilised in all three operations because to the fixed pore size of the mould. The average particle size (d50) of the mixture HM-mix powder is 3.18 µm. The optimization of slip/slurry has been done with solid loadings varying from 65% to 80% along with rheological behaviour of shear thinning which is required in pressure slip casting for better consolidation. The shear thinning behaviour that is a necessary characteristic in the development of casts is demonstrated by the rheological data stress-exponent n=0.5. The plot unequivocally exhibits a pseudoplastic behaviour appropriate for CSC and PSC processes. Under conditions of atmospheric pressure by CSC and external pressures of up to 35 bar by PSC casts for cylindrical discs, square, and Spherical Alumina balls samples were made. According to the results of the TG-DTA experiments, the samples sintering schedules developed over time at a slow heating rate of 10°C per minute up to the final sintering temperature of 1600°C.The green densities of the discs were calculated after drying and before subjecting them for sintered schedule with the peak temperature of 1600oC.It has been observed that green densities of 65%TD at 35 bar for PSC and 66%TD at 1200 bar following CIP were achieved which is attribute to interlocking nature. However, the density of the CSC samples was only 50%TD. Flexural strength and fractographic examinations were conducted and connected with the corresponding processes. Also, the samples were sintered at 1600 °C to test their sinterability. The PSC products have a high density due to the compact packing made possible by applying pressure to the slip, which complements the enhancement of the hardness. The PSC processed samples with refined grain structure and minimal imperfections/pores is found to improve the mechanical properties such as hardness, flexural strength, and fracture toughness, which are measured to be 14.92±0.15 GPa, 294.40 ± 2.5 MPa, and 4.06 ± 0.25 MPa m1/2 respectively in comparison of conventional cast sample’s respective values of 3.73 ± 0.25 MPa m1/2, 242.70 ± 2.5 MPa, and 11.77 ± 0.15 GPa, it is clear that the mechanical properties are improved. Alumina (Al2O3) is a favoured material for wear-resistant applications due to its high mechanical as well as chemical inertness. Owing to the mechanical properties, PSC alumina is shown to have a 56% lower wear rate than CSC alumina, with a wear rate as low as 2.35×10-18 m3/Nm (with 0.5 m/sec at 5N load). Commercial repercussions in the ceramic sector xii will result from PSC alumina’s improved wear rate. Successfully demonstrated that the physic thermal properties of Alumina and Aluminum Titanate were measured for a variety of geometrical shapes. Titania and Alumina MR-01 powders were combined dry in an equimolar ratio of 1 (TiO2): 1.27 (Al2O3) and ball milled for four hours. After blending, the dry mixture was heated to between 1350 -1440 degrees Celsius for two hours soaking, in order to calcinate the powder to generate the aluminium titanate phase using the solid-state reaction pathway. The X-ray diffraction method along with line scanning of FESEM Microstructures, will be used to confirm the phase. According to the same predictions, XRD patterns and FESEM results show the confirmed phase of aluminium titanate. Alumina, titanium, and aluminium titanate all had particle size distributions of 1.43 mm, 0.5 mm, and 1.27 mm, respectively. The slips have been prepared for calcined powder of Aluminum Titanate in varying proportionate ranging from 30 - 45 wt. % Solid loadings and with additions of remaining water in order to get best way of cast in both the processes. For the 45 wt.% of solid loading its giving the better required rheological behaviours and measured shear rate exponent around 0.5. The observed green, sintered densities in the cases of 3D-printed AL and AT ceramics are in the ranges of 55-57% and 65-70% of theoretical density, respectively. It is reported that the Al2TiO5 containing sintered samples made by CSC and PSC have a low thermal expansion coefficient. PSC, with a value of 1.88 × 10-6 K-1, and CSC, with a value of 2.20×10-6 K-1, have the lowest thermal expansion coefficients at 1100 °C and also the samples of sintered materials by 3D printed with a value of CTE is 2.58 ×10-6 K-1.