Formation Regularities of Grain-Boundary Interlayers of the α-Ti Phase in Binary Titanium Alloys

Abstract—The microstructure of polycrystalline alloys of titanium with chromium (2, 4, and 5.5 wt %), cobalt (2 and 4 wt %), and copper (2 and 3 wt %) is investigated. Series of prolonged isothermal annealing of these materials are performed in a temperature range from 600 to 850°C (in vacuum). Annealing temperatures fall in two-phase regions α(Ti,Me) + β(Ti,Me) of phase diagrams Ti–Cr, Ti–Co, and Ti–Cu. Temperature dependences of the fraction of grain boundaries β(Ti,Me)/β(Ti,Me) completely “wetted” by interlayers of the second solid phase α(Ti,Me) and average contact angle are measured. The results of microstructural investigations showed that the type and concentration of the second component in the alloy strongly affect the formation of equilibrium grain-boundary interlayers. A nonmonotonic temperature dependence of the fraction of grain boundaries completely wetted by interlayers of the second solid phase in the absence of ferromagnet–paramagnet phase transformations in the volume is revealed for the first time.