DISSIMILAR METALS JOINING: IRON BASED ALLOY AND TITANIUM

Joining of titanium and its alloys with Iron based alloys by welding poses significant problems. Brazing is a preferred method for joining these metals, bridging over their highly diverse physical and chemical properties.

A common used solution to join two dissimilar metals parts is to create a suitable adapter consisting of the two metals, joined by vacuum brazing.

One of the big challenges in this work was due to the small size geometry of the part, and the small contact area between the two metals.

The geometry was designed to avoid tensile stresses between the parts which could lead to cracks and failure.

A commercial Ti brazing powder with brazing temperatures below the β transus temperature of Ti6Al4V was selected for this application. The selected brazing powder was used with different process parameters, to find out its suitability for optimally manufacturing the required brazed structure. The process parameters which were examined are: brazing temperature, heating and cooling rates, brazing duration and the optimum amount of filler. The process was performed in a vacuum furnace and during the process the parts were surrounded with titanium plates acting as getter.

The brazed joints examination was made by scanning electron microscope (SEM) and energy-dispersion spectroscopy (EDS).

A successful brazing was achieved for the chosen geometry, with the brazing filler showing a very good wetting of both the iron based alloy and titanium, the brazed joints show a uniform appearance without cracks.