Key Takeaways & Executive Findings
- •• Optimal alumina fiber addition of 0.6wt.% yields the best comprehensive performance of ceramic shell molds, with high room- and high-temperature strengths and minimal self-weight deformation. • Green bending strength peaks at 6.20 MPa with 0.2wt.% alumina fibers, but further additions do not significantly enhance it. • High-temperature strength and resistance to self-weight deformation first increase then decrease with fiber content, peaking at 0.6wt.%. • Fiber reinforcement mechanisms such as bridging and pulling-out consume crack growth energy, improving shell mold strength.
Abstract
Alumina fibers, with an aspect ratio ranging from 9 to 27, were utilized as the reinforcing materials for silica-sol ceramic shell molds, and the impact of different alumina fiber additions on the green bending strength, room- and high-temperature bending strength, and self-weight deformation of ceramic shell molds was investigated. The green bending strength of shell molds is the maximum at an alumina fiber addition amount of 0.2wt.%, reaching 6.20 MPa. Further increases in alumina fiber content do not significantly affect the green bending strength. As the alumina fiber addition amount increases from 0.2wt.% to 1.0wt.%, the bending strength and the resistance to self-weight deformation of the ceramic shell molds at high-temperatures show a pattern of first increase and then decrease. The shell molds after sintering exhibit the highest room-temperature strength of 17.33 MPa and the highest high-temperature strength (18.97 MPa at 1,100 °C; 17.78 MPa at 1,200 °C; and 15.3 MPa at 1,300 °C), and the smallest self-weight deformation of 0.022% at 1,000 °C when the alumina fiber addition is 0.6wt.%. The appropriate amount of fibers in the shell mold matrix consume the energy required for crack growth through mechanisms such as bridging and pulling-out, thereby improving the strength of shell molds. In summary, the comprehensive performance of the shell molds is the best when the fiber addition amount is 0.6wt.%.
1. Introduction
Engine casings, as key load-bearing components of aircraft engines, have been limited by conventional forming technology. As a result, they were typically designed with increased wall thicknesses, simplified geometries, and relied on subsequent machining to achieve intricate thin-walled configurations. As the performance and reliability of aircraft engines continue to improve, the structural design requirements for the next generation aircraft engines with a high thrust-to-weight ratio have become increasingly stringent. A great number of complex structures characterized by high structural efficiency, large sizes, thin walls, and complex geometries are adopted[1-4]. The ceramic shell mold is an important factor determining the quality of large and complex superalloy casings. Statistical data indicate that defects originating from ceramic shell molds account for 50% to 70% of superalloy casting failures[5]. To obtain high-quality superalloy castings with large sizes and complex structures, ceramic shell molds must exhibit high bending strength and low self-weight deformation to withstand the impact of molten metal during casting. Meanwhile, the shell molds need to have sufficient strength to prevent cracking due to the expansion of the wax material during dewaxing[6-11].
Research works related to strength improvement of fiber-reinforced ceramic shell molds are extensive. Researchers have incorporated organic fibers and inorganic fibers into ceramic shell molds. The organic fibers improve the green bending strength and the permeability of the shell molds[12-17]. However, the burn out of organic fibers reduces the high-temperature bending strength of the molds. As research progresses, fiber preparation techniques are enhanced. Inorganic fibers, such as glass fibers, zirconium oxide fibers and so on, which can boast high temperature performance and physical and chemical properties, are being used for reinforcing ceramic shell molds[18-24]. However, the agglomeration of ceramic fibers and their unintended sintering with the shell matrix remain significant challenges in the fabrication of high-performance ceramic shell molds.
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Bing-zheng Fan, Ling Zhang, Lei Jin, Xin-li Guo, Lan-bo Ma, Guo-yan Shui, Xun Sun (2025). Effect of alumina fibers on ceramic shell mold properties. China Foundry. https://doi.org/10.1007/s41230-025-4054-9
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Frequently Asked Questions
What is the optimal alumina fiber content for ceramic shell molds?
The optimal alumina fiber content is 0.6wt.%, which provides the best comprehensive performance, including high room- and high-temperature strengths and minimal self-weight deformation.
How does alumina fiber addition affect green bending strength?
Green bending strength reaches a maximum of 6.20 MPa at 0.2wt.% alumina fiber addition. Further increases in fiber content do not significantly affect green bending strength.
What mechanisms improve the strength of fiber-reinforced shell molds?
The appropriate amount of fibers consumes energy required for crack growth through mechanisms such as bridging and pulling-out, thereby improving the strength of shell molds.
What are the high-temperature strengths of the optimal shell mold?
At 0.6wt.% alumina fiber addition, the high-temperature strengths are 18.97 MPa at 1,100 °C, 17.78 MPa at 1,200 °C, and 15.3 MPa at 1,300 °C.
What is the self-weight deformation at the optimal fiber content?
At 0.6wt.% alumina fiber addition, the self-weight deformation is the smallest at 0.022% at 1,000 °C.
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