Phase diagram of the system titanium-copper

Summary

The methods of metallographic, thermographic, x-ray diffraction, and microhardness analyses were used for studying alloys of the system titanium-copper in the concentration range 20–100 at. % Cu. On the basis of the results obtained and literature data, the phase diagram of the system Ti-Cu was plotted.

It is shown that the system has six intermetallic compounds, of which Ti₂Cu, TiCu, and TiCu₄ are variable-composition phases with narrow regions of homogeneity.

The existing data on the crystalline structures of the phases based on Ti₂Cu, TiCu, Ti₃Cu₄ and TiCu₂ have been confirmed and the space group of the phase based on Ti₂Cu₃ has been determined. It is shown that the intermediate phase with the highest copper content has the formula TiCu₄ and a crystalline lattice with a rhombic cell containing 20 atoms.

The compounds Ti₂Cu and TiCu melt congruently at 1015 and 984° C, respectively, while the compounds Ti₃Cu₄, TiCu₂, and TiCu₄ form from the melt by peritectic reactions at 918, 878, and 870° C, respectively. TiCu₂ exists only at high temperatures and decomposes at 850° C into TiCu₄ and Ti₂Cu₃. The compound Ti₂Cu₃ exists below 865° C and forms either at that temperature by the reaction TiCu₂ + Ti₃Cu₄ → 2Ti₂Cu₃ or at 850° C as a result of the decomposition of the compound TiCu₂.

The coordinates of the three eutectics in this system are: Theβ-Ti + Ti₂u eutectic occurs at 1003° C and 31 at. % Cu, the Ti₂Cu+TiCu eutectic at 960° C and 43 at. %Ce, and the TiCu₂ + TiCu₄ eutectic at 860° C and 73 at. % Cu.