Date of Award
10-17-2024
Publication Type
Dissertation
Degree Name
Ph.D.
Department
Mechanical, Automotive, and Materials Engineering
Keywords
AM Materials;AM Ti-TiB composite;Fatigue;Ti alloys;Ti matrix composite;Ti-TiB composite
Supervisor
Afsaneh Edrsiy
Supervisor
Reza Riahi
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Abstract
This dissertation presents the research outcomes, including both experimental and analytical findings, on the isothermal fatigue of titanium metal matrix composite (Ti MMC) reinforced with titanium boride (TiB) particles in a commercially pure alpha Ti matrix manufactured using a novel additive manufacturing (AM) technique called plasma transferred arc solid free-form fabrication (PTA-SFFF). The first set of experimental data presented in this dissertation examines the isothermal fatigue of AM Ti-TiB MMC at 350°C using fatigue test specimens with their longitudinal axis parallel to the AM build direction. These specimens are referred to as longitudinal specimens or as specimens with a 0° AM orientation in this dissertation. The fatigue data for this study were collected using a rotating beam fatigue (RBF) tester. Additionally, micrographs of the fracture surfaces of the fractured fatigue specimens were obtained using a scanning electron microscope (SEM). The fatigue experimental data from longitudinal specimens showed that the AM Ti-TiB MMC experienced a significant reduction in fatigue strength at 350 ℃ compared to its reported fatigue strength at room temperature. This loss in fatigue life is attributed to the numerous surface crack propagations observed on the fracture surfaces. Moreover, a novel modification to the Paris’ law equation is introduced in this study. This modified equation is designed to predict fatigue life under elevated temperatures, especially in scenarios involving the propagation of multiple major cracks contributing to the final fracture. Notably, this modified equation improved the fatigue failure prediction accuracy, as measured by the R^2 value, from 0.34 to 0.93, when comparing the room and elevated temperature fatigue strengths of AM Ti-TiB MMC. Materials manufactured through AM techniques often exhibit anisotropies in mechanical properties due to the layer-by-layer material build. In this regard, the second set of experiments presented in this dissertation investigates the isothermal directional fatigue of Ti-TiB MMC manufactured by PTA-SFFF. This investigation also includes an RBF test, an SEM study, and calculations for fatigue life predictions using both Paris' equation and my novel modified Paris' equation. In this set of experiments, the fatigue experiments were repeated at 350 ℃ using specimens with their test axes oriented diagonally (45°) and parallel (90°) to the AM build directions. The data from these fatigue experiments along with literature data, find that the Ti-TiB MMC manufactured via PTA-SFFF exhibit fatigue anisotropy, reporting the highest strength in 90° and lowest in longitudinal (0°) AM build directions. Furthermore, calculations were performed to evaluate the optimum values of the stress intensity modification factor (λ) for fatigue life prediction in 0°, 45°, and 90° AM build directions. It was found that for the specimens with 45°, and 90° AM build directions, the computed intensity modification factors were very similar. This suggests that the initial fatigue crack characteristics such as location, shape, and size, were similar in both 45°, and 90° AM build directions. However, in the 0° AM build direction, the computed stress intensity modification factor was different from that of the 45°, and 90° AM build directions. This indicates that the fatigue crack initiation at 0° AM build direction is different compared to the other two directions considered in this dissertation. Moreover, the R2 values calculated for Paris’ and modified Paris’ fatigue life predictions showed that the modified Paris’ equation resulted in improved prediction accuracy for all three builds. The third set of experimental data presented in this dissertation examines the room temperature fatigue crack growth behaviour of the same AM Ti-TiB MMC, that was previously examined using RBF fatigue tests, using a compact tension specimen at a stress ratio of 0.1 (R = 0.1). This set of experiments was performed perpendicularly and parallel to the additive material build, aiming to find any fatigue anisotropies at room temperature. The findings reveal that additively manufactured Ti-TiB composite shows isotropic fatigue properties with respect to fatigue crack growth behaviour in the Paris’ region. Furthermore, the fatigue crack growth mechanisms in this additive composite material were identified as void nucleation/coalescence and the bypassing of particles and matrix, depending on the interparticle distance.
Recommended Citation
Balakumar, Thevika, "Isothermal Fatigue Investigations of Additively Manufactured Ti Metal Matrix Composite with TiB Particles" (2024). Electronic Theses and Dissertations. 9419.
https://scholar.uwindsor.ca/etd/9419