B2 grain growth and particle pinning effect of Ti-22Al-25Nb orthorhombic intermetallic alloy during heating process

The B2 grain growth kinetic of Ti-22Al-25Nb alloys has been studied. The grain sizes at different heat treatment temperatures and holding time have been obtained by means of the image analysis software. Generally, the grain size increases with the increasing heating temperature. However, the growth velocity is confirmed not the same for the heating temperature below and above B2-transus. The pinning effect of the α ₂ particles significantly plays an important role for controlling the grain growth. When the alloy was heated in B2 single phase region, the activation energy was increased with extending the holding time. When the heating temperature is below 1060 °C, the pinning effect of α ₂ particles sharply influenced the B2 grain growth. Zener model is a reliable model to predict the experimental data after taking m = 1, β = 4/9 into account. However, for the Ti-22Al-25Nb alloy with initial particle size of 180 μm, it can only predict the B2 particle size when the volume fraction of the precipitations is lower than 1.48%.