Abstract

There are significant challenges for materials in extreme environments for a variety of applications such as aircraft engines, gas turbines, nuclear reactors, re-entry vehicles, and hypersonic structures. Ceramic matrix composites (CMCs) could be ideal candidates to meet these stringent requirements for materials due to their high melting temperatures, high oxidation, corrosion and ablation resistance, low creep, and thermal cycling behavior in such extreme environments. Particularly, continuous fibers can bridge cracks in CMCs and therefore improve the strength and fracture toughness of composites. Metal matrix ceramics are important materials in various industries, such as aerospace and automobile. MMCs have excellent mechanical properties, superior thermal and electrical conductivities, and resistance to radiation. Nanoparticles are introduced in CMCs and MMCs to improve their mechanical, thermal, and electrical properties. CMCs are traditionally manufactured by the melting infiltration method. With this method, the high porosity and brittle structure of fabricated CMCs are not capable of withstanding high mechanical and thermal loads. Alternatively, polymer derived ceramic composites are fabricated by incorporating carbon fibers into polymer derived ceramic matrix to achieve high fracture toughness. With the aid of protective coatings with metallic or ceramic materials, such as Nickel, carbon fiber could potentially withstand high temperatures without oxidation. Nickel coated chopped carbon fiber are used to reinforce the CMCs by hot press process. In this study, continuous fiber reinforced silicon oxycarbide composite was manufactured with polysiloxane (PSX) resin and woven carbon fabrics through the polymer infiltration and pyrolysis process (PIP). Re-infiltration of the PSX resin into the composites, curing in an autoclave, and pyrolysis for additional cycles can increase the yield of ceramics of the composites. A dense structure of the composites was observed by SEM. The EDS results showed that the elemental composition of the composites mainly consisted of carbon, silicon and oxygen. The crystalline structure of the composites was examined through XRD to indicate the degree of polymer pyrolysis to ceramics. The results of four-point bending testing of the composites showed a flexural strength of 62 MPa, a flexural modulus of 51 GPa, and a fracture toughness of 1.3×108 J/m3. The torch test was conducted to determine the thermal properties of CMCs. MMCs are processed by an electroplating process to obtain silver/silver nanocomposite coating on a substrate to increase the electrical conductivity by 4-6 times compared to pure silver coating.

Notes

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Graduation Date

2022

Semester

Fall

Advisor

Gou, Jihua

Degree

Doctor of Philosophy (Ph.D.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering

Identifier

CFE0009840; DP0027781

URL

https://purls.library.ucf.edu/go/DP0027781

Language

English

Release Date

June 2024

Length of Campus-only Access

1 year

Access Status

Doctoral Dissertation (Open Access)

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