Effects of Cooling Rate on the Microstructure and Room Temperature Tensile Properties of Orthorhombic Ti-22Al-21Nb-1Ta-1W Alloy

摘要

In order to improve high temperature mechanical properties of Ti_2AlNb based alloys, alloying with a combination of Ta and W was studied in the on-going work. The effects of cooling rate after solution heat treatment on the room temperature mechanical properties have been reported in this paper. All samples were solid solution treated at near β transus temperature, cooled at different cooling rates, and then aged at subtransus temperature. Experimental results showed that, with increasing cooling rate, room temperature yield strength decreased sharply to a minimum value, and then increased. Change of elongation exhibits a trend opposite to yield strength. Microstructure of the alloy varied from near lamellar to lamellar plus Widmanstaetten, and then to full Widmanstaetten structure with the increase of cooling rate, and the faster the cooling rate, the finer the laths of the O phase. The samples with near lamellar microstructure obtained at the cooling rate of 6℃/min possess the best ductility but relatively low yield strength.