Properties and fracture surface morphology of fiber-reinforced shell for investment casting

In order to improve the properties of silicon sol shell for investment casting process, natural plant fibers combined with aluminum silicate fibers at natural-to-aluminum silicate fibers mass ratio of 1:1 were mixed into the slurries preparing for fiber-reinforced shell. The flexural strength of specimens of green shells, fired shells at different temperatures and the self-loaded deformation of the latter at elevated temperature were investigated. The fracture surface of shell specimens was observed by SEM. The results show that the green strength of shell specimens increases firstly and then decreases with variation of content of fiber from 0.2% to 1.0%. However, the self-loaded deformation at elevated temperature firstly decreases and then increases. The green strength of shell specimens reinforced with 0.6% fibers reaches the maximum of 2.94 MPa. The bending strength of shell specimens reinforced with 0.6% fibers fired at 900℃ reaches 4.04 MPa, approaching that of the non-reinforced shell specimens. It is found by SEM that the failure of the fiber-reinforced shell specimens at the applied load is resulted in breakdown of silicon sol films and pulling-out, fracturing and debonding of fibers in the shell.