NEAR-NET-SHAPE SYNTHESES, JOINING, AND PROPERTIES OF CERAMIC/METAL COMPOSITES
Creators: name: Wang, Yujie
Publisher: name: Purdue University Graduate School
Year: 2023
Subjects: classificationCode: 401601
subject: Ceramics
classificationCode: 401602
subject: Composite and hybrid materials

description: Ceramic/metal composites are being explored as potential replacements for conventional metal alloys in high-temperature components used in aerospace and power generation applications. Co-continuous ceramic/metal composites can offer attractive combinations of properties, such as improved mechanical toughness and thermal conductivity (relative to monolithic ceramics) and enhanced stiffness and corrosion/erosion resistance (relative to monolithic metals). However, development of cost-effective and scalable manufacturing routes to dense, complex-shaped ceramic/metal composites is a non-trivial challenge.Chapter 1 of this dissertation is focused on the fabrication of WC/Cu composites using pressureless Cu liquid infiltration. The microstructure, density, porosity, phase content and properties of the resulting WC/Cu composites have been investigated. Mechanical properties, such as flexural strength and Vickers hardness have been evaluated, and the thermal cycling behavior of the WC/Cu composites have been examined. This study successfully demonstrates the fabrication of near-net-shape WC/Cu composites and provides insights into potential applications for such composites.In Chapter 2, the limitations of metal alloy-based heat exchangers are discussed, leading to the exploration of alternative materials such as composite of zirconium carbide (ZrC) and tungsten (W). The favorable properties of ZrC/W composites, such as chemical compatibility, low vapor pressure, high thermal conductivity, stiffness, and thermal cyclability are highlighted. The fabrication of ZrC/W composites using reactive infiltration processes, emphasizing the importance of scalable fabrication methods, is also demonstrated.Chapter 3 is focused on the fabrication and characterization of functionally graded ZrC/W – WC/Cu composites. These composites have been prepared by immersing WC/Cu preforms in Zr – Cu liquid at different temperatures, and the microstructures and phase distributions have been evaluated. It is observed with the same immersion time, the thickness of the ZrC/W reaction zone decreases with increasing immersion temperature due to the rapid reaction between WC and Zr at higher temperatures. Additionally, a model has been developed to describe the thermal conductivity of the composites as a function of the distance from the external surface. These findings provide insights into the fabrication and properties of functionally-graded composites for potential heat dissipation applications.In Chapter 4, the development of a Ti-bearing, Ni-based active metal braze for joining Al<sub>2</sub>O<sub>3</sub>/Cr composites to Ni-based alloys is discussed. Joining ceramic components to metal parts poses challenges due to material property mismatches and ceramic brittleness. Conventional brazing materials often suffer from oxidation at high temperatures in air which compromises joint integrity. The focus of this chapter is the evaluation of the oxidation behavior of the developed brazing material to assess the suitability of this braze for reliable joining of ceramic-based composites to Ni-based alloys for use in air at high temperatures. Differential scanning calorimetry (DSC) has also been used to evaluate the solidus and liquidus temperatures of the Ni-19Cr-10Si and Ni-18Cr-10Si-4Ti alloys.<br>