Microstructural study of rapidly solidified titanium eutectoid alloys

Abstract

Rapid solidification of Ti-7.3wt.%Cu (near-eutectoid composition), Ti-36.2wt.%Ni and Ti-34.3wt.% Ni-5.8wt.%Si alloys has been carried out by electron beam melting and splat quenching on a water-cooled rotating copper disc. The product obtained was in the form of thin ribbons 60–100 μm thick. Transmission electron microscopy studies of TiCu alloy splats showed that the microstructure consisted of a mixture of martensite and a lamellar eutectoid product. The formation of the intermetallic compound Ti 2Cu involved a diffusionless ω transformation and spinodal clustering. In the case of TiNi alloy the as-quenched microstructure is complex, consisting of α, transformed β and intermetallic phases. This could have arisen possibly as a result of local variation in cooling rates. Rapid solidification of TiNiSi alloy resulted in partial quenching of an amorphous phase. The amorphous phase was seen to be extremely hard (a Vickers hardness of about 800 HV).