Effect of Al2O3 fibers mixing methods and in-situ formed SiC nanowires on the properties of silica-sol ceramic shells for investment casting

Abstract

In this study, a silicone resin solution was used as a supplementary binding agent, and two different techniques were employed to add varying amounts and layers of Al2O3 fibers within the shell to improve the performance of investment casting shells. The Al2O3 fiber-toughened shells were characterized using a combination of three-point bending and high-temperature self-loading deformation experiments. Additionally, the fracture morphology of samples and the fiber failure mode were demonstrated through SEM (Scanning Electron Microscope). Results showed that the added Al2O3 fibers greatly improved the bending strength and the high-temperature self-loading deformation of the ceramic shells. After spraying the silicone resin solution, the green and sintered strengths of the shells reached 8.02 MPa and 9.60 MPa, respectively, when Al2O3 fibers were added to the 3–6 layers of the shell. The high-temperature self-loading deformation reached a minimum of 0.44% when Al2O3 fibers were added at 0.4 wt%. SEM analysis indicated that the incorporation of Al2O3 fibers in the backing sand resulted in a disordered and non-directional distribution pattern, which could lead to the splitting of the ceramic matrix. In contrast, Al2O3 fibers within each shell layer could uniformly disperse the external load and increase the fracture resistance of the substrate. Furthermore, the pyrolysis of the silicone resin led to the deposition of free carbon in the matrix pores, resulting in the spontaneous formation of SiC nanowires. These nanowires were observed to attach to the Al2O3 fibers, which ultimately impeded the propagation of matrix cracks.