Abstract
The microstructure evolution and strengthening behavior of the ultra-high strength Ti–15Mo–2.7Nb– 3Al–0.2Si titanium alloy were studied utilizing XRD, OM, SEM, and TEM analyses. The results show that the dislocation-strengthening and precipitation-strengthening effects could mostly affect the yield strength of this alloy. The highest yield strength of 1518 MPa was obtained under a combined process of cold rolling + recrystallization + cold rolling + duplex aging. This trend is mainly due to the high density of remaining dislocations, as well as dense and thin secondary α phases in microstructures. A theoretical composite-strengthening model was built, and the prediction error is within 16.6%. Furthermore, it is found that increasing the content of the secondary α phase can continuously strengthen the intragrain zone. This feature causes the intergranular fracture to appear and gradually dominate the fracture surface.
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