Ben M. Thomas

Over the last 20 years, there has been growing research and development investment to exploit the benefits of wire deposition additive manufacturing (AM) for the production of near-net shape components in aircraft and space applications. The wire feedstock for these processes is a significant part of the overall process costs, especially for high-value materials such as alloyed titanium. Powders for powder-based AM have tight specifications regarding size and morphology, resulting in a significant amount of waste during the powder production. In the aerospace sector, up to 95% of forged billet can be machined away, and with increasing aircraft orders, stockpiles of such machining swarf are increasing. In this study, the continuous extrusion process—Conform^TM—was employed to consolidate waste titanium alloy feedstocks in the forms of gas atomised powder and machining swarf into wire. Samples of wire were further cold-drawn down to 40% reduction, using conventional wiredrawing equipment. As close to 100% of the waste powder can be converted to wire by using the Conform^TM process. This technology offers an attractive addition to the circular economy for manufacturers and, with further development, could be an important addition as industries move toward more sustainable supply chains.

The current status of field assisted sintering technology (FAST) of structural metals from powder is critically reviewed. Recently, there have been significant increases in the uptake of FAST for metallic systems, composites and porous materials at the laboratory-scale. It is clear that FAST is tolerant of powder/particulate feedstock, allowing rapid production of materials, some of which would be challenging through conventional sintering techniques. Yet, the underlying mechanisms allowing this are not fully understood. Final specimen sizes tend to be small, which restricts rigorous mechanical assessment. This review demonstrates the clear benefits in transitioning laboratory-scale demonstrators to the industrial scale over the next few years. However, consideration will need to be given to size, throughput, and shape complexities to attract commercial investment.

It is shown for the first time that cold commercially pure titanium powder can be extruded through a standard Conform machine into fully dense wire with a fine recrystallised microstructure. The grain size has been shown to decrease with increasing wheel speed with an associated increase in tensile strength. The macrostructure of the wire extrudate exhibits a characteristic flow pattern with several regions defined by differences in average grain size and distribution. Finite-element modelling of the process shows the formation of the characteristic macrostructure from powder fed Conform. The process is continuous, utilises standard equipment and does not require powder preheating or inert gas shrouding providing a footing for a true cost reduction in long-section titanium mill product.