EFFECT OF OXYGEN ON THE MICROSTRUCTURE OF ANNEALED TiAl BASED ALLOY

摘要

The effect of oxygen on the microstructure of cast intermetallic TiAl-based alloy with nominal composition Ti-48Al-2Nb-1Cr-0.2Si (at.%) was studied after isothermal annealing at temperatures ranging from 1150 to 1320°C followed by free air cooling to room temperature. The samples for annealing were prepared from an ingot with an oxygen content of 400 wt. ppm and from cast turbocharger wheels with two different amounts of oxygen of 1000 and 1800 wt. ppm. While the microstructure of the alloy with the oxygen content of 400 wt. ppm changes from duplex one composed of lamellar α_2+γ and single phase γ grains to nearly lamellar with increasing annealing temperature, the microstructure of the annealed samples with oxygen content of 1000 and 1800 wt. ppm remains nearly lamellar within the studied temperature range. The evolution of the Vickers hardness with the annealing temperature is discussed from the point of view of volume fraction of single phase γ grains. The effect of oxygen on the Vickers hardness of studied castings is described.