Introducing high‐density dislocations and twins in Ti–46Al–2.8Fe– x Nb alloy with fully lamellar colony (β + γ) by phase proportion and interface stress regulation

Abstract In order to control the phase ratio of the β/γ phase and to improve the strength–ductility of Ti‐46Al‐2.8Fe alloy with a new (β + γ) lamellar colony, the β stabilizing element Nb is used to regulate the microstructure morphology and to introduce high‐density dislocations and twinning. As the Nb content increases, there is a reduction in the lamellar colony size from 256 to 178 μm, the content of the β phase increases from 17.0% to 21.5%, and the dislocation density within the alloy matrix is enhanced. This increase in the Nb content enhances the supersaturation of the α phase, promoting precipitation of the β‐phase while inhibiting formation of the α 2 ‐phase. The high solid solubility of Nb introduces high‐density dislocations within the β‐phase, and dislocations squeeze into the γ phase through the α 2 /β interface channel, forming a source of dislocation for the formation of stacking faults (SFs) and promoting the formation of nanotwins. Under interfacial stress, the α 2 /β interface supplies further dislocations that facilitate the development of SFs and nanotwins. Elevating the Nb content from 4% to 5.5% is found to boost the room‐temperature compressive strength from 2744 to 2966 MPa and the compressive strain from 36.8% to 39.6%. The optimal tensile strength at 750 °C is 492 MPa, and the elongation rate is 4%. When the alloy is under stress, high‐density dislocations and SFs at the γ/β interface and twin boundaries promote the formation of a nanotwin network and become dislocation storage units, forming a self‐strengthening cycle and improving the performance of the alloy.