Laser deposition-additive manufacturing of ceramics and ceramic reinforced composites
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High-performance materials, including ceramics and ceramic reinforced metal matrix composites (MMCs), are widely used in severe working conditions and have been applied in biomedical, aerospace, electronic, and other high-end engineering industries owing to their superior properties of high wear resistance, outstanding chemical inertness, and excellent properties at elevated temperatures. Among all types of high-performance materials, zirconia toughened alumina (ZTA) is favored due to the toughening effects induced by ZrO2. In addition, the mechanical properties of zirconia toughened alumina (ZTA) can be controlled via changing ZrO2 content and powder preparation (such as changing particle shape or size) for specific applications. As another type of high-performance materials, TiB reinforced titanium matrix composites (TiB-TMCs) have attracted a great amount of attentions and been extensively investigated due to the specific benefits introduced by TiB reinforcement. Firstly, TiB is a stable phase since there is no intermediate phase between TiB and titanium (Ti). Secondly, TiB and Ti have similar densities and thermal expansion coefficients, therefore, thermal stresses at their interfaces can be minimized. Thirdly, the strength of TMCs can be effectively enhanced by adding a small amount of TiB. The superior properties of high-performance materials, on the other hand, make it difficult to process these materials with conventional manufacturing methods, posing problems of high cost and energy consumptions. In addition, difficulties arise when fabricating complex-shaped components with these conventional manufacturing processes. Recently, a competitive manufacturing method, additive manufacturing (AM) with high design flexibility, high customization, lowered cost and energy usage, has gained popularity in fabrication of these high-performance materials. However, problems of low toughness, cracks, poor part quality, etc. still exist in AM manufactured high-performance materials. Facing to these problems, it is of great importance to develop new high-performance materials through establishing efficient and effective processes and tailoring novel microstructures. In this dissertation, a comprehensive literature review on laser deposition-additive manufacturing (LD-AM) of ceramics and ceramic reinforced metal matrix composites is provided. Main issues to be solved, corresponding solutions, and the trend of development are summarized and discussed. Afterwards, efforts have been made to provide engineering solutions to the existing problems in high-performance materials fabricated by LD-AM. An ultrasonic vibration-assisted LD-AM is established to reduce fabrication defects (such as porosities and cracks) in ZTA. The introduction of ultrasonic vibration is proven to be beneficial for refining grains, homogenizing material dispersion, smoothing out thermal gradient and thermal stress, reducing defects, and enhancing mechanical properties of fabricated parts. In addition to manufacturing process, the ultrasonic vibration is also effective in assisting machining process. For the purpose of reducing low precision problem (such as low dimensional accuracy and bad surface finish), a nontraditional rotary ultrasonic machining process is utilized to post-process LAM-fabricated ZTA parts. In order to reduce low toughness and ductility in TiB-TMCs, a novel network microstructure is tailored and the formation mechanism of such a microstructure is investigated. Experimental results evidence that the presence of this network microstructure is beneficial for toughening and strengthening LD-AM-fabricated TiB-TMCs.