Diffusion bonding of Ti-6Al-4V alloy at low temperature: metallurgical aspects

The diffusion bonding of the Ti-Al-4V alloy at low temperature (850°C) has been studied. The principal objective of this investigation was the development of a diffusion bonding procedure suitable for Ti-6Al-4V alloy and capable of being used as part of a superplastic forming/diffusion bonding process. It was found that high-quality joints can be obtained by bonding at 850°C, with pressures of 4 MPa and times in the range 90–120 min. Mechanical properties of the joints were determined using cylindrical and plane test pieces. Tensile, shear and peeling tests were used to determine the strength of the joints. On bonding with the above conditions, the parent alloy strength was reached. Little reduction in these values was measured because the heat treatment was applied during bonding. A metallographic study by scanning electron microscopy and energy dispersive spectroscopy was performed to determinate the influence of the previous parameters on the microstructural changes that occur in the joint. Grain growth kinetics and ratio of bonding area were also studied. The results shows that a new method of diffusion bonding for Ti-6Al-4V alloy has been developed. This method can be carried out using lower bonding temperatures than in conventional processes.