Characterisation of the deforming behaviour of titanium alloys for additive manufacturing

Abstract

Titanium holds significant importance in the aerospace sector due to its exceptional properties, such as high specific strength, low density, and good corrosion resistance. In recent years, wire arc additive manufacturing (WAAM) has gained significant attention as a promising, cost-effective technique for fabricating near-net shape components. To effectively produce the wire, mechanical properties, such as ductility, are required. The addition of zirconium to titanium reportedly enhances ductility while retaining good mechanical properties. The deformation behaviour and the microstructural changes during the wire production process have to be analysed to ensure the desired mechanical properties for further processing. Zirconium, also in the form of ZrH2 and ZrO2, was added as an alloying element in various contents along with copper. The samples were fabricated using differentmanufacturing methods like vacuum arc furnace, vacuum sintering and hot extrusion. To analyse the deformation behaviour, deformation dilatometry tests were performed at various temperatures and strain rates. A cast material in the composition of Ti5.9Cu2Fe2Al, manufactured by an external company, was deformed by hot extrusion and caliber rolling. The microstructure of samples was characterized using optical and scanning electron microscopy. The formed phases were characterized through XRD measurements. Furthermore, the c/a ratio as a function of Zr and the progression of crystallite size during deformation were analyzed. Vickers hardness HV10 and Archimedes density measurements were performed. The addition of 5 wt% zirconium decreased hardness by 30 HV10 indicating higher ductility. The hardness increased with increasing Zr content due to the progressive grain refinement. The deformation dilatometry tests did not indicate any dynamic recovery or dynamic recrystallization, as no steady flow stress was measured. The true stress increases with increasing strain rate and decreasing temperature. During the rolling process, the microstructure of Ti5.9Cu2Fe2Al exhibited elongation when preheated to 800 °C, while a significant grain refinement was observed at 1000 °C indicating dynamic recrystallization. The grain refinement is evident in the hardness increase from 300 HV10 in the cast material to 520 HV after the last deformation step. Further analyses of the investigated alloys are necessary to determine the mechanical properties, like tensile strength and elongation, the microstructural stability and consequently their suitability for wire drawing and additive manufacturing.