Powder Metallurgy and Metal Ceramics | 2019
The Effect of Composition on the Formation of a BCC Approximant in Ti–Cr–Al–Si–O Alloys
Abstract
The microstructure, phase composition, and mechanical properties of Ti–Cr–Al–Si–O alloys in ascast state and after annealing at 800°C have been studied. The as-cast alloys with 50 and 60 at.% Ti have two phases: a 1/1 α(TiCrSi) cubic approximant of the quasicrystalline phase and an intermetallic Cr2Ti(C14) Laves phase in different ratios. The as-cast alloy with a high titanium amount (72 at.%) contains three phases: a 1/1α(TiCrSi) approximant and two α-Ti and β-Ti solid solutions. The effect 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 as-cast Ti72Cr20Al2Si2(SiO2)4 alloy. The hardness of the annealed Ti50Cr30Al13Si2(SiO2)5 alloy increases to 14.8 GPa.