Mechanical Properties of Alloys Based on the Intermetallic Phases gamma-TiAl+alpha_2-Ti_3Al with a Fine-Grained Lamellar Microstructure

摘要

The problems connected with the control of the parameters of lamellar structures, namely, the size of colonies and the interlamellar spacing, in the intermetallic alloys based on titanium aluminides gamma-TiAl+alpha~2-Ti_3Al are considered. It was shown that the small size of colonies and easily controlled interlamellar spacing can be produced using the beta-solidifying alloys with boron additions; deformation treatments, including hot deformation at the temperatures corresponding to the alpha_2+gamma phase field; and a subsequent heat treatment. This method allowed us to obtain small colonies (25-50 mu m) and the short interlamellar distances in the Ti-45.2 at. percent Al-(Nb, Cr, B), Ti-44.2 at. percent Al-(Nb, Cr, B), and Ti-42 at. percent Al-(Nb, B) alloys. In the Ti-42 at. percent Al-(Nb, B) alloys, the average interlamellar spacing was about 20nm. The study of mechanical properties of Ti-45.2 at. percent Al-(Nb, Cr, B) and Ti-44.2 at. percent Al-(Nb, Cr, B) alloys in the obtained structural states showed that, in the plasticity, strength at 20-800 deg C and fracture toughness, these alloys are not inferior to the high-strength gamma+alpha_2 alloys deformed in the high-temperature alpha field. For the Ti-42 at. percent Al-(Nb, B) alloys, a maximum strength (record for the gamma-TiAl +alpha_2-Ti_3Al alloys) was reached at 600-900 deg C.