Investigation on the Thermodynamic Stability of Nanocrystalline W-Based Alloys: A Combined Theoretical and Experimental Approach

The stability of nanostructured metal alloys is currently being extensively investigated, and several mathematical models have been developed to describe the thermodynamics of these systems. However, model capability in terms of thermal stability predictions strongly relies on grain boundary-related parameters that are difficult to measure or estimate accurately. To overcome this limitation, a novel theoretical approach is proposed and adopted in this work to identify W-based nanocrystalline alloys which are potentially able to show thermodynamic stability. A comparison between model outcomes and experimental findings is reported for two selected alloys, namely W-Ag and W-Al. Experimental results clearly highlight that W-Ag mixtures retain a segregated structure on relatively coarse length scales even after prolonged mechanical treatments. Moreover, annealing at moderate temperatures readily induces demixing of the constituent elements. In contrast, homogeneous nanostructured W-Al solid solutions are obtained by ball milling of elemental powders. These alloys show enhanced thermal stability with respect to pure W even at high homologous temperatures. Experimental evidences agree with model predictions for both the investigated systems.

Novel Insole Material for Weight-Bearing Monitoring Medical Device to Be Used in Fractured Bone Clinic

Partial Weight-Bearing (PWB) regime is a part of a recreation process for patients with lower limb fractures/strains/sprains. In order to avoid a frequent foot overloading and achieve better patient compliance with requirement of PWB, the application of Weight-Bearing Monitoring System (WBMS) is highly attractive. However, it is challenging to find an affordable material for protective insole cover that is also a good shock-absorber. In this regard, a new formulation for protective covering material that preserves and isolates the sensors of WBMS device is suggested in this thesis. Twenty one samples of renewably sourced Polyurethane Foam (PUF) composed of poly (trimethylene ether) glycol (PO3G) and unmodified castor oil (CO) were synthesized and evaluated according to predetermined criteria. Response surface methodology of Box – Behnken design was applied to study the effect of the following parameters (polyols ratio, isocyanate index (II), and blowing agent ratio) on the properties (hardness, density) of PUFs. Results showed that CO/PO3G/TDI PUFs with hardness Shore A 17-22 and density of 0.19-0.25 g/cm3 demonstrate the required characteristics and can potentially be used as a durable and functional insole material. Phase separation studies have found the presence of well-segregated structure in PUFs having polyols ratio CO:PO3G 1:3 and low II, which further explains their extraordinary elastic properties (400% elongation). Analysis of cushioning performance of PUF signified that 5 samples have Cushioning Energy (CE) higher than 70 N·mm and Cushioning Factor (CF) in the range of 4-8, hence are recommended for application in WBMS due to superior weight-bearing and pressure-distributing properties. Moreover, the developed formulation undergoes anaerobic soil bacterial degradation and can be categorized as “green” bio-based material.