Effect of microstructure on the fatigue crack growth behaviour of a near-α Ti alloy

• Fatigue crack growth behaviour of different microstructures of VT-20 was studied.
• Bimodal microstructure showed the highest fatigue crack growth rate and lowest ΔKth.
• The crack path of bimodal microstructure was straight.
• Acicular (from weld) and lamellar microstructures showed a tortuous crack path.
• ΔKth was the highest for the acicular microstructure.

Fatigue crack growth behaviour of Ti–6Al–2Zr–1.5Mo–1.5V (VT-20 a near-α Ti alloy) was studied in lamellar, bimodal and acicular microstructural conditions. Fatigue crack growth tests at both increasing and decreasing stress intensity factor range values were performed at ambient temperature and a loading ratio of 0.3 using compact tension samples. Lamellar and acicular microstructures showed lower fatigue crack growth rates as compared to the bimodal microstructure due to the tortuous nature of cracks in the former and the cleavage of primary α in the latter. The threshold stress intensity factor range was highest for acicular microstructure.