Re-inforcing nano-particle integration into metal AM and produced part characterisation

Metal matrix composites (MMCs) are an important class of materials replacing monolithic alloys in applications where high specific strength and temperature and wear resistance are critical. However, the ductility of the matrix is very often negatively affected by the presence of the harder reinforcing phase and the existing production routes can be of high cost or difficult to implement either due to complex part design or the requirement for specialised equipment. Recently, the additive manufacturing technique known as laser-powder bed fusion (L-PBF) has proved a promising method for manufacturing MMCs as it promises to suppress several of the existing challenges concerning MMC production. The focus of this thesis is on the fabrication and characterisation of stainless steel 316L nanometre-scale silicon carbide and tungsten carbide reinforced MMCs, in an attempt to bring understanding and solutions to current issues concerning MMCs production and their integrity. Firstly, two aspects of L-PBF currently lacking in knowledge and that have implications on MMCs integrity were studied: assessment of part-properties dependency of on the printing location across the build platform in L-PBF, and identification of influencing factors and assessment of the optimal powder spreading conditions within the L-PBF system. Secondly a feedstock powder for L-PBF of MMCs, driven by the requirements of a homogeneous mixture and improve powder rheology, was developed and tested using the simple and cost effective route of powder metallurgy. Thirdly, the developed powder and the optimised parameters in the L-PBF of MMCs were examined. Lastly, a commercial L-PBF system was implemented to work with a colloid form of feedstock material, as well as powdered form, during the manufacturing of MMCs. Several relevant material characterisation techniques were utilised to assess the feedstock materials and the prepared samples so that meaningful scientific information could be obtained and detailed explanations of these results presented