An Investigation on the Structure/Property Relationships of Solid State Welding Processes in a Titanium Matrix Composite Alloy (Ti6Al4V [plus] 10 wt.% of TiC)

TiC particulate reinforced Ti6Al4V metal matrix composites (Ti6Al4V 10 wt.% TiC) have high strength-to-weight ratio and good high temperature properties. Although this class of composite clearly perform better than the matrix alloy itself, the successful application of such particulate-reinforced materials depends on the availability of proven joining techniques that can produce high quality joints. Due to the high chemical reactivity of titanium that may lead to a chemical interaction with the reinforcing material a poor fusion welding performance is commonly observed in these materials making solid-state diffusion bonding and rotary friction welding potential processes to produce complex structural components. Despite recent advances in processing and manufacturing technology of Ti6Al4V 10 wt.% TiC there is still a lack of understanding in the solid state joining possibilities and its microstructural changes and mechanical properties. The main objective of this work is to investigate and analyse the feasibility of joining the particulate-reinforced composite alloy by rotary friction welding and diffusion bonding processes. It is also aimed the determination and establishment of the microstructure/properties relationships of the resultant welds as well as to investigate the bonding mechanisms and understand the weldability aspects of friction welded and diffusion bonded Ti6Al4V 10 wt.% TiC. Metallurgical characterization of both base material and welded joints was performed using Optical and Scanning Electron Microscope. Mechanical assessment was accomplished using tensile, microflat tensile and fracture toughness tests. A microstructural examination of the friction-welded joints has revealed two distinct welding zones (transformed and recrystallized zone as well as heat affected zone); while no metallurgical transformation has occurred in the diffusion bonding process. In the case of rotary friction welding best results were associated with low rotational speed and low friction pressure; while in the diffusion bonding process the best results were associated with a bonding temperature and pressure of 1000C and 5MPa together with bonding times ranging from 35 and 60 minutes