Finer subgrain microstructure induced by multi-pass compression in α+β phase region in a near-β Ti-5Al-5Mo-5V-1Cr-1Fe alloy

Microstructure characteristics and restoration mechanism were studied in a near-β Ti-5Al-5Mo-5V-1Cr-1Fe alloy after the single- and multi-pass compression at 800 °C (below the β-transus) and 950 °C (above the β-transus) with the strain rate of 5s−1, 30s−1 and 50s−1. The results showed that the restoration mechanism of the alloy in β phase during the compression in β phase region was dynamic recovery (DRV) while DRV and dynamic recrystallization (DRX) occurred during the compression in α+β region. The involvement of α phase in α+β phase region promoted the DRX of β phase. Multi-pass compression at 800 °C has greater impact on the microstructure evolution of the alloy than strain rate change. The frequency of fine β grains/subgrains (grain size of 0∼5 μm) in the 800 °C/5-pass compressed sample was significantly higher than that in the 800 °C/1-pass compressed one. 5-pass compression at 800 °C results in enhanced fragmented α, which promoted the formation of finer β subgrains by introducing the heterogeneous deformation. This deformation route provides an effective way to obtain fine subgrain structure for quick forging parts of this alloy.