Role of grain boundaries in the high temperature performance of a highly stabilized beta titanium alloy I: Thermal stability

Two different microstructures with straight and bending grain boundaries were obtained after two typical heat treatments (1) annealing treatment (AnT) at 600 degrees C for 4 h followed by air cooling and (2) solution treatment at 850 degrees C for 1 h, water quenching followed by aging treatment at 550 degrees C for 6 h, air cooling (S-AT). The mechanical properties under room-temperature and thermal exposure conditions were tested for the alloy with different grain boundary morphologies. The results show that the grain boundaries morphology plays important role in thermal stability. The alloy with bending grain boundaries microstructure after AnT shows higher thermal plasticity in comparison to the ones with straight grain boundaries microstructure after S-AT, which is mainly resulting from the relatively small quantity and intermittent precipitations along bending grain boundaries in comparison to straight grain boundaries. The sequent microstructure evolution experiment for solution treatment at different temperatures shows the critical transformation temperature from bending grain boundaries to straight boundaries is in temperature range from 800 degrees C to 820 degrees C. (C) 2012 Elsevier B.V. All rights reserved.