DC plasma spray of nano-structured coatings for armour applications

• Main Author: Loke, Kelvin Zhi Cheng.
• Other Authors: Alfred Tok Iing Yoong
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Materials::Defence materials
• Online Access: http://hdl.handle.net/10356/15330
• Institution: Nanyang Technological University

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.