Abstract: The lamellar， bimodal， acicular microstructures and grain morphology of BT-20 near-α Ti alloy were observed by optical microscopy and electron backscatter diffraction. Tensile and fatigue crack growth tests were carried out to analyze the mechanical property and the influence of microstructures on fatigue crack growth rate， path and fractography. The results showed that the bimodal microstructure has the highest strength and best ductility， and acicular microstructure exhibits the lowest strength and poor ductility. The fractography of bimodal microstructure is cleavage fracture. The transgranular fracture happens when crack encounters the large primary α grain， which results in a relatively straight profile of the crack and explains the higher crack growth rate. The fractography of the lamellar and acicular microstructures is intergranular fracture. The crack path changes direction when encounters boundaries of two colonies of α grains， which results in tortuosity of the crack， lower crack growth rate and a better crack growth resistance.

Key words: BT-20, near-α Ti alloy, fatigue crack growth, microstructure, fractography