Phase evolution in laser-deposited titanium-chromium alloys

Ti-Cr alloys have been laser deposited from powder feedstock consisting of a blend of elemental powders using the laser-engineered net-shaping (LENS) process. The microstructure of the as-deposited Ti-Cr alloys primarily consists of a metastable bee matrix of beta-Ti(Cr) with precipitates along the grain boundaries. The grain-boundary precipitates have been identified to be of three types, essentially pure hcp Ti, an alloyed hcp phase designated alpha-Ti(Cr), and the C14 TiCr2 Laves phase. Initial stages of decomposition, visible within the beta matrix, suggest a spinodal clustering process resulting in a fine dispersion of second phases. Diffraction studies have revealed the presence of fine precipitates of alpha within the beta matrix. The evidence for the precipitation of the metastable omega phase within the beta matrix is not stronor. The phase evolution in the LENS-deposited Ti-Cr alloy has been discussed in the context of rapid solidification and the enthalpy of mixing of the elemental powders.