Influence of rotational speed on process characteristics in friction surfacing of Ti-6Al-4V

Friction surfacing process is employed to deposit metallic coatings, whereby similar and dissimilar material combinations can be realized. The process can be applied as a local repair technology, or the coating material can locally modify the surfaces. One advantage of this process is that the coatings are deposited in solid state without reaching the melting range of materials, thereby avoiding dilution with the substrate. The involved severe plastic deformation under high temperatures alters the microstructure of the coating material, leaving it fully dynamically recrystallized. The current work focuses on deposition of Ti-6Al-4V coatings. For that material, the process parameter rotational speed plays a major role in the material's response during processing. Two different regimes with a threshold at 2000min(-1) exist, upon which the flow behavior of Ti-6Al-4V significantly differs, affecting among others the coating dimensions. Microstructural analysis reveals that the material is deformed in a high temperature phase, and the high cooling rates (46.4 Ks(-1)) lead to martensitic transformation. The grain size differs in the low and high rotational speed regimes. This study shows that metallurgical processes play an important role in friction surfacing, since they influence all relevant process characteristics, including microstructure, material efficiency and process forces.