DC plasma spray of nano-structured coatings for armour applications

Functionally Graded Materials (FGM) were developed as armour materials for ballistic protection due to their lighter weight and better mechanical properties than that of the conventional armour materials. Previous FGM armours are made from time-consuming methods such as hot-pressing and sintering. Previous such products are also made from micron-sized powder feedstock. However, materials with nano-scale structures have been recognized to exhibit more attractive properties, including properties required for ballistic protection. The nano-structured FGM was made using the DC plasma spray technique, which is faster than traditional methods and better for making large surface areas of ceramic coatings. In this project, a comparison of nano-structured and micro-structured alumina FGM coatings was done. Nano-structured and micro-structured powders were plasma sprayed onto steel substrates. Different plasma spray parameters were also investigated on how it will affect the hardness and fractural properties of the FGM coatings. Finally, the set of optimized parameters will then be used to investigate the relationship of hardness and microstructure of the coatings. Characterisation of the nano-alumina FGM and micron-alumina FGM was done using the three-point bending test and Vickers micro-hardness tester. Visual inspection of the coatings was also done using Scanning Electron Microscopy. Experimental results have shown that nano-alumina FGM exhibit 20% improvement in flexural fracture stress and 25% improvement in flexural fracture strain over micron-alumina FGM. Micro-hardness of nano-alumina FGM is also 10% higher as compared to micro-alumina FGM systems. Compared to commercial pressed and sintered micron-alumina tiles, nano-alumina FGM also has 127% higher flexural fracture stress, 60% higher micro-hardness, and twice as much fracture toughness, with only a marginal increase in specific density. The nano-alumina FGM has also shown an ability to localise impact damage and resist shattering after repeated hits by a sharp indentor at the same point. This indicates that nano-alumina FGM is a possible projectile protection system replacement to pressed and sintered micron-alumina tiles used currently for armour applications.Bachelor of Engineering (Materials Engineering

Mechanical Properties of Cold Sprayed Aluminium 2024 and 7075 Coatings for Repairs

This study investigates the mechanical properties of aluminium 2024 (Al-2024) and aluminium 7075 (Al-7075) cold-sprayed materials and coatings for repairs. It aims to determine the acceptable data needed to meet regulatory requirement when substantiating cold spray repairs. The study focuses on repairs of non-principal structural element (PSE) structures such as skin and panels that are prone to corrosion and wear. For cold spray repair of such components, the microstructure, tensile, peel, bearing, and bending strength from the repair process and powder materials of Al-2024 and Al-7075, were identified and investigated in accordance with MIL-STD-3021. Results show an average coating porosity of <1.2% for both materials. Average tensile strength was 247.1 MPa (with elongation of 0.76%) for Al-2024 and 264.0 MPa (with elongation of 0.87%) for Al-7075. Al-2024 has an average peel strength of 71.9 MPa, while Al-7075 is at 48.9 MPa. The Al-2024 bearing test specimens gave a maximum load strength before failure of 633.6 MPa, while the Al-7075 gave 762.7 MPa. The bending tests show good flexibility for coating thickness ranges of typical skin and panel parts. The results show that cold spray can be used to restore thickness and oversized hole diameters for Al-2024 and Al-7075 skin and panels. The bearing test conducted in this study has also demonstrated a new test method to determine the bearing load and yield strength of a cold spray-repaired hole in a plate