Strength Evolution and Fracture Feature of Carbon Fiber-Reinforced Silica Sol Shell for Investment Casting

The high-strength and thin-walled shells are extremely beneficial for not only rapid solidification of metal castings but also excellent for shell removal, its low residual strength and low solid waste discharge. In this work, short carbon fibers as reinforcement were induced into the shells. The strength of specimens and their fracture behavior at ambient temperature or high temperature in loading were investigated using scanning electron microscopy (SEM) and thermogravimetric-differential scanning calorimetry technique (TG-DSC). The results show that the bending strength of the shell progressively rises initially and then decreases rapidly with increasing content of fiber with a constant length. In particular, the shell reinforced with 0.42 wt% carbon fibers of length of 2.0 mm reaches a peak of green strength of 4.68 MPa and a peak of hot strength 16.06 MPa, respectively, approximately 89.47 and 61.20% higher than that of the unreinforced. Moreover, the peak of the fired strength of shell specimens containing 0.51 wt% fibers of length of 3.0 mm reaches 7.48 MPa, increasing by 61.20% in comparison with the unreinforced. However, the high-temperature self-weight deformation of the shell does not reveal positive correlation or monotonically increasing with the amount of fiber. Furthermore, the results revealed that the fracture types and failure patterns of fibers in shells were mostly related to fiber-fracture, pull-out and/or debonding during loading. These research results are beneficial to further improve this technology and promote the practical application to greatly reduce the generation and discharge of waste shells in the production of investment castings in the future.