Diffusion bonding of steel to Ti-6Al-4V to produce hard wearing surface layers

Titanium is a light, strong alloy used extensively in applications where weight saving is important. However, the surface does not resist abrasion with the result that it cannot be used in applications where the component must resist wear, such as gear components. Attempts to harden the surface, such as nitriding, have met with limited success. To produce a light component with a hard wearing surface, steel has been diffusion bonded to titanium. This has been done using a bench top diffusion bonding rig, operating in vacuum at temperatures up to 1273 K, which has been designed and built in house. Computer control allows predetermined stresses and strains to be carefully controlled. The diffusion bond has been achieved both without interlayers and with up to three interlayers of elements such as copper, vanadium and nickel. The diffusion bonding of both flat and grooved surfaces has been investigated. Results are presented showing the effect of stress, strain, surface finish and interlayers on the strength of the diffusion bond. In many cases bond strengths approaching that of the bulk matrix have been achieved. The microstructure of the interfaces have been characterized using optical metallography and scanning electron microscopy.