Control of interfacial chemistry and mechanical properties in metal/ceramic composites. Ph.D. Thesis
Evaluation of the mechanical properties of metal/ceramic interfaces (Ti/AI2O3) was accomplished by using four-point bending tests, nanoindentation tests and fiber pushout tests. At first, the interfacial fracture energy of composites with different applied bonding temperatures from 700 C to 1000 C and thickness of the metal interlayers were measured by four-point bending tests. The mixed mode interfacial fracture energy of the Ti/Al2O3 interface was found to increase with increasing bonding temperatures up to 950 C. There is increasing interdiffusion of the constituent atoms across the interfaces with increasing temperature as verified by X-ray mapping. Thus, a stronger chemical bond forms between the Ti and the Al2O3. Above this temperature, the interfacial fracture energy drops due to the formation of a continuous brittle intermetallic compound (Ti3Al) at the Ti/Al2O3 interface. Modification of the interface was achieved with a diffusion barrier consisting of a refractory metal and Y2O3 duplex coating prepared by r.f. sputtering methods. The diffusion barrier significantly reduces the diffusion of the constituent atoms and prevents the formation of a continuous Ti3Al reaction layer, thus maintaining the chemical integrity and stability at the Ti/Al2O3 interface. The interfacial fracture energy can be further reduced by providing thinner Ti interlayers. The contribution of the energy dissipation process to the interfacial fracture energy is due to plastic energy absorption in the Ti interlayer during the fracture process. The interfacial shear strength, interfacial frictional stress and mode II interfacial fracture energy of the fiber composites were obtained by performing the fiber pushout tests. Using the Atomic Force Microscope (AFM), the surface roughness and texture of the three different Al2O3 fibers were evaluated. Incorporation of the experimental data and the theory gives the calculated frictional coefficient to be 0.35.
- Research Organization:
- Minnesota Univ., Minneapolis, MN (United States)
- OSTI ID:
- 102047
- Country of Publication:
- United States
- Language:
- English
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