THE EFFECT OF COMPOSITION ON THE FORMATION OF A BCC APPROXIMANT IN Ti–Cr–Al–Si–O

Abstract

ALLOYS The microstructure, phase composition, and mechanical properties of Ti–Cr–Al–Si–O alloys in as-cast and annealed states at 800 °С have been studied. It is established that the alloys with 50 and 60 at.% Ti in the as-cast state have two phases: 1/1 α(TiCrSi) cubic approximant of the quasicrystalline phase and intermetallic Laves phase Cr₂Ti(C14) in different ratios. The alloy with a high amount of titanium (72 at.%) in the as-cast state contains three phases: 1/1α(TiCrSi) approximant and two solid solutions based on α- and β-Ti. The influence of annealing on the phase composition of the alloys has been studied. After annealing, the alloys with the lowest (50 at.%) and highest (72 at.%) Ti contents change their phase composition with the formation of Ti₅Si₃ silicide, while the alloy with 60 at.% Ti exhibits high thermal stability—its phase composition remains unchanged. The changes in hardness of the starting and annealed alloys have been examined by automatic indentation. The highest hardness, 11.7 GPa, is shown by the Ti₇₂Cr₂₀Al₂Si₂(SiO₂)₄ alloy in as-cast state. After annealing, the hardness increases to 14.8 GPa for the Ti₅₀Cr₃₀Al₁₃Si₂(SiO₂)₅ alloy.