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The Influence of Femtosecond Laser Shock Peening on the Functional Fatigue Properties of Ti₆₇Zr₁₉Nb₁₁.₅Sn₂.₅ Bio-Compatible Shape Memory Alloy
Asim, Muhammad
Asim, Muhammad
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Description
A Master of Science thesis in Mechanical Engineering by Muhammad Asim entitled, “The Influence of Femtosecond Laser Shock Peening on the Functional Fatigue Properties of Ti₆₇Zr₁₉Nb₁₁.₅Sn₂.₅ Bio-Compatible Shape Memory Alloy”, submitted in November 2024. Thesis advisor is Dr. Wael Abuzaid. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).
Abstract
This thesis investigates the functional fatigue characteristics of Ti₆₇Zr₁₉Nb₁₁.₅Sn₂.₅, a nickel-free shape memory alloy (SMA) designed for biomedical and engineering applications, with a focus on optimizing its superelastic (SE) properties under cyclic loading conditions. Shape memory alloys, such as TiNb-based alloys, are increasingly preferred for medical applications due to their biocompatibility and superelastic properties. However, their functional fatigue performance requires further improvement for enhanced longevity in biomedical settings. This study applies femtosecond laser shock peening (F-LSP) to the chosen SMA as a novel approach to mitigate residual strain accumulation, aiming to enhance the alloy’s SE recovery and functional fatigue life. The experimental analysis involves cyclic loading tests on standard and drilled-hole specimens to replicate uniform and concentrated Stress fields. The F-LSP parameters, including laser power, scanning speed, and pulse intensity, were systematically optimized to enhance SE recovery under cyclic loading conditions. Strain mapping through Digital Image Correlation (DIC) quantified residual and recoverable strains on cyclic loading. Microstructural characterization using SEM, EDS, EBSD, and XRD revealed that F-LSP induced favourable phase transformation, which improved SE recovery without thermal degradation. The findings indicate that optimized F-LSP parameters improved the recovery of SE strains by 12% and reduced the residual strain accumulation following cyclic loading up to 25 cycles. The functional degradation of the alloy was reduced to 3.26% after F-LSP compared to the sample without LSP, which was 7.96 % after 25 loading cycles. The alloy showed apparent phase transformation at the surface from body-centred cubic (BCC) to the orthorhombic phase, potentially promoting improved superelastic recovery. These insights highlight the effectiveness of F-LSP in enhancing the functional fatigue properties of Ti-based SMAs, highlighting its potential for advancing SMA performance in high-demand biomedical applications.