Effects of double aging heat treatment on the microstructure, Vickers hardness and elastic modulus of Ti-Nb alloys

Aging heat treatment can be a good way to optimize mechanical properties, changing the microstructure, and hence, the mechanical behavior of Ti alloys. The effects of aging heat treatments on beta-type Ti-30Nb alloy were investigated to evaluate the kinetics of alpha '' -> alpha + beta transformation. The results obtained from differential scanning calorimetry and high-temperature X-ray diffraction experiments indicated the complete decomposition of orthorhombic alpha '' phase at close to 300 degrees C, followed by a phase precipitation at 470 degrees C. The aging heat treatments also enabled us to observe a transformation sequence alpha '' -> beta + omega -> beta + omega + alpha, indicating martensite decomposition and omega phase precipitation at 260 degrees C after 2 h, followed by a phase nucleation after heating at 400 degrees C for 1 h. The elastic modulus and Vickers hardness of Ti-30Nb alloy were found to be very sensitive to the microstructural changes caused by heat treatment. (C) 2011 Elsevier Inc. All rights reserved.