In situ observation of interlayer growth during heat treatment of friction weld joint between pure titanium and pure aluminium

The growth of an intermediate layer, consisting of an intermetallic compound phase, in a friction welded joint between pure Ti and pure Al heated at 853 K for up to 173 ks (580degreesC, 48 h) was elucidated via an in situ (direct) and continuous observation method using a high temperature optical microscope. The following conclusions were reached. The layer grew from the Al substrate to the Ti substrate, and neither a linear nor a parabolic time dependence could be used to describe the rate of layer growth. The layer growth stopped for some time (i.e. several hours) after every heating interval of approximately 36 ks (10 h). That is, several plateaus appeared during heat treatment. It is thought that nucleation, and growth of such nuclei, of the Al-Ti binary intermetallic phase are necessary for layer growth. The interlayer growth rate for joints between pure Ti and highly pure Al was higher than that for,joints between pure Ti and commercially pure Al. This is due to the Si content in the Al base metal. There was a slight variation of the layer growth rate with location along the radius of the joint and with friction time.