Hybrid Manufacturing of Tungsten and Tungsten Composites

Abstract

Laser Powder Bed Fusion (LPBF) is one of the standard additive manufacturing processes, known for its ability to produce near net shaped components with competitive quality and geometric complexity. This technology is highly potent across many sectors, including energy, defence, and manufacturing, as it provides greater design freedom, enabling the creation of lightweight components with higher performance and energy efficiency. Tungsten has gained significant attention in recent years as a potential candidate for high heat flux exchangers in fusion reactors. The high melting temperature of tungsten makes it suitable for operation under the extremely high temperatures inside a fusion reactor. Tungsten is also used in armour piercing artillery due to a combination of high density, strength and hardness. The manufacturing industry also relies heavily on tungsten composites like tungsten carbide cobalt, which is extensively used as a tool material in machining operations due to its superior hardness and toughness. As a result, integrating LPBF into the manufacturing routes for tungsten and its composites is essential for developing the next generation of hardware that meets the demands of the modern world. This Ph.D. research is centred on exploring the application of Laser Powder Bed Fusion for the manufacturing of tungsten composites. The research began with a first phase focused on the pure metal for potential use as a plasma facing material in fusion reactors. An essential part of this phase was conducting multi objective optimization to identify the optimal process windows for dense and crack free tungsten. The outcome of this phase indicated that achieving full solid density and eliminating cracks simultaneously, which is mandatory for the said application, are two contradicting objectives and cannot be fully satisfied by sole manipulation of process parameters. However, a significant reduction in cracking is possible with only a slight sacrifice of relative density by applying multi-objective optimization instead of single-objective optimization. The second phase of this PhD research focused on Tungsten carbide cobalt (WC-Co), for potential processability via LPBF, given its extensive use in Powder metallurgy to produce cutting tools. This phase was carried out in two parts: The first part aimed at identifying the optimum process windows for LPBF of WC-Co and developing form turning tools with integrated cooling features for machining Ti6Al4V. The second part included developing WC-Co rotating tools such as endmills, while utilizing topology optimization to optimize its weight and performance. The outcomes of this phase indicated that LPBF-ed WC-Co with 17% cobalt is suitable for cutting tool applications, including fixed and rotating tools. This phase of research also demonstrated the feasibility of several novel concepts in the spectrum of tool design, such as cooling fins, guiding fins, streamlined internal channels, and lightweight topology optimized endmills. The impact of this PhD research spans both the manufacturing and application domains of WC-Co tools: it significantly reduces the energy required for tool fabrication, while simultaneously enhancing machining performance through improved tool capabilities.