In situ TEM observation of reaction of Ti/Al multilayers

The Ti/Al multilayers of nominal periods λ = 50 nm and λ = 200 nm were deposited using double target magnetron system equipped with rotating substrate holder. The in situ TEM experiments were aimed at explaining DSC measured exothermic effects through phase transformations taking place during heating of the multilayers with small and large period. Thin foils for these examinations were cut with FIB. The performed experiments showed that the as deposited multilayers are characterized by presence of coarse pseudo-columnar crystallites built of alternating hex-Ti and fcc-Al. The intermixed region at the internal interfaces extends up to 10 nm, i.e. the areas filled with mutually alloyed material starts to dominate over those of pure metals for multilayers of λ < 30 nm. The DSC measurements indicated that in both multilayers their reaction are split to two stages, but those in the small period take place at much lower temperature range, than that in the large period one. Basing on the in situ TEM heating following reaction paths were noted:small period(λ∼50nm);fcc-Al+hcp-Ti→fcc-Al+hcp-Ti+t-Al3Ti→λ-TiAllarge period(λ∼200nm);fcc-Al+hcp-Ti→fcc-Al+hcp-Ti+c-Al3Ti→fcc-Al+hcp-Ti+t-Al3Ti→λ-TiAl+α2-Ti3Al